Brian E. Schirf

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.

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.

Comparison of gradient-echo and steady-state free precession for coronary artery magnetic resonance angiography using a gadolinium-based intravascular contrast agent.

Objectives:Intravascular contrast agents may offer longer imaging times and better vessel visualization over conventional extravascular agents for magnetic resonance coronary angiography. The purpose of this study was to evaluate the effect of intravascular contrast (B-22956/1) on coronary visualization. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were compared in inversion-recovery (IR)-prepared FLASH (fast low-angle shot) and IR-trueFISP (true fast imaging with steady-state precession) sequences before and after contrast. Materials and Methods:Numeric simulations were performed to compare blood signals in IR-trueFISP and IR-FLASH sequences. Coronary imaging was performed in 15 swine. Results:Postcontrast CNR was improved 23% with breathhold IR-FLASH and 55% with breathhold IR-trueFISP as compared with precontrast trueFISP. With free-breathing, long TR IR-FLASH provided 131% and 55.8% higher SNR and 132% and 58.7% increased CNR compared with IR-FLASH with shorter TR and IR-trueFISP, respectively. Conclusion:Intravascular contrast agents improve CNR and vessel visualization in coronary magnetic resonance angiography with IR-FLASH and IR-trueFISP.

Complications of Uterine Fibroid Embolization

Uterine fibroid embolization (UFE) is an increasingly popular, minimally invasive treatment option for women with symptomatic fibroid disease. UFE therapy in qualified hands is an effective, well-tolerated procedure that offers relief of fibroid symptoms with a low risk of complications. In the acute postprocedural period, immediate complications may relate to vascular access, thromboembolic events, infection, and pain management. Reported major complications include but are not limited to pulmonary embolus, uterine ischemia, necrosis, sepsis, and death. Non-life-threatening complications include altered ovarian and sexual function, subcutaneous tissue necrosis, expulsion of fibroid tissue, and treatment failure. Awareness of the known complications of UFE may allow more rapid diagnosis and effective therapeutic responses to complications when they occur.

Comparison of X‐ray fluoroscopy and interventional magnetic resonance imaging for the assessment of coronary artery stenoses in swine

The accuracy of a two‐step interventional MRI protocol to quantify coronary artery disease was compared to the clinical gold standard, X‐ray angiography. Studies were conducted in nine swine with a surgically induced stenosis in the proximal left circumflex coronary artery. The two‐step protocol consisted of catheter‐directed magnetic resonance angiography (MRA), which was first used to localize the stenosis, followed by MRI cross‐sectional images to quantify the degree of stenosis without the use of contrast agent. Line signal intensity profiles were drawn across the vessel diameter at the stenosis site and proximal to the stenosis for each data set to measure percentage stenosis for each animal. Catheter‐directed MRA successfully detected eight of nine stenoses. Cross‐sectional MRI accurately quantified each stenosis, with strong agreement to the measurements made using X‐ray fluoroscopy (intraclass correlation coefficient = 0.955; P < 0.05). This study demonstrates that in the future interventional MRI may be an alternative to X‐ray angiography for the detection and quantification of coronary artery disease. Magn Reson Med, 2005.

Projection imaging of the right coronary artery with an intravenous injection of contrast agent

Contrast‐enhanced (CE) MR angiography of the right coronary artery (RCA) was performed using 2D thick‐slice projection imaging with a small (8 mL) intravenous injection of contrast agent in six volunteers. With a tight contrast bolus injection, the RCA was enhanced for a few seconds after the contrast bolus was washed out of the right ventricle. This allowed data to be acquired when only the RCA was enhanced. Using 2D thick‐slice magnetization prepared steady‐state free precession (SSFP) imaging, background signal was suppressed and a complete data set was acquired in three heartbeats. A mean vessel length of 7.1 ± 0.9 cm was depicted with a signal‐to‐noise ratio of 11.8 ± 0.7 and contrast‐to‐noise ratio of 6.1 ± 0.6. Thick‐slice 2D projection CE SSFP is a promising method to depict the RCA. Magn Reson Med 52:699–703, 2004.

Comparison of Intraarterial MR Angiography at 3.0 T with X-ray Digital Subtraction Angiography for Detection of Renal Artery Stenosis in Swine

PURPOSE To compare the accuracy of catheter-directed intraarterial (IA) magnetic resonance (MR) angiography at 3.0 T with that of x-ray digital subtraction angiography (DSA) for the measurement of renal artery stenosis (RAS) in swine. MATERIALS AND METHODS Unilateral hemodynamically significant RAS (>50%) was induced surgically in six pigs with use of reverse cable ties. One to two weeks after surgery, each pig underwent x-ray DSA and MR angiography before and after percutaneous transluminal balloon angioplasty (PTA). X-ray DSA was performed before and after PTA of RAS by injection of iodinated contrast agent through a 5-F multiple-side hole angiographic catheter placed in the abdominal aorta under fluoroscopic guidance. MR angiography of RAS was performed before and after PTA of RAS on a 3.0-T clinical MR imager with use of gadolinium-based contrast agent. MR angiography and DSA images were analyzed with the full width at half maximum method. Percent stenosis measurements between x-ray DSA and MR angiography were compared with a paired t test and were correlated with linear regression and Bland Altman analysis (alpha = 0.05). RESULTS Six cases of RAS were induced and imaged successfully with DSA and MR angiography techniques before and after PTA. On x-ray DSA, median stenoses was 64% (95% CI 57%-80%) before PTA and 20% (95% CI 5%-32%) after PTA. Corresponding MR angiography median stenosis measurement was 69% (95% CI 58%-80%) before PTA and 26% (95% CI 16%-36%) after PTA. A paired t test comparison did not show a difference between DSA and MR angiography (P = .16). RAS measurements on MR angiography correlated closely (P < .01) with DSA measurements (r(2) = 0.92). CONCLUSION In swine, the accuracy of catheter-directed IA MR angiography with use of a clinical 3.0-T MR imaging unit for the measurement of RAS was similar to that of conventional x-ray DSA.

Catheter-directed MR Angiography and Cross-sectional Imaging for the Assessment of Renal Artery Stenosis

PURPOSE Catheter-directed intraarterial (IA) gadolinium (Gd)-enhanced gradient-echo (GRE) imaging has been used in the setting of magnetic resonance (MR) imaging-guided endovascular procedures for two-dimensional (2D) or three-dimensional (3D) depiction of blood vessels. In a swine model, the hypothesis was tested that the combination of 2D IA GRE and 2D cross-sectional steady-state free precession (SSFP) imaging improves assessment of renal artery stenosis (RAS) compared with 3D IA GRE imaging alone. MATERIALS AND METHODS Bilateral RAS was surgically induced in seven pigs. Detection of stenoses was then compared between the combination of 2D projection IA GRE and cross-sectional 2D SSFP imaging without contrast agent and 3D IA GRE alone. Radiographic digital subtraction angiography (DSA) was employed as the reference standard. Linear regression was used to compare stenosis measurements, with an alpha of 0.05. RESULTS Radiographic DSA and MR imaging were successful in the seven animals (14 stenoses). With use of linear regression analysis, the combination of 2D IA GRE and 2D SSFP imaging had a higher r(2) (0.87 vs 0.72) and a slope closer to unity (1.02 vs 0.77) compared with 3D IA GRE imaging alone. When comparing intercepts, the regression line for SSFP significantly differed from that of 3D IA GRE imaging (P < .05). CONCLUSION The combination of 2D IA GRE and cross-sectional 2D SSFP imaging improves the accuracy of RAS detection compared with IA 3D IA-GRE alone.

Three-dimensional contrast-enhanced steady-state free precession for improved catheter-directed coronary magnetic resonance angiography

To demonstrate the feasibility of three‐dimensional thick‐partition, contrast‐enhanced, catheter‐directed coronary artery magnetic resonance angiography (MRA) and test the hypothesis that three‐dimensional imaging improves coronary artery background contrast‐to‐noise ratio (CNR) compared to two‐dimensional imaging.

Myocardial perfusion evaluation with T2-prepared gradient echo blood oxygen level dependent imaging at 3 Tesla

Detecting myocardial perfusion reserve differences using blood oxygen level dependent (BOLD) MRI may improve at 3 T vs 1.5 T. Stenosis-model dogs (n=3) were imaged at 3 T using a gradient echo sequence (GRE) with T2-preparation for BOLD weighting and without as a control. 3 short-axis slices were acquired at rest and during stenosis and adenosine-induced stress with fluorescent microspheres injected to provide blood flow information. Quantitative measurements showed significant changes for BOLD images (left anterior descending (LAD) or septal vs left circumflex (LCX) regions=1.20/spl plusmn/0.11; LAD vs septal regions=1.03/spl plusmn/0.06; p<0.001), but not for control images (LAD or septal vs LCX regions=1.01/spl plusmn/0.04; LAD vs septal regions=0.99/spl plusmn/0.05; p=0.09). BOLD MR vs microsphere measured flow (MR=0.053*SPHERE+1.03) showed good correlation (R=0.61). In conclusion, 3 T BOLD imaging was able to identify myocardial perfusion changes.