[Heart tumors: magnetic resonance imaging and multislice spiral CT]. / Herztumoren: Magnetresonanztomographie und Mehrschicht-Spiral-CT.

Transthoracic echocardiography is usually the initial diagnostic test in patients with a suspected cardiac mass. However, this technique is restricted by its small field of views and insufficient acoustic window in some patients. Magnetic resonance imaging (MRI) and, since its introduction, multislice spiral computed tomography allow for detailed delineation of intra and pericardiac tumors, their extent, and their influence on cardiac function. Primary benign and malignant cardiac tumors have several characteristic features in MR imaging. Assessment of such features may narrow down the differential diagnosis or even allow for reliable diagnosis in selected cases. Many such features can also be assessed using MSCT. This article provides an overview of examination protocols of MRI and CT for cases in which a cardiac mass is suspected and describes the appearance of primary and secondary cardiac masses as well as intracavitary thrombi.

Magnetic resonance measurement of coronary blood flow.

Magnetic resonance (MR) flow measurement in the coronary artery can be achieved with either a breath-hold acquisition or a respiration-triggered acquisition. MR measurements of cardiac output are significantly depressed during breath-holding at deep inspiration, but the advantage is that the breath-hold method requires less scan time. Blood flow in the coronary sinus reflects the global myocardial blood flow because it represents approximately 96% of the total myocardial blood flow of the left ventricle (LV). If blood flow in the coronary sinus is measured with phase-contrast cine magnetic resonance imaging (MRI) and LV myocardial mass is measured with cine MRI, both the total myocardial blood flow and the average coronary blood flow per gram of myocardial mass can be quantified. Coronary flow reserve with volumetric MR flow measurement is measured to be within 4.2-5.0-fold. The noninvasive MR measurement of coronary flow reserve has been shown to be useful in identifying the functional significance of stenoses in the left anterior descending artery. The sensitivity and specificity of MR coronary flow velocity reserve for identifying stenosis of 70% or greater in the left main or left anterior descending artery were 100% and 83%, respectively. The MR quantification of total coronary blood flow and coronary blood flow per gram of myocardial mass seems to be an ideal method for evaluating coronary hemodynamics and may be useful in evaluating endothelial dysfunction of the coronary circulation.

[MR contrast media for cardiovascular imaging]. / Anwendung von Kontrastmitteln für die kardiale Magnetresonanztomographie.

MR contrast media improve the diagnostic capability of MRI and MRA. They are used in the discrimination of viable and non-viable myocardium, transmural and non-transmural infarction, occlusive and reperfused infarction and for measurement of myocardial perfusion. Currently, clinical studies are almost completely restricted to the use of extracellular non-specific MR contrast media (i. e., Gd-DTPA, Gd-DTPA,-BMA, Gd-BOPTA, Gd-D03A). However, the feasibility of using intravascular, necrosis specific or intracellular MR contrast media or endogeneous substrates as specific MR contrast media in cardiovascular imaging has been demonstrated in experimental and a few clinical studies. Intravascular contrast media (i. e., MS-325 or NC100150 Injection) allow assessment of microvascular integrity and performance of MR angiography. Necrosis specific contrast media (i. e., Gadophrin-2) have been used for sizing the extent of infarcted myocardium while intracellular contrast media (i. e., Mn-DPDP) delineate viable myocardium. Endogenous contrast media (i. e., Deoxyhemoglobin, Na (+) or K (+)) have been tested for detecting the alterations in concentrations of these ions in infarcted myocardium and for perfusion measurements. Furthermore, intravascular MR contrast media may be useful for MRA and MRI guided cardiovascular interventions.

Sequential magnetic resonance monitoring of pulmonary flow with endovascular stents placed across the pulmonary valve in growing Swine.

BACKGROUND: Patients with endovascular stent implantation for the treatment of right ventricular outflow tract obstruction are often left with incomplete relief of the obstruction and significant pulmonary regurgitation. A noninvasive and reproducible method for monitoring such patients is desirable. MRI in the presence of a stent, however, has to overcome the problem of potential metallic artifacts. METHODS AND RESULTS: Under x-ray fluoroscopic guidance, endovascular nitinol stents were placed across the pulmonary valve in 6 young pigs to induce pulmonary regurgitation. Five additional pigs served as controls. Initial MRI was performed after 2 days (13.5+/-1.8 kg) and follow-up after 3 months (32+/-2.9 kg). Pulmonary flow volumes and regurgitant fraction were quantified by velocity-encoded cine (VEC) MRI through (VEC-TS) and distal to (VEC-DS) the stent. VEC-TS was compared with VEC-DS and volumetric measurements of left and right ventricular stroke volumes provided by cine MRI ("gold standard"). Antegrade and retrograde pulmonary flow volumes by VEC-TS were slightly but significantly less than those with VEC-DS and cine MRI. Excellent correlations (r>0.97) for phasic pulmonary flow volumes as measured by VEC-TS and VEC-DS were shown. Pulmonary regurgitant fraction increased from 32.8+/-15% to 49.6+/-17% (P<0.05) over the course of 3 months with VEC-TS. CONCLUSIONS: MRI demonstrates the progression of pulmonary regurgitation in growing swine. VEC MRI has the ability to quantify pulmonary blood flow inside the lumen of nitinol stents. MRI appears to be ideally suited for monitoring patients with endovascular nitinol stents in the pulmonary artery or pulmonary valve position.

Assessment of nicorandil therapy in ischemic myocardial injury by using contrast-enhanced and functional MR imaging.

PURPOSE: To determine the potential of mesoporphyrin- and gadopentetate dimeglumine-enhanced and functional magnetic resonance (MR) imaging in the assessment of the acute effect of nicorandil on ischemic injury of the myocardium. MATERIALS AND METHODS: Spin-echo MR imaging was used to monitor changes in myocardial contrast and function in reperfused myocardial injury. Inversion-recovery echo-planar MR imaging was used to depict the injured region. Myocardial injury in rats was produced by using 30 minutes of coronary occlusion followed by 24 hours reperfusion. Nicorandil (n = 9) was infused during occlusion and early reperfusion. Control animals (n = 11) received no therapy. At 24 hours, after administration of mesoporphyrin and gadopentetate dimeglumine and histochemical staining, the function and size of the injured region of the left ventricle (LV) were determined. A t test was used to compare data between groups of animals, whereas regression and Bland-Altman analyses were used to determine correlation and agreement between MR imaging and histomorphometry, respectively. RESULTS: Treated animals showed reduced infarction size as compared with the control group from 25.6% +/- 7.9 (SD) to 7.9% +/- 6.8 of LV myocardial area (P < .001), as defined with mesoporphyrin-enhanced MR imaging; while the size of the rim increased from 10.8% +/- 10.0 to 16.1% +/- 14.4 (P < .05). The diastolic-midventricular cavity area was smaller in treated animals (15.2 mm(2) +/- 4.3) compared with the control group (28.5 mm(2) +/- 7.9; P < .001). At functional MR imaging, nicorandil improved systolic reduction in LV cavity area (57.5% +/- 17.3) compared with the control group (38.0% +/- 16.0; P < .05) and preserved regional LV wall thickening at the site of injury (12.2% +/- 11.1 in treated group vs 0.3% +/- 8.6 in the control group; P < .05). CONCLUSION: Contrast material-enhanced MR imaging has the potential to demonstrate reduction in size of ischemically injured myocardium, whereas functional MR imaging demonstrated the recovery of LV function 24 hours after nicorandil therapy.

Mr flow measurement in the internal mammary artery-to-coronary artery bypass graft: comparison with graft stenosis at radiographic angiography.

PURPOSE: To evaluate the sensitivity and specificity of breath-hold magnetic resonance (MR) flow measurement for detection of significant stenosis in internal mammary artery bypass grafts. MATERIALS AND METHODS: Twenty-six consecutive patients who had undergone coronary artery bypass surgery were examined. Breath-hold velocity-encoded cine MR images were obtained at the midpoint of the internal mammary artery between its origin from the subclavian artery and the distal anastomosis to the left anterior descending artery. RESULTS: MR images were obtained successfully in 24 patients. At conventional angiography, no significant stenosis was observed in 17 patients (group A), and significant stenosis (diameter > 70%) was observed in seven patients (group B). The mean diastolic-to-systolic peak velocity ratio in group B (0.61 +/- 0.44 [SD]) was significantly lower than that in group A (1.88 +/- 0.96; P <.01). Evaluation of graft stenosis with the diastolic-to-systolic peak velocity ratio revealed a sensitivity of 86% and a specificity of 88%. The mean blood flow rate at baseline in group B (16.9 mL/min +/- 5.5) was significantly lower than that in group A (79.8 mL/min +/- 38.2; P <.01). The sensitivity and specificity of MR blood flow measurement in predicting significant stenosis were 86% and 94%, respectively. The mean pharmacologic flow reserve ratios were 2.00 +/- 1.43 in group A and 1.39 +/- 1.46 in group B (P >.05). CONCLUSION: Fast MR blood flow measurement at baseline is highly useful for predicting significant stenosis in internal mammary arterial grafts.

Accuracy of segmented MR velocity mapping to measure small vessel pulsatile flow in a phantom simulating cardiac motion.

The purpose of this study was to investigate the accuracy of conventional, segmented, and echo-shared MR velocity mapping sequences to measure pulsatile flow in small moving vessels using a phantom with simulated cardiac motion. The phantom moved either cyclically in-plane, through-plane, in- and through-plane, or was stationary. The mean error in average flow was -2% +/- 3% (mean +/- SD) for all sequences under all conditions, with or without background correction, as long as the region of interest (ROI) size was equal to the vessel cross-sectional size. Overestimation of flow as a result of an oversized ROI was less than 20%, and independent of field of view (FOV) and matrix, as long as the offset in angle between the imaging plane and flow direction was less than 10 degrees. Segmented velocity mapping sequences are surprisingly accurate in measuring average flow and render flow profiles in small moving vessels despite the blurring in the images due to vessel motion. J. Magn. Reson. Imaging 2001;13:722-728.

Comparison between MR imaging and 99mTc MIBI scintigraphy in the evaluation of recurrent of persistent hyperparathyroidism.

PURPOSE: To compare the sensitivity and positive predictive value of magnetic resonance (MR) imaging and technetium 99m 2-methoxyisobutyl-isonitrile (MIBI) scintigraphy for the detection of hyperfunctioning parathyroid tissue when used alone and in combination in a large patient population with recurrent or persistent hyperparathyroidism (HPT). MATERIALS AND METHODS: In 98 consecutive patients with biochemically proved recurrent or persistent HPT after surgery, MR imaging and 99mTc MIBI study findings were retrospectively reviewed and compared with surgical and histopathologic findings. The sensitivity and positive predictive value of MR imaging and 99mTc MIBI scintigraphy were compared with each other and in combination. RESULTS: In these patients, 130 abnormal parathyroid glands were identified at surgery. The sensitivity and positive predictive value of MR imaging were 82% (95% CI: 75%, 89%) and 89%, respectively; those for (99m)Tc MIBI scintigraphy were 85% (95% CI: 79%, 91%) and 89%. No significant difference was found between MR imaging and 99mTc MIBI scintigraphy for sensitivity (P =.7). The sensitivity and positive predictive value for the detection of abnormal parathyroid tissue on a per-gland basis increased to 94% (95% CI: 90%, 98%) and 98%, respectively, when only one of the two tests was required to be positive. CONCLUSION: MR imaging and 99mTc MIBI scintigraphy have similarly good sensitivity and positive predictive value for the detection of hyperfunctioning parathyroid tissue in patients after surgery. The combination of the two tests provided a substantial increase in sensitivity and positive predictive value.

Identification of pulmonary vein stenosis after radiofrequency ablation for atrial fibrillation using MRI.

Pulmonary vein stenosis is one of the frequent complications after radiofrequency ablation for atrial fibrillation. MRI plays an important role in depicting the pathoanatomic structure of the pulmonary veins, and measuring the blood flow velocity in the pulmonary veins before and after therapy, and is superior to transesophageal echocardiography for this purpose.

Magnetic resonance characterization of the peri-infarction zone of reperfused myocardial infarction with necrosis-specific and extracellular nonspecific contrast media.

BACKGROUND: Because ischemically injured myocardium is frequently composed of viable and nonviable portions, a method to discriminate the two is useful for clinical management. METHODS AND RESULTS: Ischemically injured myocardium was characterized with extracellular nonspecific (Gd-DTPA) and necrosis-specific (mesoporphyrin) MR contrast media in rats. Relaxation rates (R1) were measured on day 1 and day 2 by inversion-recovery echoplanar imaging. Spin-echo imaging was used to define contrast-enhanced regions and regional wall thickening. Gadolinium concentration, area at risk, and infarct size were measured at postmortem examination. DeltaR1 ratio (DeltaR1(myocardium)/DeltaR1(blood)) after administration of Gd-DTPA was greater in ischemically injured myocardium (1.20+/-0.15) than in normal myocardium (0.47+/-0.05, P<0.05), which was attributed to differences in gadolinium concentration and water content. The Gd-DTPA-enhanced region on day 2 was larger (32.8+/-0.9%) than true infarction as demonstrated by triphenyltetrazolium chloride (TTC) (24.6+/-1.4%, P<0.001, r=0.21). Bland-Altman analysis revealed that the Gd-DTPA-enhanced region overestimated true infarct size by 7.8+/-5.9%. On the other hand, the mesoporphyrin-enhanced region (26.9+/-1.8%, P=NS, r=0.87) and true infarct size were identical. The difference in the areas demarcated by the 2 agents is the peri-infarction. Systolic and diastolic MR images revealed no wall thickening in the mesoporphyrin-enhanced region (0.3+/-3.3%) but reduced thickening in the Gd-DTPA-enhanced rim (8.5+/-5.5%, P<0.05). CONCLUSIONS: The Gd-DTPA-enhanced region encompasses both viable and nonviable portions of the ischemically injured myocardium. The Gd-DTPA-enhanced area overestimated infarct size, but the mesoporphyrin-enhanced area matched true infarct size. The salvageable peri-infarction zone can be characterized with double-contrast-enhanced and functional MR imaging; the mismatched area of enhancement between the 2 agents shows residual wall thickening.

Myocardial viability: magnetic resonance assessment of functional reserve and tissue characterization.

The determination of myocardial viability is crucial in patients with left ventricular dysfunction resulting from acute myocardial ischemia or chronic coronary artery disease. Viable myocardium will most likely benefit from revascularization procedures. However, the revascularization of scar tissue will not lead to improvement of ventricularfunction andfurthermore bears unnecessary riskfor the patient. Currently, echocardiographic and radionuclide techniques are the most established methods for the assessment of presence and extent of viable myocardium. Magnetic resonance imaging (MRI) also provides multiple approaches for determining viability of acute ischemically injured and hibernating myocardium. MRI can assess contractile reserve in a manner similar to echocardiography. Additionally, contrast-enhanced MRI can characterize myocardial ischemic injury, including the ability to discriminate viable from nonviable zones. Several new contrast media have been introduced for this purpose. This review addresses the progress toward the goal of defining myocardial viability based on MR techniques and focuses on the current and future role of MR in the assessment of viable myocardium.

Assessment of coronary flow velocity reserve using fast velocity-encoded cine MRI for noninvasive detection of restenosis after coronary stent implantation.

PURPOSE: Serial change of the coronary flow velocity reserve was evaluated with fast velocity-encoded cine magnetic resonance imaging (MRI) for noninvasive detection of restenosis after coronary stent implantation. METHOD: In total, 60 MRI flow studies were performed in 10 patients with coronary artery disease who undersvent elective successful stent implantation to the lesion in the proximal left anterior descending artery. Flow velocities in the segment that was distal to the stent were measured before and after intravenous injection of dipyridamole. MRI measurements of coronary flow velocity reserve were repeated every 4 weeks for 6 months, and follow-up angiography was performed 6 months after the procedure. RESULTS: In patients without restenosis (n = 7, % diameter stenosis: 27.8%+/-7.1) at follow-up angiography, the coronary flow velocity reserve remained normal during the 6-month follow-up time. The flow velocity reserve was 2.31+/-0.30 at 1 month and 2.52+/-0.25 at 6 months after stent implantation (p = NS). In contrast, the coronary flow velocity reserve showed a significant decrease after 4 months in patients with restenosis (n = 3, % diameter stenosis: 66.3%+/-8.1) at follow-up angiography. The flow velocity reserve was 2.26+/-0.49 at 1 month and 1.52+/-0.09 at 6 months after stent implantation (p < 0.05). CONCLUSION: Fast velocity-encoded cine MRI is a technique that shows promise in providing non-invasive detection of restenosis of coronary stent implantation.

Blood pool MR contrast agents for cardiovascular imaging.

Currently available magnetic resonance (MR) contrast agents are not confined to the intravascular space because of their small molecular size. These agents produce peak vascular enhancement for only a short period. Conversely, blood pool agents have longer intravascular residence time and higher relaxivity. Therefore these agents provide MR angiography with flexibility, versatility, and accuracy. With blood pool agents, the timing of contrast injection becomes less significant because the optimal imaging window is in tens of minutes rather than seconds. In addition, larger anatomic regions can be imaged optimally. Preliminary evidence appears to support the notion that blood pool agents may play a diagnostic role in coronary, peripheral, and pulmonary angiography. Besides their ability to increase vascular contrast, blood pool agents provide physiologic information, including rate of entry, rate of accumulation, and rate of elimination. MR imaging with blood pool agents also have proven to be of significant value in the assessments of myocardial perfusion and microvascular permeability. In anticipation of broad clinical use, blood pool agents are currently being evaluated in human trails. Examples include gadolinium-chelate that binds in vivo to albumin to form blood pool agents and ultrasmall superparamagnetic iron oxide particles. This review discusses the applications of MR blood pool agents in the cardiovascular system. J. Magn. Reson. Imaging 2000;12:890-898.

Coronary sinus flow measurement by means of velocity-encoded cine MR imaging: validation by using flow probes in dogs.

PURPOSE: To validate coronary sinus flow measurements for quantification of global left ventricular (LV) perfusion by means of velocity-encoded cine (VEC) magnetic resonance (MR) imaging and flow probes. MATERIALS AND METHODS: Measurements of coronary sinus flow were performed in seven dogs by using VEC MR imaging at baseline, single coronary arterial stenosis, dipyridamole stress, and reactive hyperemia. These measurements were compared with flow probe measurements of coronary blood flow (CBF) in the left anterior descending coronary (LAD) and circumflex (CFX) arteries (CBF(LAD+CFX)) and coronary sinus. LV blood perfusion was calculated in milliliters per minute per gram from coronary sinus flow, and LV mass was obtained by using VEC and cine MR imaging. LV mass was validated at autopsy. RESULTS: CBF(LAD+CFX) and coronary sinus flow at VEC MR imaging showed close correlation (r = 0.98, P: <.001). The difference between CBF(LAD+CFX) and MR coronary sinus flow was 3.1 mL/min +/- 8.5 (SD). LV mass at cine MR imaging was not significantly different from that at autopsy (73.2 g +/- 12.8 vs 69. 4 g +/- 12.8). At baseline, myocardial perfusion was 0.40 mL/min/g +/- 0.09 at VEC MR imaging, and CBF(LAD+CFX) was 0.44 mL/min/g +/- 0. 08 (not significant). Reactive hyperemia resulted in 2.7- and 2. 3-fold increases in coronary sinus flow at VEC MR imaging and flow probe CBF(LAD+CFX), respectively. CONCLUSION: VEC MR imaging has the potential to measure coronary sinus flow during different physiologic conditions and can serve as a noninvasive modality to quantify global LV perfusion in patients.