Computed Tomography (CT) Part 1 PDF

Computed Tomography - region of interest (ROI) A user-defined graphic outline that calculates the average CT number of a given...

Computed Tomography - region of interest (ROI) A user-defined graphic outline that calculates the average CT number of a given anatomic area. TOS 1.1 Illustrate scanning procedure as well as data and image acquisition in computed tomography scan. Who invented CT? Overview of the limitation of Classic Radiography Godfrey Hounsfield (conventional x-ray) - Engineer from EMI Ltd., London - Superimposition of the three dimensional information - Developed the first clinical useful CT scanner in 1971 onto two dimension causes the loss of low – tissue Allan McLeod Cormack contrast anatomic structures - South Africanborn 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 - Presence of scatter obscures low-tissue contrast anatomic CT Development structures - 1964 EMI (England) developed the CT scanner (by Mr.Hounsfield) - 1973 EMI released MARK 1 Advantages of CT over Classic Radiography Basic Principle of Data Acquisition - Three dimensional information in the form of a series of thin slices of the internal structures of the part in question Overview of the limitation of Classic Radiography - The system is much more sensitive compared to ( x-ray) 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  TOS 1.2 Show the difference 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 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 - X-rays produce “shadow-gram” 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) - The X-ray beam passes through the 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 Raw data (projections) - The sinogram is an image representation of raw data - CT images are derived by mathematical analysis of projection data sets (sinograms) at each location along the long axis. Raw data reconstruction Bone kernels and soft tissue kernels - Reconstruction Fc; also known as Filter Convolution (Fc), Bone kernels Kernel, filter or Algorithm - have less high-frequency roll-off and hence accentuate - An Fc is a mathematical process used for Raw data higher frequencies in the image at the expense of increased noise(Hamming) reconstruction Soft tissue kernels - The Fc determined how the reconstructed image will look - More roll-off at higher frequencies and therefore produce (soft tissue, bone, lung, etc. images with reduced noise but lower spatial - Projection data are convolved with a mathematical filter resolution(Shepp-Logan) before being back projected - For clinical applications in which high spatial resolution is - Convolution is type of mathematical multiplication less important than high contrast resolution – for example, in scanning for metastatic disease in the liver – soft tissue kernels are used 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 Convolution filters Lak filter - increases amplitude linearly as a function of frequency; - post processing technique applied to stacks of axial works well when there is no noise in the data image data that can be reconstructed into other Shepp-Logan filter orientations or imaging planes - incorporates some roll-off at higher frequencies, reducing high-frequency noise in the final CT image TOS - 1.3 Differentiate the structures demonstrated on Hamming filter commonly performed computed tomography images - has even more pronounced high-frequency roll-off, with better high-frequency noise suppression Cerebrovascular accident - Term used to describe stroke; no longer favored because it implies a random, unpredictable, or uncertain nature to the condition. Convolution Convolution - Process of applying a filter function to an attenuation - Mathematical filtration used by the CT system to remove profile. blurring artifacts during the back-projection method of image reconstruction. Calcium score IV Contrast Media - The amount of calcification on cardiac CT. 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 Direct coronal - Pheochromocytoma - Sickle cell carcinoma - describes position use to obtain images in coronal plane; - IV Contrast media should be used only with the approval used for head scans to provide images at the right angle of the radiologist and after careful consideration of to axial images 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 High resolution scans - Barium sulfate suspension- 1%-3% concentration can be - use of scanning parameters that enhance contrast used for abdominal CT (high concentration may cause resolution of an image, such as thin slices, high matrices, streak/beam hardening artifacts) high spatial frequency algorithms and small display FOV Contraindication to Barium Sulfate(insoluble material) - Pre-operative patient Patient suspected having gastrointestinal perforation - Bowel obstruction - Known hypersensitivity to BaSO4 Question 1. Which of the following factors may affect a patient’s calculated glomerular filtration rate (GFR)? 1. age TOS 2.1 Recognize equipment and supplies necessary to 2. sex complete commonly performed computed tomography 3. race procedures. a. 1 and 2 only b. 2 and 3 only c. 1 and 3 only Diagnostic Applications d. 1, 2, and 3 - Neurologic disorders GFR is calculated using the patient’s measured serum creatinine - Chest level and takes into account the patient’s age, sex, and race. - Abdomen - Spine 2. Which of the following intravenous contrast agent - Musculoskeletal administration methods provides the greatest overall Interventional procedures: plasma iodine concentration? - Abscess drainage a. drip infusion - Tissue biopsy b. bolus technique - Cyst aspiration c. biphasic technique d. CT portography A bolus administration of contrast agent requires the entire volume of material to be injected over the shortest possible time. Contrast media Accomplished by hand or with the use of an automatic injector, - It's used primarily to distinguish normal anatomy from bolus administration provides the maximum plasma iodine pathology and to make various diseases process more concentration and subsequent tissue enhancement. visible - Contrast media can be administered intravenously ,orally or rectally TOS 2.3 Illustrate the patient preparation necessary for Protocol for Neoplasm or Masses commonly performed computed tomography contrast studies. - Primary CNS neoplasm are the sixth most common tumors in adults with an average incidence of 5-6 per 100,000. Head CT Scan-Protocol - Approximately 20% 0f malignant tumor diagnosed under - Post traumatic abnormalities age 2o are brain tumors - Suspected brain neoplasm or masses - Key points in evaluating CT images for Neoplasm - Aneurysm - Lesion location and extent intraaxial vs. extraaxial, - Abscess supratentorial vs. infratentorial, single vs. multiple - Brain atrophy - Tumor margin or characterization well circumscribed - Brain metastasis or poorly marginated, regular or irregular, contrast - Acquired or congenital abnormalities enhancement (homogenous/inhomogeneous) - Mass effect localized, focal shift/ generalized, remote effects - Edema vasoganic, interstitial - Brain herniation may occur from one side to other or from one fossa to another Protocol for Head Trauma - Trauma - plain study(no contrast media required) - Thin slices for the base of the skull is mandatory(2/3mm) Protocol for Aneurysm and AVM - Two types of windows should always be included in filming(brain parenchyma & bone) - Aneurysm is an abnormal focal enlargement of an artery - Contrast media maybe indicated in follow-up studies or in - CT is the first modality of examination that provides an delayed scans 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 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 Protocol for Acquired or Congenital Abnormalities than 21 days - CVA/ Stroke- contrast media not required - Malformation of the CNS are relatively common, about - Routine plan of head is mandatory(2/3mm for base and 5-10 percent of all malformation and approximately 1/3 10mm for the brain) of those diagnose after birth - Bone window in not required (except for patients who - Encephalocele, sometimes known by the Latin name suffered head injury/trauma due to CVA) 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 Protocol for Chest CT are caused by failure of the neural tube to close completely during fetal development. - Contrast media is required-various methods are used(drip - Encephaloceles cause a groove down the middle of the infusion/bolus injection) skull, or between the forehead and nose, or on the back - Routine 10mm slice thickness from the apex to the side of the skull. The severity of encephalocele varies, costophrenic angle depending on its location. - Two types of windows should always be included in - Role of CT scan filming(mediastinum and lung parenchyma) - CT provides detail information of the bone abnormality - Bone window should be added in apparent bone - Thin slice 1-2 mm – use for image reformation lesion(metastasis) Abdomen CT - Because of its speed, accuracy and ability to diagnose abdominal abnormalities, imaging of the abdomen Protocol for Intracranial Metastatic Disease significantly change. Common Parenchymal Brain Metastases - The use of ERCP, lymphangiography and other imaging Adults procedures of the abdomen was reduced - Lung, Breast, Melanoma, Genitourinary tract, - Any abnormalities of the abdomen and pelvis is an Gastrointestinal tract indication for Abdominal CT Children - Metastatic lesion of the liver, pancreas, kidney or spleen, - Sarcomas, Germ cell tumors, Wilms tumor, adrenal pathology Neuroblastoma - In the region of the pelvis-prostatic, cervix, urinary bladder and ovarian carcinomas. - Plain and contrast enhanced study - Soft tissue masses, pelvic muscle abscess, and evaluation - Brain or parenchyma window and bone window in filming of the hip joint - 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)