The researcher's objective was to overcome the limits of conventional MRI, which has a spatial resolution of >0.4 mm and is not sensitive enough to visualize the digital vasculature. Dr. Wang and colleagues studied eight SSc patients (six females, two males, mean age 54.5, mean disease duration 8.3 years) and eight age- and sex-matched healthy control subjects. All had MRIs taken using a custom-made radio-frequency receive-only finger coil.
“The coil has a diameter of 25 mm to accommodate possible flexion contractures in impaired fingers. The longitudinal coverage from the coil is 65 mm so that, at a minimum, the two terminal IP [interphalangeal] joints of the index finger can be covered during the scan,” Dr. Wang said.
“Dramatically different” vasculature seen in SSc fingers
Subjects were scanned in the supine position on the right index finger. The same imaging sequence was performed twice with and without inflow saturation to distinguish arterial and venous blood flow.
Finger angiograms were evaluated for palmar digital artery lumen area to characterize the state of the arterial circulation, for lumen contours of the proper palmar digital artery at the location of the distal IP joint, and with a count of number of visible dorsal veins to characterize venous circulation. Overall finger vasculature integrity was measured using a 5-point scale from 0 (no visible vessels) to 4 (clear continuous visible vessels with sell-defined boundaries).
The investigators reported “dramatically different visual appearance of the digital vasculature” between SSc subjects and healthy controls, including generally less visible vessels and more discontinuities.
“It is also noteworthy that the radial artery of the index finger was visible in all healthy volunteers but in only four out of eight SSc subjects,” Dr. Wang said. There was also a strong correlation between disease duration and lumen area/vascular score measurements from the SSc subjects, suggesting that these digital vascular SSc lesions progress with time. Further long-term studies of disease progression are planned.
“The finger coil used in [the] study is critical to achieving the resolution and image quality needed for micro-MRA. The high spatial resolution required to accurately characterize digital arteries necessitates the use of a small volume coil for the highest intrinsic signal-to-noise ratio. The multiloop solenoid coil provides the volume coverage necessary for whole finger imaging while maintaining a high SNR. The SNR of the finger coil is up to [four] times higher than that of the wrist coil, which is otherwise the most sensitive coil provided by the manufacturer for clinical applications. With this SNR improvement, an in-plane resolution of 0.16 x 0.21 mm2 and a slice thickness of 1.2 mm can be achieved for quantitative measurements on small vessels,” the authors wrote. The new device also does not require the use of gadolinium-based contrast agents, which may be especially risky for SSc patients with compromised renal function.
Dr. Wang said that the new technique also might be useful in primary Raynaud's disease, vasculitis, and antiphospholipid syndrome, as well as in providing prospective biomarkers for use in clinical trials of SSc treatments.
Reference
1. Micro magnetic resonance angiography of the finger in systemic sclerosis. Wang J, Yarnykh VL, Molitor JA, et al. Rheumatology. 2008;47:1239-1243.
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