Double spectral attenuated inversion recovery (DSPAIR)-an efficient fat suppression technique for late gadolinium enhancement at 3 tesla.

Despite clinical use of late gadolinium enhancement (LGE) for two decades, an efficient, robust fat suppression (FS) technique still does not exist for this CMR mainstay. In ischemic and non-ischemic heart disease, differentiating fibrotic tissue from infiltrating and adjacent fat is crucial. Multiple groups have independently developed an FS technique for LGE, double spectral attenuated inversion recovery (DSPAIR), but no comprehensive evaluation was performed. This study aims to fill this gap. DSPAIR uses two SPAIR pulses and one non-selective IR pulse to enable FS LGE, including compatibility with phase sensitive inversion recovery (PSIR). We implemented a magnitude (MAGN) and a PSIR variant and compared them with LGE without FS (CONTROL) and with spectral presaturation with inversion recovery (SPIR) in simulations, phantoms, and patients. Fat magnetization by SPIR, MAGN DSPAIR, and PSIR DSPAIR was simulated as a function of pulse B1 , readout (RO) pulse number, and fat TI . A phantom with fat, fibrosis, and myocardium compartments was imaged using all FS methods and modifying pulse B1 , RO pulse number, and heart rate. Signal was measured in SNR units. Fat, myocardium, and fibrosis SNR and fibrosis-to-fat CNR were obtained. Patient images were acquired with all FS techniques. Fat, myocardium, and fibrosis SNR, fibrosis-to-fat CNR, and image and FS quality were assessed. In the phantom, both DSPAIR variants provided superior FS compared with SPIR, independent of heart rate and RO pulse number. MAGN DSPAIR reduced fat signal by 99% compared with CONTROL, PSIR DSPAIR by 116%, and SPIR by 67% (25 RO pulses). In patients, both DSPAIR variants substantially reduced fat signal (MAGN DSPAIR by 87.1% ± 10.0%, PSIR DSPAIR by 130.5% ± 36.3%), but SPIR did not (35.8% ± 25.5%). FS quality was good to excellent for MAGN and PSIR DSPAIR, and moderate to poor for SPIR. DSPAIR provided highly effective FS across a wide range of parameters. PSIR DSPAIR performed best.

Comparison of magnetization transfer-preparation and T2-preparation for dark-blood delayed-enhancement imaging.

Recently developed dark-blood techniques such as Flow-Independent Dark-blood DeLayed Enhancement (FIDDLE) allow simultaneous visualization of tissue contrast-enhancement and blood-pool suppression. Critical to FIDDLE is the magnetization preparation, which accentuates differences between myocardium and blood-pool. Here, we compared magnetization transfer (MT)-preparation and T2-preparation for use with FIDDLE. Variants of FIDDLE were developed with MT- or T2-preparation modules and tested in 35 patients (11 at 1.5 T, 24 at 3 T). Images were acquired with each FIDDLE variant in an interleaved fashion 10 minutes after gadolinium administration with otherwise identical acquisition parameters. Images were visually and quantitatively assessed for artifacts and differences in right ventricle to left ventricle (RV-to-LV) blood-pool suppression. Bright artifacts, reflecting incomplete blood-pool suppression, were frequently observed in the left atrium with T2-preparation FIDDLE at 1.5 and 3 T (82% and up to 100% of patients, respectively). MT-preparation FIDDLE resulted in fewer patients with artifacts (0% at 1.5 T, 22% at 3 T; P < .01). Left atrial blood-pool signal was significantly more homogeneous with MT-preparation than with T2-preparation at 1.5 and 3 T (P < .001 for all comparisons). Visibly different RV-to-LV blood-pool suppression was observed with T2-preparation in 36% of patients at 1.5 T and up to 94% at 3 T. In these patients, RV blood-pool signal was elevated, reducing the conspicuity of the myocardial-RV blood-pool border. Conversely, there were no visible differences in RV-to-LV blood-pool suppression with MT-preparation. Quantitative assessment of differences in blood-pool suppression and blood-pool artifacts was consistent with visual analyses. We conclude that for dark blood-blood delayed-enhancement imaging of the heart, MT-preparation results in fewer bright blood-pool artifacts and more uniform blood-pool suppression than T2-preparation.

Quantitative inversion time prescription for myocardial late gadolinium enhancement using T1-mapping-based synthetic inversion recovery imaging: reducing subjectivity in the estimation of inversion time.

To develop a quantitative T1-mapping-based synthetic inversion recovery (IRsynth) approach to calculate the optimal inversion time (TI0) for late gadolinium enhancement (LGE) imaging. Prospectively enrolled patients (n = 130, 58 ± 16 years) underwent cardiac MRI on a 1.5T system including Look-Locker TI-scout (LL), modified LL IR (MOLLI)-based T1-mapping, and LGE acquisitions. Patients were randomized into two groups: LL group (TI-scout followed T1-mapping) or MOLLI group (T1-mapping followed TI-scout). In both groups, the second acquisition was used to determine the TI0 for LGE. IRsynth images were generated from T1-maps between TI = 200-400 ms in 5 ms increments. Image quality was rated on a 3-point scale and the remote/background signal intensity ratio (SIR) was calculated. In the LL group (n = 53), the TI-scout-based TI0 was significantly shorter compared to IRsynth [230 ms (219-242) vs. 280 ms (263-297), P < 0.0001]. The TI0 used for LGE was set 30-40 ms longer [261 ms (247-276), P < 0.0001] than the TI-scout-based TI0, resulting in a TI0 ~ 20 ms shorter than what was obtained by IRsynth (P = 0.0156). In the MOLLI group (n = 63), IRsynth-based TI0 was significantly longer than the TI-scout-based TI0 [298 ms (262-334) vs. 242 ms (217-267), P = 0.0313]. The quality of myocardial nulling was rated higher [2.4 (2.2-2.5) vs. 2.0 (1.8-2.1), P = 0.0042] and the remote/background SIR was found to be more optimal (1.6 [1.1-2.1] vs. 2.6 [1.8-3.3], P = 0.0256) in the MOLLI group. T1-based IRsynth selects TI0 for LGE more accurately than conventional TI-scout imaging. IRsynth improves TI0 selection by providing excellent visualization of the representative image contrast for LGE images, reducing operator dependence in LGE acquisition.

Dark-Blood Delayed Enhancement Cardiac Magnetic Resonance of Myocardial Infarction.

OBJECTIVES: This study introduced and validated a novel flow-independent delayed enhancement technique that shows hyperenhanced myocardium while simultaneously suppressing blood-pool signal. BACKGROUND: The diagnosis and assessment of myocardial infarction (MI) is crucial in determining clinical management and prognosis. Although delayed enhancement cardiac magnetic resonance (DE-CMR) is an in vivo reference standard for imaging MI, an important limitation is poor delineation between hyperenhanced myocardium and bright LV cavity blood-pool, which may cause many infarcts to become invisible. METHODS: A canine model with pathology as the reference standard was used for validation (n = 22). Patients with MI and normal controls were studied to ascertain clinical performance (n = 31). RESULTS: In canines, the flow-independent dark-blood delayed enhancement (FIDDLE) technique was superior to conventional DE-CMR for the detection of MI, with higher sensitivity (96% vs. 85%, respectively; p = 0.002) and accuracy (95% vs. 87%, respectively; p = 0.01) and with similar specificity (92% vs, 92%, respectively; p = 1.0). In infarcts that were identified by both techniques, the entire length of the endocardial border between infarcted myocardium and adjacent blood-pool was visualized in 33% for DE-CMR compared with 100% for FIDDLE. There was better agreement for FIDDLE-measured infarct size than for DE-CMR infarct size (95% limits-of-agreement, 2.1% vs. 5.5%, respectively; p < 0.0001). In patients, findings were similar. FIDDLE demonstrated higher accuracy for diagnosis of MI than DE-CMR (100% [95% confidence interval [CI]: 89% to 100%] vs. 84% [95% CI: 66% to 95%], respectively; p = 0.03). CONCLUSIONS: The study introduced and validated a novel CMR technique that improves the discrimination of the border between infarcted myocardium and adjacent blood-pool. This dark-blood technique provides diagnostic performance that is superior to that of the current in vivo reference standard for the imaging diagnosis of MI.

T(Rho) and magnetization transfer and INvErsion recovery (TRAMINER)-prepared imaging: A novel contrast-enhanced flow-independent dark-blood technique for the evaluation of myocardial late gadolinium enhancement in patients with myocardial infarction.

PURPOSE: To evaluate a new dark-blood late gadolinium enhancement (LGE) technique called "T(Rho) And Magnetization transfer and INvErsion Recovery" (TRAMINER) for the ability to detect myocardial LGE versus standard "bright-blood" inversion recovery (SIR) imaging. MATERIALS AND METHODS: This Institutional Review Board (IRB)-approved, Health Insurance Portability and Accountability Act (HIPAA)-compliant prospective study included 40 patients (62 ± 14 years [mean ± standard deviation (SD)], 29 males) with suspected myocardial infarction (MI) referred for the assessment of myocardial viability. The patients underwent a 1.5T cardiac magnetic resonance imaging (MRI) including postcontrast SIR and TRAMINER acquisitions. Normalized images were evaluated by two readers. Subjective (3-point Likert scale) and objective image qualities were compared using Mann-Whitney U-test and paired t-test, respectively. Interobserver agreement, LGE detection rate, and level of certainty were compared using Cohen's kappa, Wilcoxon-test, and Mann-Whitney U-test, respectively. Results are reported as mean ± SD or mean [95% confidence interval]. RESULTS: Overall, image quality was rated similar between TRAMINER and SIR; however, TRAMINER performed better on a visual assessment of the ability to differentiate LGE from blood (Likert scale: 3.0 [3.0-3.0] vs. 2.0 [1.7-2.2], P < 0.0001). TRAMINER provided significantly higher signal intensity range (69.8 ± 10.2 vs. 9.6 ± 7.6, P < 0.0001) and a 4-fold higher signal intensity ratio (4.2 ± 1.9 vs. 1.1 ± 0.1, P < 0.0001) between LGE and blood signals. TRAMINER detected more patients (19/40 vs. 17/40) and segments (91/649 vs. 79/649) with LGE with higher level of certainty (2.9 [2.8-3.0] vs. 2.7 [2.5-2.8], P = 0.0185). Interobserver agreement was good to excellent for LGE detection. CONCLUSION: TRAMINER provides better contrast between LGE and blood and consequently may have increased ability to discriminate thin subendocardial and papillary muscle enhancement from the blood signal, which can have an indistinct appearance using SIR. LEVEL OF EVIDENCE: 2 J. MAGN. RESON. IMAGING 2017;45:1429-1437.

Suppression of ghost artifacts arising from long T1 species in segmented inversion-recovery imaging.

PURPOSE: We demonstrate an improved segmented inversion-recovery sequence that suppresses ghost artifacts arising from tissues with long T1 ( > 1.5 s). THEORY AND METHODS: Long T1 species such as pericardial fluid can create bright ghost artifacts in segmented, inversion-recovery MRI because of oscillations in longitudinal magnetization between segments. A single dummy acquisition at the beginning of the sequence can reduce oscillations; however, its effectiveness in suppressing long T1 artifacts is unknown. In this study, we systematically evaluated several test sequences, including a prototype (saturation post-pulse readout to eliminate spurious signal: SPPRESS) in simulations, phantoms, and patients. RESULTS: SPPRESS reduced artifact signal 90% ± 25% and 74% ± 28% compared with Control and Single-Dummy methods in phantoms. SPPRESS performed well at 1.5 Tesla (T) and 3T, with steady-state free precession (SSFP) and fast low-angle shot (FLASH) readout, with conventional and phase-sensitive reconstruction, and over a range of physiologic heart rates. A review of 100 consecutive clinical cardiac MRI scans revealed large fluid collections (eg, regions with long T1 ) in 14% of patients. In a prospectively enrolled cohort of 16 patients with visible long T1 fluids, SPPRESS appreciably reduced artifacts in all cases compared with Control and Single-Dummy methods. CONCLUSION: We developed and validated a new robust method, SPPRESS, for reducing artifacts due to long T1 species across a wide range of imaging and physiologic conditions. Magn Reson Med 78:1442-1451, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

A non-contrast self-navigated 3-dimensional MR technique for aortic root and vascular access route assessment in the context of transcatheter aortic valve replacement: proof of concept.

OBJECTIVES: Due to the high prevalence of renal failure in transcatheter aortic valve replacement (TAVR) candidates, a non-contrast MR technique is desirable for pre-procedural planning. We sought to evaluate the feasibility of a novel, non-contrast, free-breathing, self-navigated three-dimensional (SN3D) MR sequence for imaging the aorta from its root to the iliofemoral run-off in comparison to non-contrast two-dimensional-balanced steady-state free-precession (2D-bSSFP) imaging. METHODS: SN3D [field of view (FOV), 220-370 mm(3); slice thickness, 1.15 mm; repetition/echo time (TR/TE), 3.1/1.5 ms; and flip angle, 115°] and 2D-bSSFP acquisitions (FOV, 340 mm; slice thickness, 6 mm; TR/TE, 2.3/1.1 ms; flip angle, 77°) were performed in 10 healthy subjects (all male; mean age, 30.3 ± 4.3 yrs) using a 1.5-T MRI system. Aortic root measurements and qualitative image ratings (four-point Likert-scale) were compared. RESULTS: The mean effective aortic annulus diameter was similar for 2D-bSSFP and SN3D (26.7 ± 0.7 vs. 26.1 ± 0.9 mm, p = 0.23). The mean image quality of 2D-bSSFP (4; IQR 3-4) was rated slightly higher (p = 0.03) than SN3D (3; IQR 2-4). The mean total acquisition time for SN3D imaging was 12.8 ± 2.4 min. CONCLUSIONS: Our results suggest that a novel SN3D sequence allows rapid, free-breathing assessment of the aortic root and the aortoiliofemoral system without administration of contrast medium. KEY POINTS: • The prevalence of renal failure is high among TAVR candidates. • Non-contrast 3D MR angiography allows for TAVR procedure planning. • The self-navigated sequence provides a significantly reduced scanning time.

Relationship of T2-Weighted MRI Myocardial Hyperintensity and the Ischemic Area-At-Risk.

RATIONALE: After acute myocardial infarction (MI), delineating the area-at-risk (AAR) is crucial for measuring how much, if any, ischemic myocardium has been salvaged. T2-weighted MRI is promoted as an excellent method to delineate the AAR. However, the evidence supporting the validity of this method to measure the AAR is indirect, and it has never been validated with direct anatomic measurements. OBJECTIVE: To determine whether T2-weighted MRI delineates the AAR. METHODS AND RESULTS: Twenty-one canines and 24 patients with acute MI were studied. We compared bright-blood and black-blood T2-weighted MRI with images of the AAR and MI by histopathology in canines and with MI by in vivo delayed-enhancement MRI in canines and patients. Abnormal regions on MRI and pathology were compared by (a) quantitative measurement of the transmural-extent of the abnormality and (b) picture matching of contours. We found no relationship between the transmural-extent of T2-hyperintense regions and that of the AAR (bright-blood-T2: r=0.06, P=0.69; black-blood-T2: r=0.01, P=0.97). Instead, there was a strong correlation with that of infarction (bright-blood-T2: r=0.94, P<0.0001; black-blood-T2: r=0.95, P<0.0001). Additionally, contour analysis demonstrated a fingerprint match of T2-hyperintense regions with the intricate contour of infarcted regions by delayed-enhancement MRI. Similarly, in patients there was a close correspondence between contours of T2-hyperintense and infarcted regions, and the transmural-extent of these regions were highly correlated (bright-blood-T2: r=0.82, P<0.0001; black-blood-T2: r=0.83, P<0.0001). CONCLUSION: T2-weighted MRI does not depict the AAR. Accordingly, T2-weighted MRI should not be used to measure myocardial salvage, either to inform patient management decisions or to evaluate novel therapies for acute MI.

Motion and flow insensitive adiabatic T2 -preparation module for cardiac MR imaging at 3 Tesla.

A versatile method for generating T2 -weighting is a T2 -preparation module, which has been used successfully for cardiac imaging at 1.5T. Although it has been applied at 3T, higher fields (B0 ≥ 3T) can degrade B0 and B1 homogeneity and result in nonuniform magnetization preparation. For cardiac imaging, blood flow and cardiac motion may further impair magnetization preparation. In this study, a novel T2 -preparation module containing multiple adiabatic B1 -insensitive refocusing pulses is introduced and compared with three previously described modules [(a) composite MLEV4, (b) modified BIR-4 (mBIR-4), and (c) Silver-Hoult-pair]. In the static phantom, the proposed module provided similar or better B0 and B1 insensitivity than the other modules. In human subjects (n = 21), quantitative measurement of image signal coefficient of variation, reflecting overall image inhomogeneity, was lower for the proposed module (0.10) than for MLEV4 (0.15, P < 0.0001), mBIR-4 (0.27, P < 0.0001), and Silver-Hoult-pair (0.14, P = 0.001) modules. Similarly, qualitative analysis revealed that the proposed module had the best image quality scores and ranking (both, P < 0.0001). In conclusion, we present a new T2 -preparation module, which is shown to be robust for cardiac imaging at 3T in comparison with existing methods.

Respiratory motion and cardiac arrhythmia effects on diagnostic accuracy of myocardial delayed-enhanced MR imaging in canines.

PURPOSE: To prospectively compare in canines the diagnostic accuracy for myocardial infarction (MI) of standard delayed-enhancement (DE) magnetic resonance (MR) imaging versus that of subsecond DE MR imaging with and without breath holding and/or cardiac arrhythmia, with histologic findings or absence of surgical creation of MI as the reference standard. MATERIALS AND METHODS: This study was approved by the Institutional Animal Care and Use Committee; 21 canines were imaged with one standard and two subsecond DE MR techniques in four conditions: condition 1, breath holding and steady gating; 2, non-breath holding and steady gating; 3, breath holding and irregular heart rhythm; and 4, non-breath holding and irregular heart rhythm. Images were randomized and scored for diagnostic accuracy, image quality, and observer confidence. Sensitivity, specificity, and diagnostic accuracy for MI detection were calculated for each technique and clinical condition separately. The chi(2), paired t, and McNemar tests were used for comparisons. RESULTS: Fifteen dogs had MIs. Among conditions 2-4, differences were not significant (P > .05); data were pooled and referred to as group B. Condition 1 was group A. Accuracy, image quality, and observer confidence, respectively, for standard DE MR imaging were 96%, 3.7 +/- 0.8, and 2.7 +/- 0.6 in group A but only 74%, 2.4 +/- 0.8, and 1.8 +/- 0.7 in group B (P < or = .004 for each). Corresponding scores for subsecond techniques were unaffected by respiratory motion and/or arrhythmia. Subsecond techniques had higher accuracy (82% and 86% vs 74%), better image quality (3.9 +/- 0.7 and 3.2 +/- 0.8 vs 2.4 +/- 0.8), and greater confidence (2.4 +/- 0.7 and 2.1 +/- 0.7 vs 1.8 +/- 0.7) (P < or = .0002 for each) than standard DE MR imaging. In group A, standard performed better than subsecond DE MR imaging. CONCLUSION: Standard DE MR imaging is appropriate for MI detection with breath holding and regular heart rhythm, while subsecond techniques are appropriate with an irregular heart rhythm and when breath holding is not possible.

Combining spin echoes with gradient echoes in the context of the global coherent free precession pulse sequence.

To extend the signal longevity of magnetically excited spins in flowing fluids while in a state of global coherent free precession (GCFP), a refocusing radiofrequency (RF) pulse and bipolar gradient waveforms were combined with the GCFP sequence. The data demonstrate that RF refocusing in the presence of flowing blood is possible, but the improvement in signal amplitude depends on the static magnetic field homogeneity along the direction of motion and the displacement of the spins between the excitation and the RF refocusing pulse, as well as displacement during subsequent RF refocusing pulses. The least amount of phase dispersion and thus the longest lasting signal is obtained with the shortest echo spacing where only one line of data is recorded between two RF refocusing pulses. This approach was successfully used in a phantom and in vivo to image fast and slow blood flow. Depending on the experimental conditions, signal persistence is improved significantly compared to playing the same sequence without RF refocusing, but the improvement is limited by the product of blood flow velocity and the time between RF refocusing pulses.

Cardiovascular MRI: its current and future use in clinical practice.

Cardiovascular magnetic resonance (CMR) imaging is a comprehensive clinical tool for assessing a large variety of cardiovascular diseases. Using the clinical service of the Duke Cardiovascular Magnetic Resonance Center as an example, we describe how to perform image contractile function, myocardial perfusion at stress and rest, myocardial viability, cardiovascular morphology, vascular anatomy and blood flow tests. The emergence of successful dedicated CMR services presents an opportunity to optimize patient throughput by streamlining the user interface of CMR scanners, standardizing the viewing format and reporting software, and customizing training programs to focus on the standardized CMR approaches. Accordingly, we discuss potential pathways to create these standards. Finally, we discuss several promising new CMR techniques we expect will complement existing clinical procedures.

Rapid detection of myocardial infarction by subsecond, free-breathing delayed contrast-enhancement cardiovascular magnetic resonance.

BACKGROUND: An ultrafast, delayed contrast-enhancement cardiovascular magnetic resonance technique that can acquire subsecond, "snapshot" images during free breathing (subsecond) is becoming widely available. This technique provides myocardial infarction (MI) imaging with complete left ventricular coverage in < 30 seconds. However, the accuracy of this technique is unknown. METHODS AND RESULTS: We prospectively compared subsecond imaging with routine breath-hold delayed contrast-enhancement cardiovascular magnetic resonance (standard) in consecutive patients. Two cohorts with unambiguous standards of truth were prespecified: (1) patients with documented prior MI (n=135) and (2) patients without MI and with low likelihood of coronary disease (lowest Framingham risk category; n=103). Scans were scored masked to identity and clinical information. Sensitivity, specificity, and accuracy of subsecond imaging for MI diagnosis were 87%, 96%, and 91%, respectively. Compared with the standard technique (98%, 100%, 99%), the subsecond technique had modestly reduced sensitivity (P=0.0001), but specificity was excellent. Missed infarcts were generally small or subendocardial (87%). Overall, regional transmural extent of infarction scores were highly concordant (2083/2294; 91%); however, 51 of 337 regions (15%) considered predominantly infarcted (> 50% transmural extent of infarction) by the standard technique were considered viable (< or = 25% transmural extent of infarction) by the subsecond technique. Quantitative analysis demonstrated moderately reduced contrast-to-noise ratios for subsecond imaging between infarct and remote myocardium (12.0+/-7.2 versus 20.1+/-6.6; P<0.0001) and infarct and left ventricular cavity (-2.5+/-2.7 versus 3.6+/-3.7; P<0.0001). CONCLUSIONS: MI can be rapidly detected by subsecond delayed contrast-enhancement cardiovascular magnetic resonance during free breathing with high accuracy. This technique could be considered the preferred approach in patients who are more acutely ill or unable to hold their breath. However, compared with standard imaging, sensitivity is mildly reduced, and the transmural extent of infarction may be underestimated.

Technology insight: assessment of myocardial viability by delayed-enhancement magnetic resonance imaging.

Myocardial viability is of established importance to the management of cardiac patients being considered for revascularization. Existing noninvasive imaging tests to examine myocardial viability, such as stress echocardiography and nuclear scintigraphy, are of recognized utility but are subject to intrinsic limitations. Over the past few years delayed-enhancement MRI (DE-MRI) has emerged as an alternative to traditional tests and for the first time allows direct visualization of the transmural extent of myocardial viability. In this paper we review the scientific data that underlie the use of DE-MRI in patients with ischemic heart disease. Progress in this area is largely the result of the development of a new MRI pulse sequence in the late 1990s, which improved the detection of necrotic and scarred myocardial tissue. Following this technical development, a series of detailed histologic comparisons in large animal models revealed that both acute and healed myocardial infarcts appeared as brighter (hyperenhanced) areas than viable regions, and that the effect is independent of contractile function. The resulting 'bright is dead' hypothesis has thus far proven of significant use in patients with ischemic heart disease. Data are now emerging which suggest that the DE-MRI technique also has important implications for patients with nonischemic forms of cardiomyopathy.

Noninvasive assessment of blood flow based on magnetic resonance global coherent free precession.

BACKGROUND: Magnetic resonance global coherent free precession (GCFP) is a new technique that produces cine projection angiograms directly analogous to those of x-ray angiography noninvasively and without a contrast agent. In this study, we compared GCFP blood flow with "gold standards" to determine the accuracy of noninvasive GCFP blood flow measurements. METHODS AND RESULTS: The relationship between GCFP blood flow and true blood flow defined by invasive ultrasonic flow probe and by phase contrast velocity encoded MRI (VENC) was studied in anesthetized dogs (n=6). Blood flow was controlled by use of a hydraulic occluder around the left iliac artery. GCFP images were acquired by selectively exciting the abdominal aorta and visualizing temporal blood flow into the iliac arteries. GCFP flow was similar to ultrasonic blood flow at baseline (131.3+/-44.8 versus 114.8+/-34.2 mL/min), during occlusion (10.8+/-5.1 versus 6.5+/-7.2 mL/min), during reactive hyperemia (191.4+/-100.7 versus 260.3+/-138.7 mL/min), during the new resting state (135.5+/-52.4 versus 117.8+/-24.1 mL/min), and during partial occlusion (61.4+/-36.4 versus 49.3+/-13.1 mL/min, P=NS for all). Results comparing GCFP flow with VENC were similar. Statistical analysis revealed that GCFP flow was related to mean blood flow assessed by the flow probe (P<0.0001) and by VENC (P<0.0001). In the control right iliac artery, conversely, GCFP measurements were unaffected throughout all left iliac interventions (P=NS). CONCLUSIONS: GCFP blood flow is linearly related to true blood flow for a straight, cylindrical blood vessel without branches. Although more complex geometries imply a qualitative rather than a quantitative relationship, the data nevertheless suggest that GCFP may serve as the basis for a new form of noninvasive stress testing.

Infarct resorption, compensatory hypertrophy, and differing patterns of ventricular remodeling following myocardial infarctions of varying size.

OBJECTIVES: We sought to identify advantages of contrast-enhanced magnetic resonance imaging (MRI) in studying postinfarction ventricular remodeling. BACKGROUND: Although sequential measurements of ventricular volumes, internal dimensions, and total ventricular mass have provided important insights into postinfarction left ventricular remodeling, it has not been possible to define serial, directionally opposite changes in resorption of infarcted tissue and hypertrophy of viable myocardium and effects of these changes on commonly used indices of remodeling. METHODS: Using gadolinium-enhanced MRI, the time course and geometry of changes in infarcted and noninfarcted regions were assessed serially in dogs subjected to coronary occlusion for 45 min, 90 min, or permanently. RESULTS: Infarct mass decreased progressively between three days and four to eight weeks following coronary occlusion; terminal values averaged 24 +/- 3% of those at three days. Radial infarct thickness also decreased progressively, whereas changes in circumferential and longitudinal extent of infarction were variable. The ability to define the circumferential endocardial and epicardial extents of infarction allowed radial thinning without epicardial expansion to be distinguished from true infarct expansion. The mass of noninfarcted myocardium increased by 15 +/- 2% following 90-min or permanent occlusion. However, the time course of growth of noninfarcted myocardium differed systematically from that of infarct resorption. Measurements of total ventricular mass frequently failed to reflect concurrent changes in infarcted and noninfarcted regions. Reperfusion accelerated infarct resorption. Histologic reductions in nucleus-to-cytoplasm ratios corresponded with increases in noninfarcted ventricular mass. CONCLUSIONS: Concurrent directionally opposite changes in infarcted and noninfarcted myocardium can be defined serially, noninvasively, and with high spatial resolution and full ventricular coverage following myocardial infarction.

Noninvasive cineangiography by magnetic resonance global coherent free precession.

Cardiovascular disease is primarily diagnosed using invasive X-ray cineangiography. Here we introduce a new concept in magnetic resonance imaging (MRI) that, for the first time, produces similar images noninvasively and without a contrast agent. Protons in moving blood are 'tagged' every few milliseconds as they travel through an arbitrary region in space. Simultaneous with ongoing tagging of new blood, previously tagged blood is maintained in a state of global coherent free precession (GCFP), which allows acquisition of consecutive movie frames as the heart pushes blood through the vascular bed. Body tissue surrounding the moving blood is never excited and therefore remains invisible. In 18 subjects, pulsating blood could be seen flowing through three-dimensional (3D) space for distances of up to 16 cm outside the stationary excitation region. These data underscore that our approach noninvasively characterizes both anatomy and blood flow in a manner directly analogous to invasive procedures.

Rapid cine MRI of the human heart using reconstruction by estimation of lines and inhibition of fold-in.

A fast imaging method is described that yields an approximately six-fold acquisition time reduction relative to conventional techniques. The method involves: 1) acquisition of every sixth k-space line; 2) shifting of acquired k-space lines between odd and even frames; and 3) a single-frame correction image. Reconstruction is achieved by temporal interpolation for k-space lines not acquired combined with subtraction of stationary fold-in artifacts. Seven patients with heart disease and one volunteer were evaluated. SNR was measured in myocardium and the ventricular cavity for both the conventional and new technique. The method is best suited for fast imaging of moving objects confined to a small region within a larger stationary object, such as the heart within the thoracic cavity. It can be implemented in cine and functional imaging sequences and, in principle, in perfusion sequences.

Myocardial magnetic resonance imaging contrast agent concentrations after reversible and irreversible ischemic injury.

BACKGROUND: Discrepant reports have been published recently regarding the relationship of contrast-enhanced magnetic resonance image intensities to reversible and irreversible ischemic injury. Unlike image intensities, contrast agent concentrations provide data independent of the MRI technique. We used electron probe x-ray microanalysis (EPXMA) to simultaneously examine concentrations of Gd, Na, P, S, Cl, K, and Ca over a range of myocardial injuries. Methods and Results- Reversible and irreversible injury were studied in 38 rabbits divided into 4 groups defined by occlusion and reperfusion time, as well as time the animals were euthanized. Gd-DTPA was administered, and the hearts were excised and rapidly frozen, cryosectioned, freeze-dried, and examined by EPXMA in up to 3 regions: remote, infarcted, and at risk but not infarcted. Infarcted regions were defined by anti-myoglobin antibody or triphenyltetrazolium chloride staining. Regions at risk were defined by fluorescent microparticles administered during occlusion. Compared with remote regions, in acutely infarcted regions, Gd was increased (235+/-24%, P<0.005) in the same 50 x 100-microm areas in which Na was increased (154+/-5%, P<0.001) and K was decreased (52+/-8%, P<0.001). Similarly, in chronically infarcted regions, Gd was increased (472+/-78%, P<0.001) in areas in which Na was increased (332+/-28%, P<0.001) and K was decreased (47+/-5%, P<0.001). Also compared with remote regions, however, concentrations of Gd, Na, and K were not elevated after reperfusion in regions that were at risk but not infarcted (P=NS). CONCLUSIONS: Regional elevations in myocardial MRI contrast agent concentrations are exclusively associated with irreversible ischemic injury defined histologically and by regional electrolyte concentrations.