Faculty Bibliography

Background: Conventional cine MRI provides data on the variation of cardiac dimensions across the cardiac cycle; cardiac function analysis primarily focuses on the difference between end-diastolic (ED) and endsystolic (ES) dimensions of the left and right ventricles (LV and RV). With cardiorespiratory-synchronized (CRS) CMR, there is an additional effective dimension of information available, related to the effect of the respiratory cycle phase on cardiac dimensions. However, there are currently no established ways to analyze this potentially useful additional physiological data. We have developed a set of tools for the functional analysis of CRS CMR, particularly for the study of the respiratory effects on LV-RV interaction, and derived some initial normative values for the results. Methods: We have developed a set of interactive CMR function analysis programs. Images from CRS CMR are organized in a two-dimensional matrix, sorted by cardiac and respiratory cycle phases. The user can interactively position an analysis line across the ventricles in a representative image; this line can then be automatically tracked across the other cardiac and respiratory phases. The intensity profile along the line is then used to automatically track the corresponding positions of the edges of the LV and RV free walls and the interventricular septum (IVS). A variety of absolute and normalized variables can be derived from these varying positions, including ED and ES dimensions, and displayed as functional images over the cardiac and respiratory cycle dimensions. CRS CMR was performed with a sparsity-based method (XD-GRASP), using continuous acquisition of radial k-space samples with golden-angle increments and retrospective cardiac and respiratory phase sorting in reconstruction. An initial set of CRS CMR data from 9 normal subjects (age 28.33 +/- 5.85) was analyzed, as well as from 3 patients (age 40 +/- 9.66, one with HCM). Results: On visual inspection of the images, it is apparent that there is a clear shift in the relative position of the IVS over the respiratory cycle, to the left in inspiration and to the right in expiration, reflecting the LV-RV interaction; this is much more prominent near ED than ES. For the normal subjects, in midlevel short-axis views, the respiratory-related absolute shift in IVS position was 1.07-3.23 mm at ED and 0.69-2.14 mm at ES; corresponding values normalized to ED dimension were 2.65-7.08 pp and 1.99-5.18 pp. The ED-ES difference for the normalized shift ranges was -1.9-4.35 pp (median 1.35, first quartile 0.68). For the HCM patient, the difference between the shift ranges was 0.79 pp. Linear regression when plotting NCD against NEDD (reflecting the Frank-Starling relationship and giving an estimate of contractility) was 0.68 +/- 0.11 in the normal subjects. Conclusions: Novel physiologic data on LV-RV interaction can be derived from CRS CMR; this seems to show consistent ranges in normal subjects, and may provide useful information on disease-related changes in cardiac function. (Figure Presented)

Background: Three-dimensional (3D) virtual models are valuable tools that may help to better understand complex cardiovascular anatomy and facilitate surgical planning in patients with congenital heart disease (CHD). Although computed tomography (CT) images are used most commonly to create these models [1,2], Magnetic Resonance Imaging (MRI) may be an attractive alternative, since it offers superior soft-tissue characterization and flexible image contrast mechanisms, and avoids the use of ionizing radiation. However, segmentation on MRI images is inherently challenging due to noise/artifacts, magnetic field inhomogeneity, and relatively lower spatial resolution compared to CT. The purpose of this study was to evaluate the image quality and assess the feasibility of creating virtual 3D heart models using a novel prototype 3D whole heart self-navigated radial MRI technique. Methods: Free-breathing self-navigated whole heart MRI was performed on three pediatric patients: two with complex CHD (average age=17 months) and one with normal cardiac anatomy (age=17years), using a 3D radial, non-slice-selective, T2-prepared, fat-saturated bSSFP sequence on a 1.5T MRI scanner (MAGNETOM Aera, Siemens, Germany). The acquisition window (~50-55 ms) was placed in mid-diastole and was adapted for different heart rates. Imaging parameters were as follows: TR/TE=3.1/1.56 ms, FOV=200 mm3, voxel size=1 mm3, FA=115degree, and acquisition time=5-6 minutes (~12000 radial lines). Respiratory motion correction and image reconstruction was performed on the scanner as described in [3]. For comparison, conventional non-gated 3D FLASH or navigator-gated 3D bSSFP sequences were also performed. All results were blinded and randomized for image quality assessment by one pediatric cardiologist and one cardiac radiologist using a five-point scale (1=non-diagnostic, 2=poor, 3=adequate, 4=good, 5=excellent). Statistical analysis was performed to compare mean scores. DICOM images were imported to a 3D workstation (Mimics, Materialise, Leuven, Belgium) for 3D postprocessing. The cardiovascular anatomy was first segmented using a combination of automated and manual techniques; and volume rendering was performed to depict the anatomy of interest. Results: The free-breathing self-navigated 3D radial acquisition provided significantly improved image quality and myocardial wall-blood contrast (Figure 1). Mean scores were 4.58 and 2.67 for the 3D radial and FLASH/ bSSFP sequences respectively (p = 0.003). The cardiovascular anatomy was well depicted on all virtual 3D models (Figure 2). Conclusions: 3D virtual models are frequently being created to understand complex anatomy, influence surgical planning, and provide intra-operative guidance for patients with CHD. This novel free-breathing, self-navigated whole heart 3D radial sequence provided excellent image quality as compared to existing routine MR sequences. Furthermore, the (Figure Presented) superb image quality provided using this novel sequence makes it an excellent choice for the creation of 3D models

OBJECTIVE: This study aimed to demonstrate feasibility of free-breathing radial acquisition with respiratory motion-resolved compressed sensing reconstruction [extra-dimensional golden-angle radial sparse parallel imaging (XD-GRASP)] for multiphase dynamic gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced liver imaging, and to compare image quality to compressed sensing reconstruction with respiratory motion-averaging (GRASP) and prior conventional breath-held Cartesian-sampled data sets [BH volume interpolated breath-hold examination (VIBE)] in same patients. SUBJECTS AND METHODS: In this Health Insurance Portability and Accountability Act-compliant prospective study, 16 subjects underwent free-breathing continuous radial acquisition during Gd-EOB-DTPA injection and had prior BH-VIBE available. Acquired data were reconstructed using motion-averaging GRASP approach in which consecutive 84 spokes were grouped in each contrast-enhanced phase for a temporal resolution of approximately 14 seconds. Additionally, respiratory motion-resolved reconstruction was performed from the same k-space data by sorting each contrast-enhanced phase into multiple respiratory motion states using compressed sensing algorithm named XD-GRASP, which exploits sparsity along both the contrast-enhancement and respiratory-state dimensions.Contrast-enhanced dynamic multiphase XD-GRASP, GRASP, and BH-VIBE images were anonymized, pooled together in a random order, and presented to 2 board-certified radiologists for independent evaluation of image quality, with higher score indicating more optimal examination. RESULTS: The XD-GRASP reconstructions had significantly (all P < 0.05) higher overall image quality scores compared to GRASP for early arterial (reader 1: 4.3 +/- 0.6 vs 3.31 +/- 0.6; reader 2: 3.81 +/- 0.8 vs 3.38 +/- 0.9) and late arterial (reader 1: 4.5 +/- 0.6 vs 3.63 +/- 0.6; reader 2: 3.56 +/- 0.5 vs 2.88 +/- 0.7) phases of enhancement for both readers. The XD-GRASP also had higher overall image quality score in portal venous phase, which was significant for reader 1 (4.44 +/- 0.5 vs 3.75 +/- 0.8; P = 0.002). In addition, the XD-GRASP had higher overall image quality score compared to BH-VIBE for early (reader 1: 4.3 +/- 0.6 vs 3.88 +/- 0.6; reader 2: 3.81 +/- 0.8 vs 3.50 +/- 1.0) and late (reader 1: 4.5 +/- 0.6 vs 3.44 +/- 0.6; reader 2: 3.56 +/- 0.5 vs 2.94 +/- 0.9) arterial phases. CONCLUSION: Free-breathing motion-resolved XD-GRASP reconstructions provide diagnostic high-quality multiphase images in patients undergoing Gd-EOB-DTPA-enhanced liver examination.

PURPOSE: To demonstrate dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) of the prostate with both high spatial and temporal resolution via a combination of golden-angle radial k-space sampling, compressed sensing, and parallel-imaging reconstruction (GRASP), and to compare image quality and lesion depiction between GRASP and conventional DCE in prostate cancer patients. MATERIALS AND METHODS: Twenty prostate cancer patients underwent two 3T prostate MRI examinations on separate dates, one using standard DCE (spatial resolution 3.0 x 1.9 x 1.9 mm, temporal resolution 5.5 sec) and the other using GRASP (spatial resolution 3.0 x 1.1 x 1.1 mm, temporal resolution 2.3 sec). Two radiologists assessed measures of image quality and dominant lesion size. The experienced reader recorded differences in contrast arrival times between the dominant lesion and benign prostate. RESULTS: Compared with standard DCE, GRASP demonstrated significantly better clarity of the capsule, peripheral/transition zone boundary, urethra, and periprostatic vessels; image sharpness; and lesion conspicuity for both readers (P < 0.001-0.020). GRASP showed improved interreader correlation for lesion size (GRASP: r = 0.691-0.824, standard: r = 0.495-0.542). In 8/20 cases, only GRASP showed earlier contrast arrival in tumor than benign; in no case did only standard DCE show earlier contrast arrival in tumor. CONCLUSION: High spatiotemporal resolution prostate DCE is possible with GRASP, which has the potential to improve image quality and lesion depiction as compared with standard DCE.J. Magn. Reson. Imaging 2014. (c) 2014 Wiley Periodicals, Inc.

Background: For patients with impaired breath-hold capacity or arrhythmias, free breathing real-time cine MRI is preferred at the expense of compromised spatiotemporal resolution. Compressed sensing (CS) has been used to achieve higher spatiotemporal resolutions in real-time cine MRI, but the superposition of respiratory and cardiac motion limits temporal sparsity. In this work, we propose a novel approach that sorts out cardiac and respiratory motion into separated but synchronized dimensions and performs a joint multicoil CS reconstruction with different sparsity constraints on cardiac and respiratory dimensions. Golden-angle radial sampling was employed for flexible data sorting. In arrhythmias cases, data are also sorted according to cardiac cycles with different length to reconstruct both "normal" and "ectopic" cycles. Methods: Cardiac imaging was performed on one volunteer (male age = 27) and one patient (female age = 49) with Mobitz I arrhythmia during free breathing without external gating on a 1.5T MRI scanner (Avanto, Siemens). Data were continuously acquired for 15 s in a short axis plane using a 2D golden-angle radial b-SSFP sequence. Imaging parameters were: spatial resolution = 2 x 2 mm², TR/TE = 2.8/1.4 ms, FA = 70degree and slice thickness = 8 mm. Temporal evolution of the central k-space positions (green dots, Figure 1a) was used to estimate cardiac contraction and respiration from coil-elements close to the heart and diaphragm respectively (Figure 1b). Raw data were then sorted into an expanded dataset of images containing two dynamic dimensions, one for cardiac and the other for respiratory motion. As shown in Figure 1b, each colored rectangular block represents an individual cardiac phase from a short "snapshot" period (e.g. 13 adjacent spokes). Data were sorted first into a higher dimensional matrix using the cardiac motion signal (Figure 1c left) followed by a second sorting along the respiratory dimension from expiration to inspiration using the respiratory mot!

Background: Evaluation of myocardial function with MRI is challenging on patients with impaired breath-hold (BH) capabilities or arrhythmias due to the difficulty of respiratory motion suspension and synchronization of cardiac cycles. Compressed sensing (CS) enables free breathing (FB) real-time cine imaging with improved spatiotemporal resolution, but conventional temporal sparsifying transforms do not account for respiratory motion, which limits its performance. In this work, we propose to acquire data continuously in FB using a golden-angle radial sampling scheme and reconstruct images with separated but synchronized cardiac and respiratory motion dimensions using self-detected motion signals. For patients with arrhythmias, both "normal" and "ectopic" cycles are reconstructed by sorting out cardiac cycles with different lengths. The performance of the proposed method was compared to Cartesian BH approach using retrospective ECG-gating in 9 patients. Methods: Both BH and FB cine sequences (b-SSFP) were implemented on a 1.5T MRI scanner (Avanto, Siemens). Imaging parameters for BH cine were: spatial resolution = 1.8 x 1.8 mm², slice thickness = 8 mm, TR/TE = 2.5/1.25 ms, FA = 55degree. Imaging parameters for FB cine were: spatial resolution = 2 x 2 mm², slice thickness = 8 mm, TR/TE2.8/1.4 ms, FA = 70degree. Both sequences achieved temporal resolution ~30-40 ms. Cardiac imaging was performed on 9 patients (mean age = 56; 4 had normal sinus rhythm, 4 had arrhythmias including bigeminy PVCs, atrial fibrillation and Mobitz I, 1 was incapable of prolonged BH). One short axis and one 4 chamber cine image set were acquired on each patient at ~12-15s per slice. In FB cine imaging, central k-space positions (green dots, Figure 1a) were used to extract cardiac and respiratory signals from coils near the heart and diaphragm respectively (Figure 1b). Data were sorted and synchronized to separately reconstruct cardiac cycles of different lengths at different respiratory states. A mul!

For patients with impaired breath-hold capacity and/or arrhythmias, real-time cine MRI may be more clinically useful than breath-hold cine MRI. However, commercially available real-time cine MRI methods using parallel imaging typically yield relatively poor spatio-temporal resolution due to their low image acquisition speed. We sought to achieve relatively high spatial resolution ( approximately 2.5 x 2.5 mm(2) ) and temporal resolution ( approximately 40 ms), to produce high-quality real-time cine MR images that could be applied clinically for wall motion assessment and measurement of left ventricular function. In this work, we present an eightfold accelerated real-time cardiac cine MRI pulse sequence using a combination of compressed sensing and parallel imaging (k-t SPARSE-SENSE). Compared with reference, breath-hold cine MRI, our eightfold accelerated real-time cine MRI produced significantly worse qualitative grades (1-5 scale), but its image quality and temporal fidelity scores were above 3.0 (adequate) and artifacts and noise scores were below 3.0 (moderate), suggesting that acceptable diagnostic image quality can be achieved. Additionally, both eightfold accelerated real-time cine and breath-hold cine MRI yielded comparable left ventricular function measurements, with coefficient of variation <10% for left ventricular volumes. Our proposed eightfold accelerated real-time cine MRI with k-t SPARSE-SENSE is a promising modality for rapid imaging of myocardial function. J. Magn. Reson. Imaging 2012;. (c) 2012 Wiley Periodicals, Inc.