Magnetic resonance quantitative myocardial perfusion reserve demonstrates improved myocardial blood flow after angiogenic implant therapy.

PURPOSE: The purpose of this study is to follow myocardial angiogenesis temporally using quantitative magnetic resonance first pass perfusion imaging and compare this with the "gold standard" of radioactive microspheres in a random subset of animals. MATERIALS AND METHODS: Ameriod constrictors were placed around the left circumflex in 15 pigs to induce an ischemic area. Two groups were randomized to receive either a sham operation or treatment with angiogenic implants inserted into myocardium in the distribution of the left circumflex artery (LCX). These implants are designed to induce myocardial angiogenesis. Magnetic resonance first pass perfusion imaging was performed at baseline and also after treatment with either sham or implant therapy by using first pass perfusion imaging with a TurboFLASH sequence. Absolute myocardial blood flow was derived by applying a quantitative Fermi function model. Radioactive microspheres were also injected into a random subset of animals to measure myocardial blood flow. RESULTS: Angiogenic implant therapy increased absolute myocardial blood flow in the left circumflex territory relative to baseline and sham treated groups during adenosine infusion. Myocardial blood flows measured with radioactive microspheres was increased significantly in both the LCX and LAD territories during stress. Myocardial Perfusion reserve was also significantly increased in both the LCX and left anterior descending territories relative to baseline. Ejection Fraction during stress with dobutamine infusion increased significantly in the implant therapy group while that in the sham group was not affected. CONCLUSION: Quantitative MR myocardial first pass perfusion imaging can be used to track the development of angiogenesis as corroborated by radioactive microspheres. Angiogenic implant therapy is a new device based therapy that has potential to protect an ischemic region by accelerating angiogenesis although further research is necessary with this device.

Ethical considerations in CT angiography.

The rapid development and clinical deployment of CT angiography raises several important issues, including assurance of professional competence and technical quality, self-referral, the relative role of radiologists and cardiologists, appropriateness and proper indications, the detection and disposition of unexpected or incidental findings and the concern for the rapidly increasing costs of health care and imaging. These questions are properly addressed within the framework of medical ethics, including principles of beneficence, autonomy and justice.

Magnetic resonance first pass perfusion imaging for detecting coronary artery disease.

Magnetic resonance first pass perfusion imaging can be used to detect abnormalities in myocardial blood flow. This technique involves imaging the first pass of gadolinium based contrast through the myocardium. Images are initially read qualitatively for areas of reduced signal intensity. Additionally, at our institution a quantitative method is applied that can aid both detection and diagnosis of perfusion defects. This method involves fitting the myocardial signal intensity curves and then calculates absolute myocardial blood flow. Our approach to first pass perfusion imaging will be reviewed. Magnetic resonance first pass perfusion imaging has a complimentary role with coronary angiography either non-invasively using CT or with catheterization. Perfusion imaging defines the physiology and angiography in the anatomy of coronary artery disease.

Utility of cardiac magnetic resonance imaging in the diagnosis of hypertrophic cardiomyopathy.

BACKGROUND: Two-dimensional echocardiography is currently the standard test for the clinical diagnosis of hypertrophic cardiomyopathy (HCM). The present study was undertaken to determine whether cardiac MRI (CMR) affords greater accuracy than echocardiography in establishing the diagnosis and assessing the magnitude of left ventricular (LV) hypertrophy in HCM. METHODS AND RESULTS: Forty-eight patients (age 34+/-16 years) suspected of having HCM (or with a confirmed diagnosis) were imaged by both echocardiography and CMR to assess LV wall thickness in 8 anatomic segments (total n=384 segments) and compared in a blinded fashion. Maximum LV thickness was similar by echocardiography (21.7+/-9.1 mm) and CMR (22.5+/-9.6 mm; P=0.21). However, in 3 (6%) of the 48 patients, echocardiography did not demonstrate LV hypertrophy, and CMR identified otherwise undetected areas of wall thickening in the anterolateral LV free wall (17 to 20 mm), which resulted in a new diagnosis of HCM. In the overall study group, compared with CMR, echocardiography also underestimated the magnitude of hypertrophy in the basal anterolateral free wall (by 20+/-6%; P=0.001), as well as the presence of extreme LV wall thickness (> or =30 mm) in 10% of patients (P<0.05). CONCLUSIONS: CMR is capable of identifying regions of LV hypertrophy not readily recognized by echocardiography and was solely responsible for diagnosis of the HCM phenotype in an important minority of patients. CMR enhances the assessment of LV hypertrophy, particularly in the anterolateral LV free wall, and represents a powerful supplemental imaging test with distinct diagnostic advantages for selected HCM patients.

Improved myocardial function after transmyocardial laser revascularization according to cine magnetic resonance in a porcine model.

OBJECTIVE: This study was undertaken to demonstrate that transmyocardial laser revascularization of hypoperfused myocardium improves regional and global myocardial function. METHODS: Cine magnetic resonance imaging was used to monitor regional wall thickening (in millimeters) and cardiac output (in milliliters per kilogram per minute). Cine magnetic resonance imaging was performed before and 8 weeks after transmyocardial laser revascularization was applied to the hypoperfused lateral wall of the left ventricle (target area) in a porcine model (n = 9, transmyocardial laser revascularization group). A second group of animals was left untreated (n = 8, control group). RESULTS: Regional wall thickening in the target area improved after transmyocardial laser revascularization (0.7 +/- 0.3 mm to 3.7 +/- 1.9 mm, P <.02) and was significantly higher (P <.01) after transmyocardial laser revascularization than in the control group, in which it did not improve (0.5 +/- 0.6 mm to 0.5 +/- 1.2 mm). Accordingly, cardiac output and microsphere-derived myocardial blood flows were significantly higher than in the control group (P <.01), and the amount of triphenyltetrazolium chloride-stained myocardium was lower (P <.01). CONCLUSION: Cine magnetic resonance imaging demonstrates improved global and regional myocardial function after transmyocardial laser revascularization in a porcine model.

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.

Reduced myocardial perfusion reserve and transmural perfusion gradient in heart transplant arteriopathy assessed by magnetic resonance imaging.

OBJECTIVES: The goal of this study was to detect transplant arteriopathy (Tx-CHD) by a reduced myocardial perfusion reserve (MPR) and resting endomyocardial/epimyocardial perfusion ratio (Endo/Epi ratio). BACKGROUND: Transplant arteriopathy often lacks clinical symptoms and is the reason for frequent surveillance angiography in heart transplant (Tx) recipients. Magnetic resonance perfusion imaging (MRPI) allows noninvasive assessment of transmural and selective endomyocardial and epimyocardial perfusion. METHODS: Fifteen healthy volunteers (controls) and three groups (A, B, C) of Tx recipients were included. In controls and patients, MPR (hyperemic/resting perfusion) and Endo/Epi ratio were determined with MRPI after injection of gadolinium-diethylenetriamine pentaacetic acid at rest and during hyperemia (intravenous adenosine). Group A (n = 10) had no left ventricular (LV) hypertrophy and/or prior rejection, while patients in group B (n = 10) had at least one of these characteristics. Patients in group A and B had a normal coronary angiogram and a coronary flow reserve (CFR) of > or =2.5 (CFR = hyperemic/resting blood flow). Group C (n = 7) had Tx-CHD diagnosed by angiography and a reduced CFR (<2.5). RESULTS: In group C, MPR (1.7 +/- 0.5) and Endo/Epi ratio (1.1 +/- 0.2) were significantly reduced compared with controls (4.2 +/- 0.7 and 1.6 +/- 0.3; both p < 0.0001), group A (3.6 +/- 0.7 and 1.6 +/- 0.2; both p < 0.0001) and B (2.7 +/- 0.9, p < 0.01 and 1.4 +/- 0.1, p < 0.04). Transplant arteriopathy can be excluded by an MPR of >2.3 with sensitivity and specificity of 100% and 85%. If LV hypertrophy and prior rejection are excluded, Tx-CHD can be excluded by an Endo/Epi ratio of >1.3 with 100% and 80%. CONCLUSIONS: Magnetic resonance perfusion imaging detects Tx-CHD by a decreased MPR. After exclusion of LV hypertrophy and prior rejection, resting Endo/Epi ratio alone might be sufficient to indicate Tx-CHD.

Magnetic resonance imaging guided cardiovascular interventions in congenital heart diseases.

The purpose of this article is to present some recent applications of diagnostic and interventional MRI in congenital heart disease. To date x-ray-based techniques have been the norm for most diagnostic and therapeutic applications. With the advent of ultrafast MRI and the development of MRI-compatible catheters and guide wires, the goal of achieving real-time guidance by MRI for interventions in congenital heart diseases has proven feasible. We briefly review the latest advances in cardiovascular MRI, and the development of MR-compatible devices for diagnostic and therapeutic applications such as ASD closure and pulmonary artery dilation.

Magnetic resonance image-guided transcatheter closure of atrial septal defects.

BACKGROUND: Recent developments in cardiac MRI have extended the potential spectrum of diagnostic and interventional applications. The purpose of this study was to test the ability of MRI to perform transcatheter closures of secundum type atrial septal defects (ASD) and to assess ASD size and changes in right cardiac chamber volumes in the same investigation. METHODS AND RESULTS: In 7 domestic swine (body weight, 38+/-13 kg), an ASD (Q(p):Q(s)=1.7+/-0.2) was created percutaneously by balloon dilation of the fossa ovalis. The ASD was imaged and sized by both conventional radiography and MRI. High-resolution MRI of the ASD diameters correlated well with postmortem examination (r=0.97). Under real-time MR fluoroscopy, the introducer sheath was tracked toward the left atrium with the use of novel miniature MR guide wires. The defect was then closed with an Amplatzer Septal Occluder. In all animals, it was possible to track and interactively control the position of the guide wire within the vessels and the heart, including the successful deployment of the Amplatzer Septal Occluder. Right atrial and ventricular volumes were calculated before and after the intervention by using cine-MRI. Both volumes were found to be significantly reduced after ASD closure (P<0.005). CONCLUSIONS: These in vivo studies demonstrate that catheter tracking and ASD device closure can be performed under real-time MRI guidance with the use of intravascular antenna guide wires. High-resolution imaging allows accurate determination of ASD size before the intervention, and immediate treatment effects such as changes in right cardiac volumes can also be measured.

Transmyocardial laser revascularization preserves regional myocardial perfusion: an MRI first pass perfusion study.

OBJECTIVE: It is controversial whether transmyocardial laser revascularization (TMLR) improves myocardial perfusion. Therefore, we assessed myocardial perfusion before and after TMLR with quantitative magnetic resonance perfusion imaging (MRPI) in an animal study. METHODS: One week after partial occlusion of the left circumflex artery (LCx) in 12 pigs, resting perfusion (ml/g/min), perfusion reserve (PR) with adenosine, regional wall thickening (RWT), cardiac output (CO) were quantified with MRI in the LCx (lateral) and LAD (septal) dependent myocardium. Subsequently, six animals were treated with TMLR of the lateral left ventricle (LV). Six animals were left untreated. A final MR was performed 8 weeks later. MRPI data were compared to microsphere-derived blood flow and % LV necrosis (TTC). 'Normal' myocardial perfusion was assessed with MRPI in 12 non-instrumented animals. RESULTS: Resting perfusion prior to TMLR (0.7-0.9+/-0.3) in the LV-lateral myocardium was preserved after TMLR (1.0+/-0.3) and decreased without TMLR (0.3+/-0.1, P<0.05). There was a significant difference (P<0.01) between the TMLR treated and untreated group. Compared to 'normals' (1.2+/-0.2) perfusion of the LV-lateral wall was not different after TMLR but reduced (P<0.02) without TMLR. PR was not different between TMLR-treated (1.4+/-0.9) and untreated (1.9+/-0.6) group but was reduced (P<0.04) compared to PR of 'normals' (2.7+/-0.8). MRPI data and microsphere-derived perfusion were significantly correlated (P<0.01). RWT in the LCx-dependent myocardium improved (P<0.02) after TMLR. CO decreased (P<0.02) and TTC-staining indicated more LV-necrosis without TMLR (6.6+/-1.6 vs. 3.7+/-1.5, P<0.01). CONCLUSION: TMLR preserves regional myocardial perfusion and improves function as shown with MRPI.

Cardiac Magnetic Resonance Imaging for the Assessment of Myocardial Angiogenesis.

Research in biology and applications of growth factors in coronary artery disease (CAD) has progressed considerably over recent years. Vascular endothelial growth factor and fibroblast growth factor-2 have been more successful in animal models of myocardial ischemia and Phase I studies than in placebo-controlled trials. However, cardiac magnetic resonance (CMR), with its higher sensitivity and specificity indices for identification of CAD, has not been extensively used in trials of angiogenic therapies. Data in animals and in patients suggest that CMR can reliably identify collateral vessels. Therefore, we hypothesize that CMR may depict collateralization induced by angiogenic therapy better than currently used nuclear perfusion imaging modalities. Versatility of the assessment of myocardial function and perfusion in one imaging session, combined with the noninvasive nature of the test, may considerably lower the cost of clinical trials. Use of CMR-derived surrogate end points may provide better risk stratification and assessment of efficacy in patients receiving growth factor therapy.