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Most radiation therapy is planned using the results of a 3D CT scan. A 3D scan largely presents a snapshot of the body at a particular point in time, however due to the time of the acquisition, in which the patient is likely to have moved in some way (even if only breathing), there will be an element of blurring or averaging in the 3D scan. [6]
State of the art modern CT scanners with a scan rate of up to 320 mm/s can acquire all the images within a 1-second X-ray exposure, avoiding the problems of respiratory motion, cardiac motion and contrast draining from the pulmonary circulation during the study. Even though the actual scan may be completed in 1 second or less, considerable ...
In conventional CT machines, an X-ray tube and detector are physically rotated behind a circular shroud (see the image above right). An alternative, short lived design, known as electron beam tomography (EBT), used electromagnetic deflection of an electron beam within a very large conical X-ray tube and a stationary array of detectors to achieve very high temporal resolution, for imaging of ...
The risks of CT scan radiation are especially important in patients undergoing recurrent CT scans within a short time span of one to five years. [157] [158] [159] Some experts note that CT scans are known to be "overused," and "there is distressingly little evidence of better health outcomes associated with the current high rate of scans."
A positive result suggests hemoperitoneum; often CT scan will be performed if the patient is stable [22] or a laparotomy if unstable. In those with a negative FAST result, a search for extra-abdominal sources of bleeding may still need to be performed.
Projectional radiography, CT scan and nuclear medicine imaging result some degree of ionizing radiation exposure, but have with a few exceptions much lower absorbed doses than what are associated with fetal harm. [20] At higher dosages, effects can include miscarriage, birth defects and intellectual disability. [20]
The temporal resolution of cesium iodide detectors in CBCT slows data acquisition time to approximately 5 to 20 seconds, which increases motion artifacts. The time required for image reconstruction takes longer for CBCT (1 minute) compared to MDCT (real time) due to the computationally demanding cone beam reconstruction algorithms. [3] [29]
This gives a total scan time of 15–20 minutes. Multi-headed gamma cameras can accelerate acquisition. For example, a dual-headed camera can be used with heads spaced 180 degrees apart, allowing two projections to be acquired simultaneously, with each head requiring 180 degrees of rotation.