Jordin D. Green

Saturation recovery single-shot acquisition (SASHA) for myocardial T1 mapping

To validate a new saturation recovery single‐shot acquisition (SASHA) pulse sequence for T1 mapping and to compare SASHA T1 values in heart failure patients and healthy controls.

Comparison of long and short axis quantification of left ventricular volume parameters by cardiovascular magnetic resonance, with ex-vivo validation

BackgroundThe purpose of the study was to compare the accuracy and evaluation time of quantifying left ventricular (LV), left atrial (LA) volume and LV mass using short axis (SAX) and long axis (LAX) methods when using cardiovascular magnetic resonance (CMR).Materials and methodsWe studied 12 explanted canine hearts and 46 patients referred for CMR (29 male, age 47 ± 18 years) in a clinical 1.5 T CMR system, using standard cine sequences. In standard short axis stacks of various slice thickness values in dogs and 8 mm slice thickness (gap 2 mm) in patients, we measured LV volumes using reference slices in a perpendicular, long axis orientation using certified software. Volumes and mass were also measured in six radial long axis (LAX) views.LV parameters were also assessed for intra- and inter-observer variability. In 24 patients, we also analyzed reproducibility and evaluation time of two very experienced (> 10 years of CMR reading) readers for SAX and LAX.ResultsIn the explanted dog hearts, there was excellent agreement between ex vivo data and LV mass and volume data as measured by all methods for both, LAX (r2 = 0.98) and SAX (r2 = 0.88 to 0.98). LA volumes, however, were underestimated by 13% using the LAX views. In patients, there was a good correlation between all three assessed methods (r2 ≥ 0.95 for all). In experienced clinical readers, left-ventricular volumes and ejection fraction as measured in LAX views showed a better inter-observer reproducibility and a 27% shorter evaluation time.ConclusionWhen compared to an ex vivo standard, both, short axis and long axis techniques are highly accurate for the quantification of left ventricular volumes and mass. In clinical settings, however, the long axis approach may be more reproducible and more time-efficient. Therefore, the rotational long axis approach is a viable alternative for the clinical assessment of cardiac volumes, function and mass.

Real-Time Magnetic Resonance Imaging-Guided Coronary Catheterization in Swine

Background—We tested the hypothesis that real-time magnetic resonance imaging (MRI) can guide coronary artery catheterization in swine via a percutaneous femoral artery approach. Methods and Results—In 12 pigs, we accessed femoral arteries percutaneously. We used 6- or 7-French coronary Judkins catheters filled with dilute 4% gadolinium (Gd) contrast agent and coaxially inserted 0.030-inch diameter active guidewires as endovascular devices. For catheter tracking, we used a 2-dimensional (2D) inversion recovery–prepared spoiled gradient echo sequence at a temporal resolution of 7 frames/s. For guidewire tracking, we used 2D steady-state free precession imaging at a temporal resolution of 9 frames/s. Coronary artery catheterization under MRI guidance was successful in 12/12 pigs. Successful coronary catheterization was verified by obtaining MR angiographic images after direct catheter-based injections of dilute Gd. Conclusions—Real-time MRI-guided catheterization of coronary arteries in swine is feasible via a percutaneous femoral artery approach. Selective coronary MR angiography can then be performed with dilute contrast agent injections.

Oxygenation-sensitive CMR for assessing vasodilator-induced changes of myocardial oxygenation.

BackgroundAs myocardial oxygenation may serve as a marker for ischemia and microvascular dysfunction, it could be clinically useful to have a non-invasive measure of changes in myocardial oxygenation. However, the impact of induced blood flow changes on oxygenation is not well understood. We used oxygenation-sensitive CMR to assess the relations between myocardial oxygenation and coronary sinus blood oxygen saturation (SvO2) and coronary blood flow in a dog model in which hyperemia was induced by intracoronary administration of vasodilators.ResultsDuring administration of acetylcholine and adenosine, CMR signal intensity correlated linearly with simultaneously measured SvO2 (r2 = 0.74, P < 0.001). Both SvO2 and CMR signal intensity were exponentially related to coronary blood flow, with SvO2 approaching 87%.ConclusionsMyocardial oxygenation as assessed with oxygenation-sensitive CMR imaging is linearly related to SvO2 and is exponentially related to vasodilator-induced increases of blood flow. Oxygenation-sensitive CMR may be useful to assess ischemia and microvascular function in patients. Its clinical utility should be evaluated.

Cerebral and myocardial blood flow responses to hypercapnia and hypoxia in humans

In humans, cerebrovascular responses to alterations in arterial Pco(2) and Po(2) are well documented. However, few studies have investigated human coronary vascular responses to alterations in blood gases. This study investigated the extent to which the cerebral and coronary vasculatures differ in their responses to euoxic hypercapnia and isocapnic hypoxia in healthy volunteers. Participants (n = 15) were tested at rest on two occasions. On the first visit, middle cerebral artery blood velocity (V(P)) was assessed using transcranial Doppler ultrasound. On the second visit, coronary sinus blood flow (CSBF) was measured using cardiac MRI. For comparison with V(P), CSBF was normalized to the rate pressure product [an index of myocardial oxygen consumption; normalized (n)CSBF]. Both testing sessions began with 5 min of euoxic [end-tidal Po(2) (Pet(O(2))) = 88 Torr] isocapnia [end-tidal Pco(2) (Pet(CO(2))) = +1 Torr above resting values]. Pet(O(2)) was next held at 88 Torr, and Pet(CO(2)) was increased to 40 and 45 Torr in 5-min increments. Participants were then returned to euoxic isocapnia for 5 min, after which Pet(O(2)) was decreased from 88 to 60, 52 and 45 Torr in 5-min decrements. Changes in V(P) and nCSBF were normalized to isocapnic euoxic conditions and indexed against Pet(CO(2)) and arterial oxyhemoglobin saturation. The V(P) gain for euoxic hypercapnia (%/Torr) was significantly higher than nCSBF (P = 0.030). Conversely, the V(P) gain for isocapnic hypoxia (%/%desaturation) was not different from nCSBF (P = 0.518). These findings demonstrate, compared with coronary circulation, that the cerebral circulation is more sensitive to hypercapnia but similarly sensitive to hypoxia.

Use of Internal Coils for Independent and Direct MR Imaging–guided Endovascular Device Tracking

PURPOSE To test the hypotheses that a single internal guide wire coil (i) permits independent and direct depiction of guide wires and catheters and (ii) improves catheter-tracking accuracy and depiction compared to external receiver coils. MATERIALS AND METHODS Standard 5-6-F angiographic catheters were filled with dilute 4% gadolinium chelate. A single 0.030-inch-diameter internal guide wire coil was placed inside the catheter. True fast imaging with steady-state precession was used to directly visualize the guide wire. Inversion recovery-prepared fast low-angle shot technique was used to track catheters over a thick slice. In phantom experiments, we compared catheter signal-to-noise ratios (SNRs) with the internal coil and a phased-array surface coil with use of the Wilcoxon signed-rank test. Tip-tracking accuracy was assessed with use of linear regression. In pigs (n = 7), catheters and guide wires were independently tracked in real time. RESULTS In phantoms, catheter SNR with the internal coil (12.0) was significantly greater than that with the surface coil (4.0; P =.001). Tip-tracking accuracy was also improved with use of the internal coil (R(2) = 0.94 vs 0.50). In swine vasculature, catheters and guide wires could be directly and independently tracked at 1.7-2.0 frames per second. Catheters were clearly visualized with use of the internal coil, with a typical catheter background contrast-to-noise ratio of 6.6. Catheters were not visible with use of the external coil because of the small catheter size compared to the slice thickness. CONCLUSION Internal guide wire coils permit independent and direct depiction of guide wires and catheters in vivo for MR imaging-guided endovascular interventions. They also improve catheter tracking accuracy and depiction compared to external coils.

Three-dimensional breathhold magnetization-prepared TrueFISP: A pilot study for magnetic resonance imaging of the coronary artery disease

Purpose:X-ray angiography is currently the standard test for the assessment of coronary artery disease. A substantial minority of patients referred for coronary angiography have no significant coronary artery disease. The purpose of this work was the evaluation of the accuracy of a three-dimensional (3D) breathhold coronary magnetic resonance angiography (MRA) technique in detecting hemodynamically significant coronary artery stenoses in a patient population with x-ray angiographic correlation. Materials and Methods:Sequential subjects (n = 33, M/F = 22/11, average age = 57) who were referred for conventional coronary angiography were enrolled in the study. The study protocol was approved by our institutional review board. Each subject gave written informed consent. Volume-targeted 3D breathhold coronary artery scans with ECG-triggered, segmented True Fast Imaging with Steady-state Precession (TrueFISP) were acquired for the left main (LM), left anterior descending (LAD), and right coronary arteries (RCAs). Coronary MRA was evaluated with conventional angiography as the gold standard. Results:The overall sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) for diagnosing any hemodynamically significant coronary artery disease (≥50% diameter reduction) with coronary MRA was 87%, 57%, 72%, 68%, and 80%, respectively. The sensitivity of the technique in the LM, LAD, and RCA was 100%, 83%, and 100%, respectively. The NPV of the technique in the LM, LAD, and RCA was 100%, 82%, and 100%, respectively. Conclusions:Three-dimensional breathhold True Fast Imaging with Steady-state Precession is a promising technique for coronary artery imaging. It has a relatively high sensitivity and NPV. Results of this study warrant further technical improvements and clinical evaluation of the technique.

Catheter-directed contrast-enhanced coronary MR angiography in swine using magnetization-prepared True-FISP

Contrast‐enhanced (CE) coronary magnetic resonance angiography (MRA) following intraarterial (IA) injection of contrast agent was compared using two sequences in swine: magnetization‐prepared fast imaging with steady‐state precession (True‐FISP), and magnetization‐prepared fast low‐angle shot (FLASH). Thick‐slice projection images were acquired with submillimeter in‐plane spatial resolution (0.9 × 0.8 mm2). The magnetization‐preparation scheme provided a clear delineation of the major coronary arteries with excellent background suppression. The True‐FISP acquisition resulted in an increase in signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) by approximately a factor of 2 over FLASH (P < 0.05). Magnetization‐prepared True‐FISP is a promising technique for catheter‐directed CE thick‐slice projection coronary MRA. Magn Reson Med 50:1317–1321, 2003.

Passive Catheter Tracking Using MRI: Comparison of Conventional and Magnetization-Prepared FLASH

To compare a magnetization‐prepared gradient‐echo (GRE) sequence with a conventional GRE sequence for visualizing contrast agent‐filled catheters.

T2-dependent errors in MOLLI T1 values: simulations, phantoms, and in-vivo studies

Background Diffuse myocardial fibrosis occurs in various cardiomyopathies and can be indirectly assessed with blood and myocardial T1 mapping at baseline and after gadolinium administration. The widely used MOdified Look-Locker Inversion-recovery (MOLLI) [1] sequence is known to underestimate myocardial T1 at higher heart rates, but its dependence on T2 has not been explored. We investigate MOLLI’s T1 accuracy in phantoms and confirm with simulations and in-vivo studies. T1 values are further compared with a saturation-recovery T1 mapping sequence [2].