Arthur E. Stillman

ACCF/ACR/AHA/NASCI/SCMR 2010 Expert Consensus Document on Cardiovascular Magnetic Resonance A Report of the American College of Cardiology Foundation Task Force on Expert Consensus Documents

Robert A. Harrington, MD, FACC, FAHA, Chair nnJeffrey L. Anderson, MD, FACC, FAHA[††][1]nnEric R. Bates, MD, FACCnnCharles R. Bridges, MD, MPH, FACC, FAHAnnMark J. Eisenberg, MD, MPH, FACC, FAHAnnVictor A. Ferrari, MD, FACC, FAHAnnCindy L. Grines, MD, FACC[††][1]nnMark A. Hlatky, MD, FACC,

Magnetic resonance quantification of the myocardial perfusion reserve with a Fermi function model for constrained deconvolution

The myocardial perfusion reserve, defined as the ratio of hyperemic and basal myocardial blood flow, is a useful indicator of the functional significance of a coronary artery lesion. Rapid magnetic resonance (MR) imaging for the noninvasive detection of a bolus-injected contrast agent as a MR tracer is applied to the measurement of regional tissue perfusion during rest and hyperemia, in patients with microvascular dysfunction. A Fermi function model for the distribution of tracer residence times in the myocardium is used to fit the MR signal curves. The myocardial perfusion reserve is calculated from the impulse response amplitudes for rest and hyperemia. The assumptions of the model are tested with Monte Carlo simulations, using a multiple path, axially distributed mathematical model of blood tissue exchange, which allows for systematic variation of blood flow, vascular volume, and capillary permeability. For a contrast-to-noise ratio of 6:1, and over a range of flows from 0.5 to 4.0 ml/min per g of tissue, the ratio of the impulse response amplitudes for hyperemic and basal flows is linearly proportional to the ratio of model blood flows, if the mean transit time of the input function is shorter than approximately 9 s. The uncertainty in the blood flow reserve estimates grows both at low (< 1.0 ml/min/g) and high (> 3-4 ml/min/g) flows. The predictions of the Monte Carlo simulations agree with the results of MR first pass studies in patients without significant coronary artery lesions and microvascular dysfunction, where the perfusion reserve in the territory of the left anterior descending coronary artery (LAD) correlates linearly with the intracoronary Doppler ultrasound flow reserve in the LAD (r = 0.84), in agreement with previous PET studies.

Functional magnetic resonance imaging of Broca's area during internal speech

Conventional gradient-echo magnetic resonance imaging (MRI) at 4 Tesla was used successfully to study the activity of Brocas area during internal speech word generation in healthy right-handed volunteers. Activity was demonstrated in the internal gray matter surrounding the ascending ramus of the lateral sulcus, deep to the cortical surface representation of Brocas area, in all the subjects. These studies demonstrate the capability of functional MRI to non-invasively map language related cognitive functions. Such functional mapping has value for both the study of basic neuroscience and neurosurgical planning.

MR imaging of arrhythmogenic right ventricular cardiomyopathy: Morphologic findings and interobserver reliability

Background: Magnetic resonance (MR) imaging is frequently used to diagnose arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). However, the reliability of various MR imaging features for diagnosing ARVC/D is unknown. The purpose of this study was to determine which morphologic MR imaging features have the greatest interobserver reliability for diagnosing ARVC/D. Methods: Forty-five sets of films of cardiac MR images were sent to 8 radiologists and 5 cardiologists with experience in this field. There were 7 cases of definite ARVC/D as defined by the Task Force criteria. Six cases were controls. The remaining 32 cases had MR imaging because of clinical suspicion of ARVC/D. Readers evaluated the images for the presence of (a) right ventricle (RV) enlargement, (b) RV abnormal morphology, (c) left ventricle enlargement, (d) presence of high T1 signal (fat) in the myocardium, and (e) location of high T1 signal (fat) on a Likert scale with formatted responses. Results: Readers indicated that the Task Force ARVC/D cases had significantly more (χ2 = 119.93, d.f. = 10, p < 0.0001) RV chamber size enlargement (58%) than either the suspected ARVC/D (12%) or no ARVC/D (14%) cases. When readers reported the RV chamber size as enlarged they were significantly more likely to report the case as ARVC/D present (χ2= 33.98, d.f. = 1, p < 0.0001). When readers reported the morphology as abnormal they were more likely to diagnose the case as ARVC/D present (χ2 = 78.4, d.f. = 1, p < 0.0001), and the Task Force ARVC/D (47%) cases received significantly more abnormal reports than either suspected ARVC/D (20%) or non-ARVC/D (15%) cases. There was no significant difference between patient groups in the reported presence of high signal intensity (fat) in the RV (χ2 = 0.9, d.f. = 2, p > 0.05). Conclusions: Reviewers found that the size and shape of abnormalities in the RV are key MR imaging discriminates of ARVD. Subsequent protocol development and multicenter trials need to address these parameters. Essential steps in improving accuracy and reducing variability include a standardized acquisition protocol and standardized analysis with dynamic cine review of regional RV function and quantification of RV and left ventricle volumes.

Analysis of myocardial perfusion MRI

Rapid MR imaging (MRI) during the first pass of an injected tracer is used to assess myocardial perfusion with a spatial resolution of 2–3 mm, and to detect any regional impairments of myocardial blood flow (MBF) that may lead to ischemia. The spatial resolution is sufficient to detect flow reductions that are limited to the subendocardial layer. The capacity of the coronary system to increase MBF severalfold in response to vasodilation can be quantified by analysis of the myocardial contrast enhancement. The myocardial perfusion reserve (MPR) is a useful concept for quantifying the vasodilator response. The perfusion reserve can be estimated from the ratio of MBFs during vasodilation and at baseline, in units identical to those used for invasive measurements with labeled microspheres, or from dimensionless flow indices normalized by their value for autoregulated flow at rest. The perfusion reserve can be reduced as a result of a blunted hyperemic response and/or an abnormal resting blood flow. The absolute quantification of MBF removes uncertainties in the evaluation of the vasodilator response, and can be achieved without the use of complex tracer kinetic models; therefore, its application to clinical studies is feasible. J. Magn. Reson. Imaging 2004;19:758–770.

Bradykinin Antagonism Inhibits the Antigrowth Effect of Converting Enzyme Inhibition in the Dog Myocardium After Discrete Transmural Myocardial Necrosis

BACKGROUNDnConverting enzyme inhibitor (CEI) therapy, but not angiotensin II subtype I receptor blockade, has been shown to attenuate left ventricular remodeling in the dog after transmyocardial direct current (DC) shock. The purpose of this study was to address the importance of preservation of bradykinin to the antiremodeling effect of CEI treatment in this model.nnnMETHODS AND RESULTSnTwenty-four hours after DC shock, adult mongrel dogs were assigned to one of three groups: a control group; a group treated with ramipril 10 mg BID; and a group treated with ramipril 10 mg BID along with a continuous subcutaneous infusion of HOE 140, a bradykinin antagonist. To assess change in left and right ventricular structure, a magnetic resonance imaging (MRI) study was performed 4 weeks after DC shock and compared with a baseline MRI study performed before DC shock. The increase in left ventricular mass (mean +/- SEM) in the control group was similar to that observed in the CEI-HOE 140 group (+0.73 +/- 0.19 versus +0.75 +/- 0.18 g/kg, P = NS), but both were greater than the change in mass in the ramipril group (-0.48 +/- 0.13 g/kg, P = .004 and P = .0005, respectively). No significant change occurred in left ventricular volume or right ventricular structure in any group. Mean arterial pressure was reduced by ramipril compared with the control group (-8 +/- 2 versus +7 +/- 2 mm Hg, P = .03), and this effect was not blunted by the addition of HOE 140 (-7 +/- 3 mm Hg).nnnCONCLUSIONSnPrevention by ramipril of the early increase in left ventricular mass in the DC shock model appears to be related to the preservation of bradykinin.

Non-invasive assessment of plaque morphology and remodeling in mildly stenotic coronary segments: comparison of 16-slice computed tomography and intravascular ultrasound

BackgroundNon-invasive identification and characterization of mildly stenotic atherosclerotic lesions is an increasingly important focus of coronary imaging. DesignWe examined the accuracy of multi (16)-slice computed tomography (MSCT) for imaging of these lesions in comparison with intravascular ultrasound (IVUS). MaterialsMildly stenotic segments of the left coronary artery were identified by coronary angiography and analyzed using IVUS and contrast-enhanced MSCT. Independent reviewers evaluated the accuracy of MSCT for presence, composition and distribution of atherosclerotic plaque and remodeling response in comparison to IVUS using receiver operating characteristic (ROC) data analysis. ResultsOf 46 segments in 14 patients, diagnostic characterization by MSCT was possible in 37 (80.4%) segments. In these segments the accuracy of MSCT for identifying plaque presence, calcification, distribution and positive remodeling was consistently greater than 0.90 (reader 1) and 0.87 (reader 2). ConclusionState-of-the-art MSCT can accurately identify mildly stenotic coronary atherosclerosis and provide an assessment of morphology and remodeling response.

Magnetic resonance first-pass myocardial perfusion imaging: clinical validation and future applications.

Clinical studies suggest that magnetic resonance first‐pass (MRFP) perfusion imaging is comparable to current diagnostic tests that are used clinically for the assessment of myocardial perfusion. In addition, magnetic resonance imaging (MRI) perfusion imaging is a noninvasive method for determining myocardial blood flow. The spatial resolution (in‐plane spatial resolution < 3 mm) is sufficient to differentiate between subendocardial perfusion and subepicardial perfusion. The measurement can be repeated regularly without any adverse effects for the patient. MRI perfusion measurements can be combined with the evaluation of global function and regional wall thickening. Currently, there is no other imaging technique that offers similar advantages. The MRI perfusion measurements can be carried out during baseline conditions and during maximal hyperemia induced with either adenosine or dipyridamole. The ratio of the measured myocardial blood flows provides an estimate of the absolute and relative myocardial perfusion reserve. The perfusion reserve determined with MRFP imaging is a quantitative measure for the assessment of the collateral‐dependent myocardial flow. Based on the available data using MRFP perfusion imaging, the current clinical first‐line perfusion imaging tests are going to be challenged in the near future. J. Magn. Reson. Imaging 1999;10:676–685.

Relative effects of alpha 1-adrenoceptor blockade, converting enzyme inhibitor therapy, and angiotensin II subtype 1 receptor blockade on ventricular remodeling in the dog.

BackgroundProgressive ventricular remodeling after myocardial damage is associated with a poor prognosis. Optimal prevention of the histopathological processes involved in remodeling requires a more complete understanding of the mechanisms involved in initiating and maintaining these structural changes. Since the sympathetic nervous system and the renin-angiotensin system may be involved in the remodeling process, the structural effects of pharmacological inhibitors have been evaluated in a canine model of localized myocardial injury resulting from transmyocardial DC shock. Methods and ResultsThe study is comprised of two protocols run in series. In protocol 1, zofenopril (Z), a converting enzyme inhibitor (CEI), prevented the increase in left ventricular mass (LVM) and end-diastolic volume (LVV) observed in the control group (C) at 16 weeks (Z: LVM, 69.8 ± 3.4 to 65.4 ± 2.6 g, P = NS; LVV, 45.4 ± 2.7 to 51.6 ± 2.7 mL, P = NS; C: LVM, 68.4 ± 3.2 to 91.4 ± 2.9 g, P = .0001; LVV, 56.6 ± 3.0 to 71.9 ± 2.4 mL, P = .0003). Terazosin, an alpha 1- adrenoceptor antagonist, failed to prevent remodeling at 16 weeks despite continued receptor blockade. In protocol 2, the antiremodeling effect of full-dose CEI therapy with ramipril was confirmed. Low-dose ramipril that exerted no hemodynamic effect failed to prevent remodeling (LVM, 89.7 ± 4.6 to 105.7 ± 3.4 g, P = .01; LVV, 61.8 ± 3.8 to 76.8 ± 3.3 mL, P = .002). An angiotensin II subtype 1 receptor blocker also failed to prevent the increase in LVM or LVV (LVM, 89.0 ± 4.6 to 109.7 ± 5.3 g, P = .0001; LVV, 66.0 ± 1.9 to 78.4 ± 3.6 mL, P = .007). ConclusionsHigh-dose CEI therapy can prevent progressive structural changes resulting from localized myocardial damage induced by DC shock. The failure of α1-adrenoceptor blockade and angiotensin II subtype 1 blockade to attenuate remodeling argues against an important direct role for norepinephrine acting through α1-receptors or angiotensin II acting through the type 1 receptor in the remodeling process in this model.

Ultrasmall superparamagnetic iron oxide to enhance MRA of the renal and coronary arteries: Studies in human patients

OBJECTIVEnOur goal was to determine the feasibility of using an intravascular MR contrast agent to improve 3D MRA.nnnMATERIALS AND METHODSnThree-dimensional TOF MRA was performed in nine patients both prior to and following the administration of an ultrasmall particle superparamagnetic iron oxide contrast agent (AMI 227). The lengths of both renal arteries were measured from the maximum intensity projection (MIP) images as well as the individual partitions. Seven of these patients also were studied by a 3D coronary artery MRA sequence. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements of the right coronary artery were determined both prior to and following the administration of AMI 227. Statistical analysis of both renal artery lengths and right coronary SNR and CNR was performed using a one tailed paired t test comparing pre- and postcontrast images.nnnRESULTSnThe renal artery lengths significantly increased (right and artery: 30%, p = 0.001; left renal artery: 25%, p < 0.008) when measured from the individual axial slice partitions. No significant increase in length was observed on the MIP images following contrast. In the right coronary artery, the SNR increased by an average of 80% (p = 0.008) and CNR increased by an average of 109% (p = 0.007). Increased background signal and superimposed venous structures reduced the measurable lengths of the renal arteries from the MIP images.nnnCONCLUSIONnThese studies support the hypothesis that 3D MRA in the body will benefit from the use of intravascular contrast agents. Nevertheless, conventional MIP processing is unable to reveal the full advantage of the contrast improvement.