Smartma; Organ Dose Modulation (Odm) - GE Revolution CT User Manual

2.6.2 SmartmA

In addition to adjusting for patient attenuation in the z-axis, SmartmA adjusts patient exposure
as a function of X-ray tube angle as the tube rotates around the patient, thus leading to mA
modulation in the x, y and z-axes. For each scanned section in the z-axis direction, the system
calculates an mA for the lateral and anterior-posterior patient axes from an estimation of the
patient attenuation through the long and short axes, respectively.
Patient exposure for a SmartmA scan is reduced when compared to a similar scan employing
manual mA. This is shown in
angle for manual mA and SmartmA of a uniform oval shaped phantom. The image on the left
shows the fixed mA and SmartmA mA profiles as a function of X-ray tube angle, with an
accompanying reduction in overall patient exposure. In this case a manual mA technique can be
thought of as the equivalent of an AutomA based modulation, as employed in the AutomA
feature on previous products.
While the SmartmA mA table specifies different mA values per rotation, corresponding to the
mA in the anterior-posterior direction and in the lateral direction, i.e. at 0, 180° and 90° and
270°, respectively, the actual mA is continually varying in a smooth fashion between the
specified mA values as a function of X-ray tube angle to the patient, as shown in
Illustration 2 shows a sample SmartmA mA profile as a function of gantry rotation for a uniform
oval polyethylene phantom with the same prescribed Noise Index using (blue) Manual mA and
(orange) the SmartmA mode of Automatic Exposure Control (AEC). The reduction in patient
exposure enabled by SmartmA is clearly illustrated as a function of X-ray tube angle compared
to the patient exposure illustrated by the manual mA profile. The expected mA reduction range
when using SmartmA depends on the size and shape of the patient, and on the prescribed
Noise Index, with a greater reduction expected for a relatively larger and more asymmetric
patient, when a relatively low Noise Index is prescribed.

2.6.3 Organ Dose Modulation (ODM)

Organ Dose Modulation (ODM) provides a mode to reduce X-ray tube current (mA) in anterior
direction of the patient where the most radiation sensitive organs are located while maintaining
overall diagnostic image quality by modulating X-ray tube current (mA) according to the X-ray
tube angle.
Chapter 11 Scan
Illustration 2 which illustrates the mA as a function of rotation
Revolution CT User Manual
Direction 5480385-1EN, Revision 1
Illustration 2.
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