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BACKGROUND A low-cryogen, compact 3T (C3T) MRI scanner with high-performance gradients capable of simultaneously achieving 80 mT/m gradient amplitude and 700 T/m/second slew rate has been in use to study research patients since March 2016 but has not been implemented in the clinical practice. PURPOSE To compare head MRI examinations obtained with the C3T system and a conventional whole-body 3T (WB3T) scanner in seven parameters across five commonly used brain imaging sequences. STUDY TYPE Prospective. SUBJECTS Thirty patients with a clinically indicated head MRI. SEQUENCE 3T; T1 FLAIR, T1 MP-RAGE, 3D T2 FLAIR, T2 FSE, and DWI. ASSESSMENT All patients tolerated the scans well. Three board-certified neuroradiologists scored the comparative quality of C3T and WB3T images in blinded fashion using a five-point Likert scale in terms of: signal-to-noise ratio, lesion conspicuity, motion artifact, gray/white matter contrast, cerebellar folia, susceptibility artifact, and overall quality. STATISTICAL TEST Left-sided, right-sided, and two-sided Wilcoxon signed rank test; Fisher's method. A P value

Image guidance aids neurosurgeons in making critical clinical decisions to achieve a safe maximal resection of diseased tissue. The brain however undergoes significant nonlinear structural deformation due to multiple factors, including dura opening, fluid shifts, and tissue resection. While ultrasound (US) has shown promise in monitoring brain deformation and as a navigation image source in its own right, magnetic resonance imaging (MRI) generally provides better contrast between tumor and brain tissue and pre-operative imaging can provide functional and connectivity information not available in US. Mapping pre-operative MRI (pMRI) onto intraoperative US (iUS) is therefore desirable for multimodal neurosurgical guidance. In this work, we present a novel approach that uses T1 intensity gradients to non-rigidly register pMRI to iUS. The method was validated on 22 datasets from the MICCAI CuRIOUS Challenge 2018 and an average landmark error of 4.89mm was achieved.

The sound generated by diseased carotid arteries was investigated through computational means using three-dimensional, idealized, stenosed carotid bifurcation models. Stenosis levels of 50% and 70% with axi-symmetric and asymmetric stenosis shapes were considered. The hemodynamic flow field was obtained by solving the incompressible, Navier-Stokes equations. The resulting pressure fluctuations at the vessel walls were then used as input for a linearized wave equation for the propagation of vibrations through the modeled surrounding tissue. As observed in prior studies, the sound spectra obtained at the tissue surface indicate a ‘break frequency’, i.e. a frequency beyond which there is a drop-off in sound spectra intensity. This frequency was found to scale with stenosis diameter and average velocity at the stenosis throat, provided the stenosis shape remained the same. This has important implications on past attempts to estimate stenosis diameter from the break frequency.

Image guidance aids neurosurgeons in making critical clinical decisions of safe maximal resection of diseased tissue. The brain however undergoes significant non-linear structural deformation on account of dura opening and tumor resection. Deformable registration of pre-operative ultrasound to intra-operative ultrasound may be used in mapping of pre-operative planning MRI to intraoperative ultrasound. Such mapping may aid in determining tumor resection margins during surgery. In this work, brain structures visible in pre- and intra-operative 3D ultrasound were used for automatic deformable registration. A Gaussian mixture model was used to automatically segment structures of interest in pre- and intra-operative ultrasound and patch-based normalized cross-correlation was used to establish correspondences between segmented structures. An affine registration based on correspondences was followed by B-spline based deformable registration to register pre- and intra-operative ultrasound. Manually labelled landmarks in pre- and intra-operative ultrasound were used to quantify the mean target registration error. We achieve a mean target registration error of 1.43±0.8 mm when validated with 17 pre- and intra-operative ultrasound image volumes of a public dataset.

Purpose To investigate the feasibility of substantially reducing acoustic noise while performing diffusion tensor imaging (DTI) on a compact 3T (C3T) MRI scanner equipped with a 42-cm inner-diameter asymmetric gradient. Methods A-weighted acoustic measurements were made using 10 mT/m-amplitude sinusoidal waveforms, corresponding to echo-planar imaging (EPI) echo spacing of 0.25 to 5.0 ms, on a conventional, whole-body 3T MRI and on the C3T. Acoustic measurements of DTI with trapezoidal EPI waveforms were then made at peak gradient performance on the C3T (80 mT/m amplitude, 700 T/m/s slew rate) and at derated performance (33 mT/m, 10 to 50 T/m/s) for acoustic noise reduction. DTI was acquired in two different phantoms and in seven human subjects, with and without gradient-derating corresponding to multi- and single-shot acquisitions, respectively. Results Sinusoidal waveforms on the C3T were quieter by 8.5 to 15.6 A-weighted decibels (dBA) on average as compared to the whole-body MRI. The derated multishot DTI acquisition noise level was only 8.7 dBA (at 13 T/m/s slew rate) above ambient, and was quieter than non-derated, single-shot DTI by 22.3 dBA; however, the scan time was almost quadrupled. Although derating resulted in negligible diffusivity differences in the phantoms, small biases in diffusivity measurements were observed in human subjects (apparent diffusion coefficient = +9.3 ± 8.8%, fractional anisotropy = +3.2 ± 11.2%, radial diffusivity = +9.4 ± 16.8%, parallel diffusivity = +10.3 ± 8.4%). Conclusion The feasibility of achieving reduced acoustic noise levels with whole-brain DTI on the C3T MRI was demonstrated. Magn Reson Med 79:2902-2911, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

We developed a magnetic resonance compatible real-time, three-dimensional imaging ultrasound probe for motion management of radiation therapy for liver cancer. The probe contains an 18,000-element, 46.8 mm × 21.5 mm matrix array constructed from three tiled transducer modules with integrated beamforming ASICs. The center frequency and −6 dB fractional bandwidth of the probe was 3.6 MHz and 85 percent respectively. Ferromagnetic materials in the acoustic stack, flex interconnect and electronics boards were greatly minimized for magnetic resonance compatibility. The probe and cable were shielded to minimize the impact of radiofrequency noise on both the ultrasound and magnetic resonance images. The probe’s low-profile, side-viewing design allows it to be strapped to a patient so that images may be acquired hands-free. We present simultaneously acquired ultrasound and 3 Tesla magnetic resonance images with minimal artifacts in both images.

Purpose To investigate the effects on echo planar imaging (EPI) distortion of using high gradient slew rates (SR) of up to 700 T/m/s for in vivo human brain imaging, with a dedicated, head-only gradient coil. Materials and Methods Simulation studies were first performed to determine the expected echo spacing and distortion reduction in EPI. A head gradient of 42-cm inner diameter and with asymmetric transverse coils was then installed in a whole-body, conventional 3T magnetic resonance imaging (MRI) system. Human subject imaging was performed on five subjects to determine the effects of EPI on echo spacing and signal dropout at various gradient slew rates. The feasibility of whole-brain imaging at 1.5 mm-isotropic spatial resolution was demonstrated with gradient-echo and spin-echo diffusion-weighted EPI. Results As compared to a whole-body gradient coil, the EPI echo spacing in the head-only gradient coil was reduced by 48%. Simulation and in vivo results, respectively, showed up to 25–26% and 19% improvement in signal dropout. Whole-brain imaging with EPI at 1.5 mm spatial resolution provided good whole-brain coverage, spatial linearity, and low spatial distortion effects. Conclusion Our results of human brain imaging with EPI using the compact head gradient coil at slew rates higher than in conventional whole-body MR systems demonstrate substantially improved image distortion, and point to a potential for benefits to non-EPI pulse sequences. J. Magn. Reson. Imaging 2016;44:653–664.

PURPOSE To characterize peripheral nerve stimulation (PNS) of an asymmetric head-only gradient coil that is compatible with a commercial high-channel-count receive-only array. METHODS Two prototypes of an asymmetric head-only gradient coil set with a 42-cm inner diameter were constructed for brain imaging at 3T with maximum performance specifications of up to 85 mT/m and 708 T/m/s. Tests were performed in 24 volunteers to measure PNS thresholds with the transverse (x = left-right; y = anterior-posterior [A/P]) gradient coils of both prototypes. Fourteen of these 24 volunteers were also tested for the z-gradient PNS in the second prototype and were scanned with high-slew-rate echo planar imaging (EPI) immediately after the PNS tests. RESULTS For both prototypes, the y-gradient PNS threshold was markedly higher than the x-gradient threshold. The z-gradient threshold was intermediate between those for the x- and y-coils. Of the 24 volunteers, only two experienced y-gradient PNS at 80 mT/m and 500 T/m/s. All volunteers underwent the EPI scan without PNS when the readout direction was set to A/P. CONCLUSION Measured PNS characteristics of asymmetric head-only gradient coil prototypes indicate that such coils, especially in the A/P direction, can be used for fast EPI readout in high-performance neuroimaging scans with substantially reduced PNS concerns compared with conventional whole body gradient coils. Magn Reson Med 76:1939-1950, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Purpose: To demonstrate a three-echo fat-referenced MR thermometry technique that estimates and corrects for time-varying phase disturbances in heterogeneous tissues. Materials and Methods: Fat protons do not exhibit a temperature-dependent frequency shift. Fat-referenced thermometry methods exploit this insensitivity and use the signal from fat to measure and correct for magnetic field disturbances. In this study, we present a fat-referenced method that uses interpolation of the fat signal to correct for phase disturbances in fat free regions. Phantom and ex vivo tissue cool-down experiments were performed to evaluate the accuracy of this method in the absence of motion. Non-heated in vivo imaging of the breast and prostate was performed to demonstrate measurement robustness in the presence of systemic and motion-induced field disturbances. Measurement accuracy of the method was compared to conventional proton resonance frequency shift MR thermometry. Results: In the ex vivo porcine tissue experiment, maximum measurement error of the fat-referenced method was reduced 42% from 3.3 to 1.9°C when compared to conventional MR thermometry. In the breasts, measurement errors were reduced by up to 70% from 6.4 to 1.9°C. Conclusion: Ex vivo and in vivo results show that the proposed method reduces measurement errors in the heterogeneous tissue experiments when compared to conventional MR thermometry. J. Magn. Reson. Imaging 2012;36:722–732. © 2012 Wiley Periodicals, Inc.

Background— X-ray fluoroscopy constitutes the fundamental imaging modality for catheter visualization during interventional electrophysiology procedures. The minimal tissue discriminative capability of fluoroscopy is mitigated in part by the use of electroanatomic mapping systems and enhanced by the integration of preacquired 3-dimensional imaging of the heart with computed tomographic or magnetic resonance (MR) imaging. A more ideal paradigm might be to use intraprocedural MR imaging to directly image and guide catheter mapping procedures. Methods and Results— An MR imaging–based electroanatomic mapping system was designed to assess the feasibility of navigating catheters to the left ventricle in vivo using MR tracking of microcoils incorporated into the catheters, measuring intracardiac ventricular electrograms, and integrating this information with 3-dimensional MR angiography and myocardial delayed enhancement images to allow ventricular substrate mapping. In all animals (4 normal, and 10 chronically infarcted swine), after transseptal puncture under fluoroscopic guidance, catheters were successfully navigated to the left ventricle with MR tracking (13 to 15 frames per second) by both transseptal and retrograde aortic approaches. Electrogram artifacts related to the MR imaging gradient pulses were successfully removed with analog and digital signal processing. In all animals, it was possible to map the entire left ventricle and to project electrogram voltage amplitude maps to identify the scarred myocardium. Conclusions— It is possible to use MR tracking to navigate catheters to the left ventricle, to measure electrogram activity, and to render accurate 3-dimensional voltage maps in a porcine model of chronic myocardial infarction, completely in the MR imaging environment. Myocardial delayed enhancement guidance provided dense sampling of the proximity of the infarct and accurate localization of complex infarcts.

Objectives Our goal was to investigate whether the association between established cardiovascular risk factors and arterial reactivity differs between the lower and upper extremities. Background Resistance artery reactivity in the arm is associated with cardiovascular risk factors, coronary disease, and events. However, the relationship of lower versus upper extremity vasoreactivity to increasing cardiovascular risk factors has not been determined. Methods We studied 82 subjects in 3 groups: 33 young healthy (YH) (21 to 41 years), 30 older healthy (OH) (>50 years), and 19 older type 2 diabetic subjects (OD). We directly measured systolic shear rate, flow, and radius in brachial and femoral arteries at rest and during post-occlusion hyperemia using magnetic resonance imaging. Results Brachial and femoral systolic shear rate, flow, and radius were similar among the groups at rest. Brachial hyperemic shear rate and hyperemic flow normalized as a function of baseline radius were not statistically different when YH were compared with OH and OH with OD. In contrast, femoral hyperemic shear rate and hyperemic flow normalized to baseline radius were lower in OH than YH (680 ± 236 s−1 vs. 843 ± 157 s−1, p = 0.001, and 0.84 ± 0.25 mm1.27/s vs. 1.01 ± 0.16 mm1.27/s, p = 0.001) and lower in OD than OH (549 ± 183 s−1, p = 0.02, and 0.74 ± 0.19 mm1.27/s, p = 0.046). Conclusions Persons with increasing cardiovascular risk factor burden had progressively reduced arterial reactivity in lower but not upper extremities. This may help to explain why atherosclerosis usually develops more severely in legs than in arms, and suggests that legs may be more sensitive than arms for assessing early global atherosclerotic risk.

Purpose To develop a method for fat suppression in myocardial delayed enhancement (MDE) studies that achieves effective signal intensity reduction in fat but does not perturb myocardial signal suppression. Materials and Methods A new approach to fat suppression that uses a spectrally-selective inversion-recovery (SPEC-IR) tip-up radio frequency (RF) pulse following the conventional nonselective IR RF pulse together with a second SPEC-IR RF pulse is proposed. The tip-up pulse restores the fat longitudinal magnetization after the nonselective IR pulse and allows the fat magnetization to recover more fully toward its equilibrium value, providing for better fat suppression by the second SPEC-IR RF pulse. This new approach was validated in phantom studies and in five patients. Results Effective fat suppression was achieved using the proposed technique with minimal impact on normal myocardial signal suppression. Mean fat suppression achieved using this approach was 67% ± 8%, as measured in the chest wall immediately opposite the heart. Conclusion The results indicate this modular-type approach optimizes fat suppression in myocardial delayed enhancement studies but does not perturb the basic IR pulse sequence or change basic acquisition parameters. J. Magn. Reson. Imaging 2007;26:927–933. © 2007 Wiley-Liss, Inc.

Purpose To develop a gated single-breathhold, high temporal resolution three-dimensional (3D) CINE imaging technique and to evaluate its accuracy in volumetric and functional quantification in patients with chronic myocardial infarction. Materials and Methods A 3D CINE steady-state free precession (SSFP) pulse sequence was developed incorporating variable temporal sampling of the low and high spatial frequency k-space data to reduce breathhold time and parallel imaging to increase temporal resolution. Reconstruction with retrospective interpolation enabled complete R-R interval coverage. Feasibility was assessed in eight patients with chronic myocardial infarction and ventricular functional values were compared to those of a 2D CINE acquisition. Results There was no significant difference between the 3D CINE and 2D CINE for end-diastolic volume (168 ± 73 vs. 177 ± 59 mL, respectively; P < 0.27), end-systolic volume (81 ± 62 vs. 79 ± 53 mL; P < 0.81), and ejection fraction (EF) measurements (55 ± 14% vs. 58 ± 14%; P < 0.14). The mean difference in EF was less than 2.5%. A wall motion assessment indicated a good agreement, with a weighted kappa value of 0.62. Conclusion High temporal resolution 3D CINE SSFP imaging of the whole heart can be obtained in a single breathhold and yield ventricular function measurements similar to 2D CINE methods. J. Magn. Reson. Imaging 2007;25:1141–1146. © 2007 Wiley-Liss, Inc.

Radiation therapy (RT) plays an essential role in the management of cancers. The precision of the treatment delivery process in chest and abdominal cancers is often impeded by respiration induced tumor positional variations, which are accounted for by using larger therapeutic margins around the tumor volume leading to sub-optimal treatment deliveries and risk to healthy tissue. Real-time tracking of tumor motion during RT will help reduce unnecessary margin area and benefit cancer patients by allowing the treatment volume to closely match the positional variation of the tumor volume over time. In this work, we propose a fast approach which enables transferring the pre-estimated target (e.g. tumor) motion extracted from ultrasound (US) image sequences in training stage (e.g. before RT) to online data in real-time (e.g. acquired during RT). The method is based on extracting feature points of the target object, exploiting low-dimensional description of the feature motion through slow feature analysis, and finding the most similar image frame from training data for estimating current/online object location. The approach is evaluated on two 2 D + time and one 3 D + time US acquisitions. The locations of six annotated fiducials are used for designing experiments and validating tracking accuracy. The average fiducial distance between expert's annotation and the location extracted from our indexed training frame is 1.9±0.5 mm . Adding a fast template matching procedure within a small search range reduces the distance to 1.4±0.4 mm . The tracking time per frame is on the order of millisecond, which is below the frame acquisition time.

Purpose To validate partial Fourier phase contrast magnetic resonance (PC MR) with full number of excitation (NEX) PC MR measurements in vitro and in vivo. Materials and Methods MR flow measurements were performed using a partial Fourier and a full NEX PC MR sequence in a flow phantom and in 10 popliteal and renal arteries of 10 different healthy volunteers. Average velocity, peak velocity, and flow results were calculated and compared with regression analysis. Results Excellent correlations in average velocities (r = 0.99, P < 0.001), peak velocities (r = 0.99, P < 0.001), and flow rates (r = 0.98, P < 0.001) were demonstrated in vitro between the two different acquisitions. For the popliteal arteries there was excellent correlation between peak velocities for both acquisitions (r = 0.98, P < 0.0001); the correlation of average velocity measurements when using all data points in the cardiac cycle for all volunteers was 0.96 (P < 0.001). For the renal arteries the same comparison resulted in a good correlation for average velocity (0.93, P < 0.001) and peak velocity measurements (r = 0.91, P = 0.002), although the correlation coefficient for flow rates was 0.88 (P = 0.004). Blurring of the vessel margins was consistently observed on magnitude images acquired with the partial Fourier method, causing overestimation of the vessel area and some error in the flow measurements. Conclusion Partial Fourier PC MR is able to provide comparable average and peak velocity values when using 1 NEX PC MRI as a reference. J. Magn. Reson. Imaging 2006. © 2005 Wiley-Liss, Inc.

In delayed contrast-enhanced MRI for the assessment of myocardial viability, the TI time in a gated inversion-recovery segmented gradient echo sequence is usually selected to null signal from normal myocardium. Although this TI time generates good contrast between the enhancing infarcted tissue and normal myocardium, there is usually less contrast between the infarct and the blood pool. A subtractive technique utilizing two acquisitions at a long and short TI time is proposed to improve the delineation between infarct-blood and infarct-myocardium. The concept was demonstrated in six mongrel dogs with reperfused myocardial infarction. Infarct-normal myocardium contrast (signal difference) using the proposed enhanced viability imaging (ENVI) technique was 142 ± 50% (P < 0.001) that of standard magnitude inversion recovery (IR), while at the same TI time for the primary image, infarct-blood contrast, was 247 ± 136% (P < 0.002) that of magnitude IR. Accounting for increased noise due to the subtraction, signal difference-to-noise ratios (SDNR) did not show a significant change for infarct-myocardium but infarct-blood SDNR for ENVI was 174 ± 105% that of magnitude-IR (P < 0.03). Thus, marked improvement in the delineation of the infarcted zone was noted over a range of TI times. Magn Reson Med 53:1484–1489, 2005. © 2005 Wiley-Liss, Inc.

To compare two-dimensional and three-dimensional techniques in the detection of myocardial infarction (MI) and in the grading transmural extent (TE).Twelve patients with clinically proven MI were examined using two-dimensional and three-dimensional techniques with cardiac-gated, breath-hold, T1-weighted gradient echo sequence with an inversion recovery pulse following gadopentetate dimeglumine (Gd-DTPA) at 0.2 mmol/kg. Contrast-to-noise, signal-to-noise, and signal intensity ratios (CNR, SNR, and SIR, respectively) were derived and compared for each technique.From two-dimensional to three-dimensional, statistical significant difference was found in the mean CNR (11.65 vs. 56.59; P = 0.002), SNR (18.03 vs. 76.90; P0.001), and SIR (3.6 vs. 6.36; P = 0.05). Intraobserver agreement (kappa) between two-dimensional and three-dimensional were R1 = 74% and R2 = 90%. Interobserver agreements between the readers were two-dimensional = 77% and three-dimensional = 79%.Mean CNR, SNR, and SIR are significantly increased in the three-dimensional technique compared to the conventional two-dimensional technique.

Peripheral magnetic resonance angiography (MRA) is growing in use. However, methods of performing peripheral MRA vary widely and continue to be optimized, especially for improvement in illustration of infrapopliteal arteries. The main purpose of this project was to identify imaging factors that can improve arterial visualization in the lower leg using bolus chase peripheral MRA. Eighteen healthy adults were imaged on a 1.5T MR scanner. The calf was imaged using conventional three-station bolus chase three-dimensional (3D) MRA, two dimensional (2D) time-of-flight (TOF) MRA and single-station Gadolinium (Gd)-enhanced 3D MRA. Observer comparisons of vessel visualization, signal to noise ratios (SNR), contrast to noise ratios (CNR) and spatial resolution comparisons were performed. Arterial SNR and CNR were similar for all three techniques. However, arterial visualization was dramatically improved on dedicated, arterial-phase Gd-enhanced 3D MRA compared with the multi-station bolus chase MRA and 2D TOF MRA. This improvement was related to optimization of Gd-enhanced 3D MRA parameters (fast injection rate of 2 mL/sec, high spatial resolution imaging, the use of dedicated phased array coils, elliptical centric k-space sampling and accurate arterial phase timing for image acquisition). The visualization of the infrapopliteal arteries can be substantially improved in bolus chase peripheral MRA if voxel size, contrast delivery, and central k-space data acquisition for arterial enhancement are optimized. Improvements in peripheral MRA should be directed at these parameters.

Cardiac MRI continues to develop and advance. MRI accurately depicts cardiac structure, function, perfusion, and myocardial viability with an overall capacity unmatched by any other single imaging modality. MRI is an accepted and widely utilized tool for cardiovascular research. Its clinical use has been limited, but is increasing because of its proven clinical efficacy, the proliferation of cardiac-capable MRI systems, and the development of improved pulse sequences. The following article reviews the landmark developments in this field, with an emphasis on recent progress in the evaluation of ischemic or acquired heart disease.

Contrast-enhanced magnetic resonance angiography (CE MR angiography) has benefited from advancements in MR imaging speed, pulse sequence design, and dedicated equipment and algorithms for its performance. These improvements have greatly expanded the number of options available to the operator and enabled the application of CE MR angiography to a broader range of clinical applications. In this article, the various timing options, pulse sequence innovations, and contrast administration concerns related to clinical CE MR angiography are reviewed. Pertinent issues related to multiphase and multistation bolus chase CE MR angiography also will be discussed.

The authors evaluated a magnetization preparation scheme with a "notched" section profile for T1-weighted first-pass myocardial perfusion magnetic resonance (MR) imaging at 1.5 T. The pulse sequence consisted of a preparation sequence followed by an interleaved gradient-echo echo-planar sequence. Image contrast was evaluated in a feasibility study in 12 adult patients. The notched saturation pulse allowed long magnetization recovery times without sacrificing section coverage. Image contrast between normal and ischemic myocardium was excellent.

A comparison between the prospective and retrospective respiratory navigator gating in MR coronary angiography was performed with eight normal subjects. A three-dimensional (3D) ECG-gated fast gradient echo pulse sequence was used for image data acquisition. The results show that the MR coronary angiography obtained using retrospective gating retains a considerable amount of motion artifacts. In this study, the images acquired using prospective navigator gating demonstrated significantly reduced motion artifacts (p = 0.009), improved vessel visibility (p = 0.021) with reduced imaging time (p = 0.013) compared to the images obtained using retrospective navigator gating.

Purpose: To investigate the feasibility of preferential arterial imaging using gadolinium-enhanced thick-slice phase-contrast imaging. Methods: Six healthy volunteers were studied using a peripheral-gated segmented k-space CINE phase-contrast pulse sequence using four views per RR interval with flow encoding in the superior-inferior direction. Images at the level of the popiteal trifurcation were acquired postcontrast with different section thicknesses (4–8 cm) and VENC values (20–150 cm/sec), and phase-difference processing. Results: The post-gadolinium contrast-enhanced thick-slice phase-contrast acquisitions demonstrated the ability to visualize the tibio-peroneal (trifurcation) arteries, especially in systole. With MR contrast agents, the signal from blood is raised significantly above that of stationary tissue from T1 shortening such that the partial volume artifact is reduced in thick-slice acquisitions. Furthermore, by selecting the VENC value as a function of the cardiac cycle, the noise floor can be raised to selectively suppress flow values less than that of the noise threshold, allowing better accentuation of arterial structures at systole. Conclusions: Thick-slice phase-contrast acquisition with phase-difference processing has been observed to reduce partial volume artifacts when an MR contrast agent substantially increases signal in the vasculature over that of normal background tissue. Preferential arterial images can be obtained by either increasing the VENC value to selectively suppress signal from slow flow in the veins or by subtracting the diastolic phase image from the peak systolic phase image. J. Magn. Reson. Imaging 2001;13:714–721. © 2001 Wiley-Liss, Inc.

Coronary artery magnetic resonance imaging strategies have tended to focus on the use of a single method performed during either breath-holding or free-breathing for all patients. However, significant variations exist among patients in terms of breath-holding ability and respiratory regularity that make the use of a single technique alone not universally successful. Therefore, it is prudent to make available a number of magnetic resonance imaging methods such that an appropriate respiratory motion reduction strategy can be tailored to suit the patient's respiratory pattern and characteristics. A tailored approach that can draw on different image acquisition techniques for coronary artery imaging is presented. A decision tree is proposed to triage patients into imaging regimes with the greatest probability of success, according to the patient's ability to breath-hold or exhibit steady respiration. Methods include volume free-breathing acquisitions using navigator echoes for respiratory monitoring in the 8- to 10-min scan time range, two-dimensional spiral navigators (2- to 3-min scan time), breath-held multislice and vessel-tracking spirals (16- to 20-second scan time), and real-time imaging approaches incorporating adaptive signal averaging. The development of multiple acquisition strategies substantially improves the opportunities to generate high-quality, diagnostic images of the coronary arteries.

In this pilot study, using a standard 40 mL gadolinium (Gd) chelate contrast dose, dual-rate (first 20 mL at 0.5 mL/sec; remaining 20 mL at 1.5 mL/sec) and fixed-rate (entire 40 mL dose at either 0.7 mL/sec or 2.0 mL/sec) injection schemes for multistation, bolus-chase magnetic resonance angiography (MRA) were compared in normal volunteers. Signal-to-noise ratio, contrast-to-noise ratio, and physician preference were determined for nine arterial segments. At the terminal station (calf), the dual-rate contrast injection improved arterial signal and contrast compared with both fixed-rate injection schemes and improved subjective vessel appearance compared with the 2.0 mL/sec, but not the 0.7 mL/sec, fixed-rate scheme.

Bolus chase 3-dimensional MR angiography (3D MRA) is a recent development that extends the effective field of view for arterial imaging from the typical single 40-50 cm to over 100 cm. This technique is well suited for imaging long vascular territories such as the lower extremity. Bolus chase peripheral 3D MRA is achieved with overlapping 3D gradient-echo scans during the arterial transit of a single intravenous injection of gadolinium-chelate contrast media. This technique can depict the arteries from the infrarenal aorta to the ankles in less than 2 minutes. The initial experiences with bolus chase peripheral MRA using an automated algorithm that controls both table translation and 3D data acquisition are described. Suggestions for future refinements to the technique are also discussed.

Gadolinium (Gd)-enhanced three-dimensional (3D) magnetic resonance angiography (MRA) is a quick method for performing noninvasive diagnostic angiography. A major technical obstacle to the successful implementation of this technique, however, is the proper coordination of the data acquisition with th

A method is proposed to reconstruct multiphase images that accurately depicts the entire cardiac cycle. A segmented, gradient-recalled-echo sequence (FASTCARD) was modified to acquire data continuously. Images were reconstructed retrospectively by selecting views from each heartbeat based on cardiac phase rather than the time elapsed from the QRS complex. Cardiac phase was calculated using a model that compensates for beat-to-beat heart rate changes. Images collected using cardiac phase to order reconstruction (CAPTOR) depict the entire cardiac cycle and lack the temporal gap that is characteristic of prospectively reconstructed sequences. Time-volume curves of the left ventricle capture the contribution of atrial contraction to end-diastolic volume (EDV). Transmitral phase-contrast flow measurements show a second peak inflow (alpha wave) that is absent in the standard sequence. Because atrial contraction contributes to ventricular EDV, images using CAPTOR potentially may provide a more reliable measure of EDV, stroke volume, and ejection fraction than standard techniques.

Automatic triggering of magnetic resonance (MR) angiography with detection of a contrast material bolus was evaluated. Signal intensity changes with time were tracked in a prescribed tracking or monitoring volume by a parallel signal processing unit that automatically started data acquisition once user-defined thresholds were exceeded. This technique, referred to as MR Smartprep, was reliable and avoided the inconsistencies of manual timing.

It was the purpose of this study to demonstrate the feasibility of performing coronary artery flow and coronary flow reserve (CFR) measurements in normal human volunteers using a magnetic resonance (MR) phase contrast technique.Coronary flow rate, flow velocity, peak flow and CFR were determined at rest and during pharmacologically induced hyperemia in 10 healthy volunteers. The flow measurements were obtained during a single breath-hold by using a fast, prospectively gated, segmented k-space gradient-echo phase contrast acquisition with view sharing (FASTCARD PC) that was modified to improve sampling of the diastolic flow. Data were processed using the standard phase difference (PD) processing techniques as well as a new complex difference (CD) flow measurement method intended to improve the accuracy of flow measurements in small vessels.Mean hyperemic flow velocity (40 +/- 16 cm/s) and blood flow (3.9 +/- 1.5 ml/s) rates differed significantly from resting velocity (13 +/- 6.6 cm/s) and flow (1.1 +/- 0.4 ml/s) measurements (p0.0001). PD methods consistently measured larger flow rates at rest (24% larger, p0.0005) and stress (29% larger, p0.0001). CFR, calculated as the ratio of the mean PD flows (4.7 +/- 2.8), was higher than CFR calculated as the ratio of mean CD flows (4.2 +/- 1.8); however, the differences did not reach statistical significance (p = 0.07). Flow measurements performed in adjacent slices of the same vessel correlated well (r = 0.88).Coronary flow and CFR measurements using the MR techniques are feasible and are similar to those reported in the literature for healthy volunteers.

To measure coronary vasodilator reserve with breath-hold velocity-encoded cine magnetic resonance (MR) imaging.Eight healthy adult volunteers underwent 1.5-T MR imaging. Velocity-encoded cine images were acquired at seven to 13 temporal phases in 25 seconds, with k-space segmentation and view-sharing reconstruction (+/- 1 m/sec velocity-encoding value) (repetition time msec/echo time msec = 16/9). Flow velocity in the left anterior descending (LAD) artery was measured twice before and twice after administration of dipyridamole (0.56 mg per kilogram of body weight).Peak diastolic coronary flow velocity in the LAD artery was 14.8 cm/sec +/- 1.9 (mean +/- standard deviation) in the baseline state. It increased significantly (P.01) to 46.3 cm/sec +/- 10.2 after dipyridamole administration, with an average coronary reserve of 3.14 +/- 0.59. Interstudy and interobserver reproducibilities for measurement of peak diastolic velocity were, respectively, 9.5% +/- 1.6 and 7.0% +/- .2.5 in the baseline state and 6.8% +/- 2.2 and 3.4% +/- 1.5 after dipyridamole administration.Breath-hold velocity-encoded cine MR imaging provided reproducible assessment of coronary flow reserve in humans.

Breath-hold velocity-encoded cine MR (VENC-MR) imaging is a feasible method for measuring phasic blood flow velocity in small vessels that move during respiration. The purposes of the current study are to compare breathhold VENC-MR measurements of flow velocities in the internal mammary arteries (IMA) with nonbreath-hold measurements and to characterize the systolic and diastolic flow velocity curves in a cardiac cycle in native IMA and IMA grafts. Flow velocity in 30 native IMA and 8 IMA grafts were evaluated with a breath-hold VENC-MR sequence with K-space segmentation and view-sharing reconstruction (TR/TE = 16/9 msec, VENC = 100 cm/s). In 10 native IMA, nonbreath-hold VENC-MR images were acquired as well for comparison. Breath-hold VENC-MR imaging showed significantly higher systolic and diastolic peak velocities in native IMA (43.1 cm/second +/- 15.0 and 10.0 cm/second +/- 4.8), in comparison to those of nonbreath-hold VENC-MR imaging (27.6 cm/second +/- 10.2 and 7.3 cm/second +/- 3.9, P.05). The diastolic/systolic peak velocity ratio in the IMA grafts (.88 +/- .41) was significantly higher than that in native IMA (.24 +/- .08, P.01). Interobserver variability in the flow velocity measurement was less than 4%. Breath-hold VENC-MR imaging demonstrated higher peak flow velocity in the IMA than nonbreath-hold VENC-MR imaging. This technique is a rapid and effective method for the noninvasive assessment of blood flow velocity in IMA grafts.

Our goal was to determine if breath-hold cine MRI in transaxial planes can be used for the evaluation of thoracic aortic dissection instead of conventional cine MRI since rapid imaging is required in this clinical setting.Twelve patients with thoracic aortic dissection were imaged using a 1.5 T imager. Breath-hold images were acquired with fast cine MR sequence (TR/TE = 9/2.8, 20 degrees flip angle) using segmented k-space data acquisition. Conventional non-breath-hold cine MR images (TR/TE = 22/7.5, 35 degrees flip angle, 2 averages) were taken with flow and respiratory compensation.Sharpness of edges of the vessels on fast cine MR images was better than that on conventional cine MR images in 34 (57%) of 60 images. Inhomogeneous blood signal in aortic lumen due to motion artifacts was found in 2 (3%) of fast cine MR images and in 15 (25%) of conventional cine MR images. The contrast-to-noise ratios of fast cine MR images were significantly better than those of conventional cine MR images (26.4 +/- 9.1 vs. 18.5 +/- 10.1; p0.05) when the region of interest for noise was placed to include ghosting artifacts.Breath-hold cine MRI is a rapid technique that gives high quality images of thoracic aortic dissection and can provide a diagnosis in10 min of imaging time.

To improve the accuracy of ventricular volume estimates and effective temporal resolution in fast cardiac acquisitions.Data sets at intermediate temporal phases were generated by means of sharing of views from two temporally adjacent data sets. A simulated model was used, and studies with patients and volunteers were conducted. View sharing was implemented in both fast gradient-echo and fast phase-contrast cine acquisitions; breath holding was used when possible.Uniform repetition time (TR) radio-frequency (RF) excitation allowed a better assessment of the end-diastolic ventricular volume. In addition, view sharing provided a better estimate of end-systolic ventricular volume in cases in which rapid changes in volume occurred at or about the temporal boundary of the source images. View sharing also provided a much smoother representation of dynamic cardiac motion when viewed in a cine loop.View sharing and uniform TR RF excitation improve the accuracy of end-systolic and end-diastolic ventricular volume measurements by improving the effective temporal resolution.

Purpose: To develop and validate a real-time motion management platform for radiotherapy that directly tracks tumor motion using ultrasound and MRI. This will be a cost-effective and non-invasive real-time platform combining the excellent temporal resolution of ultrasound with the excellent soft-tissue contrast of MRI. Methods: A 4D planar ultrasound acquisition during the treatment that is coupled to a pre-treatment calibration training image set consisting of a simultaneous 4D ultrasound and 4D MRI acquisition. The image sets will be rapidly matched using advanced image and signal processing algorithms, allowing the display of virtual MR images of the tumor/organ motion in real-time from an ultrasound acquisition. Results: The completion of this work will result in several innovations including: a (2D) patch-like, MR and LINAC compatible 4D planar ultrasound transducer that is electronically steerable for hands-free operation to provide real-time virtual MR and ultrasound imaging for motion management during radiation therapy; a multi- modal tumor localization strategy that uses ultrasound and MRI; and fast and accurate image processing algorithms that provide real-time information about the motion and location of tumor or related soft-tissue structures within the patient. Conclusion: If successful, the proposed approach will provide real-time guidance for radiation therapy without degrading image or treatment plan quality. The approach would be equally suitable for image-guided proton beam or heavy ion-beam therapy. This work is partially funded by NIH grant R01CA190298

We compared the conspicuity of acute pulmonary emboli with contrast-enhanced spiral computed tomography (CT) and two- and three-dimensional time-of-flight magnetic resonance (MR) techniques. Seven dogs who received experimental pulmonary emboli and one control were imaged with spiral CT and with 2-D (FMPVAS and FASTCARD) and 3-D time-of-flight MR. Blinded, independent, prospective evaluations of the CT and MR images by two MR radiologists and two chest radiologists were then compared to the location of the emboli as determined by subsequent pathologic evaluation of the excised lungs. Embolus/blood contrast-to-noise ratios (CNRs) were calculated on both MR and CT images for pulmonary emboli that could be identified. Fifty emboli ranging from 1.0 to 5.5 mm (mean, 2.7, +/- 0.14 SEM) in diameter and from 3.0 to 60 mm (mean, 28.1 +/- 1.9 SEM) in length were found in the seven embolized dogs on pathologic examination. Three of the four radiologists identified more thrombi on CT images than they did on their best MR pulse sequence (FASTCARD) and with greater confidence. The fourth radiologist identified an equal percentage of clot on CT and FASTCARD images with confidence slightly greater on FASTCARD MR than on spiral CT. Mean CNR for the best MR technique was 43.4 (+/- 3.9 SEM) and for CT was 20.7 (+/- 1.3 SEM). In general, pulmonary emboli were detected more accurately on contrast-enhanced spiral CT than on MR. This occurred although the embolus/blood CNR was higher on MR than on CT. Better pulmonary embolus conspicuity on CT images was attributed to better spatial resolution and fewer artifacts on CT than on MR. One MR radiologist performed equally well with both spiral CT and FASTCARD techniques, suggesting that experience may be a factor in performance.

PURPOSE: To evaluate the differences in contrast between 1-second delay and zero delay (for magnetization recovery) before the preparation radio-frequency pulse in three-dimensional, inversion-recovery (IR) fast gradient-echo (GRE) acquisitions. MATERIALS AND METHODS: Mathematical simulations and measurements of brain image contrast were performed with healthy volunteers and 10 patients. RESULTS: The zero-delay sequence generated T1-weighted contrast similar to that obtained with 1-second delay but was accompanied by a substantial reduction in imaging time. However, the zero delay prohibits full recovery of the longitudinal magnetization. Hence, the signal null characteristic of IR experiments is not easily observed, since it occurs (as a function of tissue T1) at very short inversion times (< 150 msec). CONCLUSION: T1-weighted contrast comparable with that of magnetization-prepared rapid GRE sequences with a 1-second delay and preparation time (TP) of 600-700 msec can be achieved in less time by using a ...

Purpose: To optimize and validate a modified cine inversion recovery sequence (MCine-IR) for myocardial T1 quantification and gadolinium partition coefficient (λGd) estimation at 1.5 T. Materials and Methods: The original version of the cine inversion recovery sequence was modified to allow fully transverse magnetization recovery between two successive inversion pulses. Sixty heart phases were acquired from a number of heart cycles determined on a patient heart rate basis. Phantom studies were carried out to find the optimal effective TR for myocardial and blood pool T1 quantifications in pre- and postcontrast studies. Four patients with myocardial infarct (MI) and 22 dilated cardiomyopathy (DCM) were investigated, as well as 11 healthy subjects used as controls. Results: Effective TR was identified to be 5000 msec and 2000 msec, respectively, for pre- and postcontrast studies. A longer precontrast (948 ± 102 msec) and shorter postcontrast (348 ± 27 msec) T1 in ischemic patients relative to DCM (815 ± 98 msec, P = 0.03 and 409 ± 42 msec, P = 0.001) were noted in delayed enhancement (DE) areas. In MI patients λGd resulted higher than in DCM in DE areas (609 ± 167 vs. 422 ± 52, P = 0.01) but lower in segments not exhibiting DE (355 ± 100 vs. 398 ± 54, P = 0.02). Conclusion: It was feasible to measure T1 and λGd with MCine-IR and the results were in good agreement with the literature. J. Magn. Reson. Imaging 2013;37:109–118. © 2012 Wiley Periodicals, Inc.

Introduction: The accurate and reproducible assessment of cardiac volumes, function, and mass is of paramount importance in cardiology. In the present study we sought to determine whether the 3D cine-magnetic resonance (MR) technique, using the variable asymmetric sampling in time (VAST) approach, provided an accurate assessment of LV functional parameters when compared with the conventional 2D cine-MR technique. Methods: A total of 43 consecutive patients referred for a CMR examination for clinical reasons and 14 healthy volunteers were included in the study. Cine images were acquired using a steady-state free precession pulse sequence. Two different multiphase acquisitions were performed: conventional 2D cine-MR and 3D cine-MR. The short-axis cine images acquired by both cine-MR techniques were used for the quantitative assessment of LV end-diastolic, end-systolic and stroke vol- umes, LV mass and ejection fraction. Results: All CMR examinations were completed successfully, with both cine-MR imaging techniques yielding interpret- able diagnostic results in all patients. Regarding the quantitative assessment, Bland-Altman analyses demonstrated a good agreement between the measurements of both cine-MR techniques for all LV parameters. In addition, the agreement be- tween 2D and 3D cine-MR techniques for the qualitative assessment of LV global function was perfect (kappa = 1.0, P

To prospectively evaluate three magnetic resonance (MR) imaging techniques for detection of pulmonary embolism.Eighteen patients in whom the presence of acute or chronic pulmonary emboli was suspected underwent examination with the following pulse sequences: cardiac-gated spin echo, cine spatial modulation of magnetization, and two-dimensional time-of-flight pulmonary breath-hold (PBH) MR angiography. Three radiologists independently and blindly reviewed each case and graded a total of 518 arterial segments for each pulse sequence with a continuous scale of 0%-100% for likelihood of pulmonary embolism.The overall sensitivity of PBH MR angiography for detection of acute pulmonary emboli was 0.85; for chronic emboli, which were smaller in anteroposterior (AP) diameter, the overall sensitivity was 0.42. Emboli larger than 1 cm in AP diameter were typically identified with75% confidence with all pulse sequences.Acute pulmonary emboli greater than 1 cm in AP diameter were as accurately identified on PBH MR angiograms obtained in 15 seconds as they were on MR images obtained with longer pulse sequences not dependent on breath holding.

Objective: To identify the pulsatile small vascular lesion by echocardiogram (ECG)-gated computed tomographic (CT) and magnetic resonance (MR) angiographies. Methods: Seven patients who exhibited small evagination at the cerebral artery bifurcations on 3-dimensional (3D) time-of-flight MR angiogram were enrolled. They were examined by conventional/ECG-gated CT angiogram (n = 6) and ECG-gated MR angiogram (n = 5). Echocardiogram-gated MR angiogram was performed with 3D time of flight, triggered after each time window. From ECG-gated CT and MR angiograms, consecutive 10-phase images within a single cardiac cycle were obtained. Results: The pulsatile change of evagination was demonstrated on both ECG-gated CT angiogram (5 of 6 patients) and ECG-gated MR angiogram (all 5 patients). Flattening of the evagination during the diastolic phase was observed in 4 of 6 ECG-gated CT angiograms and 3 of 5 ECG-gated MR angiograms. Of note was a patient with a tiny evagination (

Thirteen patients underwent magnetic resonance (MR) imaging of the patellofemoral joint in an evaluation of passive positioning and active movement kinematic MR imaging techniques. Sixteen joints were symptomatic, and 10 were not. Delineation of normal and abnormal patellar alignment and tracking was similar with the two techniques, but kinematic MR imaging performed with active movement allowed a substantial reduction in examination time while permitting evaluation of the contribution of associated activated muscles and soft-tissue structures to patellofemoral joint function.

An ultrafast spoiled gradient-recalled acquisition in the steady state pulse sequence was developed that permits multiple images to be obtained at a temporal resolution suitable for examining the patellofemoral joint during active flexion. This pulse sequence was used to perform kinematic magnetic resonance imaging of patellar alignment and tracking in five healthy subjects and seven patients with a provisional clinical diagnosis of abnormal patellofemoral joints.

Distinct peptide maps of two rabbit lung Ca2(+)-dependent phospholipid-binding proteins (PLBPs), 36,000 and 33,000, were generated by cyanogen bromide (CNBr) cleavage, trypsin or Staphylococcus aureus V8 proteinase digestion. The amino acid sequence of a CNBr-cleaved peptide of the 36,000 PLBP was aligned to the amino terminus of human lipocortin I with more than 77% identity, but had no identity with the known amino terminal sequence of other known annexins. Partial amino acid sequence of a 33,000 PLBP peptide demonstrated a close (56%) relationship to endonexin II, human placental anticoagulant protein, and porcine intestine protein II, but shared only 32% identity with lipocortin I, 30% with lipocortin II. Antiserum generated against purified 36,000 PLBP reacted strongly with the 33,000 PLBP, but did not react with any other rabbit lung cytosolic proteins. Both PLBPs inhibited the phospholipase A2 reaction when dioleoyl phosphatidylcholine and phosphatidylglycerol vesicles or monolayers were used as substrates. In the vesicle assay, the phospholipase A2 reaction was inhibited at lower substrate phospholipid concentrations but not at nearly saturating substrate concentrations. In the monolayer assay, the phospholipid-binding proteins did not inhibit phospholipase A2 at a low phospholipid surface concentration of 3.8.10(-3) molecules/A2, but they did at higher surface concentrations between 1.1 x 10(-2) and 3.8 x 10(-2) molecules/A2. The inhibition of phospholipase A2 by rabbit lung phospholipid-binding proteins is most likely due to the prevention of penetration by phospholipase A2 into the interface, a requirement for the enzyme to act on the substrate.

Dr Goldberger highlights several considerations when using electrophysiological testing to stratify patients at risk for lethal ventricular arrhythmias. The comments about our study’s electrophysiological protocol are important; indeed, we had acknowledged them as potential limitations. The incremental value of adding a second site for programmed stimulation, even in patients presenting with monomorphic ventricular tachycardia (MVT), has been debated.1 We chose an accelerated protocol at a single site in patients not undergoing a full electrophysiological study to limit the implantable cardioverter-defibrillator implantation …

Background— The extent of the peri-infarct zone by magnetic resonance imaging (MRI) has been related to all-cause mortality in patients with coronary artery disease. This relationship may result from arrhythmogenesis in the infarct border. However, the relationship between tissue heterogeneity in the infarct periphery and arrhythmic substrate has not been investigated. In the present study, we quantify myocardial infarct heterogeneity by contrast-enhanced MRI and relate it to an electrophysiological marker of arrhythmic substrate in patients with left ventricular (LV) systolic dysfunction undergoing prophylactic implantable cardioverter defibrillator placement. Methods and Results— Before implantable cardioverter defibrillator implantation for primary prevention of sudden cardiac death, 47 patients underwent cine and contrast-enhanced MRI to measure LV function, volumes, mass, and infarct size. A method for quantifying the heterogeneous infarct periphery and the denser infarct core is described. MRI indices were related to inducibility of sustained monomorphic ventricular tachycardia during electrophysiological or device testing. For the noninducible versus inducible patients, LV ejection fraction (30±10% versus 29±7%, P =0.79), LV end-diastolic volume (220±70 versus 228±57 mL, P =0.68), and infarct size by standard contrast-enhanced MRI definitions ( P =NS) were similar. Quantification of tissue heterogeneity at the infarct periphery was strongly associated with inducibility for monomorphic ventricular tachycardia (noninducible versus inducible: 13±9 versus 19±8 g, P =0.015) and was the single significant factor in a stepwise logistic regression. Conclusions— Tissue heterogeneity is present and quantifiable within human infarcts. More extensive tissue heterogeneity correlates with increased ventricular irritability by programmed electrical stimulation. These findings support the hypothesis that anatomic tissue heterogeneity increases susceptibility to ventricular arrhythmias in patients with prior myocardial infarction and LV dysfunction.

Use of magnetic resonance (MR) imaging for diagnosis of cardiac diseases and treatment monitoring is expanding. Delayed myocardial enhancement MR imaging is performed after administration of paramagnetic contrast agents and is used for a growing number of clinical applications. This technique was developed primarily for characterization of myocardial scarring after myocardial infarction. On delayed enhancement MR images, scarring or fibrosis appears as an area of high signal intensity that is typically subendocardial or transmural in a coronary artery distribution. However, delayed myocardial enhancement is not specific for myocardial infarction and can occur in a variety of other disorders, such as inflammatory or infectious diseases of the myocardium, cardiomyopathy, cardiac neoplasms, and congenital or genetic cardiac conditions, as well as after cardiac interventions. In nonischemic myocardial disease, the delayed enhancement usually does not occur in a coronary artery distribution and is often midwall rather than subendocardial or transmural. Therefore, the patient's clinical history is critical in the evaluation of delayed myocardial enhancement MR images.