Computed Tomography Scan Review 2023 PDF

COMPUTED TOMOGRAPHY SCAN Jenerlito R. Casaje,RRT,MPA Radiologic Technologist V Philippine Orthopedic Center  TOS * 1.1 Illustrate scanning procedure as well as data and image acquisition in computed tomography scan.  Overview of the limitation of Classic...

COMPUTED TOMOGRAPHY SCAN Jenerlito R. Casaje,RRT,MPA Radiologic Technologist V Philippine Orthopedic Center  TOS * 1.1 Illustrate scanning procedure as well as data and image acquisition in computed tomography scan.  Overview of the limitation of Classic Radiography(conventional x-ray) * Superimposition of the three dimensional information onto two dimension causes the loss of low –tissue contrast anatomic structures * Presence of scatter obscures low-tissue contrast anatomic structures  Advantages of CT over Classic Radiography — Three dimensional information in the form of a series of thin slices of the internal structures of the part in question  Advantages of CT over Classic Radiography — The system is much more sensitive compared to conventional radiography so that differences in tissue can be clearly delineated(.5%-1%) — CT measures x-ray attenuation of individual tissues accurately, allowing the basic nature of tissue to be studied region of interest (ROI) A user-defined graphic outline that calculates the average CT number of a given anatomic area.  Who invented CT? * Godfrey Hounsfield * Engineer from EMI Ltd., London * Developed the first clinical useful CT scanner in 1971 * Allan McLeod Cormack -South African- born of Tufts University in Massachusetts independently invented a similar process * Hounsfield and Cormack shared the 1979 Nobel Prize in Medicine * The first EMI-Scanner was installed in Atkinson Morley Hospital in Wimbledon, England, and the first patient brain-scan was done on 1 October 1971 CT development 1964 EMI (England) developed the CT scanner (by Mr.Hounsfield) 1973 EMI released MARK 1 CT development Basic Principle of Data Acquisition x-ray tube Parallel beam geometry (1st generation scanner) x-ray beam x-ray detector object to be scanned  Milestone * 1963- Cormack contributes the first mathematical implementation for tomographic reconstruction in South Africa * 1969- Hounsfield shows proof of the principles with the CT scanner based on a radioactive source at the EMI research laboratory * 1972- Hounsfield and Ambrose publish the first clinical scan with an EMI head scanner * 1975- Set up of the first whole body scanner with a fan beam system * 1979- Hounsfield and Cormack received the Nobel prize for medicine * 1983- Demonstration of electron beam CT(EBCT) * 1989- Dr. Kalender publishes the first clinical spiral CT * 1991- Demonstration of the multi-slice CT(MSCT)  Gen. Source Source Collimation Detector 1st Single X-ray Tube Pencil Beam Single 2nd Single X-ray Tube Fan Beam (not enough to Multiple cover FOV) 3rd Single X-ray Tube Fan Beam (enough to Many cover FOV) 4th Single X-ray Tube Fan Beam covers FOV Stationary Ring of Detectors 5th Many tungsten Fan Beam Stationary anodes in single Ring of large tube Detectors 6th 3G/4G 3G/4G 3G/4G 7th Single X-ray Tube Cone Beam Multiple array of Detectors  TOS *1.2 Show thedifference between reconstructing and reformatting an image.  Reconstruction * process of creating a digital image from raw data Data collection X-ray produces “shadow-gram” Flattens 3D information into 2D Detector X-ray Tube Data collection * X-rays produce “shadow-gram” Data collection The X-ray beam passes through the X-ray tube patient The attenuated beam is collected by the detector The detector converts these attenuated X-ray photons to an electrical signal The signal is passed on to the data acquisition system (DAS) The DAS converts the signal into a digital form. We call this raw data Detector DAS Raw data (projections) The sinogram is an image representation of raw data Raw data reconstruction Reconstruction Fc; also known as Filter Convolution (Fc), Kernel, filter or Algorithm An Fc is a mathematical process used for Raw data reconstruction The Fc determined how the reconstructed image will look (soft tissue, bone, lung, etc. Raw Data Raw data reconstruction Raw Data X-ray tube Reconstruction  Convolution filters * Lak filter -increases amplitude linearly as a function of frequency; works well when there is no noise in the data * Shepp-Logan filter -incorporates some roll-off at higher frequencies, reducing high-frequency noise in the final CT image * Hamming filter -has even more pronounced high-frequency roll-off, Convolution- Mathematical with better high-frequency noise filtration used by the CT system suppression to remove blurring artifact during the back-projection method of image reconstruction.  Bone kernels and soft tissue kernels * Bone kernels have less high-frequency roll-off and hence accentuate higher frequencies in the image at the expense of increased noise(Hamming) * For clinical applications in which high spatial resolution is less important than high contrast resolution – for example, in scanning for metastatic disease in the liver – soft tissue kernels are used * Soft tissue kernels- More roll-off at higher frequencies and therefore produce images with reduced noise but lower spatial resolution(Shepp-Logan)  Multi Planar Reconstructed (MPR) * Although diagnosis is usually made from axial images alone, MPR or reformatting program adds new dimension to CT imaging. * It give different perspective of anatomy(from axial to sagittal,coronal and even oblique) * It is done without additional doses of radiation * Increased comfort to patient who cannot assumed desired positioning * Three dimensional MPR algorithm * 1. MIP-maximum intensity projection-ct angio * 2. SSD-shaded surface display * 3. SVD- shaded volume display Multiplanar reconstruction (MPR) * post processing technique applied to stacks of axial image data that can be reconstructed into other orientations or imaging planes  High-Resolution Ankle Study Axial Imaging with Multiplanar Results Coronal Reformat Axial Image 1 mm, Pitch 2, Emotion Sagittal Reformat  TOS *1.3 Differentiate the structures demonstrated on commonly performed computed tomography images  Cerebrovascular accident * Term used to describe stroke; no longer favored because it implies a random, unpredictable, or uncertain nature to the condition.  Convolution * Process of applying a filter function to an attenuation profile.  Calcium score * The amount of calcification on cardiac CT.  Direct coronal * describes position use to obtain images in coronal plane; used for head scans to provide images at the right angle to axial images  High resolution scans * use of scanning parameters that enhance contrast resolution of an image, such as thin slices, high matrices, high spatial frequency algorithms and small display FOV  TOS *2.1 Recognize equipment and supplies necessary to complete commonly performed computed tomography procedures.  Diagnostic Applications * Neurologic disorders * Chest * Abdomen * Spine * Musculoskeletal * Interventional procedures: * Abscess drainage * Tissue biopsy * Cyst aspiration  Contrast media * Its used primarily to distinguish normal anatomy from pathology and to make various diseases process more visible * Contrast media can be administered intravenously ,orally or rectally  IV Contrast Media * IVU- intravenous urogram(excretory urography) * Ionic Organic Iodide(Ionic)-High osmolality and greater change of reaction * Nonionic Organic Iodide(Nonionic)- Low osmolality and less chance of reaction * Contraindications: * Hypersensitivity * Anuria * Multiple myeloma * Diabetes mellitus * Severe renal or hepatic disease * Congestive heart failure * Pheochromocytoma * Sickle cell carcinoma * IV Contrast media should be used only with the approval of the radiologist and after careful consideration of patient history  Bolus * preset amount of radiopaque contrast medium injected rapidly per IV administration to visualize high flow vascular structure, usually in conjunction with dynamic scan; most often injected using a pressure injector  Oral or Rectal Contrast Media — Two types of contrast media for GI tract — Barium sulfate suspension- 1%-3% concentration can be used for abdominal CT(high concentration may cause streak/beam hardening artifacts) — Contraindication to Barium Sulfate(insoluble material) — Pre-operative patient — Patient suspected having gastrointestinal perforation — Bowel obstruction — Known hypersensitivity to BaSO4  Question * Which of the following factors may affect a patient’s calculated glomerular filtration rate (GFR)? * 1. age * 2. sex * 3. race * a. 1 and 2 only * b. 2 and 3 only * c. 1 and 3 only * d. 1, 2, and 3  Answer D. 1, 2, and 3 *GFR is calculated using the patient’s measured serum creatinine level and takes into account the patient’s age, sex, and race.  Question * Which of the following intravenous contrast agent administration methods provides the greatest overall plasma iodine concentration? * a. drip infusion * b. bolus technique * c. biphasic technique * d. CT portography  Answer * B. bolus technique * A bolus administration of contrast agent requires the entire volume of material to be injected over the shortest possible time. Accomplished by hand or with the use of an automatic injector, bolus administration provides the maximum plasma iodine concentration and subsequent tissue enhancement.  TOS * 2.3 Illustrate the patient preparation necessary for commonly performed computed tomography contrast studies.  Oral or Rectal Contrast Media — Water soluble solutions (diatrizoate meglumine and diatrizoate sodium)is an alternative for opacification of the GI tract — Extreme care must be used in the preparation of water-soluble solutions 2-5 % dilution have been found generally safe and clinically useful (15-40% considered hypertonic and may cause hypovolemia) — 20-30ml of CM to be diluted in 1,000 ml of solution(970ml of H2O)  TOS * 2.2 Explain the computed tomography acquisition protocol for commonly performed head/neck, thorax, and abdomen procedures.  Head CT Scan-Protocol — Post traumatic abnormalities — Suspected brain neoplasm or masses — Aneurysm — Abscess — Brain atrophy — Brain metastasis — Acquired or congenital abnormalities  Protocol for Head Trauma — Trauma- plain study(no contrast media required) — Thin slices for the base of the skull is mandatory(2/3mm) — Two types of windows should always be included in filming(brain parenchyma & bone) — Contrast media maybe indicated in follow-up studies or in delayed scans  Protocol for Stroke/CVA * Stroke is the third leading cause of death in the US * Clinical Stroke Terminology * Transient ischemic attack(TIA)- sudden neurologic deficit persisting < 15 min. with complete resolution by 24 hr. * Reversible ischemic stroke(RIND)- sudden neurologic deficit more than 24 hr. with resolution in 3 weeks * Completed stroke- sudden neurologic deficit lasting more than 21 days * CVA/ Stroke- contrast media not required * Routine plan of head is mandatory(2/3mm for base and 10mm for the brain) * Bone window in not required (except for patients who suffered head injury/trauma due to CVA)  Protocol for Neoplasm * Primary CNS neoplasm are the sixth most or Masses common tumors in adults with an average incidence of 5-6 per 100,000. * Approximately 20% 0f malignant tumor diagnosed under age 2o are brain tumors * Key points in evaluating CT images for Neoplasm * Lesion location and extent - intraaxial vs. extraaxial, supratentorial vs. infratentorial, single vs. multiple * Tumor margin or characterization- well circumscribed or poorly marginated, regular or irregular, contrast Grade III astrocytoma in a 33- enhancement(homogenous/inhomogeneous) year-old woman. Nonenhanced studies (right) * Mass effect- localized, focal shift/ generalized, show a mixed-attenuation remote effects lesion (solid and cystic areas) in the right parietal lobe with * Edema- vasoganic, interstitial adjacent vasogenic edema. * Brain herniation- may occur from one side to After contrast enhancement other or from one fossa to another (left), the solid component is enhancing.  Protocol for Neoplasm and Abscess *Plain and contrast studies is mandatory *Routine plan of head (2/3mm for base and 10mm for the brain) *Brain /parenchyma window is only required  Protocol for Aneurysm and AVM * Aneurysm is an abnormal focal enlargement of an artery * CT is the first modality of examination that provides an approach to selecting patients who needs further investigation * MRI can be performed to further characterized the lesion * Angiography is often necessary for the definite examination before treatment planning * Plain and contrast study in most cases * Although contrast enhancement has allowed for the direct visualization of the ruptured aneurysm in patients with subarachnoid hemorrhage , most institution would not routinely use CM.  Protocol for Acquired or Congenital Abnormalities * Malformation of the CNS are relatively common, about 5-10 percent of all malformation and approximately 1/3 of those diagnose after birth * Encephalocele, sometimes known by the Latin name cranium bifidum, is a neural tube defect characterized by sac-like protrusions of the brain and the membranes that cover it through openings in the skull These defects are caused by failure of the neural tube to close completely during fetal development. * Encephaloceles cause a groove down the middle of the skull, or between the forehead and nose, or on the back side of the skull. The severity of encephalocele varies, depending on its location. * Role of CT scan * CT provides detail information of the bone abnormality * Thin slice 1-2 mm – use for image reformation  Protocol for Intracranial Metastatic Disease * Common Parenchymal Brain Metastases * Adults- Lung,Breast, Melanoma, Genitourinary tract, Gastrointestinal tract * Children- Sarcomas, Germ cell tumors, Wilms tumor, Neuroblastoma * Plain and contrast enhanced study * Brain or parenchyma window and bone window in filming  Chest CT Scan — CT of the chest serve as diagnostic adjunct to conventional radiography, it serves as valuable imaging modality in the staging and management of the previously diagnose condition — Mediastinal and hilar lesions — Aneurysms — Abscess — Cardiac and pericardial disease — Evaluation of pulmonary nodules(benign/malignant)  Protocol for Chest CT — Contrast media is required-various methods are used(drip infusion/bolus injection) — Routine 10mm slice thickness from the apex to the costophrenic angle — Two types of windows should always be included in filming(mediastinum and lung parenchyma) — Bone window should be added in apparent bone lesion(metastasis)  Abdomen CT — Because of its speed, accuracy and ability to diagnose abdominal abnormalities imaging of the abdomen significantly change. — The use of ERCP, lymphangiography and other imaging procedures of the abdomen was reduced — Any abnormalities of the abdomen and pelvis is an indication for Abdominal CT — Metastatic lesion of the liver, pancreas, kidney or spleen, adrenal pathology — In the region of the pelvis-prostatic, cervix, urinary bladder and ovarian carcinomas. — Soft tissue masses, pelvic muscle abscess, and evaluation of the hip joint  TOS * 2.4 Distinguish the type, dosage, purpose, and route of contrast administration for common computed tomography procedures.  Protocol for Abdominal CT — Oral Contrast media administration and volume — Whole abdomen-700-900ml orally 30-45mins prior to scan, 300ml immediately before scan,800-1000ml enema immediately before scan — Upper abdomen- 400- 600ml orally 15-30 mins prior to scan, 300 ml immediately before scan  Protocol for Abdominal CT — Planning- 10mm slice thickness is usually required for the scanning of the abdomen with 10 mm table increments(can do additional thin slices in suspected areas) — Only one window setting is needed in filming CT of the abdomen(narrow scale 350- 400ww and 10-40wl) — However in study of the pelvis where trauma is one of the indications, bone window using wider window width is necessary to evaluate presence of fracture  Protocol for the Biliary Track * Optimal visualization of the biliary track requires modification of the examination technique * Factors that can affects * 1. The use oral and IV contrast * Use of oral can cause steak artifact across the CBD that can cause CBD stone * Scanning should be performed without oral contrast or with water to distend the stomach and the duodenum * The use of Glucagon to decrease peristalsis can help to improve image quality * When evaluating the presence of intrahepatic or CBD stones, scans should first be obtain without IV contrast * 2. Axial vs. Helical scanning * 3. Slice thickness and spacing(3-5mm) * 4. Selection of technical factors(mA/s)  Protocol for Pancreas(mass/pancreatitis) * For initial study of non contrast * Start at the bottom of the pancreas or at the iliac crest and scan upward(5mm at 5 mm interval ) * Bolus IV injection of CM (3ml/sec) * Oral contrast of 750-1000 ml 3% iodine water solution * For helical scanners: * 30-35 sec delay for arterial phase(3-5mm) * 70 sec total delay for venous phase(5mm) * For follow-up study – a routine abdominal scan is usually adequate * Direct contrast –starts at the top of the liver  Protocol for the Kidney(renal neoplasm) * CT is currently the method of choice for evaluation/staging suspected renal neoplasm * Both pre-and post contrast images are mandatory * Pre contrast – 5mm at 5mm increments * For lesion less than 2cm in diameter 3-5mm contiguous section should be used * At least 30-40g of iodine(150-180ml) IV contrast injected as bolus * Scans are obtained 60 sec after the initiation of CM from the diaphragm to the top of the kidney(5mm at 10mm interval an 5mm at 5mm through both kidneys) * Helical Mode: * 70 sec after CM initiation- using 1 sec scan time at 1:1 pitch) * 7mm by 7mm through the liver, 5mm by 5mm through the kidneys  TOS *2.5 Assess images for positioning, centering, appropriate anatomy and overall image quality.  Isocenter * The absolute center of the gantry  In-plane resolution * Resolution in the x y direction.  Reference detectors * Included in the detector array and help to calibrate data and reduce artifacts  Images * The HU value of water is 0, the HU value of dense bone is +1000, and the HU value of air is –1000 CT numbers or Hounsfield units Isotropic voxels Isotropic voxels Not Isotropic Isotropic 0.98mm x 0.98mm x 5mm 0.98mm x 0.98mm x 1mm 5mm Collimation 1mm Collimation Calibrated Field of View (C-FOV) C-FOV: also known as the “scan FOV” (raw data) C-FOV is determined by the collimation used to shape the beam Only objects that reside within the C-FOV are imaged The C-FOV should be slightly larger than the actual area of interest Large Small Large C-FOV C-FOV C-FOV Small C-FOV Display field of view (D-FOV) D-FOV: also known as the “reconstruction FOV” (image data) D-FOV can be set to reconstruct anywhere and any size within the C-FOV Since no data exists outside of the C-FOV, no image can be reconstructed there The D-FOV is used to focus in on the area of interest Large C-FOV D-FOV Field of view Display (DFOV) Calibrated (CFOV) Image Data Raw Data CFOV 180mm SS 18cm CFOV 240mm S 24cm y 320mm M 32cm DFOV 400mm L 40cm 500mm LL 50cm  Image Display * Each pixels is normally represented by 12 bits or 4096 gray levels, which is larger than the display range of the monitors or film * Window width and window level are used to optimize the appearance of CT images by determining the contrast and brightness levels assigned to the CT image data  Image Display * Window level or center * Is the CT number or HU value to be displayed as the medium of intensities in the image * The window level is normally chosen close to the average HU value of the tissue of interest (e.g. 10-50 HU for soft tissue) * Window width * It is the range of CT number displayed around the selected center and therefore determines the contrast * A narrow window width provides higher contrast than a wide window width  WW= 300 WL=0 WW=300 WL= 200 FIRST 300/2=150 SECOND 150-200=-50 THIRD 150+200=350 GRAY SCALE =-50 to 350  TOS * 3.1 Illustrate the technological * advancements in computed tomography application from single slice to helical/spiral, multi slice, and computed tomography angiographies  Helical(Spiral) Scanners * The x-ray beam central ray entering the patient follows a helical path during the scan } The relationship between the patient and tube motion is called pitch, which is define as the table movement during each revolution of x-ray tube divided by the collimation with(thickness) } Pitch=TM/ST } eg. For 5mm section thickness, the patient may move 10mm during the 1 second it takes for the tube to rotate through 360 degrees, and the pitch would thus be equal to 2 Multi-slice Spiral CT Scanners In multi-slice spiral CT scanners, instead of one row set of detectors, there are multiple rows. Single spiral vs multislice spiral Multi-slice 4 Slice 8 & 16 Slice 32 & 64 Slice Z-Axis 1mm x 15 1mm x 12 0.5mm x 4 0.5mm x 16 0.5mm x 64 1mm x 15 1mm x 12 30,464 Elements 35,840 Elements 57,344 Elements In MDCT scanners a single gantry rotation can produce multiple slices. Therefore, MDCT provides longer and faster z axis coverage per gantry rotation. MSCT Detector Configurations  TOS * 3.1 Illustrate the technological * advancements in computed tomography application from single slice to helical/spiral, multi slice, and computed tomography angiographies  Bolus triggering * Method of individualizing the scan delay using the contrast bolus itself to initiate the scan. It uses a series of low-radiation scans to monitor the progress of the contrast bolus. Once an adequate level of enhancement is achieved, the table moves to the starting level and scanning begins.  ß-blockers * Pharmaceuticals used to reduce motion artifact on cardiac CTA images by temporarily lowering a patient’s heart rate Maximum-intensity projection (MIP) * 3D technique that selects voxels with the highest value to display * reconstruction of brightness pixels from stack of image data into a 3D image  Virtual bronchoscopy * A form of volume rendering designed to reveal the inside of the airways. The technique is also called endoluminal imaging. Parenchyma contrast protocol Scan protocols must be different for best organ specific contrast enhancement Late Early arterial Arterial Venous 10s 30s 50s 70s 90s 110s Cortico Medullary nephrographic Phase Phase 10s 30s 50s 70s 90s 110s Pancreatic Arterial Phase Venous 10s 30s 50s 70s 90s 110s Liver Hypervascular tumor Non contrast Early AP (20s) Late AP (35s) Mix phase (45s) PVP (65s) Late phase (90s) Liver Hypovascular tumor Non contrast Early AP (20s) Late AP (35s) Mix phase (45s) PVP (65s) Late phase (90s)  TOS *3.2 Apply the methods for reducing radiation dose to the patient and the radiologic technologist's exposure to scatter radiation.  Bow tie filters * Mechanical filter that removes soft, or low energy, x-ray beams, minimizing patient exposure and providing a more uniform beam intensity  Automatic tube current modulation * An equipment option that will make changes in tube current (mA) based on the estimated attenuation of the patient at a specific location. * The estimations are derived from scout views done in both the antero posterior and lateral projections or from the previous slices. From these views, the mA will be programmed to vary by location along the length of the patient. The exact details of the option vary by manufacturer.  Beam pitch * Table movement per rotation divided by beam width. * The acronym CTDI is used to describe which of the following? * a. a specialized CT imaging technique used to measure bone mineral density * b. a quality control test that measures the accuracy of the laser lighting system * c. the radiation dose to the patient during a CT scan * d. a high-speed CT scanner used for cardiac imaging * C. the radiation dose to the patient during a CT scan * The CT dose index (CTDI) is used to quantify the radiation dose received by the patient during a CT scan. It involves the use of an ionization chamber to accurately measure radiation exposure for a given set of technical factors.  Question * Which of the following technical factors has a direct effect on patient dose? * a. matrix size * b. algorithm * c. mAs * d. window level  Answer * C. mAs * With no consideration of image quality, reductions in mA and/or scan time (seconds) are direct methods of decreasing patient dose during a CT exam.  Question * Which of the following devices is used to measure the patient dose from a CT examination? * a. Geiger counter * b. proportional counter * c. ionization chamber * d. film badge  Answer * C. ionization chamber * An ionization chamber is a device used to accurately measure radiation exposure. Radiation causes ionization within the chamber, which is measured by an electrode. * The amount of charged particles is proportional to the radiation exposure. The ionization chamber is an extremely accurate device that is used to quantify radiation exposure from a CT scan. Thank You