MRA: Low Dose to No Dose
Wednesday 22 April 2009
Room 313A 10:30-12:30


Ruth P. Lim and Mitsue Miyazaki

10:30 419. Critical Concentration of Contrast Agents for Quantification of Enhancement: Another Reason for Dose Reduction
    Abbas Nasiraei Moghaddam1, Reza Habibi1, Tariq Balawi1, J. Paul Finn1
Radiology, UCLA, Los Angeles, CA, USA
    Dose-minimization in CEMRA not only increases the safety measure in clinical practice but also keeps the relation between the image enhancement and contrast agent concentration in the linear range. This linearity is required for applications such as quantitative perfusion imaging and prediction of contrast agents’ dynamics in MR angiography, using the theory of linear time-invariant systems. In this study we introduce the “critical” concentration up to which the signal intensity is a linear function of [Gd]. We also show in the routine range of flip angles the obtained enhancement is robust against RF filed inhomogeneity. Experimental verification is also presented.
10:42 420. Feasibility of Combined Low-Dose (0.07mmol/kg) Continuous Table Movement MRA of the Peripheral Vessels with Ultra-Low Dose (0.03mmol/kg) TWIST-MRA of the Calf Station
    Henrik Jakob Michaely1, Matthias Voth1, Stefan Haneder1, Stefan Oswald Schoenberg1
Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Mannheim, Germany
    At 3.0T peripheral continuous table movement MRA with 0.07mmol/kg gadobutrol and TWIST MRA with 0.03mmol/kg can be acquired in a single session with good image quality.
10:54 421. SNR Optimized Contrast-Enhanced MRA of the Peripheral Vasculature Using Patient Specific Timing Parameters:  Comparison  Between High and Conventional Relaxivity Contrast Agents in Patient Suspected of Arterial Occlusive Disease
    George Rachid de Oliveira1, Earl Michael Chester2, Gregory Wilson1,3, Jeffrey H. Maki1,4
Radiology, University of Washington, Seattle, WA, USA; 2Medicine, University of Washington, Seattle, WA, USA; 3Radiology, Philips Healthcare, Cleveland, OH; 4Radiology, Puget Sound VA Health Care System, Seattle, WA, USA

The objective was to compare qualitative and quantitative peripheral MRA (pMRA) image quality with different dose high vs. conventional relaxivity contrast agents (HRCA vs. CRCA). SNR and timing optimized 3 station pMRA was performed using similar doses (~0.2 mmol/kg) of HRCA vs. CRCA, as well as a smaller dose (~0.1 mmol/kg) of HRCA. No statistically significant qualitative or quantitative differences were observed between same dose HRCA and CRCA. Furthermore, no differences were observed between 0.2 and 0.1 mmol/kg dosing for HRCA, suggesting low dose HRCA is equivalent to high dose CRCA, and increasing HRCA dose has little benefit for pMRA.



11:06 422. Effect of Flip Angle Evolution on Flow Sensitivities in ECG-Gated Fast Spin Echo MRA Methods at 3T
    Iliyana P. Atanasova1,2, Pippa Storey1, Ruth P. Lim1, Jian Xu1, Qin Chen3, Andrew Laine2, Vivian S. Lee3
Department of Radiology , New York University Medical Center, New York, USA; 2Columbia University, New York, USA; 3Department of Radiology, New York University Medical Center, New York, USA
    ECG-gated 3D fast spin-echo based techniques, which exploit differences in arterial and venous flow during systole and diastole, have been developed for non-contrast-enhanced MRA. We investigate the flow sensitivity of fast spin echo with constant (CFL) versus variable flip angle (VFL) echo-train evolutions at different stations of the peripheral vasculature. Out data demonstrate that velocity sensitivities depend on the flip angle magnitude, with shorter sensitivity range for lower flip angles. With the VFL approach near complete signal void occurs for velocities as low as 5 cm/s, which renders the technique suboptimal for imaging vessels where diastolic flow exceeds this threshold.
11:18 423. Non Contrast MRA of the Hand in Patients with Raynauds Disease Using Flow Sensitized Dephasing Prepared SSFP
    John J. Sheehan1, Zhaoyang Fan2, James C. Carr1,2, Debiao Li2
Cardiovascular Imaging, Northwestern Memorial Hospital, Chicago, IL, USA; 2Cardiovascular Imaging, Northwestern University, Chicago, IL, USA
    This study assessed the diagnostic quality and accuracy of a flow-sensitized dephasing (FSD)-prepared SSFP MRA in patients with Raynauds disease. The FSD method acquires a bright-artery scan using ECG-triggered SSFP and a dark-artery scan using ECG-triggered, FSD-prepared SSFP. Subtraction of the two results in bright arteries. Comparison revealed better quality grades for the FSD NC-MRA compared to contrast MRA . FSD identified 95% of luminal narrowings and all arterial occlusions. FSD of the hand in patients with Raynauds compares favorably with contrast enhanced MRA demonstrating in many cases improved resolution and visualization of normal and vasospastic vessels.
11:30 424. Non-Invasive Assessment of Transstenotic Pressure Gradients Utilizing 3D Phase Contrast MRA: Validation Against Endovascular Pressure Measurements in a Porcine Study
    Thorsten Alexander Bley1, Kevin M. Johnson2, Oliver Wieben2, Christopher J. Francois1, Scott B. Reeder1, Mark L. Schiebler1, Darren P. Lum1, Thomas M. Grist1
Radiology, University of Wisconsin - Madison, Madison, WI, USA; 2Radiology and Medical Physics, University of Wisconsin - Madison, Madison, WI, USA
    This study evaluates noninvasive assessment of transstenotic pressure gradients (TSPG) utilizing phase contrast with vastly under sampled isotropic projection reconstruction (PC VIPR) MRA for quantification of renal artery stenosis (RAS) in a porcine model. TSPG over surgically created bilateral RAS in 11 swine were compared to invasive endovascular pressure measurements obtained with pressure sensing guidewires. Excellent correlation of TSPG assessed with PC VIPR and the gold standard were found (Pearson correlation coefficient of 0.977), indicating the feasibility of this novel method for noninvasive assessment of the hemodynamic severity of RAS.
11:42 425. B1 Inhomogeneity in the Thigh at 3T and Implications for Peripheral Vascular Imaging
    Pippa Storey1, Vivian S. Lee1, Daniel K. Sodickson1, Davide Santoro1, Bei Zhang1, Ruth P. Lim1, Iliyana P. Atanasova1, David R. Stoffel1, Qun Chen1, Graham C. Wiggins1
NYU School of Medicine, New York, NY , USA
    Signal loss in the proximal right femoral artery is evident to some degree on contrast-enhanced MR angiograms, and to a greater extent on non-contrast MRA. Using 3D B1 mapping and RF field simulations, we show that the B1 profile exhibits a rotational symmetry in the thighs, with minima on the anterior medial side of the right leg, and the posterior medial side of the left leg. The fact that the proximal right femoral artery coincides with a B1 minimum explains the signal loss. We investigate the use of dielectric pads and a coupling coil to mitigate the problem.
11:54 426. Ungated Ghost MR Angiography
    Ioannis Koktzoglou1, Robert R. Edelman1
Department of Radiology, NorthShore University HealthSystem, Evanston, IL, USA
    We present a novel contrast mechanism for creating MR angiograms on the basis of ghost artifacts originating from pulsatile arterial flow. The method, which we call “Ghost MRA”, is amenable to numerous pulse sequences and does not require cardiac synchronization or image subtraction to suppress background tissue.
12:06 427. Non-Contrast-Enhanced Flow-Independent Peripheral Angiography with Magnetization-Prepared IDEAL Balanced-SSFP
    Tolga Çukur1, Ann Shimakawa2, Huanzhou Yu2, Brian A. Hargreaves1, Bob S. Hu3, Dwight G. Nishimura1, Jean H. Brittain2
Stanford University, Stanford, CA, USA; 2Applied Science Laboratory, GE Healthcare, USA; 3Palo Alto Medical Foundation, USA
    There has been renewed interest in non-contrast-enhanced angiography due to the recent discovery of the link between the use of gadolinium-based contrast agents and nephrogenic systemic fibrosis. Because most non-contrast-enhanced techniques rely on blood flow, the reliability of the generated contrast is compromised in cases of slow flow, such as occluded vessels. On the other hand, flow-independent angiography only relies on the inherent T1, T2 and chemical shift differences of the tissues. 3D complex-sum IDEAL balanced-SSFP can reliably suppress the fat signal. Meanwhile, frequent magnetization preparation coupled with parallel imaging can reduce the long-T1 and muscle signal without compromising the scan efficiency.
12:18 428. Flow Saturation Inversion Recovery Non-Contrast-Agent MR Angiography for Lower Extremity
    Mitsuharu Miyoshi1, Naoyoki Takei1, Tetsuji Tsukamoto1
Japan Applied Science Laboratory, GE Yokogawa Medical Systems Ltd., Hino, Tokyo, Japan
    For arterial/venous separation, Non-Contrast-Agent MR Angiography (NCA-MRA) often uses image subtraction, which is sensitive to patient motion. In this paper, Flow Saturation Inversion Recovery (FS-IR) pulse is used to eliminate subtraction. Three volunteer images of popliteal artery and trifurcation were compared between subtraction method and FS-IR. Signal intensity and scanning time of FS-IR is 66% and 89% of subtraction method, respectively. Large arteries were depicted in both methods. However, small arteries were depicted well in subtraction method because of higher signal intensity. FS-IR method could eliminate subtraction and it was an effective method for NCA-MRA.