Background—Contrast MRI enhancement patterns in several pathophysiologies resulting from ischemic myocardial injury are controversial or have not been investigated. We compared contrast enhancement in acute infarction (AI), after severe but reversible ischemic injury (RII), and in chronic infarction. Methods and Results—In dogs, a large coronary artery was occluded to study AI and/or chronic infarction (n=18), and a second coronary artery was chronically instrumented with a reversible hydraulic occluder and Doppler flowmeter to study RII (n=8). At 3 days after surgery, cine MRI revealed reduced wall thickening in AI (5±6% versus 33±6% in normal, P<0.001). In RII, wall thickening before, during, and after inflation of the occluder for 15 minutes was 35±5%, 1±8%, and 21±10% and Doppler flow was 19.8±5.3, 0.2±0.5, and 56.3±17.7 (peak hyperemia) cm/s, respectively, confirming occlusion, transient ischemia, and reperfusion. Gd-DTPA–enhanced MR images acquired 30 minutes after contrast revealed hyperenhancement...

Relationship of MRI delayed contrast enhancement to irreversible injury, infarct age, and contractile function.

This paper was guest edited by Dr. E. Fleck. Deutsches Herzzentrum Berlin, Germany

Cardiovascular magnetic resonance (CMR) is established in clinical practice for the diagnosis and management of diseases of the cardiovascular system. However, current guidelines for when this technique should be employed in clinical practice have not been revised since a Task Force report of 1998.1 Considerable technical and practice advances have been made in the intervening years and the level of interest from clinicians in this field is at an unprecedented level. Therefore the aim of this report from a Consensus Panel of established experts in the field of CMR is to update these guidelines. As CMR is a multi-disciplinary technique with international interest, the Consensus Panel was composed of European and American cardiologists and radiologists with major input from members with additional established expertise in paediatric cardiology, nuclear cardiology, magnetic resonance physics and spectroscopy, as well as health economics. The Consensus Panel was originated, approved and funded in its activities by the Working Group on CMR of the European Society of Cardiology and the Society for Cardiovascular Magnetic Resonance.

The Consensus Panel recommendations are based on evidence compiled from the literature and expert experience. If there is insufficient evidence in the literature, this is indicated in the report but usually no recommendations are made under these circumstances. The appropriateness of using CMR is described for the frequent disease entities where imaging information may be warranted. The diagnostic use of CMR will be described in the context of other, competing imaging techniques, with particular emphasis on the differential indications with respect to echocardiography.

The usefulness of CMR in specific diseases is summarized by means of the following classification:

/pdf/clinical-indications-for-cardiovascular-magnetic-resonance-2ac8qd9w41.pdf

Clinical indications for cardiovascular magnetic resonance (CMR): Consensus Panel report.

Background In cardiac syndrome X (a syndrome characterized by typical angina, abnormal exercise-test results, and normal coronary arteries), conventional investigations have not found that chest pain is due to myocardial ischemia. Magnetic resonance techniques have higher resolution and therefore may be more sensitive. Methods We performed myocardial-perfusion cardiovascular magnetic resonance imaging in 20 patients with syndrome X and 10 matched controls, both at rest and during an infusion of adenosine. Quantitative perfusion analysis was performed by using the normalized upslope of myocardial signal enhancement to derive the myocardial perfusion index and the myocardial-perfusion reserve index (defined as the ratio of the myocardial perfusion index during stress to the index at rest). Results In the controls, the myocardial perfusion index increased in both myocardial layers with adenosine (in the subendocardium, from a mean [±SD] of 0.12±0.03 to 0.16±0.03 [P=0.02]; in the subepicardium, from 0.11±0.02...

Abnormal Subendocardial Perfusion in Cardiac Syndrome X Detected by Cardiovascular Magnetic Resonance Imaging

Background— With MRI, an index of myocardial perfusion reserve (MPRI) can be determined. We assessed the value of this technique for the noninvasive detection of coronary artery disease (CAD) in patients with suspected CAD. Methods and Results— Eighty-four patients referred for a primary diagnostic coronary angiography were examined with a 1.5 T MRI tomograph (Philips-ACS). For each heartbeat, 5 slices were acquired during the first pass of 0.025 mmol gadolinium-diethylenetriamine pentaacetic acid/kg body weight before and during adenosine vasodilation by using a turbo-gradient echo/echo-planar imaging-hybrid sequence. MPRI was determined from the alteration of the upslope of the myocardial signal intensity curves for 6 equiangular segments per slice. Receiver operating characteristics were performed for different criteria to differentiate ischemic and nonischemic segments. Prevalence of CAD was 51%. Best results were achieved when only the 3 inner slices were assessed and a threshold value of 1.1 was use...

Magnetic Resonance Perfusion Measurements for the Noninvasive Detection of Coronary Artery Disease

Background Contrast-enhanced fast magnetic resonance (MR) images of acute, reperfused human infarcts demonstrate regions of hypoenhancement and hyperenhancement. The relations between the spatial extent and time course of these enhancement patterns to myocardial risk, infarct, and no-reflow regions have not been well characterized. 

Methods and Results The proximal left anterior descending coronary artery was occluded in 11 closed-chest dogs for 90 minutes followed by 2 days of reperfusion. Regional blood flow was determined by use of radioactive microspheres. The animals were studied at the 2-day time point with contrast-enhanced fast MRI (Signa 1.5 T, General Electric). Thioflavin-S was administered to demarcate no-reflow regions. The hearts were then excised, sectioned into five base-to-apex slices, stained with 2,3,5-triphenyltetrazolium chloride (TTC), and photographed under room light (for TTC) and ultraviolet light (for thioflavin). The spatial extents of thioflavin-negative, TTC-negative, and risk regions were compared planimetrically with MRI hypoenhanced and hyperenhanced regions. The spatial locations of subendocardial hypoenhancement in MR images correlated closely with those of thioflavin-negative regions. Microsphere blood flow in these regions was significantly reduced compared with remote regions (0.37±0.09 versus 0.88±0.10 mL/min per gram, respectively, P <.001) and with baseline (0.37±0.09 versus 0.87±0.15 mL/min per gram, P <.01). The spatial extent of hyperenhancement was smaller than the risk region ( r =.64, slope=0.48, P <.001) but highly correlated with TTC-negative regions and were, on average, 12% larger ( r =.93, slope=1.12, P =.035). 

Conclusions In contrast-enhanced MR images of 2-day-old reperfused canine infarcts, myocardial regions of hypoenhancement are related to the no-reflow phenomenon. Approximately 90% of the myocardium within hyperenhanced regions is nonviable.

Physiological Basis of Myocardial Contrast Enhancement in Fast Magnetic Resonance Images of 2-Day-Old Reperfused Canine Infarcts

The sensitivity of contrast-enhanced MR first pass perfusion imaging in detection and quantification of hypoperfused myocardium was evaluated using an instrumented, closed-chest dog model where graded regional hypoperfusion was induced by applying predetermined levels of stenosis to the left anterior descending artery (LAD). All measurements were performed at rest and under stress induced by dipyridamole (DIP). Myocardial perfusion was assessed both with MR and radiolabeled microspheres injected immediately before the administration of the MR contrast agent. Ultrafast MR imaging was performed using a Turbo FLASH sequence with a 180 degrees inversion prepulse. A Gd-DTPA bolus was injected into the left atrium and T1-weighted images were acquired with every heart beat. Signal intensity measured from the images in regions of the LAD and left circumflex (LCx) perfusion beds was plotted against time to generate signal intensity versus time curves (SI time curve). Various flow indices were derived according to the indicator dilution theory, and compared with and without volume correction due to vasodilation to the myocardial blood flow (MBF) calculated from radiolabeled microspheres. Correlation of the MR and MBF data demonstrated that different transmural and regional myocardial perfusion levels can be easily visualized in the perfusion images and accurately monitored by the SI time curves. Detection of the impairment of myocardial perfusion improved significantly after administration of DIP. The inverse mean transit time calculated from the SI time curve was found to yield a linear correlation to absolute MBF derived from the microsphere data. These results suggest that with intracardiac injections of exogenous contrast agent, myocardial perfusion can be assessed parametrically with first pass contrast enhanced ultrafast MRI.

H. Lüdemann

Papers

Contrast-enhanced first pass myocardial perfusion imaging: Correlation between myocardial blood flow in dogs at rest and during hyperemia