American Journal of Roentgenology, Vol 164, 301-307, Copyright © 1995 by American Roentgen Ray Society
Noninvasive assessment of myocardial perfusion and metabolism: feasibility of registering gated MR and PET images
S Sinha, U Sinha, J Czernin, G Porenta and HR Schelbert
Department of Radiological Sciences, UCLA School of Medicine 90024.
OBJECTIVE: Positron emission tomography (PET), the reference technique for
in vivo noninvasive assessment of myocardial perfusion and metabolism, is
hampered by limited resolution and low signal-to-noise ratio. Cardiac MR
imaging, on the other hand, provides excellent soft- tissue contrast. This
study examines the feasibility of combining the information of these two
complementary techniques by the three- dimensional superimposition of
regional myocardial blood flow or substrate metabolism as depicted in
cardiac PET images on comparable MR images at the same cardiac phase and
spatial location. SUBJECTS AND METHODS: Three-dimensional, gated PET and MR
images of the heart were acquired at different phases of the cardiac cycle
from six normal volunteers and from one patient with coronary artery
disease that had been detected by coronary angiography. An interactive
algorithm using morphologic operators was developed to contour the left
ventricle on the MR and PET images. A three-dimensional surface-fitting
technique was used to register the left ventricle surfaces. The accuracy of
registration was estimated using 80 internal landmarks from six volunteer
scans. RESULTS: These techniques yielded PET images resliced along the same
spatial location and orientation as the MR images both in the transaxial
and short-axis views. The average residual, a measure of the goodness of
fit, was 26 (+/- 5.6) for the systolic and 13 (+/- 6.1) for the diastolic
images compared with an increase of that index from 9.3 at the best fit to
13.2 when the images were deliberately misaligned by 2 mm in each of two
directions. We verified that MR and PET images could be aligned with an
accuracy of 1.95 mm (+/- 1.6), which was approximately equal to the larger
of the two pixel sizes (i.e., 1.6 mm on PET images). CONCLUSION: MR and PET
images of the heart at identical cardiac phases can be accurately
superimposed. Both transaxial and short-axis views can be obtained, the
latter being more useful for PET quantification. This technique offers the
potential for characterizing regional interactions among contractile
function, blood flow, and substrate metabolism, especially when these are
altered regionally in cardiac diseases.