When compared to conventional radiography, the organ doses from CT scanning are much larger; for example, an abdominal CT scan delivers 50 times more stomach dose than a conventional anterior-posterior abdominal x-ray exam. In any given CT study, the radiation doses to particular organs depends on various factors, which includes the number of scans, the tube current and scanning time in milliamp-seconds (mAs), the patient size, the axial scan range, the scan pitch, the tube voltage in the kilovolt peaks (kVp), and the specific design of the scanner. These parameters can be adjusted according to patient’ s size and clinical requirements, so that reduction of radiation dose can be achieved while still acquiring diagnostic images.
This is the information that I have learned most from studying in this unit. During the course of my training, I came to know that there are three ways to reduce the radiation risk from CT. One is to reduce the CT-related dose, secondly by replacing CT with other modalities like ultrasound and magnetic resonance imaging (MRI), whenever possible, and thirdly by decreasing the number of CT studies that are prescribed.
I came to know that other than noise filtering techniques and scanner geometry, a very effective method of lowering radiation dose is tube current modulation. This could be angular tube current modulation, longitudinal tube current modulation, and Angular-longitudinal tube current modulation. Angular tube current modulation involves the variation of the tube current to equalize the photon flux to the detector as the x-ray tube rotates about the patient. I remember choosing the initial value of the tube current– time product and also having modulated the tube current within one gantry rotation.
Longitudinal tube current modulation involves the variation of the radiation dose among anatomic regions (e. g. shoulders vs. abdomen vs. pelvis). I have observed that this is done by varying the tube current along the z-axis of the patient.
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