Image quality is an important value of all radiographic imaging procedures. Accurate measures of both image quality and patient radiation risk are needed for effective optimization of diagnostic imaging. Images are acquired for specific purposes, and the result depends on how well this task is performed. The imaging performance is mainly influenced by the imaging procedure, examined object, contrast agents, imaging system, electronic data processing, display, maintenance and the operator. Spatial resolution (sharpness), contrast resolution and sensitivity, artifacts and noise are indicators of image quality.
A high image contrast provides the discrimination between tissues of different densities.
The image resolution states the distinct visibility of linear structures, masses and calcifications.
Noise and artifacts degrade the image quality. In computed tomography (CT), high spatial resolution improves the visibility of small details, but results in increased noise. Increased noise reduces the low contrast detectability. Noise can be reduced by the use of large voxels, increased radiation dose, or an additional smoothing filter, but this type of filter increases blurring.
An image acquisition technique taking these facts into account maximizes the received information content and minimizes the radiation risk or keeps it at a low level.

See also As Low As Reasonably Achievable.

(CCTA) Coronary computed tomography angiography is a diagnostic imaging procedure to visualize the coronary arteries. CCTA is a non-invasive angiogram that allows the assessment of narrowed and clogged arteries that can cause heart attack and stroke.
Coronary CTA is a non-invasive alternative to traditional angiography that offers detailed images of heart function, resulting in faster, more accurate diagnosis. It helps stratify cardiac risk in patients with low to intermediate likelihood of coronary artery disease. For some patients with chest pain, coronary CTA can rule out the need for cardiac catheterization.
Coronary imaging requires a very fast CT scan, because the coronary arteries and other cardiac structures move rapidly during the cardiac cycle. The current 'state of the art' 64 slice multi-detector row CT systems rotate around the patient in less than 500 ms. The data must be acquired monitored by an electrocardiogram, which allows the computer to reconstruct retrospectively slices at different small segments of the cardiac cycle. This cardiac synchronization reduces motion artifacts in the coronary arteries and provides movies of the beating heart and valve motion.
See also Coronary Angiogram, Calcium Score, Cardiac Phase, Cine Mode and Defibrillator.

ECG trigger methods synchronize the heartbeat in order to minimize motion artifacts, whereat the r-wave is used as the trigger. ECG gating techniques are useful whenever data acquisition is too slow to occur during a short fraction of the cardiac cycle.

See also Triggering and Trigger Delay.

VoLumen® is a low density barium sulfate contrast agent especially designed for MDCT (multi-detector row CT) and PET/CT exams to mark the bowel. Volumen is useful for CT studies of the small bowel and mesenteric vessels.
Positive oral contrast media may limit the delineation between soft bowel tissues and the lumen and may cause artifacts. Water or methyl-cellulose transits very rapidly and may limit bowel distention and soft tissue differentiation. Volumen, similar to water appears hypodense (low Hounsfield values) on CT scan and can be used in conjunction with IV contrast. VoLumen's low density formulation is well-suited for computed tomography enterography.