"By combining the physiological - or functional - images of the blood flow to the heart muscle at stress and at rest with the high-resolution anatomical depiction of coronary arteries and their blockages, we can determine the diagnosis of coronary artery disease more accurately", explained Piotr Slomka, a research scientist with the Artificial Intelligence in Medicine Programme at the departments of Medicine and Imaging at Cedars-Sinai Medical Center in Los Angeles, California.
"The idea is to combine two different images of the heart obtained by two different techniques: single photon emission computed tomography (SPECT) and cardiac computed tomography (CT) angiography", stated Piotr Slomka, who is also an associate professor with the David Geffen School of Medicine at the University of California in Los Angeles. A cardiac CT angiography is a tomographic X-ray procedure that produces detailed images of coronary vessels of the heart. SPECT is a non-invasive imaging technique that uses short-lived radio-active substances to produce three-dimensional images of the blood flow to the heart muscle.
"These scans are obtained at different times - and even at different locations - but our computer software puts the information together in 3D", he explained. "This synergistic integration allows simultaneous analysis of the heart muscle blood flow with a highly accurate image of coronary arteries and their blockages", he noted. "It eliminates the limitations of imaging with either SPECT or CT alone", detailed Piotr Slomka.
"This combination could be accomplished also by specialized hybrid scanners; however, our software approach is more flexible since the combination is required only in a subset of cases. We can use the best possible CT angiography equipment and SPECT at much lower cost than the dedicated combined scanner. In any case, the hybrid scanners would still require software techniques similar to ours due to the heart motion", stated Piotr Slomka.
About 7 million Americans suffer from coronary heart disease, and about 500.000 will die from the disease annually. Coronary artery disease, the most common form of heart disease, occurs when the arteries that supply blood to the heart muscle become hardened and narrowed, according to Piotr Slomka. The arteries harden and narrow due to build-up of a material called plaque on their inner walls. Over time, blood flow to the heart muscle is reduced, and, because blood carries much-needed oxygen, the heart muscle is not able to receive the amount of oxygen it needs.
"The fusion can be used selectively for the diagnosis of patients who undergo one of the exams - either SPECT or CT angiography - with inconclusive results because there was some difficulty in interpretation. In these difficult cases, a complementary anatomical or physiological scan - and this kind of image integration - helps a physician make a better diagnosis", stated Piotr Slomka. Additional research is needed. "We need to obtain more data to determine which patients would benefit most from this technique. We need to further automate the software to provide highly accurate alignment of the images", he added.
"This work illustrates the value of a combined 3D display of blood flow together with CT angiography imaging data", explained Josef Machac, SNM's Scientific Programme Committee cardiovascular vice chair. "Used together in this way, the modalities demonstrate performance superior to that of either modality alone. This has been speculated on previously, but now we have empirical evidence that it is true", added the director of nuclear medicine at the Mount Sinai School of Medicine in New York City.
The authors of the scientific paper titled "Software Fusion of 64-slice CT Angiography and Myocardial Perfusion SPECT: Evidence of Synergy", are P.J. Slomka, Y. Suzuki, S. Van Kriekinge, P.B. Kavanagh, A. Gutstein, D.S. Berman and G. Germano, all with Cedars-Sinai Medical Center, Los Angeles, California; Y. Elad, R. P. Karlsberg, Cardiovascular Medical Group of Southern California, Los Angeles, California.
SNM is an international scientific and professional organisation of more than 16.000 members dedicated to promoting the science, technology and practical applications of molecular and nuclear imaging to diagnose, manage and treat diseases in women, men and children. Founded more than 50 years ago, SNM continues to provide essential resources for health care practitioners and patients; publish the most prominent peer-reviewed journal in the field - the Journal of Nuclear Medicine; host the premier annual meeting for medical imaging; sponsor research grants, fellowships and awards; and train physicians, technologists, scientists, physicists, chemists and radiopharmacists in state-of-the-art imaging procedures and advances.
SNM members have introduced - and continue to explore - biological and technological innovations in medicine that non-invasively investigate the molecular basis of diseases, benefiting countless generations of patients. SNM is based in Reston, Virginia.