An investigation involving 31 patients found the sensitivities and specificities for the detection of peripheral artery obstructions to range from 90% to 96% and 98% to 99%, respectively. Agreement with DSA was substantial (k-values between 0.88 and 0.98). Implementation of hybrid MRA led to changes in seven patients' treatment plans. These changes were due to the detection of patent infrageniculate ar¬teries that were not seen on DSA images.12
Researchers in a later study labeled a significantly higher number of calf and foot segments as diagnostic when using time-resolved MRA instead of a standard bolus chase MRA protocol.14
Contrast-enhanced pedal MRA can be performed routinely in patients after bypass grafting. Vessel imaging may be supplemented by soft-tissue imaging for the delineation of associated inflammatory and necrotic complications and Charcot's osteoarthritis in the diabetic foot (Figure 3). Pedal soft-tissue enhancement is a common finding on time-resolved MRA of the feet that may be used to identify sites of subclinical pedal soft-tissue injury.15
Diabetes can be regarded as a disease with systemic manifestations. Hybrid bolus chase MRA may be replaced by whole-body MRA in these patients.16-18 Techniques used for whole-body MRA are being improved by the introduction of time-resolved protocols and data acquisition with a continually moving table.19
Implementation of new MR sequences and parallel acquisition techniques means that submillimeter 3D data sets can be acquired in just a few seconds.18,19 MRA images with perfect arterial enhancement can be attained without bolus-timing. The rapid succession of 3D data sets allows the assessment of flow and function. If you need only a few seconds for acquisition of a 3D data set, and if you repeat it several times, then you obtain some kind of 4D image that delivers some information on flow.
These protocols for whole-body MRA may, in the future, be complemented by cardiac and brain MRI. The result will be disease-specific whole-body imaging.20 For this to be possible, however, multiple coil systems, receiver channels, and parallel imaging techniques will be required to ensure sufficient temporal and spatial resolution.
References
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Dr. Kreitner is an assistant professor and staff radiologist in the department of diagnostic and interventional radiology at Johannes Gutenberg-University in Mainz, Germany.
