The year in cardiac imaging

Patients with exercise-associated ventricular ectopy present evidence of myocarditis

BACKGROUND

The origin and clinical relevance of exercise-induced premature ventricular beats (PVBs) in patients without coronary heart disease or cardiomyopathies is unknown. Cardiovascular magnetic resonance enables us to non-invasively assess myocardial scarring and oedema. The purpose of our study was to discover any evidence of myocardial anomalies in patients with exercise-induced ventricular premature beats.

METHODS

We examined 162 consecutive patients presenting palpitations and documented exercise-induced premature ventricular beats (PVBs) but no history or evidence of structural heart disease. Results were compared with 70 controls matched for gender and age. ECG-triggered, T2-weighted, fast spin echo triple inversion recovery sequences and late gadolinium enhancement were obtained as well as LV function and dimensions.

RESULTS

Structural anomalies in the myocardium and/or pericardium were present in 85 % of patients with exercise-induced PVBs. We observed a significant difference between patients with PVBs and controls in late gadolinium enhancement, that is 68 % presented subepicardial or midmyocardial lesions upon enhancement, whereas only 9 % of the controls did so (p < 0.0001). More patients presented pericardial enhancement (35 %) or pericardial thickening (27 %) compared to controls (21 % and 13 %, p < 0.0001). Myocardial oedema was present in 37 % of the patients and in only one control, p < 0.0001. Left ventricular ejection fraction did not differ between patients and controls (63.1 ± 7.9 vs. 64.7 ± 7.0, p = 0.13).

CONCLUSIONS

The majority of patients with exercise-associated premature ventricular beats present evidence of myocardial disease consistent with acute or previous myocarditis or myopericarditis.

The ovine corpus luteum angiogenesis model: a tool for developing imaging technology

Robust tools for the quantitation of perfusion are not fully developed using contrast enhanced ultrasound (CEUS). The ovine corpus luteum (CL) is a transient gland in the ovary that is formed to produce the hormone progesterone essential for maintenance of pregnancy. Importantly, it has a dense microvascular network with predictable and well-regulated angiogenic mechanisms. In a number of different experiments it was shown that this property may be used to investigate and refine imaging methodology. Using a Philips iU22 ultrasound scanner (Philips Medical Systems Corp, Seattle, WA) in contrast imaging mode it was shown that a highly controlled experiment may produce high levels of reproducibility in the transit of contrast with standard uncertainty below 10%. Also, compartmental kinetics models were tested. The use of prostaglandin F2alpha promotes an intense anti-angiogenesis, allowing monitoring with CEUS prior to and following the demise of the CL microvasculature within 24 hours. Finally, the robust angiogenic property of the CL during the oestrous cycle allows further refinement of CEUS in vivo. In conclusion, the CL offers an attractive changing vascular bed for assessing existing and developing new clinically relevant perfusion imaging methodology.

A minimally-invasive closed chest myocardial occlusion-reperfusion model in rhesus monkeys (Macaca mulatta): monitoring by contrast-enhanced ultrasound imaging

Myocardial infarction is frequently developed in canine and porcine models but exceptionally in non-human primates. The aim of this study was to develop a minimally invasive myocardial ischemic/reperfusion model in the monkey intended to be combined with imaging techniques, in particular myocardial contrast echocardiography (MCE). A balloon-tipped catheter was advanced via the femoral artery into the left anterior descending artery (LAD) under fluoroscopic guidance in ten anaesthetized male rhesus monkeys (Macaca mulatta). The balloon was inflated to completely occlude the vessel. Coronary angiography (CA) was performed to control the reality of the LAD occlusion/reperfusion. The ischemia period was followed by 3-6 h of reperfusion. Myocardial perfusion was evaluated during ischemia and at reperfusion by MCE using a novel ultrasound contrast agent (BR38). Occlusion was successfully induced during 18-50 min in nine out of the ten evaluated monkeys. ST segment elevation indicated myocardial ischemia. MCE showed complete transmural arrest of myocardial blood flow during the ischemia period and no persistent microvascular perfusion defects during reperfusion. A minimally invasive closed-chest model was successfully developed for creating myocardial ischemia in the rhesus monkey (Macaca mulatta). This technique could have an important role in mimicking acute coronary syndrome under physiologically and ethically-acceptable conditions. MCE provides non-invasively information on myocardial perfusion status, information not available from CA.

A comparison of the image quality of full-time myocardial perfusion SPECT vs wide beam reconstruction half-time and half-dose SPECT

OBJECTIVES

Wide Beam Reconstruction (WBR) (UltraSPECT, Ltd) uses resolution recovery and noise modeling to cope with decreased SPECT count statistics. Because WBR processing reconstructs half the usual SPECT count statistics, we postulate that image quality equivalent to a full-time acquisition can be achieved in either half the time or with half the radiopharmaceutical activity.

METHODS

In 156 consecutive patients (pts) rest and 8-frame gated post-stress myocardial perfusion SPECT was performed following 333-444 and 1184-1480 MBq (9-12 and 32-40 mCi) Tc-99m sestamibi injections, respectively, with full-time (rest = 14 min; stress = 12.3 min) acquisitions processed with OSEM and also separate "half-time" acquisitions processed with WBR. A subsequent group of 160 consecutive pts matched in gender, weight, and chest circumference received "half-dose" rest and stress injections 214.6 ± 22.2 and 647.5 ± 92.5 MBq (5.8 ± 0.6 and 17.5 ± 2.5 mCi) with full-time SPECT acquisitions. Image quality (1 = poor to 5 = excellent) was judged by myocardial count density and uniformity, endocardial edge definition, perfusion defect delineation, right ventricular visualization, and background noise.

RESULTS

Mean image quality for rest, stress, and post-stress gated images were 3.6 ± 0.7, 3.8 ± 0.7, and 3.9 ± 1.0, respectively, for "full-time OSEM; 3.7 ± 0.8, 4.0 ± 0.7, and 4.8 ± 0.4 for "half-time" WBR; and 4.3 ± 0.8, 4.6 ± 0.6, and 4.7 ± 0.6 for "half-dose" WBR. "Half-time" and "half-dose" WBR image quality were both superior to standard full-time OSEM (P's < .001). There was no significant difference between the summed stress and rest scores for "full-time" OSEM vs "half-time" WBR in 82 patients with perfusion defects.

CONCLUSIONS

Both "half-time" and "half-dose" WBR provide myocardial perfusion SPECT quality superior to full-time OSEM, with an associated decrease in scan acquisition time and patient radiation exposure, respectively.

Myocardial viability imaging and revascularization in chronic ischemic left ventricular systolic dysfunction

The high rate of periprocedural morbidity and mortality associated with revascularization in moderate-to-severe left ventricular systolic dysfunction has provided the rationale for noninvasive viability imaging. The most established viability imaging techniques are PET, single-photon emission computed tomography and dobutamine echocardiography. Cardiac MRI is gaining widespread use and accessibility, and computed tomography is emerging as a promising technique. Each imaging modality has unique advantages but also suffers from limitations. Furthermore, evidence of the impact of viability imaging on patient outcomes has generally been limited to observational studies. Uncertainty remains regarding the optimal treatment strategy in this patient subset. This review describes the current status of viability imaging and revascularization in chronic moderate-to-severe ischemic left ventricular systolic dysfunction.

Radiation dose reduction in computed tomography: techniques and future perspective

Despite universal consensus that computed tomography (CT) overwhelmingly benefits patients when used for appropriate indications, concerns have been raised regarding the potential risk of cancer induction from CT due to the exponentially increased use of CT in medicine. Keeping radiation dose as low as reasonably achievable, consistent with the diagnostic task, remains the most important strategy for decreasing this potential risk. This article summarizes the general technical strategies that are commonly used for radiation dose management in CT. Dose-management strategies for pediatric CT, cardiac CT, dual-energy CT, CT perfusion and interventional CT are specifically discussed, and future perspectives on CT dose reduction are presented.