Required Image Attributes For Perfusion Imaging; Contrast Injection Considerations; Other Considerations And References - GE Revolution CT User Manual

epilation (hair loss). The necessity for repeated scanning of the same location over extended
times results in skin doses that can be higher than those associated with routine CT
applications. Factors that influence these doses include kV, mA, scan time, perfusion acquisition
type, and table movement, if any, during the perfusion acquisitions. As with patient dose, lower
kV settings are recommended and should be used as appropriate to achieve appropriate image
quality for perfusion evaluation with respect to image noise based on body size, region scanned,
and scanner type. In all cases, you should refer to the manufacturers' reference perfusion
protocols as they reflect the appropriate kV, mA, and scan times for typical perfusion
acquisitions. Additional guidance may be found at professional society and/or regulatory
websites. See the recommended readings.

2.2.2.5 Required image attributes for perfusion imaging

The purpose of a CT perfusion series is to assess tissue perfusion and delivery of blood to the
organ and/or tissues of the organ; the acquisition parameters are different from those needed
for routine low contrast CT imaging applications. The acceptable noise level in CT perfusion is
typically higher than that for acquisitions routinely used in diagnostic imaging. Automatic
exposure control should not be used unless the manufacturer's reference perfusion protocol
employs it. Protocols should be adjusted accordingly for patient age, injection rate, injection
volume, and exam type (stroke versus tumor evaluation and head versus body).
CT perfusion scans need to acquire data over a sufficiently long duration to accommodate the
transit time associated with the physiological process of the contrast bolus moving through the
vascular system. The acquisition duration for a stroke study must cover the time from prior to
the arrival of the contrast material bolus through the approach of the venous signal to baseline.
This duration is directly dependent on the volume of contrast material injected, the rate of
injection, and the patient's cardiac output. If contrast material volumes or injection rates change
from exam to exam, the scan duration will need to be adjusted accordingly. Consult the
perfusion post-processing software manual for more detailed imaging and CT perfusion
information.

2.2.2.6 Contrast injection considerations

As the iodine concentration of contrast material decreases, contrast material volume or flow rate
may need to be adjusted to deliver the required enhancement. You should pay close attention to
the shape of the bolus, follow the bolus with saline, and use an injector capable of delivering the
required injection rates.
The contrast injection rate should be determined by referring to the applicable section of this
user manual, contrast agent labeling, and in consultation with a physician. Special consideration
should be given for children due to their smaller size.

2.2.2.7 Other considerations and references

Due to the necessity to obtain data over an extended time period in order to calculate relevant
perfusion parameters, repeated scanning of the same location is required. As a result, CT
perfusion acquisitions produce peak skin doses higher than those associated with routine
diagnostic CT imaging. Deterministic effects (e.g., tissue reactions such as skin reddening and
hair loss) are a dose-threshold phenomena that can appear with peak skin doses > 2 Gy. As
with all CT scanning, the CTDI
confirmed prior to the scan. For CT perfusion without table motion, the value of CTDI
over estimate the actual peak skin dose by approximately a factor of two (see reference to
Chapter 11 Scan
value displayed on the operator console should always be
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