Special Imaging Techniques Chapter 6 Bushong

Dynamic Computed Tomography (DCT) Dynamic scanning implies 15 or more scans in rapid sequence within one minute Dynamic scanning us used for trauma, cardiac, and vascular imaging Dynamic scanning allows imaging in the arterial phase following a bolus injection

DCT Typical dynamic scanning would be 15 one second scans, separated by a two-second interscan time during which the couch would increment a distance equal to the slice thickness Tube cooling will limit the extent of dynamic scanning Dynamic scanning has largely been replaced by spiral CT

DCT Spiral CT permits imaging of the entire liver and pancreas at a specified time phase such as arterial, portal, or venous CT guided biopsy is performed to localize using a region of interest feature Radiopaque markers are used to help guide a needle to the area of interest

DCT Wide window width (WW = 500 to 1000), low window level (WL = 40 to 60) for bone imaging Wide WW (700 – 900), high WL (800) for lung imaging Narrow WW (200 – 400), low WL (40 – 60) for abdomen and pelvis imaging Computed tomography fluoroscopy provided 8 images/second for near real time imaging

DCT Computed tomography fluoroscopy is most useful for angiointervention in the abdomen and chest Computed tomography fluoroscopy results in high patient and personnel dose CT fluoroscopy is particularly helpful for CT- guided biopsy Patient dose during CT fluoro is kept low by using low mA (30)

Quantitative CT Quantitative CT (QCT) employs an ROI to determine the average CT number of a tissue as an aid to diagnosis QCT can be helpful in characterizing a tumor QCT can distinguish between cystic and solid lesions

QCT With spirometric control and breath-triggered imaging, QCT can measure the density and characterize the structure of lung tissue QCT is very helpful for measuring tissue perfusion following bolus injection of an iodinated contrast media QCT allow measurement of cerebral blood flow following xenon inhalation

Heart Scan Electron Beam CT (EBCT) of the heart can reveal plaque volume and calcium content in coronary arteries EBCT of the heart is a cost effective screening for coronary artery disease with no patient discomfort A typical heart scan consists of 40 ECG triggered 3 mm images acquired at 100 ms each

Heart Scan Calcium is a natural marker in atherosclerotic plaques making EBCT an effective screening device

CT Angiography (CTA) CTA allows maximum visualization of the pulmonary artery and its segmental branches Stroke is the highest cause of morbidity and the third highest cause of mortality CTA requires low kVp and mA (90kVp, 100mA) CTA is best performed with spiral CT

CTA Unlike MRA, CTA is not susceptible to motion or flow artifacts CTA is much less invasive and lower in dose than conventional angiograms Bone is removed from CTA maximum intensity projection images by an editing procedure called image segmentation

CTA CTA requires less film than conventional angiography CTA requires less staff than conventional angiography CTA requires less contrast media than conventional angiography CTA is at least a factor of two less expensive than conventional angiography

CTA CTA employs MIP and multiplanar reconstruction to maximum advantage CTA success depends on collimation, pitch, vessel orientation, and reconstruction interval

Multislice Imaging (MI) This development was first produced by Elscint and is now available from all CT manufacturers Multislice imaging incorporates two or more contiguous detector arrays Multislice imaging produces two or more section images simultaneously Multislice imaging is a spiral CT technique

MI Multislice imaging greatly reduces imaging time, from approximately 3 minutes with conventional CT to less than 30 seconds The main advantage to MI is faster imaging with better spatial resolution Complete x-ray tube/detector array rotation in less than 1s Partial scan images can be obtained in approximately 100ms

MI Best imaging requires a pitch of 3:1 to 6:1 Multislice imaging requires exceptional engineering because of the mechanical forced produced by gantry rotation Image reconstruction uses 360 degree interpolation rather than 180 degree interpolation

MI 360 degree interpolation of multislice images allows faster imaging with improved spatial and temporal resolution and reduced noise Misregistration of anatomy is reduced because of the faster couch speed Motion artifacts are greatly reduced Patient breath-hold is much less demanding

MI Imaging larger z-axis volume in less time is possible with MI Less contrast media is required Patient throughput is increased with MI Variable slice thickness can be produced with postprocessing. In many cases, rescan is unnecessary because of postprocessing

MI CTA is greatly improved with MI Because of imaging speed, coronary artery calcification assay with MI is a challenge to EBCT