Phase-contrast magnetic resonance imaging (PC-MRI) can be used to produce multiframe cine flow images of the coronary arteries. Accurate coronary flow measurement requires the elimination of respiratory motion artifacts using k-space segmentation to acquire the data in a single breath-hold. However, the duration of the breath-hold is proportional to the number of cine frames. In the present study, the number of cine frames was varied and the accuracies of the coronary flow measurements were assessed using perivascular US. For the range of flows studied (2 ml/min to 147 ml/min), the correlation coefficients for PC-MRI and US increased (.70-.98) and the limits of agreement improved (+/-45 ml.min-1 to +/-10 ml.min-1) as the number of cine frames increased from one to six. The results suggest that the accuracy of breath-hold cine PC-MRI measurements of coronary artery flow improves as the number of cine frames increases.

Animals↗

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Acceptance testing of magnetic resonance imaging systems: report of AAPM Nuclear Magnetic Resonance Task Group No. 6.

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Humans↗

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Choice of phantom material and test protocols to determine radiation exposure rates for fluoroscopy.

The image intensifier entrance exposure rate (IIEER)) and entrance skin exposure rate (ESER) are two characteristics that can be used to determine whether a fluoroscope is adjusted to operate at an optimal dose rate level. This article presents solutions to some of the practical problems that are encountered when measuring these parameters. Because the energy response of the ion chamber used to measure exposure rates is different from that of the image intensifier, a fluoroscope with a perfect automatic exposure rate control will have an IIEER that depends on the phantom composition, phantom thickness, and x-ray tube potential. The authors developed a simple mathematic model to investigate the relationship of ion chamber response to image intensifier response and to determine the effects of phantom composition and thickness. Results from this model were compared with measurements made with two C-arm fluoroscopes. Variations of 40% or more in the IIEER and ESER can be ascribed to these phenomena.

Acrylic Resins↗