Acute versus Chronic Myocardial Infarction: Diagnostic Accuracy of Quantitative Native T1 and T2 Mapping versus Assessment of Edema on Standard T2-weighted Cardiovascular MR Images for Differentiation.

Purpose To analyze the diagnostic accuracy of native T1 and T2 mapping compared with visual and quantitative assessment of edema on T2-weighted cardiac magnetic resonance (MR) images to differentiate between acute and chronic myocardial infarction. Materials and Methods This study had institutional ethics committee approval. Written informed consent was obtained from 67 consecutive patients (57 years ± 12; 78% men) with a first acute myocardial infarction, who were prospectively enrolled between April 2011 and June 2015. Four serial 1.5-T MR imaging examinations were performed at 8 days ± 5, 7 weeks ± 2, 3 months ± 0.5, and 6 months ± 1.4 after infarction and included T2-weighted, native T1/T2 mapping, and late gadolinium enhancement MR imaging. Complete follow-up data were obtained in 42 patients. Regional native T1/T2 relaxation time, T2-weighted ratio, and extracellular volume were serially measured in infarcted and remote myocardium. Receiver operating characteristic (ROC) analysis was used to determine the diagnostic accuracy of the MR imaging parameters for discriminating between acute and chronic myocardial infarction. Results Native T1 of infarcted myocardium decreased from 1286 msec ± 99 at baseline to 1077 msec ± 50 at 6 months (P < .0001), whereas T2 decreased from 84 msec ± 10 to 58 msec ± 4 (P < .0001). The T2-weighted ratio decreased from 4.1 ± 1.0 to 2.4 ± 0.6 (P < .0001). Of all the MR imaging parameters obtained, native T1 and T2 yielded the best areas under the ROC curve (AUCs) of 0.975 and 0.979, respectively, for differentiating between acute and chronic myocardial infarction. Visual analysis of the presence of edema at standard T2-weighted cardiac MR imaging resulted in an inferior AUC of 0.863 (P < .01). Conclusion Native T1 and T2 of infarcted myocardium are excellent discriminators between acute and chronic myocardial infarction and are superior to all other MR imaging parameters. Online supplemental material is available for this article.

Evaluation of MRI protocols for the assessment of lumbar facet joints after MR-guided focused ultrasound treatment.

BACKGROUND: MR-guided focused ultrasound (MRgFUS) might be a very safe and effective minimally invasive technique to treat facet joint pain caused by arthritis and other degenerative changes. However, there are still safety concerns for this treatment and challenges regarding MR imaging and temperature mapping due to susceptibility effects between the bone and soft tissue near the joint, which has resulted in poor MR image quality. The goal of this research was to evaluate multiple magnetic resonance imaging (MRI) pulse sequences for characterizing ablated lumbar facet joint lesions created by high-intensity focused ultrasound (FUS) and compare the findings to histological tissue assessment. In particular, we investigated the use of T2-weighted MRI to assess treatment effects without contrast administration. METHODS: An IACUC approved study (n = 6 pigs) was performed using a 3T widebore MRI system equipped with an MRgFUS system. Facet joints of the lumbar vertebra were ablated using 1-MHz frequency and multiple sonication energies (300-800 J). In addition to T2-weighted MRI for treatment planning, T1-, T2-, and T2*-weighted and perfusion MRI sequences were applied. Signal intensity ratios of the lesions were determined. Histopathology was used to characterize cellular changes. RESULTS: Ablation of the facet joint, using MRgFUS, was successful in all animals. T2-weighted images showed high signal intensity in the edematous facet joint and adjacent muscle, while delayed contrast-enhanced T1-weighted images showed an enhanced ring surrounding the target volume. T2*-weighted GRE images revealed inconsistent lesion visualization. Histopathology confirmed the presence of cellular coagulation (shrinkage), extracellular expansion (edema), and hemorrhage in the bone marrow. CONCLUSIONS: MRgFUS provided sufficient precision and image quality for visualization and characterization of ablated facet joints directly after ablation. MRI may help in monitoring the efficacy of FUS ablation without contrast after treating patients with back pain.

Renal ablation using magnetic resonance-guided high intensity focused ultrasound: Magnetic resonance imaging and histopathology assessment.

AIM: To use magnetic resonance-guided high intensity focused ultrasound (MRg-HIFU), magnetic resonance imaging (MRI) and histopathology for noninvasively ablating, quantifying and characterizing ablated renal tissue. METHODS: Six anesthetized/mechanically-ventilated pigs underwent single/double renal sonication (n = 24) using a 3T-MRg-HIFU (1.1 MHz frequency and 3000J-4400J energies). T2-weighted fast spin echo (T2-W), perfusion saturation recovery gradient echo and contrast enhanced (CE) T1-weighted (T1-W) sequences were used for treatment planning, temperature monitoring, lesion visualization, characterization and quantification, respectively. Histopathology was conducted in excised kidneys to quantify and characterize cellular and vascular changes. Paired Student's t-test was used and a P-value < 0.05 was considered statistically significant. RESULTS: Ablated renal parenchyma could not be differentiated from normal parenchyma on T2-W or non-CE T1-W sequences. Ablated renal lesions were visible as hypoenhanced regions on perfusion and CE T1-W MRI sequences, suggesting perfusion deficits and necrosis. Volumes of ablated parenchyma on CE T1-W images in vivo (0.12-0.36 cm(3) for single sonication 3000J, 0.50-0.84 cm(3), for double 3000J, 0.75-0.78 cm(3) for single 4400J and 0.12-2.65 cm(3) for double 4400J) and at postmortem (0.23-0.52 cm(3), 0.25-0.82 cm(3), 0.45-0.68 cm(3) and 0.29-1.80 cm(3), respectively) were comparable. The ablated volumes on 3000J and 4400J double sonication were significantly larger than single (P < 0.01), thus, the volume and depth of ablated tissue depends on the applied energy and number of sonication. Macroscopic and microscopic examinations confirmed the locations and presence of coagulation necrosis, vascular damage and interstitial hemorrhage, respectively. CONCLUSION: Contrast enhanced MRI provides assessment of MRg-HIFU renal ablation. Histopathology demonstrated coagulation necrosis, vascular damage and confirmed the volume of damage seen on MRI.

Magnetic resonance imaging and multi-detector computed tomography assessment of extracellular compartment in ischemic and non-ischemic myocardial pathologies.

Myocardial pathologies are major causes of morbidity and mortality worldwide. Early detection of loss of cellular integrity and expansion in extracellular volume (ECV) in myocardium is critical to initiate effective treatment. The three compartments in healthy myocardium are: intravascular (approximately 10% of tissue volume), interstitium (approximately 15%) and intracellular (approximately 75%). Myocardial cells, fibroblasts and vascular endothelial/smooth muscle cells represent intracellular compartment and the main proteins in the interstitium are types I/III collagens. Microscopic studies have shown that expansion of ECV is an important feature of diffuse physiologic fibrosis (e.g., aging and obesity) and pathologic fibrosis [heart failure, aortic valve disease, hypertrophic cardiomyopathy, myocarditis, dilated cardiomyopathy, amyloidosis, congenital heart disease, aortic stenosis, restrictive cardiomyopathy (hypereosinophilic and idiopathic types), arrythmogenic right ventricular dysplasia and hypertension]. This review addresses recent advances in measuring of ECV in ischemic and non-ischemic myocardial pathologies. Magnetic resonance imaging (MRI) has the ability to characterize tissue proton relaxation times (T1, T2, and T2*). Proton relaxation times reflect the physical and chemical environments of water protons in myocardium. Delayed contrast enhanced-MRI (DE-MRI) and multi-detector computed tomography (DE-MDCT) demonstrated hyper-enhanced infarct, hypo-enhanced microvascular obstruction zone and moderately enhanced peri-infarct zone, but are limited for visualizing diffuse fibrosis and patchy microinfarct despite the increase in ECV. ECV can be measured on equilibrium contrast enhanced MRI/MDCT and MRI longitudinal relaxation time mapping. Equilibrium contrast enhanced MRI/MDCT and MRI T1 mapping is currently used, but at a lower scale, as an alternative to invasive sub-endomyocardial biopsies to eliminate the need for anesthesia, coronary catheterization and possibility of tissue sampling error. Similar to delayed contrast enhancement, equilibrium contrast enhanced MRI/MDCT and T1 mapping is completely noninvasive and may play a specialized role in diagnosis of subclinical and other myocardial pathologies. DE-MRI and when T1-mapping demonstrated sub-epicardium, sub-endocardial and patchy mid-myocardial enhancement in myocarditis, Behcet's disease and sarcoidosis, respectively. Furthermore, recent studies showed that the combined technique of cine, T2-weighted and DE-MRI technique has high diagnostic accuracy for detecting myocarditis. When the tomographic techniques are coupled with myocardial perfusion and left ventricular function they can provide valuable information on the progression of myocardial pathologies and effectiveness of new therapies.

Imaging assessment of a portable hemodialysis device: detection of possible failure modes and monitoring of functional performance.

BACKGROUND: The purpose of this study was to investigate the utility and limitations of various imaging modalities in the noninvasive assessment of a novel compact hemodialyzer under development for renal replacement therapy, with specific aim towards monitoring its functional performance. METHODS: The prototype is a 4×3×6 cm aluminum cartridge housing "blood" and "dialysate" flow paths arranged in parallel. A sheet of semipermeable silicon nanopore membranes forms the blood-dialysate interface, allowing passage of small molecules. Blood flow was simulated using a peristaltic pump to instill iodinated contrast through the blood compartment, while de-ionized water was instilled through the dialysate compartment at a matched rate in the countercurrent direction. Images were acquired under these flow conditions using multi-detector computed tomography (MDCT), fluoroscopy, high-resolution quantitative computed tomography (HR-QCT), and magnetic resonance imaging (MRI). MDCT was used to monitor contrast diffusion efficiency by plotting contrast density as a function of position along the path of flow through the cartridge during steady state infusion at 1 and 20 mL/min. Both linear and exponential regressions were used to model contrast decay along the flow path. RESULTS: Both linear and exponential models of contrast decay appeared to be reasonable approximations, yielding similar results for contrast diffusion during a single pass through the cartridge. There was no measurable difference in contrast diffusion when comparing 1 mL/min and 20 mL/min flow rates. Fluoroscopy allowed a gross qualitative assessment of flow within the device, and revealed flow inhomogeneity within the corner of the cartridge opposite the blood inlet port. MRI and HR-QCT were both severely limited due to the paramagnetic properties and high atomic number of the target material, respectively. During testing, we encountered several causes of device malfunction, including leak formation, trapped gas, and contrast-mediated nanopore clogging. We illustrate the imaging manifestations of each. CONCLUSIONS: Despite the inherent challenges in imaging a predominantly metallic device, some modalities show potential in the non-invasive assessment of a novel compact hemodialyzer. The approaches described here could potentially be translated to device evaluation in the implanted setting.

Assessment of microembolization associated with revascularization in acute myocardial infarction: MDCT cardiac perfusion and function study.

To use multi-detector computed tomography (MDCT) for assessing the effects of coronary microemboli on pre-existing acute myocardial infarct (AMI) and to compare this pathology to LAD microembolization and occlusion/reperfusion. An angioplasty balloon catheter was placed in the LAD coronary artery of pigs under X-ray guidance. Four animals served as controls without intervention (group A) and an additional 24 animals (8/group) were subjected to microembolization (group B), occlusion/reperfusion (group C) or combination of the two insults (group D). MDCT was used to assess perfusion, LV function and viability. At postmortem, the LV sections were stained with hematoxylin/eosin and triphenyltetrazolium chloride (TTC). Dynamic perfusion and helical cine MDCT demonstrated decline in regional LV perfusion and function, respectively, after all interventions. MDCT showed significant differences in ejection fraction between groups: A = 57.5 ± 4.7%, B = 40.3 ± 0.5% P < 0.05, C = 34.9 ± 1.3% P < 0.05 and D = 30.7 ± 1.2% P < 0.05, while viability MDCT demonstrated differences in enhancement patterns and extents of damage between the groups (B = 9.1 ± 0.4% LV mass, C = 11.9 ± 0.7% and D = 16.2 ± 1.2%, P < 0.05) and extent of microvascular obstruction (MVO) (group C = 3.2 ± 1.0% LV mass versus D = 5.2 ± 0.7%, P < 0.01). DE-MDCT overestimated all types of myocardial damage compared with TTC, but showed a close correlation (r > 0.7). Microscopic examination confirmed the presence of patchy and contiguous necrosis, MVO, edema and calcium deposits. Dynamic and helical cine MDCT imaging can grade LV dysfunction and perfusion deficit, respectively. DE-MDCT demonstrated a large and persistent MVO zone after microembolization of pre-existing AMI. Furthermore, it has the potential to visualize patchy microinfarct, detect perfusion deficits and dysfunction at the border zone after microembolization of pre-existing AMI.

Coronary microemboli effects in preexisting acute infarcts in a swine model: cardiac MR imaging indices, injury biomarkers, and histopathologic assessment.

PURPOSE: To use cardiac magnetic resonance (MR) imaging indices, injury biomarkers, and microscopy for quantifying the effects of defined microemboli volume and sizes on viability, left ventricular (LV) function, and perfusion in preexisting acute myocardial infarcts in a swine model. MATERIALS AND METHODS: Institutional approval was obtained to perform x-ray fluoroscopy and 90-minute left anterior descending coronary artery occlusion-reperfusion (single ischemic insult) in 16 pigs and coronary embolization in eight of the 16 pigs (32 mm(3), 40-120 µm microemboli) (double ischemic insults). Another eight pigs served as controls. Cardiac MR imaging results (viability, function, and perfusion), injury biomarkers (creatine-kinase-MB and troponin I), and histopathologic evaluations were quantified. Analysis of variance was performed, and a P value less than .02 was considered to indicate a significant difference. RESULTS: Delayed contrast material-enhanced MR imaging allowed simultaneous visualization of hyperenhanced large infarcts, hypoenhanced microvascular obstruction (MVO) zones, and moderately enhanced patchy microinfarcts in border zones, which represent different degrees of contraction and perfusion in the respective regions, in pigs subjected to double ischemic insults. The increase in myocardial damage was smaller in pigs with double insults (15.7% ± 1.1% of total LV mass) than in those with a single insult (12.4% ± 1.2%, P < .02), but the reduction in LV ejection fraction was disproportional (32% ± 0.6% and 38% ± 1%, P < .02, respectively). Delayed contrast-enhanced imaging can allow quantification of the MVO zone but can result in underestimation of the extent of myocardial damage compared with microscopy in animals subjected to double insults (18.2 ± 1.6, P < .02). A significant increase in cardiac injury biomarkers was observed at 18-24 hours in both cohorts. The additional effect of microemboli on troponin I was demonstrated at 68-72 hours (3.2 ng/mL ± 0.85 [3.20 µg/L ± 0.85] vs 1.34 ng/mL ± 0.43 [1.34 µg/L ± 0.43], P < .02). CONCLUSION: MR imaging has the potential to allow visualization of acute myocardial infarcts, MVO zones, and patchy microinfarcts simultaneously. The accentuated LV dysfunction caused by double ischemic insults was linked to expansion of the MVO zone, perfusion deficits, and myocardial damage.

Multidetector computed tomography in reperfused acute myocardial infarction. Assessment of infarct size and no-reflow in comparison with cardiac magnetic resonance imaging.

OBJECTIVES: (1) To determine the accuracy of delayed enhancement multidetector computed tomography (MDCT) in measuring the extent of acute myocardial infarct and no-reflow areas using cardiac magnetic resonance imaging (MRI) as standard of reference and (2) to define the optimum timing between injection and MDCT image acquisition to characterize infarcted myocardium and no-reflow areas after reperfusion therapy. MATERIALS AND METHODS: Nineteen patients were prospectively included after acute myocardial infarction and revascularization. Each patient had an MDCT acquisition before and 5 and 10 minutes after injection of 1.5 mL/kg iodinated contrast medium, and a contrast-enhanced MRI at 5 and 10 minutes after injection of 0.2 mmol/kg gadolinium chelate. We assessed image quality and infarct extent using MDCT and MRI, and we measured parameters related to iodinated contrast media kinetics (DeltaHU and DeltaHU ratio). RESULTS: The areas of hyperenhanced myocardium located on the MDCT corresponded to the occluded vessel located on the coronary angiogram (kappa = 0.9). There were strong correlations between the extent of hyperenhanced infarcted myocardium on MDCT and MRI at 5 minutes (20.4% +/- 2.7% of left ventricle (LV) and 20.9% +/- 2.4%, respectively, R = 0.85; P < 0.0001) and 10 minutes after injection (21.0% +/- 2.9% of LV and 19.4% +/- 2.5%, respectively, R = 0.80; P < 0.0001). However, the correlation between the area of hypoenhanced myocardium measured using MDCT and CMR 5 minutes after injection (R = 0.86; P < 0.0001) was better than the measurement obtained 10 minutes after injection (R = 0.64; P = 0.002). On contrast-enhanced MDCT, 5 minutes after injection, the signal-to-noise ratio was significantly higher than at 10 minutes after injection in LV blood (28 +/- 1 to 21 +/- 1, respectively; P = 0.0007), normal myocardium (18 +/- 1 to 15 +/- 1; P = 0.0009), and hyperenhanced infarcted myocardium (24 +/- 1 to 20 +/- 1; P = 0.004). MDCT image quality was significantly better at 5 minutes (3.2 +/- 0.1) than at 10 minutes (2.8 +/- 0.2, P = 0.01, kappa = 0.4). The DeltaHU ratio increased slightly but significantly between 5 minutes (0.83 +/- 0.01) and 10 minutes (0.93 +/- 0.01; P = 0.01), suggesting a slow wash-in and wash-out of contrast medium in infarcted myocardium. CONCLUSION: In ST segment elevation myocardial infarction patients contrast-enhanced MDCT is an accurate method for characterizing and sizing myocardial infarct and no-reflow. Contrast-enhanced MDCT performed 5 minutes after injection yields a higher signal-to-noise ratio and image quality than the 10 minutes time point with no difference in the extent of infarct measurement.

Permanent coronary artery occlusion: cardiovascular MR imaging is platform for percutaneous transendocardial delivery and assessment of gene therapy in canine model.

PURPOSE: To provide evidence that vascular endothelial growth factor (VEGF) genes delivered transendocardially with magnetic resonance (MR) imaging guidance may neovascularize or improve vascular recruitment in occlusive infarction. MATERIALS AND METHODS: All experimental procedures received approval from the institutional committee on animal research. Dogs with permanent coronary artery occlusion were imaged twice (3 days after occlusion for assessment of acute infarction; a mean of 50 days after occlusion +/- 3 [standard error of the mean] for assessment of chronic infarction). A mixture of plasmid VEGF and plasmid LacZ (n = 6, treated animals) or plasmid LacZ and sprodiamide (n = 6, placebo control animals) was delivered to four sites. MR fluoroscopy was used to target and monitor delivery of genes. The effectiveness of this delivery approach was determined by using MR imaging methods to assess perfusion, left ventricular (LV) function, myocardial viability, and infarct resorption. Histologic evaluation of neovascularization was then performed. RESULTS: MR fluoroscopic guidance of injectates was successful in both groups. Treated animals with chronic, but not those with acute, infarction showed the following differences compared with control animals: (a) steeper mean maximum upslope perfusion (200 sec(-1) +/- 32 vs 117 sec(-1) +/- 15, P = .02), (b) higher peak signal intensity (1667 arbitrary units +/- 100 vs 1132 arbitrary units +/- 80, P = .002), (c) increased ejection fraction (from 27.9% +/- 1.2 to 35.3% +/- 1.6, P = .001), (d) smaller infarction size (as a percentage of LV mass) at MR imaging (8.5% +/- 0.9 vs 11.3% +/- 0.9, P = .048) and triphenyltetrazolium chloride staining (9.4% +/- 1.5 vs 12.7% +/- 0.4, P = .05), and (e) higher vascular density (as number of vessels per square millimeter) at the border (430 +/- 117 vs 286 +/- 19, P = .0001) and core (307 +/- 112 vs 108 +/- 17, P = .0001). CONCLUSION: The validity of plasmid VEGF gene delivered with MR fluoroscopic guidance into occlusive infarction was confirmed by neovascularization associated with improved perfusion, LV function, and infarct resorption.

MR assessment of myocardial perfusion, viability, and function after intramyocardial transfer of VM202, a new plasmid human hepatocyte growth factor in ischemic swine myocardium.

PURPOSE: VM202, a newly constructed plasmid human hepatocyte growth factor, was transferred intramyocardially after infarction for the purpose of evaluating this strategy as a therapeutic approach for protection from left ventricular (LV) remodeling. MATERIALS AND METHODS: The institutional animal care and use committee approved this study. Pigs underwent coronary artery occlusion and reperfusion and served as either control (n = 8) or VM202-treated (n = 8) animals. VM202 was transferred intramyocardially into four infarcted and four periinfarcted sites. Cardiac magnetic resonance (MR) imaging (cine, perfusion, delayed enhancement) was performed in acute (3 days) and chronic (50 days +/- 3 [standard error of the mean]) infarction. Histopathologic findings were used to characterize and quantify neovascularization. The t test was utilized to compare treated and control groups and to assess changes over time. RESULTS: In acute infarction, MR imaging estimates of function, perfusion, and viability showed no difference between the groups. In chronic infarction, however, VM202 increased maximum signal intensity and upslope at first-pass perfusion imaging and reduced infarct size at perfusion and delayed-enhancement imaging. These changes were associated with a decrease in end-diastolic (2.15 mL/kg +/- 0.12 to 1.73 mL/kg +/- 0.10, P < .01) and end-systolic (1.33 mL/kg +/- 0.07 to 0.92 mL/kg +/- 0.08, P < .001) volumes and an increase in ejection fraction (38.2% +/- 1.3 to 47.0% +/- 1.8, P < .001). In contrast, LV function deteriorated further in control animals. Compared with control animals, VM202-treated animals revealed peninsulas and/or islands of viable myocardium in infarcted and periinfarcted regions and greater number of capillaries (218 per square millimeter +/- 19 vs 119 per square millimeter +/- 17, P < .05) and arterioles (21 per square millimeter +/- 4 vs 3 per square millimeter +/- 1, P < .001). CONCLUSION: Intramyocardial transfer of VM202 improved myocardial perfusion, viability, and LV function.

MR imaging assessment of the kinetics of P846, a new gadolinium-based MR contrast medium, in ischemically injured myocardium.

The objectives of the study were: (1) to compare the kinetics of a new gadolinium-based low-diffusibility magnetic resonance (MR) contrast medium, P846 and Gd-DOTA in left ventricular (LV) blood and in normal and ischemically injured myocardium using inversion recovery echo-planar imaging (IR-EPI) and (2) to compare the enhancement pattern after injection of P846 with Gd-DOTA, using T1-weighted spin-echo imaging (T1-SE). Sixteen rats were subjected to left descending artery (LAD) occlusion for 30 min, followed by 2.5 h reperfusion. MR imaging was performed before and after administration of the contrast medium in two different groups of animals: one group (n = 8) received 0.05 mmol kg(-1) P846 and the other (n = 8) 0.1 mmol kg(-1) Gd-DOTA. A blipped IR-EPI and a multislice T1-SE were performed before injection and for 90 min after injection. T1-values were derived by fitting regional signal intensity on the IR-EPI images, the R1, DeltaR1 (R(1postcontrast) - R(1precontrast)) and DeltaR1 ratios were calculated in LV blood, normal and injured myocardium. On SE-T(1), the signal intensity ratio (SI) and extent of injury were measured. True infarct size was measured using histochemical staining. Changes in DeltaR(1) were 4.8 times greater with 0.05 mmol kg(-1) P846 than with 0.1 mmol kg(-1) Gd-DOTA in LV blood (6.3 +/- 0.9 vs 0.9 +/- 0.1 s(-1), p < 0.0001), normal (1.7 +/- 0.2 vs 0.34 +/- 0.03 s(-1), p < 0.0001) and ischemically injured myocardium (5.4 +/- 0.4 vs 1.6 +/- 0.1 s(-1), p < 0.0001). MR imaging experiments showed that the signal enhancement with P846 is longer (90 min), which might be explained by a lower diffusion of P846 compared with Gd-DOTA (30 min). P846 differentiates viable and nonviable myocardium. Despite lower gadolinium dose, P846 permits differentiation of viable and nonviable myocardium owing to a high contrast and a long imaging window with conventional t1-weighted SE sequence.

An overview on the advances in cardiovascular interventional MR imaging.

Interventional cardiovascular magnetic resonance imaging (iCMR) represents a new discipline whose systematic development will foster minimally invasive interventional procedures without radiation exposure. New generations of open, wide and short bore MR scanners and real time sequences made cardiovascular intervention possible. MR compatible endovascular catheters and guide-wires are needed for delivery of devices such as stents or atrial septal defect (ASD) closures. Catheter tracking is based on active and passive approaches. Currently performed MR-guided procedures are used to monitor, navigate and track endovascular catheters and to deliver local therapeutic agents to targets, such as infarcted myocardium and vascular walls. Heating of endovascular MR catheters, guide-wires and devices during imaging still presents high safety risks. MR contrast media improve the capabilities of MR imaging by enhancing blood signal, pathologic targets (such as myocardial infarctions and atherosclerotic plaques), endovascular catheters and by tracking injected therapeutic agents. Labeling injected soluble therapeutic agents, genes or cells with MR contrast media enables interventionalists to ensure the administration of the drugs in the target and to trace their distribution in the targets. The future clinical use of this iCMR technique requires (1) high spatial and temporal resolution imaging, (2) special catheters and devices and (3) effective therapeutic agents, genes or cells. These conditions are available at a low scale at the present time and need to be developed in the near future. Such progress will lead to improved patient care and minimize invasiveness.

Delivery and assessment of endovascular stents to repair aortic coarctation using MR and X-ray imaging.

PURPOSE: To investigate the utility of MR and X-ray imaging for characterizing aortic coarctation and flow, and guiding the endovascular catheter to place a stent to repair the coarctation. MATERIALS AND METHODS: The descending aorta in eight dogs was looped with elastic band and tightened distal to the subclavian artery. Balanced fast field echo (bFFE) and velocity-encoded cine (VEC) MRI sequences were used for device tracking and measuring aortic flow. A T1-weighted fast-field echo sequence (T1-FFE) was used to visualize the coarctation and roadmap the aorta. Nitinol stents were guided by a nitinol guidewire and placed under MR guidance. RESULTS: Aortic coarctation was visible on MR and X-ray imaging. The procedure success rate was 88%. VEC MRI measured the changes in aortic flow (baseline = 1.3 +/- 0.2, coarctation = 0.2 +/- 0.02, and stent placement = 0.8 +/- 0.1 liters/minute). A significant reduction in iliac blood pressure was measured after coarctation, but it was reversed by stent placement. The stent lumen was visible on X-ray fluoroscopy, but not on MRI. CONCLUSION: Stent deployment to repair aortic coarctation is feasible under MR guidance. The combined use of MR and X-ray imaging is effective for anatomic and functional evaluation of aortic coarctation dilation, which may be crucial for optimal therapy.

Myocardial blood flow in patients with dilated cardiomyopathy: quantitative assessment with velocity-encoded cine magnetic resonance imaging of the coronary sinus.

PURPOSE: To quantify global myocardial perfusion using magnetic resonance imaging (MRI) in patients with heart failure due to idiopathic dilated cardiomyopathy (IDC) and to compare myocardial perfusion and microvascular reactivity with healthy subjects. MATERIALS AND METHODS: A total of 19 subjects (healthy volunteers (N = 12) and IDC patients (N = 7)) were studied using cine MRI to measure left ventricular (LV) mass and a velocity-encoded cine MRI technique to measure coronary sinus flow at rest and after dipyridamole-induced hyperemia. Absolute values of total myocardial blood flow (MBF) were calculated from coronary sinus flow and LV mass. RESULTS: At baseline, MBF was not significantly different in patients with IDC (0.48 +/- 0.07 mL/minute/g) and healthy subjects (0.55 +/- 0.19 mL/minute/g, P= 0.41). After dipyridamole administration, MBF in IDC patients increased to a level significantly less than that in normal volunteers (1.05 +/- 0.35 mL/minute/g vs. 1.99 +/- 1.05 mL/minute/g, P < 0.05). Consequently, MBF reserve was impaired in patients with IDC (2.19 +/- 0.77) compared to that in healthy subjects (3.51 +/- 1.29, P < 0.05). A moderate correlation was found between MBF reserve and LV ejection fraction (r = 0.48, P < 0.05). CONCLUSION: MBF reserve is reduced in patients with IDC, indicating that coronary microcirculatory flow is impaired. This integrated MRI approach allows quantitative measurement of global MBF in humans and may have the potential to study the effects of pharmacological interventions on myocardial perfusion.

Balloon sizing and transcatheter closure of acute atrial septal defects guided by magnetic resonance fluoroscopy: assessment and validation in a large animal model.

PURPOSE: To quantitatively assess atrial septal defects (ASDs) with small shunts using MRI followed by transcatheter closure monitored by MR fluoroscopy. MATERIALS AND METHODS: Acute ASDs were created in 14 pigs under x-ray fluoroscopy. Six animals were studied in order to select MR-compatible delivery systems and imaging strategies. ASDs in eight animals were examined with balloon sizing under MR fluoroscopy, flow measurements, and contrast media injections, after which transcatheter closure was performed under MR fluoroscopy. The delivery system was assembled from commercially available materials. RESULTS: The ratio of pulmonary to systemic flow (Qp/Qs) was reduced from 1.23 +/- 0.15 before ASD closure to 1.07 +/- 0.11 after ASD closure (P < 0.001). In two out of eight animals Qp/Qs was close to 1.0 before closure despite the presence of defects >15 mm. The ASDs were measurable with MR balloon sizing in all of the animals. Balloon sizing was identical with MR (16.9 +/- 2.3 mm) and x-ray fluoroscopy (17.1 +/- 1.3 mm). The in-house-assembled delivery system allowed successful placement of closure devices under MR guidance. CONCLUSION: Assessment and closure of small shunts with MR fluoroscopy is feasible. A barrier to the rapid implementation of transcatheter closure in patients is uncertainty about the MR safety of guidewires and device delivery systems.

Accentuation of high susceptibility of hypertrophied myocardium to ischemia: complementary assessment of Gadophrin-enhancement and left ventricular function with MRI.

The aim of the study was to compare infarction size and left ventricular (LV) function in normal and hypertrophied hearts after brief ischemia using Gadophrin-enhancement and functional assessment by MRI. Rats (n = 20) were assigned to aortic banding to induce LV hypertrophy or control. Eight weeks later, rats were subjected to 25 min of regional myocardial ischemia followed by 3 hr of reperfusion. The necrosis-specific agent Gadophrin-3 was injected to delineate infarcted myocardium on MRI. Effects of aortic banding and ischemia on LV mass and function were determined. At postmortem, areas at risk and infarction were measured. Close correlation was found between LV mass measured with MRI and at postmortem (r = 0.98). LV mass measured with MRI was significantly greater (0.81 +/- 0.02 g) in animals with aortic banding compared to control (0.62 +/- 0.02 g; P < 0.001). Infarction size was larger in hypertrophied hearts (19.0 +/- 1.4% / 18.3 +/- 1.5%) than in control (9.8 +/- 1.7% / 9.2 +/- 2.0%) on Gadophrin-enhanced MRI and at postmortem, respectively. Similarly, greater impairment in ejection fraction was observed in hypertrophied hearts with MRI (39 +/- 4% vs. 49 +/- 2%; P = 0.02). Gadophrin-3 provides accurate estimation of infarct size in hypertrophied hearts. Hypertrophied hearts are more sensitive to ischemia than nonhypertrophied hearts. The complementary assessment of Gadophrin-enhancement and LV function with MRI provides unique information about myocardium sensitivity to ischemia.

Endovascular stents in pulmonary valve and artery in swine: feasibility study of MR imaging-guided deployment and postinterventional assessment.

PURPOSE: To assess the feasibility of using magnetic resonance (MR) imaging to guide stent deployment in the pulmonary valve and artery and evaluate, after stent deployment, the position and morphology of and blood flow through the stent. MATERIALS AND METHODS: Angiography and 1.5-T MR imaging were performed in a dual-imaging suite. Nitinol stents were placed in the pulmonary valve and main pulmonary artery in five pigs by using MR imaging guidance. For interactive MR imaging monitoring of catheter manipulation and stent delivery, balanced fast field-echo and T1-weighted turbo field-echo sequences were used. Visualization of the delivery system was based on T2* (with air as the contrast material) or T1 (with gadodiamide as the contrast material). After stent deployment, the position and morphology of and flow through the stent were verified with multiphase multisection balanced fast field-echo and velocity-encoded cine MR imaging. Findings at angiography and postmortem examination also helped verify stent placement. The paired Student t test was used for data analysis. RESULTS: The stent was successfully deployed in all animals. The stent was placed distal to the pulmonary valve in four animals and across the pulmonary valve in one animal. The position and morphology of the stent were clearly depicted on balanced fast field-echo images. In the animal with the stent placed across the pulmonary valve, the pulmonary regurgitant fraction was 37%; this was not seen in the animals with stents placed distal to the pulmonary valve. No complication (eg, stent migration, intramural injury, or vascular perforation) was noted during the intervention. Findings at angiography and postmortem examination confirmed the position of the stents. CONCLUSION: MR imaging has the potential to guide stent placement in the pulmonary valve or artery and to evaluate flow volume within the stent lumen after the intervention.

Close association between the reduction in myocardial energy metabolism and infarct size: dose-response assessment of cyclosporine.

Cyclosporine protects the heart against ischemia/reperfusion injury, but its effect on cardiac metabolism is largely unknown. We assessed cyclosporine-induced metabolic changes in the rat heart prior to occlusion using magnetic resonance spectroscopy (MRS) and correlated effects with infarct size in a coronary occlusion/reperfusion model. The two study groups were cyclosporine and cyclosporine + coronary occlusion (n = 20/group). Rats were pretreated with cyclosporine (5, 10, 15, and 25 mg/kg/day) or the vehicle by oral gavage for 3 days (n = 4/dose). On day 4, hearts of rats in the cyclosporine group were excised, and extracted cell metabolites were measured using (1)H and (31)P MRS. The second group was subjected to 30 min of coronary artery occlusion followed by 24 h of reperfusion. Infarct size and area at risk were measured using a double staining method. In the cyclosporine group, cyclosporine reduced cardiac energy metabolism (ATP: r = -0.89, P < 0.001) via depression of oxidative phosphorylation and the Krebs' cycle in a dose-dependent manner. The decrease of ATP levels was positively correlated with changes of NAD(+) (r = 0.89), glutamate (r = 0.95), glutamine (r = 0.84), and glucose concentrations (r = 0.92, all P < 0.002). It was inversely correlated with lactate (r = -0.93, P < 0.001). In the coronary occlusion group, cyclosporine dose dependently reduced the ratio [area of infarct/area of the left ventricle] (r = -0.86, P < 0.01), with 15 mg/kg/day being the most effective cyclosporine dose. The reduction in infarct size correlated with the reduction in oxidative phosphorylation (ATP: r = 0.97; NAD(+): r = 0.82, P < 0.01). The reduction in cardiac energy metabolism before occlusion may be the cause of myocardial preservation during ischemia/reperfusion.

Noninvasive assessment of the effects of nicorandil on left ventricular volumes and function in reperfused myocardial infarction.

OBJECTIVE: Nicorandil, a K-ATP channel opener with a nitrate-like effect, is a potent vasodilator and has favorable hemodynamic effects in heart failure patients. While its cardio-protective properties in the setting of acute ischemia are well known, the long-term effects of oral nicorandil therapy on post-infarction left ventricular (LV) dilatation have not been investigated. METHODS: Myocardial infarction (MI) was induced in 30 Sprague-Dawley rats by 1 h of coronary artery occlusion followed by reperfusion. After matching for infarction size, animals were randomly assigned to nicorandil treatment (3 mg/kg/day) given in tap water or no treatment (control group). Treatment was started 2 days after MI and continued for 8 weeks. Contrast-enhanced and functional magnetic resonance imaging (MRI) were used to determine infarction size, LV volumes, mass, ejection fraction, and regional wall thickness. RESULTS: Nicorandil significantly decreased end-systolic volumes (0.33+/-0.02 ml; P<0.05) and improved LV ejection fraction (37+/-2%; P<0.01) compared to control rats (0.43+/-0.04 ml and 28+/-2%, respectively) 8 weeks after MI. During the study period, the increase in LV mass (DeltaLVM) was significantly greater in control (0.09+/-0.03 g) than in treated animals (0.02+/-0.02 g, P<0.05). Moreover, nicorandil improved systolic wall thickening of the rim of infarction (P<0.001) and remote non-infarcted regions (P<0.01). CONCLUSION: These results demonstrate that the long-term oral treatment with nicorandil started 2 days after MI attenuates left ventricular dilatation and improves cardiac function in rats with reperfused MI.