During the multi-modality imaging session, four specialists discussed the role of nuclear and CT imaging in the evaluation of ischemic heart disease. Although there are differences between different modalities, the overall message indicates that it is important to assess the physiologic effects of stenosis rather than just identifying a stenosis and that there is no perfect test for everyone. Choosing the appropriate diagnostic test not only depends on the individual being evaluated but also the capabilities and expertise of the medical centre.
Matthias Gutberlet, MD PhD (University Leipzip – Heart Center)
Dr. Gutberlet reminded us that not only Germany is the World Champion in football, but also in coronary angiography. He stressed that ischemia is not driven by morphology alone and that perfusion is an important part of assessment for ischaemia. Although there are concerns about radiation, the new technologies have allowed ultra-low dose SPECT studies to be performed at 1mSv. While CT has demonstrated significant prognostic information via calcium scoring in asymptomatic patients, it can further risk stratify patients with perfusion defects on SPECT imaging. CT can also improve SPECT perfusion interpretation by providing information for tissue attenuation correction. With the advancement of low dose CT and low dose SPECT, Dr. Gutberlet proposed that a future clinical hybrid imaging protocol with SPECT-CT can be performed in <30 minutes, and <5mSv.
Christopher Herzog, MD (Radiologie München)
Each year, there are millions of patients who present to the emergency department with the complaint of chest pain. Not only the ability to make the correct diagnosis, but also the efficiency is crucial to patient care. Dr. Herzog presented on this very topic and the challenges, which cardiac CT has demonstrated to work well in this setting. Dr. Herzog described how physicians in the emergency unit utilise the “three pillars” to assess a patient with chest pain: clinical presentation, ECG, and troponin. However, this may still miss 2-6% of patients who would have a major cardiovascular adverse event (MACE) within 30 days. This would translate into a large number of patients each year. Despite stress testing, there was no change in admission rate, repeat ED visits, decrease in MACE. With cardiac CT compared to stress testing, it has demonstrated high negative predictive value (99%), and decreased length of stay. There was no significant difference in 30-day MACE and overall cost. Dr. Herzog summarised:
He also touched on the subject of triple rule out (assessment of pulmonary embolism, coronary artery and aortic dissection) with CT. Despite the attractiveness of the test, he urged that there are many logistic and conceptual challenges. Because of these challenges, he advises that “Compromise would compromise everything”, and decreasing the diagnostic quality of each portion of the assessment.
João A. C. Lima, MD (Johns Hopkins University)
Dr. Lima gave a fantastic overview of the use of CT perfusion (CTP) in the assessment of coronary artery disease. He presented much of the data from the Core320 study, which obtained not only coronary anatomy by cardiac CTA, but also stress perfusion with CT in comparison to SPECT imaging. Patients with history of myocardial infarction (25%) and/or percutaneous coronary intervention (29%) were included in the study. The ROC curve for CTA and CTP for diagnosis of flow limiting stenosis had AUC of 0.87; whereas, CTA alone was 0.82 (p<0.001). When comparing CTP and SPECT, there was no significant difference in predicting ≥70% stenosis. He did point out that there are cases where CTP was able to pick up regional decrease in perfusion, which SPECT imaging missed on multi-vessel disease. At the end of the session, Dr. Lima stressed that in symptomatic patients, CTA should be performed rather than just a coronary calcium score, as patients with no coronary calcium can still have obstructive disease.
Osman Ratib, MD, PhD (University Hospital of Geneva)
As if MRI scanners aren’t complicated enough, trying to add another machine to perform hybrid imaging is almost an insurmountable challenge. In Dr. Ratib’s presentation, he was able to show us that it is possible, and how to take advantage of both imaging modalities. With technological advances, hybrid PET-MRI systems are being developed into an integrated system. With the MRI scanner, we are able to obtain great anatomical, functional data, as well as perfusion and scar assessment. With PET imaging, we are able to not only perform quantitative perfusion, but also assess metabolism. There are new tracers that are being developed (e.g. F-18 Flurpiridaz) which has a longer half-life than N13 ammonia and has a more linear correlation between myocardial uptake and coronary perfusion flow than the current SPECT radiotracers, which may help with better perfusion quantification in centres without cyclotrons. The use of PET with FDG may also help guide us in cases of mixed viability in cardiac MRI. However, he does warn us that we still have a lot to learn, as active inflammation can also cause an increase in metabolism, which may give a false positive reading regarding viability. There are also new PET techniques, which can demonstrate areas of angiogenesis and gene expression by integrating expression markers to radiotracers. By combining it with cardiac MRI, we can determine the specific areas of expression of these markers. Dr. Ratib concluded that
Reported by Steve Leung, MD (University of Kentucky)
Courtesy of Dr. Ratib in the utility of hybrid PET-MR
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