ABSTRACT
PURPOSE: To test intra-arterial spin labeling (iASL) using active guiding catheters for myocardial perfusion measurements during magnetic resonance (MR)-guided interventions in a pig study. METHODS: In this work, a single-loop radiofrequency (RF) coil at the tip of a 6F active coronary catheter was used as a transmit coil for local spin labeling. The transmit magnetic RF field (B1) of the coil and the labeling efficiency were determined, and iASL was tested in two pigs after the catheter was engaged in the aortic root, the ostium of the left coronary artery (LCA) under MR-guidance. The iASL effect was assessed by the signal difference between spin-labeling On and control (spin-labeling OFF) images, and in a cross-correlation between ON/Off states of spin-labeling a binary labeling paradigm. In addition, quantitative myocardial perfusion was calculated from the iASL experiments. RESULTS: The maximum B1 in the vicinity of the catheter coil was 2.1⯵T. A strong local labeling effect with a labeling efficiency of 0.45 was achieved with iASL both in vitro and in vivo. In both pigs, the proximal myocardial segments supplied by the LCA showed significant labelling effect up to distances of 60â¯mm from the aortic root with a relative signal difference of (3.14⯱â¯2.89)% in the first and (3.50⯱â¯1.25)% in the second animal. The mean correlation coefficients were Râ¯=â¯0.63⯱â¯0.22 and 0.42⯱â¯0.16, respectively. The corresponding computed myocardial perfusion values in this region of the myocardium were similar to those obtained with contrast perfusion methods ((1.2⯱â¯1.1) mL/min/g and (0.8⯱â¯0.6) mL/min/g). CONCLUSION: The proposed iASL method demonstrates the feasibility of selective myocardial perfusion measurements during MR-guided coronary interventions, which with further technical improvements may provide an alternative to exogenous contrast-based perfusion. Due to the invasive nature of the iASL method, it can potentially be used in concert with MRI-guided coronary angioplasty.
ABSTRACT
Oxygen metabolism is altered in brain tumor regions and is quantified by the cerebral metabolic rate of oxygen consumption (CMRO2). Direct dynamic 17O MRI with inhalation of isotopically enriched 17O2 gas can be used to quantify CMRO2; however, pixel-wise CMRO2 quantification in human brain is challenging due to low natural abundance of 17O isotope and, thus, the low signal-to-noise ratio (SNR) of 17O MR images. To test the feasibility CMRO2 mapping at a clinical 3 T MRI system, a new iterative reconstruction was proposed, which uses the edge information contained in a co-registered 1H gradient image to construct a non-homogeneous anisotropic diffusion (AD) filter. AD-constrained reconstruction of 17O MR images was compared to conventional Kaiser-Bessel gridding without and with Hanning filtering, and to iterative reconstruction with a total variation (TV) constraint. For numerical brain phantom and in two in vivo data sets of one healthy volunteer, AD-constrained reconstruction provided 17O images with improved resolution of fine brain structures and resulted in higher SNR. CMRO2 values of 0.78 - 1.55µmol/gtissue/min (white brain matter) and 1.03 - 2.01µmol/gtissue/min (gray brain matter) as well as the CMRO2 maps are in a good agreement with the results of 15O-PET and 17O MRI at 7 T and at 9.4 T. In conclusion, the proposed AD-constrained reconstruction enabled calculation of 3D CMRO2 maps at 3 T MRI system, which is an essential step towards clinical translation of 17O MRI for non-invasive CMRO2 quantification in tumor patients.
