Photo CT device of the Prefectural Preventive Medicine Association.Achieves low-dose inspection with high technology of engineers
Lung Cancer CT Safety Certified Prefectural Preventive Medicine Association, Certified as Excellent Facility
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There are more than 5 low-dose examinations by computed tomography (CT) annually.
The Prefectural Preventive Medicine Association (Chairman Noriaki Ohara) of Kitaiioka, Morioka City is the first facility in the prefecture to be certified by the Lung Cancer CT Screening Certification Organization (Tokyo). → Continue reading
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Computed tomography(Computers are so busy,British: computed tomography, Abbreviation:CT) IsradiationScan an object usingComputerA technology for constructing an internal structure of an object as an image by processing with, or a device for performing it.
"Computed tomographyAs the name suggests, it is originally a technology to obtain a cross-sectional image of an object (such as a round slice), but these inspection technologies are not only used as a cross-sectional image, but also an arbitrary cross-sectional image reconstruction by improving image processing technology. (MPR) And "Curved MPR" (or Curved Planer Reconstruction) that projects a curved surface onto a plane, maximum projection image (MIP)), Surface rendering, volume rendering, etc.3D graphicsIs often displayed as, which contributes to the improvement of diagnostic imaging technology.
In the broad sense of "CT",RadioisotopeTo obtain a tomographic image based on gamma rays emitted from the bodyPositron tomography(PET) AndSingle photon emission tomography(SPECT), And a tomographic image of a limited range is obtained by rotating or translating the detector that irradiates X-rays from outside the body but synchronizes with the X-ray tube below 180 degrees.X-ray tomosynthesisEtc. are mentioned as a kind of "CT".However, when we generally say "CT", it was almost always the first to be put into practical use.X-rayIt has come to refer to CT that obtains a tomographic image by rotating an X-ray tube of 180 degrees or more and a detector using.Also, when we simply say "CT", we use a conical beam.Cone beam CTIt does not refer to fan beam CT that uses a fan-shaped beam.Strictly speaking, the multi-row detector CT developed after the 1990s, which will be described later, is a cone beam CT that uses a pyramidal beam with a width in the cephalopod direction, but is treated as a fan beam CT in practice.
In this section, mainly, the X-ray fan-shaped beam from outside the subject is spirally rotated while continuously rotating.Or intermittently while rotatingA CT device and its examination for the purpose of obtaining a tomographic image of a subject by irradiation are described.
Before the birth of computers, the tomography method used to be used by Italian radiologists in the 1930s.Alessandro VallebonaBytomographyThe principle of was invented.this isRadiographythe filmIt was a projection of the body in a circle.
In 1953,Hirosaki University OfShinji TakahashiDeveloped "X-ray rotary cross-sectional imaging device"..This was to photograph a tomographic image with an analog mechanical device that did not use a computer.
The first commercial CTThorn EMI Central LaboratoryIn the EnglishGodfrey HounsfieldInvented by.It can control the device and perform image processing by a computer. It was devised in 1967 and announced in 1972.Hounsfield's study in MassachusettsAlan comacBased on the theory of 1979, theyNobel Prize in Physiology or MedicineWas awarded.
The prototype, created in 1971, performed 1 parallel read scans in 160 ° increments, taking more than 180 minutes to scan over 5 °.After scanning the image, it takes 2.5 hours on a large computer.Radon transformAnd its inverse conversion are repeatedTomographic reconstructionObtained by
The first X-ray CT produced (called an EMI scanner) was used for brain tomography. It took about 2 minutes to get the two fault data.Then, it took about 4 minutes for each image to obtain a tomographic image using a data general minicomputer.
In addition, I belonged to EMIビ ー ト ル ズCT scanners are also said to be "the Beatles' greatest legacy," as the record sales of records may have been the source of funding for EMI's scientific research, including CT scanners.
The introduction of CT in Japan is with EMIRecord business(Toshiba EMI) Had a partnershipToshibaImported in August 1975,Tokyo Women's Medical University HospitalInstalled inBrain tumorIt was the beginning that I caught.However, this scannerNixon shock1 million yen (currently) even after the introduction of the floating exchange rate system[When?]It is a substitute that costs less than 10 billion yen)Japanese govermentOn the sideLiability insurance OfOperationFrom profitTraffic accidentof timeHead injuryIt was decided to be funded in a research sense that would be useful for.
After that, the helical CT (helical scan) was developed in 1986, and the 1998-row MDCT appeared in 4. Since the 2000s, CT technological innovation has progressed, and as will be described later, the one that uses the successive approximation method for the image reconstruction algorithm, and the dual energy CT that has made it possible to reduce metal artifacts by using X-rays of two energies. Alternatively, MDCTs with a maximum of 2 rows and those using a flat panel detector for the detector have appeared.
The radiation source and detector rotate around the inspection target, the inspection target receives X-rays from all directions, the irradiated X-rays pass through the inspection target, are partially absorbed by the target and attenuated, and then the radiation source. It reaches and is recorded by the X-ray detector located on the opposite side of.After recording how much was absorbed in each direction,ComputerImage withFourier transformReconstruct with.
Divide one cross section into a grid and determine the absorption rate of each part.UnknownAnd so that the total is equal to the actual absorption amountSimultaneous equationsAnd solve this.HugequeueIt is an operation..In general, there are many models that divide one cross section into a 1 pixel square grid.[Annotation 1]Is a space that can be divided into 1,024 pixels square and processedresolutionThere are also high-end models.
Image reconstruction algorithm
CT image reconstruction methods are roughly divided into analytical reconstruction methods, algebraic reconstruction methods, and statistical reconstruction methods, back projection methods are classified into analytical reconstruction methods, and successive approximation image reconstruction methods are algebraic. It is classified into reconstruction method and statistical reconstruction method...Until now, the mainstream CT image reconstruction method has been the filter correction back projection method (FBP method).), But in recent years, it has the effect of reducing image noise.artifact"Sequential approximation image reconstruction method" (IR method), which is expected to have a reduction effect) Is increasing.. In order to overcome the weakness of the IR method, which is the length of time required for image reconstruction, there is also a successive approximation applied reconstruction method that incorporates the principle of the IR method into the FBP method.
- Back projection
- In the back projection method, the solution (reconstruction image) can be obtained by one calculation..
- Iterative image reconstruction method
- The successive approximation method is a method that first assumes an initial image and improves the consistency between the projection (forward projection) created by calculation from this image and the measured projection by iterative calculation, and requires a lot of calculation time due to iterative calculation. However, as computers speed up, the nature of statistical noise, the resolution of equipment,subjectThe flexibility to incorporate prior information such as the smoothness of the formula into the formula and the remarkable development in recent yearsCompressed sensingGradually increasing by incorporating theory.
In addition, in the multi-row detector CT (MDCT) created by the development of X-ray CT, the signal is distorted in the cephalopod direction when the number of detector rows increases to 64 rows, 256 rows, and 320 rows. Felt comp method for the purpose of correctionIs used.By using a conical beam instead of a fan-shaped beam, a three-dimensional projected image can be obtained without moving the subject in the direction of the head and foot. Cone beam CT (conical beam CT, CBCT)In), an algorithm developed from the back projection method called "cone beam back projection method" is used.There are also CBCT devices that use the successive approximation image reconstruction method.
- Non-helical scan
- A shooting structure in which the bed is moved and stopped sequentially for each slice.Conventional scan in the sense of the traditional methodAlthough it is sometimes called, recently, it is often called non-helical CT as a term for helical CT.Cluster scanThere is also a name called.The shooting time will be longer,ArtifIt is necessary to detect a subtle density difference by taking advantage of the fact thatbrainIn routine photography, non-helical scans with thick slices continue to be common.
- Helical scan
- A shooting structure in which the sleeper is continuously moved at a constant speed in a continuously rotating radiation source.From the patient's point of view, the radiation source will move in a spiral.Also known as a spiral scan.Compared to non-helical scan (conventional scan), the scanning time can be shortened, and it is possible to image the entire trunk with a single breath hold.Current[When?]All commercially available CT scanners support this imaging method.However, it may be disadvantageous in terms of image quality in situations where there is a lot of X-ray scattering such as around bones.This is mostly used for imaging below the neck, except for special examinations.
- Single row detector CT (old CT)
- In the early days, CT had only one row of detectors, and only one image could be obtained with one rotation, and the drawback was that the imaging time was long.
- Multi-row detector CT (MDCT)）
- It is a CT that irradiates X-rays in a fan shape at a slightly wide angle, and the detector itself on the opposite side is subdivided into multiple rows, and it is possible to take a larger range with one rotation of the radiation source. In 1, a CT with four or more rows of detectors was developed, and in 1998, a CT with 4 or more rows of detectors was developed and became widespread. year 2002MDCT with up to 320 rows of detectors is on sale, and it is possible to take almost the entire heart and brain with one rotation.
A CT that takes pictures without using a contrast medium is called a simple CT.generalscreeningOften used as.Since contrast is counterproductive depending on the purpose of the examination, simple CT may be actively selected.
Also, to investigate the cause of death of those who died of unknown cause at the hospitalImage diagnosis at death(Ai, Or PMI) Is also used. In Ai, for the subjectRadiation exposurebyRadiation hazardTherefore, it is not necessary to consider the above, so the image is taken with the highest possible image resolution and contrast resolution using a high dose.Contrast media cannot be used because the subject has lost physiological functions such as blood circulation and respiration.
Contrast agentContrast-enhanced CT (CECT) is taken after administration of). In CT, iodine contrast medium with high X-ray absorption rate is used.Blood vesselInside (usually of the limbs静脈It is common to inject into (inside) and take a picture.Contrast-enhanced CT is usually referred to as this, and when other contrast media are used, it is often referred to by another special name (Later).
After being injected, the contrast agent is distributed along the bloodstream in blood vessels throughout the body, and thenCapillariesfrom拡 散More slowly extravascularExtracellular fluidIt also shifts to and dyes the parenchyma of various organs.Blood vesselThe inside and the tissue with abundant blood flow are drawn dark (white), and the imageコ ン ト ラ ス トBecomes clearer and more detailed observation becomes possible.
Depending on the purpose of imaging, the timing of imaging after contrast enhancement differs.Roughly speaking, if the main purpose is to evaluate blood vessels, imaging in the early phase (15 to 30 seconds after the start of injection) is the main purpose, and if the purpose is to evaluate organs.Portal veinShooting in the phase or delayed phase (80 seconds or later after the start of injection) is suitable.The injection rate of the contrast medium and the iodine concentration of the contrast medium are also variously selected depending on the purpose of the examination.
Iohexol (Omnipark), Iopamidor (Iopamiron), Iomeprol (Iomeron), Iopersol (Optilei), etc. are used as iodine contrast media for CT (the names in parentheses are trade names in Japan).
Special contrast CT imaging method
A special contrast-enhanced CT imaging method is shown below.
- Dynamic CT
- Rapid intravenous injection of contrast medium (3 per second)mL(Above), and the same site is repeatedly photographed at each time (mostly arterial phase, equilibrium phase, and venous phase).It makes it easier to detect lesions and contributes to qualitative diagnosis, but it also increases exposure.
- Perfusion CT
- Similar to dynamic CT, this is a method in which a large number of time phases are photographed after rapid intravenous injection of a contrast medium, and the time change of the contrast medium concentration is imaged in color.
- CT angiography (CTA)）
- By rapidly injecting a contrast medium and taking a CT at the timing (arterial phase) where the concentration of the contrast medium in the artery is highest,coronary arteryAn imaging method that clearly depicts the running of blood vessels.aneurysmIt is used for the diagnosis of arterial diseases such as.This is an inspection method that has a particularly high affinity with 3D rendering.
- catheterA CT performed during an examination.In addition to being used to confirm the position of the catheter, if CT imaging is performed while injecting a contrast medium directly into a specific artery or vein, only the targeted blood vessel or organ can be strongly imaged, and it is expected that the accuracy rate will increase. Will be done.Depending on the facility, a CT device dedicated to IVR-CT may be installed in the catheter examination room.
- Intravenous drip infusion Gallbladder contrast CT (DIC CT)
- bileA contrast examination that visualizes the biliary system by photographing the upper abdomen after administration of a special contrast medium excreted inside.
- Xenon CT
- mainlybrainPerformed in blood flow assessment, non-radioactivexenonTake a picture while inhaling.
The basic image obtained by CT is a monochrome image showing a cross section of the body.The white part (high CT value) on the image corresponds to the high X-ray absorption, and the black part (low CT value) corresponds to the low X-ray absorption.The former is also expressed as "high absorption region", "high concentration region", and "permeability reduction region", and the latter is also expressed as "low absorption region", "low concentration", and "permeability enhancement region".
As a unit of absorption rate, "空 気Minus 1000HU, "WedHU defined as 0HUThe unit is used, and the expression of transmittance by this is especially "CT value"Other substances are indicated by the relative value of X-ray absorption with these.Inside or outside the body金属(DentureEtc.) exhibit very high CT values (thousands of HU).Bone is also a metallic element (calcium) Is contained in a large amount, so it shows a high absorption value of about several hundred HU.Most of the other organs in the body, such as muscles, brain, and liver, are densely distributed in a relatively narrow absorption value region of about 20HU to 70HU when no contrast medium is used, and this concentration range is collectively distributed. "Soft tissueCollectively called "concentration".What is characteristic isfatIt is the only major component in the body that shows a negative CT value (around -20 HU) except for the lung field, so it can be easily detected by CT.
In this way, the pixel value of CTDynamic rangeHowever, at the same time, when observing organs, a concentration difference of only a few HU becomes a problem.The density resolution of the human eye is limited, and if -1000 HU to 5000 HU are evenly assigned to a black-and-white image, most of the major organs will be almost invisible due to poor contrast.When observed by humans, the range from black to white in the image (general)monitorIf so, the CT value is allocated and observed according to the organ that one wants to observe in the range of brightness 0 to 255), and this allocation method is called "condition".
For example, if you want to observe the internal structure of the lungsAlveoliIt is necessary to observe the image under conditions where the air inside can be distinguished from the bronchi and blood vessels, but when observed under such conditions, organs such as fat, heart, and esophagus become pure white on the image.On the contrary, when observing small changes in the concentration of the liver, the lungs turn black.
Because of this situation, the imagethe filmIn some cases, the same cross section must be baked under a plurality of different conditions to make a sufficient diagnosis.Since observation on a computer monitor has become widespread, diagnosticians have been able to observe CT images while switching between multiple conditions in real time.
What is obtained by CT is basically a set of images (slices) on a plane.Previously these images were simplythe filmBurned inSchaukastenBy etc.Fluorescent lightI was observing by holding it over the light of.
0.5 due to the development of imaging technology such as helical scan and multi-row detector CTmm(500microns) When it became possible to image very thin slices such as thick slices in many facilities on a daily basis, a huge number of cross-sectional images came to be output.Current[When?]In many facilities, images can be viewed while paging like a movie on a monitor instead of film.
In addition, since the slice thickness has become sufficiently thin, it has become possible to reconstruct the CT image of "round slices" as a three-dimensional image. All pixels obtained in one shot are 3D CT valuesqueueIt is regarded as.Emphasize that these three-dimensional pixels are especially three-dimensional.VoxelsCall.
Enough in any directionresolutionIt is now possible to acquire 3D voxel data with, and to store and process it.memoryAnd because the processing equipment has become cheaper, various CT observation methods such as those listed below are used.
Arbitrary cross-section reconstruction
Arbitrary cross-section reconstruction (MPR) to reconstruct and display a cross-section of an object in any direction).MPR greatly contributed to the diagnosis because it is difficult to grasp the running of small blood vessels and the growth of tumors from only one cross section.When reconstructing a plane other than the sagittal and coronal planes perpendicular to the cross section, it is called an oblique MPR, and in head CT, an oblique MPR parallel to the orbit-ear hole line is used.As a modified method, there is also a method of projecting voxel data on a cylindrical surface or above, diagnosing deformed spinal lesions by reconstructing a curved surface along the vertebral body, and dentistry by reconstructing a curved surface along the jawbone. It is applied in areas such as diagnosis.
One-way projection image
Latham image with integrated voxel values in any directionAllows you to create an image similar to an X-ray photograph when X-rays are exposed from that direction.There is also a MIP image in which the highest CT value on an arbitrary straight line is projected onto a plane instead of integration.
: Voxel data with sufficiently high resolution can be displayed as 3D graphics that can be intuitively grasped by humans by applying appropriate shading and perspective on a computer.There are two main types of 3D rendering methods: "surface rendering" that looks at the surface of a mass above a certain threshold, and "volume rendering" that allows you to see the contents by changing the opacity...It is not suitable for strict measurement purposes because it requires manual labor during reconstruction to some extent, but it is difficult to recognize in cross section, complicated vascular structure, and parts where it is difficult to grasp the three-dimensional structure (頭蓋骨Etc.) is useful for grasping the whole picture.Also preoperative planning,Explanation to the patientIt can also be used for.A virtual that places the viewpoint in the trachea or large intestine and displays the inner surface of these organs in three dimensions.EndoscopeHas also been put into practical use.In an era when computer specifications were scarce, 3D rendering was difficult.However, since 2000, computers have made remarkable progress, and 3D rendering methods have advanced.
Cardiac CT / 4D CT
Always keep moving at high speed心 臓Is one of the organs that CT has been the weakest at, but it has become possible to take a wide range of images at high speed using the multi-row detector CT.electro-cardiogramWith the development of synchronization technology and high-speed source rotation technology, CT has become effective in the cardiac field as well.Currently, even the stenosis of blood vessels with a diameter of 2 mm on the surface of the heart is visualized, and some blood vesselscatheterIt is becoming possible to replace the inspection.Toshiba Medical Systems (currently Canon medical systemsWith the advent of ultra-multi-row detector CTs such as the 320-row detector CT of) and the 256-row detector CT of GE, it has become possible to even create an animated 3D image of the moving heart.Cerebral aneurysmIt is also beginning to be used in studies attempting to predict the risk of rupture of an unruptured cerebral aneurysm by examining its pulsation.
Use of CT images in radiation therapy
CT for treatment planning
Radiation therapyIn, the CT value of the CT image is the "CT value-electron density conversion table" measured in advance for each model and each X-ray energy.[Annotation 2]Except for substances with extremely high CT such as internal metals, there is no linear relationship, but there is a one-to-one correspondence with the electron density of the substance.The electron density of matter is the main interaction that gives absorbed dose in X-rays in the high energy region.Compton scatteringIt is closely related to the probability of occurrence of X-ray CT images and is indispensable for calculating absorbed dose in radiation therapy planning.Therefore, all patients undergoing extracorporeal radiation therapy will have a CT scan.However, it is meaningless unless the body position in radiotherapy and the body position at the time of CT imaging are exactly the same, so almost all radiotherapy facilities are equipped with a dedicated X-ray CT in the radiotherapy room. It has been devised so that the body position at the time of treatment and at the time of photography are exactly the same.The major difference from the X-ray CT device used for diagnostic imaging is that the bed of the diagnostic CT has an arc shape that follows the contour of the patient's body, whereas the therapeutic CT has a flat plate.This is because the bed of the radiotherapy machine uses a flat bed.
Cone beam CT with radiation therapy equipment
- When performing image-guided radiation therapy, CT is taken to confirm that the body position immediately before and after each treatment is the same as at the time of treatment planning.At this time, even if they are not exactly the same, it is judged that treatment is possible if they are within the set tolerance.Even if the margin of error is exceeded, it can be suppressed within the margin of error by translating, rotating and tilting the sleeper in the direction of reducing the error by cooperating with the radiation therapy sleeper before treatment. It has become.Position / angle error immediately before each treatment (daily error)) And position / angle error immediately after each treatment (daily error)) Is for radiation therapyquality managementIn that respect, it is very important information.Since the housing of the radiotherapy equipment is very large and heavy, it is not possible to rotate the housing at high speed like the fan beam CT.Therefore, cone beam CT is used.On the other hand, some models are capable of high-speed rotation, and there are also models that can perform image-guided radiation therapy using fan beam CT..
Chest x-ray CT
CT anatomy of the lung
BronchiとPulmonary arteryAs a general rule, they run adjacent to each other and run in parallel.It runs in the lung area, sub-area, and the center of the lobules.Pulmonary veins, on the other hand, run on these boundaries. In CT, the blood vessel adjacent to the bronchus is the pulmonary artery, and the blood vessel between the pulmonary arteries is the pulmonary vein.In normal humans, the bronchi can only be traced to the subregion, which is an effective method.The functional artery of the lung is the pulmonary artery, but other than that, as a feeding blood vesselBronchial arteryExists.The bronchial artery branches directly from the descending aorta, but is normally thin, so contrast-enhanced CT only confirms its proximal part.The lungs are lymph-rich tissue.Peribronchial, peripulmonary vascular, interlobular septum,pleuraIt is distributed in the interstitium.Particularly well developed are around the bronchi and around the pulmonary arteries.Basically, it flows from the periphery of the lung to the hilar region.Lymphatic vessels themselves cannot be confirmed by CT, but when lymphedema occurs, such as in congestive heart failure, the bronchial wall thickens, the vascular shadow expands, and the lobular septum can be confirmed.
The concept that is indispensable for understanding the structure of the lung is called the secondary lobe.The most famous is the definition by Miller.The bronchi and pulmonary arteries run through the center of the secondary lobules, and the pulmonary veins run through the interlobular septum.It is a polyhedron surrounded by a leaflet septum that can be visually confirmed.This concept helps to understand interstitial lesions.The secondary leaflets are said to be made up of about 30 thin leaves that cannot be confirmed by CT.
It is easy to follow the bronchi to identify the subregions of the lungs.As a general rule, the number of the area bronchus and the number of the lung area match, and the subarea can be identified even after surgery or in the displaced lung, keeping in mind that the bronchus generally passes through the center of the lung area.
- Upper right lobe
- The right main bronchus first branches upward in the upper right lobe bronchus, and the upper right lobar bronchus branches upward (outside) B1, posteriorly B2, and anteriorly B3.It should be noted that the numbers are numbered counterclockwise. B1 is the area bronchus of S1 (the apex of the lung), B2 is the area bronchus of S2 (posterior upper lobe), and B3 is the area bronchus of S3 (anterior upper lobe).The right main bronchus is called the intermediate bronchus (not present on the left) after branching the upper right lobe bronchus.
- Right middle leaf
- The intermediate bronchial canal branches anteriorly to the right middle lobe branch.The right middle leaf branch branches into outer (anterior) B4 and medial (posterior) B5. B4 is the S4 (outer pars intermedia) and B5 is the S5 (medial pars intermedia) bronchus.
- Lower right lobe
- Immediately after branching the right middle leaf branch, B6 branches posteriorly.Next, B7 branches inwardly in front and below, B8 branches outward in front and below, and B9 + 10 branches downward and posteriorly. B6 is S6 (upper and lower lobe), B7 is S7 (medial lung floor), B8 is S8 (anterior lung floor), B9 + 10 is S9 (lateral lung floor), S10 (posterior lung floor). is there.
- Upper left lobe
- The upper left lobe bronchus branches upward from the left main bronchus.The upper left lobe bronchus branches into an ascending upper branch and an anterior lower tongue branch.The upper branch branches into B1 + 2 on the upper rear and B3 on the front.The tongue branch is divided into a front B4 and a lower outer B5. B1 + 2 is S1 + 2 (posterior lung segment), B3 is S3 (anterior upper lobe segment), B4 is S4 (upper tongue segment), and B5 is S5 (lower tongue segment).
- Lower left lobe
- Immediately after branching the upper left lobe bronchus, B6 branches posteriorly.S7 (medial lung floor) is often absent on the left side, branching B8 in the anterior and inferior and B9 + 10 in the posterior. B9 + 10 branches into outer B9 and inner B10. B6 is the S6 (upper and lower lobe section), B8 is the S8 (anterior lung floor section), B9 is the S9 (lateral lung bottom section), and B10 is the S10 (posterior lung bottom section).
Diffuse lesions of the lungs
- Cavity shadow
- It is called airspace shadow, alveolar shadow, lobular shadow, and infiltration shadow.The alveolar space is almost completely occupied by liquids and other substances.Often accompanied by an air bronchogram due to the air in the bronchi.Basically, the shadows are unclear and easy to fuse.Insufficient occupancy of the alveolar space, with some air remaining, increases permeability and approaches frosted glass shadows.
- Frosted glass shade ground glass opacity (GGO)
- The shadow that allows the existing pulmonary blood vessels to be seen through with a slight increase in concentration is called ground glass shadow.In particular,Incomplete alveolar cavity occupationOrThickening of the alveolar wallCaused by.In the case of incomplete alveolar space occupation, the mechanism is that the air in the air cavity decreases and the others increase, so the average concentration increases, but the concentration is not as high as the air-cavity shadow because it is mixed with air. Occurs in.Alveolar proteinosis, Peripheral adenocarcinoma, bronchiolar alveolar epithelial carcinoma, early or curativePulmonary Edema, Pulmonary hemorrhagepneumoniaSeen at.Thickening of the alveolar wall is caused by thickening of the alveolar septum.Diffuse thickening and nodular thickening are classified according to distribution, and diffuse thickening isInterstitial pneumoniaSeen in, nodular thickeningsarcoidosis, Histhiocytosis X,Hypersensitivity pneumonia,tuberculosisIt is found in granulomatous diseases such as.
- Bronchiole wall, vascular wall thickening
- Clear punctate or branched images due to thickening of the bronchiolar wall are observed in the central lobe.Diffuse panbronchiolitisSee a typical example.However, although these findings are present, they are distinguished because the alveolar wall is also thickened.
- Leaflet central shadow
- Leaf spacing wall thickening image
- Abnormal linear shadow orthogonal to the pleura.Accompanying interstitial lesions.
- Bronchial wall thickening image
- It is the terminal elephant of the fibrotic lung.
- Abnormal dilation of the air space peripheral to the terminal bronchioles.
Massive lesions of the lung
It is very important to distinguish between cancer and benign disease for mass lesions.Is there a tendency to increase compared to the previous image?If so, how fast it grows is very important.In addition to pointing out the findings, where and how large the site of occurrence is, the rate of increase is derived from the previous comparison, and a complex diagnosis is made based on the contour of the nodule, internal properties, and surrounding conditions.
- Nodule contour
- Describe whether the contours are clear or indistinct, whether there are depressions and lobulation, or whether there is spiculation.The presence of exudate between the nodule and lung tissue creates ground glass shadows that obscure the boundaries.It is common in cases of malignant tumors that do not destroy inflammatory changes or alveolar septa.
- Internal properties
- The internal structure can be predicted by whether the concentration is uniform, whether there are calcifications, fats, cavities (air), or what the contrast effect is.
- Surrounding condition
- The nature of the mass can be predicted by the presence or absence of pleural invagination, daughter nodule, bronchial thickening, atelectasis, obstructive pneumonia, bronchial mucus plug, and lymphadenopathy.
CT findings of mass lesions are benign if no increase is observed for more than 2 years, almost the entire mass is heavily calcified, or fat is found in the mass.Common but undecided findings in lung cancer include surface depression, lobulation, spine formation, uneven internal concentrations, pleural invagination, low Hounsfield scale, and lymphadenopathy.Common but undecided findings in benign tumors include clear and smooth edges and uniform internal concentrations.Findings such as indistinct margins, cavities in the mass, foamy air, and air bromchogram are found in both lung cancer and inflammation.Daughter nodules, bronchial thickening, and small calcifications are common in inflammation but also in lung cancer. It is difficult to make a diagnosis only by CT, and it is important to combine bronchoscopy, biopsy, and cytology in the diagnosis.
There are always two types of chest CT: lung field conditions and mediastinal conditions.If the image is composed of actual CT values, it cannot be recognized by the human eye, so the CT image is processed.Specifically, it represents a dozen levels of grayscale shading according to the CT value.The range represented in grayscaleWindow width (WW)And the CT value at the centerWindow level (WL)That is.For example, if WW / WL = 300HU / 10HU, 10HU will be gray around 300HU.That is, if it is 160 HU or more, it is pure white, and if it is -140 HU or less, it is pure black. The lung field condition makes it easier to extract lung field lesions by setting WW / WL, and the mediastinal condition makes it easier to extract mediastinal lesions.The mediastinal condition is often relatively close to the abdominal condition.
MediastinumIs divided into various categories according to the book.These divisions are for convenience only, as there are no clear anatomical structures in the divisions.
- Front mediastinum
- On the ventral side of the cardiovascular system, the ventral side of the upper macrovascular and the lower cardiodiaphragmatic angle are the main sites.The former isThymusLesions of origin (thymoma, etc.), lesions of ectopic thyroid gland, embryonic cell tumors, and neuroendocrine tumors are common.Most of the cystic diseases are thymic cyst, pericardial cyst, teratoma, and lymphangioma.
- Middle mediastinum
- It includes large blood vessels other than the descending aorta, heart, trachea, and bronchi, and is the part from the anterior surface of the heart to the ventral side of the esophagus.There are many lesions derived from these organs and lymph nodes.Foregut cysts are the most common cystic disease.
- Rear mediastinum
- It includes the paraspinal groove, which is not originally divided into the mediastinum as a habit in the dorsal part including the esophagus.Nerve tumors and meningoceles often occur in the paravertebral groove.Often accompanied by neurointestinal cysts.
Mediastinal cysts are often classified as monocystic or polyvesicular.Monocystic includes anterior intestinal cysts (bronchial cysts, esophageal duplication cysts, neurointestinal cysts), pericardial cysts, pericardial diverticulum, thoracic cysts, pancreatic pseudocysts, and polyvesicular lymphangiomaTeratomaIs mentioned.
Body cavity continuity
Independent cavities in the human bodyPeritoneal cavity,Pericardial cavityThere are only three.Normally, there is no traffic from other sources.The exception is the female peritoneal cavity, which communicates to the outside world through the fallopian tubes.Other than thisMediastinum, Extrapleural space, peritoneal space, and subcutaneous tissue are continuous with each other.Increased air cavity and intestinal pressuresteroidIt is known that air leaks are likely to occur when using.Specifically, interstitial emphysema,pneumothorax,, Cardiac emphysema, peritoneal embolus, retroperitoneal emphysema, intestinal wall emphysema, subcutaneous emphysema, and systemic air embolism are known to easily migrate to each other.
Lymph node evaluation
Lymph nodeEvaluation ofLung cancer,tuberculosisIt is very important for the discrimination of.Chest X-ray CT can evaluate cervical lymph nodes, mediastinal lymph nodes, and hilar lymph nodes.Contrast agentIt should be noted that if you do not use, the lymph nodes and blood vessels will have the same concentration, so it may not be possible to distinguish them.As a general rule, if the minimum diameter is 10 mm or more, the lymph node becomes pathologically swollen, and the possibility of metastatic lymph node increases.If you find a pathological swelling of the lymph nodes and it is due to lung cancer, you need to stage it based on the lung cancer handling rules. N of TNM classification will be determined, but N0 has no lymph node metastasis, N1 has positive metastasis of peribronchial and hilar lymph nodes on the ipsilateral side of lung cancer, N2 has positive mediastinal lymph node metastasis on the ipsilateral side, and N3. Is positive for contralateral mediastinal lymph node or or oblique muscle lymph node metastasis.Importantly, the ipsilateral and contralateral sides are determined by the tracheal midline and esophageal midline.Then, supraclavicular lymph node metastasis and scalene muscle lymph node metastasis become N3 regardless of ipsilateral or contralateral, and contralateral hilar lymph node metastasis becomes M1.
The site of the swollen lymph node is then identified.The lymph nodes that are cranial to the mediastinum, including the level at which the left brachiocephalic artery crosses the midline, are the upper mediastinal lymph nodes.Below that, all anterior to the superior vena cava and the anterior margin of the ascending aorta are the anterior mediastinal lymph nodes.
If a lymph node metastasis is found, determine if it can be dissected.It is often difficult to dissect if it invades large blood vessels or bronchi, if many lymph nodes are fused, or if it is irregular.
CT evaluation of blood vessels
Important in the neck and chestartery,静脈To be described.First, there are aortas such as the ascending aorta and the aortic arch from the left ventricle.The aorta branches in the order of the brachiocephalic artery (which eventually branches into the right common carotid artery and the right subclavian artery), the left common carotid artery, and the left subclavian artery.The left and right brachiocephalic veins merge on the ventral side to form the superior vena cava, which connects to the right atrium.From the dorsal side before connecting to the right atriumAzygos veinThe bow connects to the superior vena cava.The cervical lymph nodes will be identified from these positional relationships.Aortic calcification and mitral valve calcification are common findings in patients with atherosclerotic disorders such as hypertension.If you see calcification of the arteryAortic aneurysm,Aortic dissectionCheck for the presence of.Since calcification of the aorta occurs in the intima, calcification on the outer wall is the true lumen.
Abdominal x-ray CT
CT anatomy of the liver
Area anatomy is very important in diagnosing the site of the liver.This is because the surgical method differs depending on the site.Subsegmental resection, segmental resection, lobectomy, and enlarged right lobectomy are known as liver surgery.When diagnosing the area of the liver, the structure of the liver is often used as a clue.Liver gateIs the gap between the medial left lobe (S4) and the caudate lobe (S1).Portal vein,bile ductIt is the doorway of.Round ligament of liverIs the place where the round ligament of liver (umbilical vein in the embryonic period) is attached and borders the lateral section (S2, S3) and the medial section (S4).Vein cleftBounds the caudate lobe (S1) and the lateral segment (S2, S3) by the running gap during the embryonic period.The line connecting the inferior vena cava groove and the gallbladder fossaCountry lineIt borders the surgical left and right lobes.These cannot always be confirmed by CT, but they are very useful when it is difficult to confirm the vascular system described later.The vascular system is the easiest to understand for diagnosing the hepatic region and subhepatic region.The basic structure of the blood vessels of the liver is that the portal vein runs in the center of each sub-segment and the hepatic vein runs at the boundary of each sub-segment.The hepatic artery and bile duct run side by side in the portal vein, and this structure persists to the level of the hepatic lobule.Is basically three lines: left, middle, and right.The main trunk of the left hepatic vein runs in the center of the lateral section of the left lobe (S3, S2) and borders the lateral posterior subsection (S3) and the lateral anterior subsection (S2).The main trunk of the middle hepatic vein borders the medial segment (S3) and the anterior segment of the right lobe (S4, S5).This is a boundary that almost coincides with the country line.The main trunk of the right hepatic vein penetrates the center of the right lobe and borders the right lobe anterior segment (S8, S5) and posterior segment (S8, S6).Curiously, there is no structure that borders the upper and lower subdivisions of the right leaf.Portal veinThe main trunk is divided into a left lobe main branch and a right lobe main branch.The left lobe branch enters the round ligament of liver fissure, first branching the lateral posterior subregional branch, and then extending ventrally into the lateral anterior subregional branch and the medial segmental branch.This part is called U point because the umbilical vein used to communicate.The right leaf branch is divided into anterior segment branch and posterior segment branch.The anterior segment branch is divided into an anterior superior subregion branch and an anterior inferior subregion branch.The posterior segment branch is called point P.The posterior segment branch is divided into the posterior superior subregion branch and the posterior inferior subregion branch.The portal vein is sometimes expressed as Px according to the area it controls.For example, the portal vein running in the center of the anterior subregion (S7) is P7.
The Quino classification is often used to describe the subregion of the liver, which is numbered counterclockwise when viewed from the visceral surface of the liver.The right lobe anterior subdivision, which cannot be confirmed from the visceral surface, is designated as S8.
|Quino classification||Sub-area name||Traditional name|
|S1||Caudate leaf||Caudate leaf|
|S2||Outer rear sub-ward||Outer ward|
|S3||Outer front sub-ward||Outer ward|
|S4||Inner ward (square leaf)||Inner ward|
|S5||Maeshita Aku||Front zone|
|S7||Maegami Sub-ku||Front zone|
|S8||Shota Gogami||Back ward|
CT anatomy of abdominal blood vessels
(SMA) branches anteriorly from the level of L1 and descends in front of the left renal vein and the horizontal duodenum.The middle colic artery, ileal artery, and right colic artery branch.The superior mesenteric vein (SMV) ascends to the right of the SMA and joins the splenic vein through the dorsal side of the pancreatic body.The inferior mesenteric artery (IMA) branches anteriorly from the abdominal aorta at L3 level and heads to the lower left.The left colic artery and sigmoid artery branch.The inferior mesenteric vein ascends to the left side of the IMA and joins the splenic vein at the L3 level.The left egg (testicular) vein merges with the left renal vein and cannot be traced to the cranial side.
Side effects and problems
CT is widely used in most of the large hospitals in developed countries and is performed on a daily basis.Side effectsThere is.
|Medical imageInEffective dose|
|Target organ||Inspection||Effective dose (adult)||Environmental radiation Of|
|headCT||Simple CT||2 mSv||8 months|
|Contrast agentuse||4 mSv||16 months|
|chest||Chest CT||7 mSv||2|
|lungCancer screeningChest CT for||1.5 mSv||6 months|
|chestSimple radiography||0.1 mSv||10 Day|
|心 臓||Coronary CTAngiography||12 mSv||4|
|Coronary CT, calcium scanning||3 mSv||1|
|abdomen||Abdominal / pelvic CT||10 mSv||3|
|Abdominal / pelvic CT, low dose protocol||3 mSv||1|
|Abdominal / pelvic CT, with contrast medium||20 mSv||7|
|CT colon examination||6 mSv||2|
|Intravenous renal pelvis imaging||3 mSv||1|
|Upper partGastrointestinal angiography||6 mSv||2|
|beneathGastrointestinal angiography||8 mSv||3|
|vertebral||Simple X-ray of the spine||1.5 mSv||6 months|
|Spine CT||6 mSv||2|
|Limbs||LimbsSimple radiography||0.001 mSv||3 hours|
|Lower limb CTAngiography||0.3 --1.6 mSv||5 weeks-6 months|
|Dental radiography||0.005 mSv||1 Day|
|Bone density measurement(DEXA method)||0.001 mSv||3 hours|
|Mammography||0.4 mSv||7 weeks|
By CTExposureThe dose belongs to the larger of the various radiological examinations...The exposure dose varies depending on the inspection site, inspection method, equipment performance and settings, but depending on the inspection, dozens of times at one time.mSv ――You may be exposed to X-rays exceeding 100 mSv.However, various procedures performed under fluoroscopy, includingIVR) Is generally less exposed to CT, andRadiation therapyCompared to the dose used for the purpose, it is only tens to hundreds of times.In general, among the health hazards caused by radiation, there is a possibility that CT may cause radiation damage in the acute phase, which is considered to be a deterministic effect (an effect that occurs in anyone above a certain threshold and never occurs below a certain threshold). Is none (that is,White blood cellDecrease /脱毛・ Nausea is unlikely to occur within a few weeks). The problem with CT is the increased risk of cancer that first becomes apparent months to decades later.Or to offspringHeredityIt is an impact.These are called stochastic effects, and it is "assumed" that no matter how small the dose, the risk is not zero and there is a small amount of risk for a small amount of exposure (No linear threshold hypothesis).Therefore, in principle, radiological examinations should be performed only to the minimum necessary to prevent unnecessary exposure.
It is difficult to statistically estimate the specific health hazards caused by CT exposure.It requires at least several years of follow-up, and people who have a CT usually have some symptoms, such as already having cancer.Tracking healthy adults in groups with / without CTethicsThere are also problems, and the more CT is performed, the more asymptomatic early-stage malignant tumors are found, so the apparent cancer incidence increases.
Bedlington and Derby are in 14 countries including the United Kingdom, the United States and Japan[Annotation 3]0.6% to 3.2% of carcinogenesis in Japan is evaluated to be due to diagnostic radiation such as CT..But these are JapanAtomic bombWhat is estimated in comparison with the A-bomb survivor tracking results, Because it adopts the hypothesis without linear threshold, Some have questioned the evaluation based on these, and opinions are divided among experts.In addition, especially young people with high radiation sensitivity (Genital,breastEtc.) are easily affected when shooting repeatedly.
Still morePregnant womanIn the case of fetalMalformationOccurrence can be a problem,International Commission on Radiation ProtectionIs 100 mmGy(= 100 mmSv) It is concluded that there is no statistically significant increase in malformations with the following fetal exposures, and it is unlikely that the foetation will be exposed to this amount even if the pelvis is directly imaged by CT..
Adverse effects on medical devices
Traditionally,Heart pacemakerIn 2005, some cardiac pacemakers identified a rare event that caused a reset during a CT scan, although it was said to have no effect on the patient.Implantable cardioverter defibrillatorMalfunctions have also been reported.These can be life-threatening, and each hospital is taking measures such as preventing the equipment from being irradiated with X-rays and reducing the irradiation time.
Psychological effects on people with claustrophobia
CTMRIThe inspection is completed in a short time compared to the above, and there is less pressure from the inspection equipment, but it is severe.ClaustrophobiaIt can cause fear and panic in patients and can be difficult to administer.
Side effects of iodine contrast media during contrast examination
In mild cases, temporary nausea and itching of the skin occur in a few percent of patients who use contrast media.Less than 1% of patients have dyspnea or allergic reactions that require treatment.Very rarely with iodine contrast agentAnaphylaxisShockAcute renal failureSerious side effects such as these may occur, and there are cases of death at a frequency of about 1 in hundreds of thousands of contrast media...Due to the rapid injection, subcutaneous leakage of the injection may cause strong swelling.
In addition, while CT is a valuable examination that is also effective in the emergency field, the equipment is huge, and it is necessary to keep medical staff away from the patient to prevent radiation exposure at the time of imaging and to minimize the equipment for life support. There is.shockIn critically ill patients, the CT scan itself can be a life-threatening examination that requires more than a dozen staff.
Insufficient sharing of diagnostic results, etc.
As a problem other than side effects, even if an image showing the possibility of illness is obtained, it does not lead to the start of treatment, especiallycancerSome patients die.This is a case where another doctor who received the medical examination overlooks the necessity of the detailed examination described in the diagnostic imaging report and does not perform the necessary additional examination or medical treatment.As a countermeasure, some medical institutions have introduced a mechanism to check with the attending physician whether they have read the report and grasped the contents...Also, the discovery of lesions at the interpretation stageArtificial intelligenceTechnology development supported by (AI) is also being carried out.
Comparison with MRI
With X-ray CTMRIAlthough the principle of is completely different, it is often compared as the same sliced image inspection. It can be said that X-ray CT has the following advantages and disadvantages over MRI.
- 利 点
- Inspection is short
- 空间resolutionIs high
- MagneticBecause it does not use metal (Heart pacemakerEtc.) Can be applied to users (however, see the side effect column for pacemakers)
- ArtifA wide range of shooting is possible with little (image distortion)
- Less noise and blockage
- High penetration rate and relatively inexpensive
Very roughly,boneDiseaseslungdisease,Digestive tractDisease, orBleedingIn the case of emergency diseases such as, CT is often more useful than MRI.On the other handBrain tumor,uterus-Ovary-筋肉In such diseases, the soft tissue resolution of MRI is often effective.
As of January 2018, CT equipment is mainly developed and sold by the following companies.
- Medical CT equipment
- Dental CT equipment[Annotation 4]
- Cone beam CT device with radiation therapy equipment
- Industrial CT equipment
CT for non-medical purposes
If the health effects of radiation exposure and the unavoidable movement restrictions caused by handling living organisms are eliminated, the resolution of CT can be further increased.
- ^ Fast Fourier transformIn order to utilize the property of, it is convenient for calculation if it is a number represented by the product of two prime factors.
- ^ It is created by associating the obtained CT value with the electron density by photographing an object with a known electron density with CT.
- ^ Australia, Canada, Croatia, Czech Republic, Finland, Germany, Japan, Kuwait, Netherlands, Norway, Poland, Sweden, Switzerland, United States
- ^ All dental CT devices are cone beam CT.
- ^ British: multi-planar reconstruction
- ^ British: maximum intensity projection
- ^ Helical CT or spiral CT
- ^ Non-helical CT or conventional CT
- ^ (PDF, 200.48KB) --Industrial Technology History Information Center (National Science Museum)
- ^ Shinji Takahashi, "Study on X-ray Rotation Imaging," Japan Radiological Society Homework Report, 1951.
- ^ Takahashi S (March 1957). Rotation Radio1ogy. Japan Society for the Promotion of Science.
- ^ a b c d e f g h i j Hiroyuki Toda. X-ray CT-Practical use of tomography in industry and science and engineeringKyoritsu Shuppan. ISBN 978-4-320-08222-9
- ^ a b c d ( Let's understand the current state of CT image reconstruction method!
- ^ British: filtered back projection
- ^ British: iterative reconstruction
- ^ British: back projection}
- ^ British: iterative reconstruction
- ^ Hiroyuki Kudo,Concept and wonder of CT image reconstruction method using successive approximation method Medical Imaging Technology. 2005 Vol. 23, No. 1, p.23-, two:10.11409 / mit.23.23
- ^ Feldkamp
- ^ cone-beam CT
- ^ British: conventional scan
- ^ British: cluster scan
- ^ British: multi detector-row CT
- ^ Providing low-dose imaging technology for all Aquilion ONE systems equipped with 320-row detectors-Achieving up to 75% reduction in radiation exposure- - Toshiba Medical Systems, March 2012, 3 (JST)
- ^ British: autopsy imaging
- ^ British: post-mortem imaging
- ^ British: contrast enhanced CT
- ^ British: perfusion CT
- ^ British: CT angiography
- ^ British: hounsfield unit
- ^ British: CT number
- ^ British: multiplanar reconstruction
- ^ British: RaySUM image
- ^ British: inter-fractional error
- ^ British: intra-fractional error
- ^ Accurey, Varian Halcyon, etc.
- ^ a b Unless otherwise specified in boxes, reference is:
- "Radiation Dose in X-Ray and CT Exams". by . 2017/10/23Browse.
- ^ Brisbane, Wayne; Bailey, Michael R .; Sorensen, Mathew D. (2016). “An overview of kidney stone imaging techniques”. Nature Reviews Urology (Springer Nature) 13 (11): 654–662. two:10.1038 / nrurol.2016.154. ISSN 1759-4812. PMC: 5443345.
- ^ Zhang, Zhuoli; Qi, Li; Meinel, Felix G .; Zhou, Chang Sheng; Zhao, Yan E .; Schoepf, U. Joseph; Zhang, Long Jiang; Lu, Guang Ming (2014). of Lower Extremity CT Angiography Using 70 kVp, High Pitch Acquisition and Sinogram-Affirmed Iterative Reconstruction ”. PLoS ONE 9 (6): e99112. two:10.1371 / journal.pone.0099112. ISSN 1932-6203.
- ^ a b c d e Berrington, Darby (2004)
- ^ ICRP: Pregnancy and Medical Radiation. ICRP Publication 84, 2000, pp15-17
- ^ Yoshifumi Narumi and Hitoshi Nakamura, "Frequency Survey of Severe Side Effects and Deaths of Nonionic Iodine Contrast and Gadolinium Contrast," Journal of the Japanese Society of Medical Radiology, Vol. 65, No. 3, July 2005, 7, pp. 25-300,NOT 10016604063
- ^ "Imaging diagnosis report" Insufficient confirmation one after another Important information is not shared / Measures to prevent recurrence one after another"Nikkei" morning edition March 2018, 3 (medical and health aspects)
- ^ AI will support diagnosis of future CT images!The correct answer rate for similar cases is 85%, and the diagnosis time is 6/1.Fujitsu (viewed April 2018, 4)
- ^ Egyptian cat mummy succeeds in shooting with new X-ray technology / Unravels the internal composition without peeling off the wrapped clothNational Geographic Japanese site (viewed December 2017, 12)
- ^ Buddha statues are also active in the era of CT scanning, grasping the womb and "health diagnosis"``Asahi Shimbun'' morning edition February 2017, 11
- Berrington, Amy; Darby, Sara (2004). “(PDF)" (English). Lancet. 2011/6/13Browse.
- R. Gordon, SA Johnson "Three-dimensional reproduction of medical X-ray images" "Science],Nihon Keizai Shimbun, February 1975, p. 12.
- Richard Gordon; Gabor T. Herman; Steven A. Johnson (October 1975). “Image Reconstruction from Projections”. Scientific American (Nature Publishing Group) 233 (4): 56-68.
- Chest CT Diagnosis 90 Step 1 ISBN 4498031121
- Chest CT Diagnosis 90 Step 2 ISBN 4498031148
- Abdominal CT diagnosis 120 steps ISBN 4498013409
- Alan comac,Godfrey Hounsfield --CT developer. 1979,Nobel Prize in Physiology or MedicineAward.
- Katsumi Tsujioka -Helical scan CT developer in Japan.Fujita Health UniversityAssociate Professor, Department of Radiology, Faculty of Medical Sciences.
- Medical image processing
- Diagonal CT
- Hippocrates -The role of a brain surgeonOsamu KitayamaWith the development of CT scansビ ー ト ル ズThere is a scene explaining the relationship with.