Assessment of left ventricular function during treadmill exercise with a new method of motion correction of first-pass radionuclide angiography using a multiwire gamma camera

Abstract

Background: Earlier studies with first-pass radionuclide angiography during treadmill exercise used Anger(single-crystal) or multi-crystal gamma camera, a technetium tracer and either did not correct for motion or used external point sources. Motion correction by such dual-isotope method is limited to plane movement corrections and inherently assumes that the patient is rotationally fixed. Method: In this study we used a Multiwire gamma camera (MWGC), a generator-produced Ta-178, which has a low energy and a short half-life (9.3 min) and a novel method of motion correction during treadmill exercise testing. Motion correction was achieved by incorporating an electromagnetic tracking device to track the movement of left ventricle (LV) center, based on real-time six-dimensional position and orientation of a sensor attached to the patient's back, and LV center rotation in patient's chest contour. Result: We studied 72 patients who had normal rest and stress gated single-photon emission tomography (SPECT) myocardial perfusion images. There were 42 men and 30 women, aged 51±12 years. The resting gated SPECT LV ejection fraction (EF) was 61±10% (range 26 to 87%). The resting EF in the upright position by MWGC was 58±11% ( r = 0.33, p = 0.005 vs gated SPECT). At peak exercise the EF by MWGC was 62±24% if uncorrected for motion and 70±11% when motion corrected. A normal response to exercise , defined as resting EF>50%, and an increase in EF from rest to exercise of 5% or more, was seen in 22 patients (30%) with the uncorrected method and 42 patients (58%) with the corrected method (p < 0.05). Abnormal EF response despite normal perfusion is not unexpected in patients with hypertension or other conditions. Conclusion: Thus, assessment of LV function at rest or peak treadmill exercise is feasible with a MWGC and a novel motion correction algorithm. The method may offer a cost-effective and rapid screening strategy to identify low- and high-risk patients with suspected or known CAD.