3.0‐T MR‐guided focused ultrasound for preoperative localization of nonpalpable breast lesions: An initial experimental ex vivo study

Purpose

To compare the accuracy of magnetic resonance‐guided focused ultrasound (MRgFUS) with MR‐guided needle‐wire placement (MRgNW) for the preoperative localization of nonpalpable breast lesions.

Materials and Methods

In this experimental ex vivo study, 15 turkey breasts were used. In each breast phantom an artificial nonpalpable “tumor” was created by injecting an aqueous gel containing gadolinium. MRgFUS (n = 7) was performed with the ExAblate 2000 system (InSightec). With MRgFUS the ablated tissue changes in color and increases in stiffness. A rim of palpable and visible ablations was created around the tumor to localize the tumor and facilitate excision. MRgNW (n = 8) was performed by MR‐guided placement of an MR‐compatible needle‐wire centrally in the tumor. After surgical excision of the tumor, MR images were used to evaluate tumor‐free margins (negative/positive), minimum tumor‐free margin (mm), and excised tissue volume (cm³).

Results

With MRgFUS localization no positive margins were found after excision (0%). With MRgNW two excision specimens (25%) had positive margins (P = 0.48). Mean minimum tumor‐free margin (±SD) with MRgFUS was significantly larger (5.5 ± 2.4 mm) than with MRgNW (0.9 ± 1.4 mm) (P < 0.001). Mean volume ± SD of excised tissue did not differ between MRgFUS and MRgNW localization, ie, 44.0 ± 9.4 cm³ and 39.5 ± 10.7 cm³ (P = 0.3).

Conclusion

The results of this experimental ex vivo study indicate that MRgFUS can potentially be used to localize nonpalpable breast lesions in vivo. J. Magn. Reson. Imaging 2009;30:884–889. © 2009 Wiley‐Liss, Inc.     

Interventional MRI using multiple 3D angiography roadmaps with real‐time imaging

Purpose:

To enhance real‐time magnetic resonance (MR)‐guided catheter navigation by overlaying colorized multiphase MR angiography (MRA) and cholangiopancreatography (MRCP) roadmaps in an anatomic context.

Materials and Methods:

Time‐resolved MRA and respiratory‐gated MRCP were acquired prior to real‐time imaging in a pig model. MRA and MRCP data were loaded into a custom real‐time MRI reconstruction and visualization workstation where they were displayed as maximum intensity projections (MIPs) in distinct colors. The MIPs were rendered in 3D together with real‐time multislice imaging data using alpha blending. Interactive rotation allowed different views of the combined data.

Results:

Fused display of the previously acquired MIP angiography data with real‐time imaging added anatomical context during endovascular interventions in swine. The use of multiple MIPs rendered in different colors facilitated differentiation of vascular structures, improving visual feedback during device navigation.

Conclusion:

Interventional real‐time MRI may be enhanced by combining with previously acquired multiphase angiograms. Rendered as 3D MIPs together with 2D slice data, this technique provided useful anatomical context that enhanced MRI‐guided interventional applications. J. Magn. Reson. Imaging 2010;31:1015–1019. ©2010 Wiley‐Liss, Inc.     

MRI‐guided procedures in various regions of the body using a robotic assistance system in a closed‐bore scanner: Preliminary clinical experience and limitations

Purpose:

To present the clinical setup and workflow of a robotic assistance system for image‐guided interventions in a conventional magnetic resonance imaging (MRI) environment and to report our preliminary clinical experience with percutaneous biopsies in various body regions.

Materials and Methods:

The MR‐compatible, servo‐pneumatically driven, robotic device (Innomotion) fits into the 60‐cm bore of a standard MR scanner. The needle placement (n = 25) accuracy was estimated by measuring the 3D deviation between needle tip and prescribed target point in a phantom. Percutaneous biopsies in six patients and different body regions were planned by graphically selecting entry and target points on intraoperatively acquired roadmap MR data.

Results:

For insertion depths between 29 and 95 mm, the average 3D needle deviation was 2.2 ± 0.7 mm (range 0.9–3.8 mm). Patients with a body mass index of up to ≈30 kg/m² fitted into the bore with the device. Clinical work steps and limitations are reported for the various applications. All biopsies were diagnostic and could be completed without any major complications. Median planning and intervention times were 25 (range 20–36) and 44 (36–68) minutes, respectively.

Conclusion:

Preliminary clinical results in a standard MRI environment suggest that the presented robotic device provides accurate guidance for percutaneous procedures in various body regions. Shorter procedure times may be achievable by optimizing technical and workflow aspects. J. Magn. Reson. Imaging 2010;31:964–974. ©2010 Wiley‐Liss, Inc.     

Intraprocedural diffusion‐weighted PROPELLER MRI to guide percutaneous biopsy needle placement within rabbit VX2 liver tumors

Purpose

To test the hypothesis that diffusion‐weighted (DW)‐PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) magnetic resonance imaging (MRI) can be used to guide biopsy needle placement during percutaneous interventional procedures to selectively target viable and necrotic tissues within VX2 rabbit liver tumors.

Materials and Methods

Our institutional Animal Care and Use Committee approved all experiments. In six rabbits implanted with 15 VX2 liver tumors, baseline DW‐PROPELLER images acquired prior to the interventional procedure were used for apparent diffusion coefficient (ADC) measurements. Next, intraprocedural DW‐PROPELLER scans were performed with needle position iteratively adjusted to target viable, necrotic, or intermediate border tissue regions. DW‐PROPELLER ADC measurements at the selected needle tip locations were compared with the percentage of tumor necrosis qualitatively assessed at histopathology.

Results

DW‐PROPELLER images demonstrated intratumoral tissue heterogeneity and clearly depicted the needle tip position within viable and necrotic tumor tissues. Mean ADC measurements within the region‐of‐interest encompassing the needle tip were highly correlated with histopathologic tumor necrotic tissue assessments.

Conclusion

DW‐PROPELLER is an effective method to selectively position the biopsy needle tip within viable and necrotic tumor tissues. The DW‐PROPELLER method may offer an important complementary tool for functional guidance during MR‐guided percutaneous procedures. J. Magn. Reson. Imaging 2009;30:366–373. © 2009 Wiley‐Liss, Inc.     

Image registration for targeted MRI-guided transperineal prostate biopsy

Purpose:

To develop and evaluate image registration methodology for automated re‐identification of tumor‐suspicious foci from preprocedural MR exams during MR‐guided transperineal prostate core biopsy.

Materials and Methods:

A hierarchical approach for automated registration between planning and intra‐procedural T2‐weighted prostate MRI was developed and evaluated on the images acquired during 10 consecutive MR‐guided biopsies. Registration accuracy was quantified at image‐based landmarks and by evaluating spatial overlap for the manually segmented prostate and sub‐structures. Registration reliability was evaluated by simulating initial mis‐registration and analyzing the convergence behavior. Registration precision was characterized at the planned biopsy targets.

Results:

The total computation time was compatible with a clinical setting, being at most 2 min. Deformable registration led to a significant improvement in spatial overlap of the prostate and peripheral zone contours compared with both rigid and affine registration. Average in‐slice landmark registration error was 1.3 ± 0.5 mm. Experiments simulating initial mis‐registration resulted in an estimated average capture range of 6 mm and an average in‐slice registration precision of ±0.3 mm.

Conclusion:

Our registration approach requires minimum user interaction and is compatible with the time constraints of our interventional clinical workflow. The initial evaluation shows acceptable accuracy, reliability and consistency of the method. J. Magn. Reson. Imaging 2012;36:987–992. © 2012 Wiley Periodicals, Inc.     

Time‐resolved dual‐station calf–foot three‐dimensional bolus chase MR angiography with fluoroscopic tracking

Purpose:

To refine, adapt, and evaluate the technical aspects of fluoroscopic tracking for generating dual‐station high‐spatial‐resolution MR angiograms of the calves and feet using a single injection of contrast material.

Materials and Methods:

Nine subjects (seven healthy volunteers followed by two patients) were imaged using a two‐station calf–foot three‐dimensional time‐resolved bolus chase MR angiography protocol which provided <1.0 mm³ spatial resolution throughout and 2.5‐ and 6.6‐s frame times at the calf and foot stations, respectively. Real‐time reconstruction of calf station time frames allowed visually guided triggering of table advance to the foot station. The studies were independently read and scored by two radiologists in six image quality categories.

Results:

On average, overall diagnostic quality at the calf and foot stations was good‐to‐excellent, the calf arteries and all but the smallest foot arteries had good‐to‐excellent signal and sharpness, artifact and venous contamination were minor, and signal continuity across the inter‐station interface was good.

Conclusion:

The feasibility of fluoroscopic tracking has been demonstrated as an efficient approach for high spatiotemporal imaging of the arteries of the calves and feet with good‐to‐excellent diagnostic quality and low degrading venous contamination. J. Magn. Reson. Imaging 2012;36:1168–1178. © 2012 Wiley Periodicals, Inc.     

MRI-compatible manipulator with remote-center-of-motion control

Purpose

To develop and assess a needle‐guiding manipulator for MRI‐guided therapy that allows a physician to freely select the needle insertion path while maintaining remote center of motion (RCM) at the tumor site.

Materials and Methods

The manipulator consists of a three‐degrees‐of‐freedom (DOF) base stage and passive needle holder with unconstrained two‐DOF rotation. The synergistic control keeps the Virtual RCM at the preplanned target using encoder outputs from the needle holder as input to motorize the base stage.

Results

The manipulator assists in searching for an optimal needle insertion path which is a complex and time‐consuming task in MRI‐guided ablation therapy for liver tumors. The assessment study showed that accuracy of keeping the virtual RCM to predefined position is 3.0 mm. In a phantom test, the physicians found the needle insertion path faster with than without the manipulator (number of physicians = 3, P = 0.001). However, the alignment time with the virtual RCM was not shorter when imaging time for planning were considered.

Conclusion

The study indicated that the robot holds promise as a tool for accurately and interactively selecting the optimal needle insertion path in liver ablation therapy guided by open‐configuration MRI. J. Magn. Reson. Imaging 2008. © 2008 Wiley‐Liss, Inc.     

Automatic temperature control for MR‐guided interstitial ultrasound ablation in liver using a percutaneous applicator: Ex vivo and in vivo initial studies

Image‐guided thermal ablation offers minimally invasive options for treating hepatocellular carcinoma and colorectal metastases in liver. Here, the feasibility and the potential benefit of active temperature control for MR‐guided percutaneous ultrasound ablation was investigated in pig liver. An MR‐compatible interstitial ultrasound applicator (flat transducer), a positioning system with rotation‐translation guiding frame, and an orbital ring holder were developed. Step‐by‐step rotated elementary lesions were produced, each being formed by directive heating of a flame‐shaped volume of tissue. In vivo feasibility of automatic temperature control was investigated on two pigs. Proton Resonance Frequency Shift (PRFS)‐based MR thermometry was performed on a 1.5‐T clinical scanner, using SENSE acceleration and respiratory gating. MR follow‐up of animals and macroscopic analysis were performed at 3 and, respectively, 4 days postprocedure. No sonication‐related radiofrequency artifacts were detected on MR images. The temperature controller converged to the target elevation within ±2°C unless the requested power level exceeded the authorized limit. Large variability of the controller's applied powers from one sonication to another was found both ex vivo and in vivo, indicating highly anisotropic acoustic coupling and/or tissue response to identical beam pattern along different radial directions. The automatic control of the temperature enabled reproducible shape of lesions (15 ± 2 mm radial depth). Magn Reson Med 63:667–679, 2010. © 2010 Wiley‐Liss, Inc.     

In vivo metabolite profile of adult zebrafish brain obtained by high‐resolution localized magnetic resonance spectroscopy

Purpose

To optimize high‐resolution MR spectroscopy (MRS) for obtaining neurochemical composition of adult zebrafish brain in vivo.

Materials and Methods

A flow‐through setup for supporting MRS of living zebrafish has been designed. In vivo MR microscopy (MRM) images were obtained using a rapid acquisition with relaxation enhancement (RARE) sequence to select a volume of interest. In vivo MR spectra from zebrafish brain were obtained using an optimized point‐resolved spectroscopy (PRESS) sequence preceded by a variable pulse power and optimized relaxation delays (VAPOR) sequence for global water suppression interleaved with outer volume suppression (OVS). In vitro MR spectra in the brain extract were obtained by using correlated spectroscopy (COSY) sequences.

Results

Optimized high‐resolution localized MRS at 9.4T in conjunction with a strong gradient system, efficient shimming, and the water suppression scheme resulted in a reasonable separation of resonances from various metabolites in vivo from a voxel as small as 3.3 μL placed in the zebrafish brain. In addition, more than 14 metabolites were identified in adult zebrafish brain extracts.

Conclusion

We have successfully optimized a high‐resolution localized in vivo MRS technique to get access to the zebrafish brain, and obtained for the first time the neurochemical composition of the zebrafish brain. J. Magn. Reson. Imaging 2009;29:275–281. © 2009 Wiley‐Liss, Inc.     

Magnetic resonance image-guided trans-septal puncture in a swine heart

PURPOSE: To test the feasibility of performing magnetic resonance (MR)-guided trans-septal punctures in the swine heart. MATERIALS AND METHODS: All procedures were performed in a 1.5-T MR scanner. A novel, active MR intravascular needle system was utilized for needle tracking and septal punctures. Trans-septal punctures were performed in five swine using electrocardiogram (ECG)-gated high resolution and non-ECG-gated, real-time MR imaging techniques. The intravascular needle was advanced over a guidewire from the femoral vein. Once the needle was in proper position, trans-septal punctures were made. RESULTS: Active tracking of the needle traversing the septum was possible. The location of the catheter tip was confirmed using real time gradient recalled echo (GRE). After a confirmatory ventriculogram with gadolinium-DTPA, a 0.014-inch guidewire was advanced into the left atrium and left ventricle. All punctures were made with no change in cardiac rhythm or rate; postmortem analysis was performed on all animals and demonstrated that 18/19 (95%) punctures were directly through the fossa ovalis. CONCLUSION: Using only MR guidance and a novel active intravascular needle system, we were able to repeatedly puncture the fossa ovalis in a swine heart from a transfemoral approach, with direct visualization of all components, including the needle, the atria, the fossa ovalis, and the surrounding vasculature.     

Toward MR-guided high intensity focused ultrasound for presurgical localization: focused ultrasound lesions in cadaveric breast tissue

Purpose:

To investigate magnetic resonance image‐guided high intensity focused ultrasound (MR‐HIFU) as a surgical guide for nonpalpable breast tumors by assessing the palpability of MR‐HIFU‐created lesions in ex vivo cadaveric breast tissue.

Materials and Methods:

MR‐HIFU ablations spaced 5 mm apart were made in 18 locations using the ExAblate2000 system. Ablations formed a square perimeter in mixed adipose and fibroglandular tissue. Ablation was monitored using T1‐weighted fast spin echo images. MR‐acoustic radiation force impulse (MR‐ARFI) was used to remotely palpate each ablation location, measuring tissue displacement before and after thermal sonications. Displacement profiles centered at each ablation spot were plotted for comparison. The cadaveric breast was manually palpated to assess stiffness of ablated lesions and dissected for gross examination. This study was repeated on three cadaveric breasts.

Results:

MR‐ARFI showed a collective postablation reduction in peak displacement of 54.8% ([4.41 ± 1.48] μm pre, [1.99 ± 0.82] μm post), and shear wave velocity increase of 65.5% ([10.69 ± 1.60] mm pre, [16.33 ± 3.10] mm post), suggesting tissue became stiffer after the ablation. Manual palpation and dissection of the breast showed increased palpability, a darkening of ablation perimeter, and individual ablations were visible in mixed adipose/fibroglandular tissue.

Conclusion:

The results of this preliminary study show MR‐HIFU has the ability to create palpable lesions in ex vivo cadaveric breast tissue, and may potentially be used to preoperatively localize nonpalpable breast tumors. J. Magn. Reson. Imaging 2012;35:1089‐1097. © 2011 Wiley Periodicals, Inc.     

Transperineal prostate biopsy under magnetic resonance image guidance: a needle placement accuracy study

Purpose

To quantify needle placement accuracy of magnetic resonance image (MRI)‐guided core needle biopsy of the prostate.

Materials and Methods

A total of 10 biopsies were performed with 18‐gauge (G) core biopsy needle via a percutaneous transperineal approach. Needle placement error was assessed by comparing the coordinates of preplanned targets with the needle tip measured from the intraprocedural coherent gradient echo images. The source of these errors was subsequently investigated by measuring displacement caused by needle deflection and needle susceptibility artifact shift in controlled phantom studies. Needle placement error due to misalignment of the needle template guide was also evaluated.

Results

The mean and standard deviation (SD) of errors in targeted biopsies was 6.5 ± 3.5 mm. Phantom experiments showed significant placement error due to needle deflection with a needle with an asymmetrically beveled tip (3.2–8.7 mm depending on tissue type) but significantly smaller error with a symmetrical bevel (0.6–1.1 mm). Needle susceptibility artifacts observed a shift of 1.6 ± 0.4 mm from the true needle axis. Misalignment of the needle template guide contributed an error of 1.5 ± 0.3 mm.

Conclusion

Needle placement error was clinically significant in MRI‐guided biopsy for diagnosis of prostate cancer. Needle placement error due to needle deflection was the most significant cause of error, especially for needles with an asymmetrical bevel. J. Magn. Reson. Imaging 2007;26:688–694. © 2007 Wiley‐Liss, Inc.     

Hybrid of opposite‐contrast MRA of the brain by combining time‐of‐flight and black‐blood sequences: Initial experience in major trunk stenoocclusive diseases

Purpose:

To assess the feasibility of a new MR angiography (MRA) technique named hybrid of opposite‐contrast MRA (HOP MRA) that combined the time‐of‐flight (TOF) MRA with a flow‐sensitive black‐blood (FSBB) sequence in the diagnosis of major trunk stenoocclusive diseases.

Materials and Methods:

On a 1.5 Tesla imager using a dual‐echo three‐dimensional (3D)‐gradient‐echo sequence, we obtained the first echo for TOF MRA followed by the second echo for FSBB. We then subtracted the FSBB data set from that of TOF MRA followed by maximum intensity projection. In four normal volunteers and 19 patients with chronic stenoocclusive disease of the major trunk, we performed HOP MRA along with 3D‐TOF MRA and compared the findings.

Results:

In the volunteer group, the HOP MRA technique improved the demonstration of distal arterial branches. In 12 of the 19 patients, the HOP MRA better visualized branches distal to the lesion as well as distal branches of normal trunks than 3D‐TOF MRA, while both techniques provided equivalent depiction of branches distal to the lesion but better depiction of normal distal branches in three patients.

Conclusion:

The HOP‐MRA technique is promising in major trunk stenoocclusive diseases as it better demonstrates distal branches probably representing collaterals than 3D‐TOF MRA. J. Magn. Reson. Imaging 2010;31:56–60. © 2009 Wiley‐Liss, Inc.     

Reproducibility of MRI‐determined proton density fat fraction across two different MR scanner platforms

Purpose:

To evaluate magnetic resonance imaging (MRI)‐determined proton density fat fraction (PDFF) reproducibility across two MR scanner platforms and, using MR spectroscopy (MRS)‐determined PDFF as reference standard, to confirm MRI‐determined PDFF estimation accuracy.

Materials and Methods:

This prospective, cross‐sectional, crossover, observational pilot study was approved by an Institutional Review Board. Twenty‐one subjects gave written informed consent and underwent liver MRI and MRS at both 1.5T (Siemens Symphony scanner) and 3T (GE Signa Excite HD scanner). MRI‐determined PDFF was estimated using an axial 2D spoiled gradient‐recalled echo sequence with low flip‐angle to minimize T1 bias and six echo‐times to permit correction of T2* and fat‐water signal interference effects. MRS‐determined PDFF was estimated using a stimulated‐echo acquisition mode sequence with long repetition time to minimize T1 bias and five echo times to permit T2 correction. Interscanner reproducibility of MRI determined PDFF was assessed by correlation analysis; accuracy was assessed separately at each field strength by linear regression analysis using MRS‐determined PDFF as reference standard.

Results:

1.5T and 3T MRI‐determined PDFF estimates were highly correlated (r = 0.992). MRI‐determined PDFF estimates were accurate at both 1.5T (regression slope/intercept = 0.958/‐0.48) and 3T (slope/intercept = 1.020/0.925) against the MRS‐determined PDFF reference.

Conclusion:

MRI‐determined PDFF estimation is reproducible and, using MRS‐determined PDFF as reference standard, accurate across two MR scanner platforms at 1.5T and 3T. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

MRI‐guided vacuum‐assisted breast biopsy: A phantom and patient evaluation of targeting accuracy

Purpose

To determine the spatial localization errors of magnetic resonance imaging (MRI)‐guided core biopsy for breast lesions using the handheld vacuum‐assisted core biopsy device in phantoms and patients.

Materials and Methods

Biopsies were done using a 10‐gauge handheld vacuum‐assisted core biopsy system (Vacora, Bard, AZ, USA) on a 1.5T MRI scanner (Philips Achieva, Best, The Netherlands). A standardized biopsy localization protocol was followed by trained operators for multiplanar planning of the biopsy on a separate workstation. Biopsy localization errors were determined as the distance from needle tip to center of the target in three dimensions.

Results

Twenty MRI‐guided biopsies of phantoms were performed by three different operators. The biopsy target mean size was 6.8 ± 0.6 mm. The overall mean three‐dimensional (3D) biopsy targeting error was 4.4 ± 2.9 mm. Thirty‐two MRI breast biopsies performed in 22 patients were reviewed. The lesion mean size was 10.5 ± 9.4 mm. The overall mean 3D localization error was 5.7 ± 3.0 mm. No significant differences between phantom and patients biopsy errors were found (P > 0.5).

Conclusion

MRI‐guided handheld vacuum‐assisted core biopsy device shows good targeting accuracy and should allow localization of lesions to within ～5 to 6 mm. J. Magn. Reson. Imaging 2009;30:424–429. © 2009 Wiley‐Liss, Inc.     

Phase‐field dithering for active catheter tracking

A strategy to increase the robustness of active MR tracking of microcoils in low signal‐to‐noise ratio conditions was developed and tested. The method employs dephasing magnetic field gradient pulses that are applied orthogonal to the frequency‐encoding gradient pulse used in conventional point‐source MR tracking. In subsequent acquisitions, the orthogonal dephasing gradient pulse is rotated while maintaining a perpendicular orientation with respect to the frequency‐encoding gradient. The effect of the dephasing gradient is to apply a spatially dependent phase shift in directions perpendicular to the frequency‐encoding gradient. Since the desired MR signal for robust MR tracking comes from the small volume of nuclear spins near the small detection coil, the desired signal is not dramatically altered by the dephasing gradient. Undesired MR signals arising from larger volumes (e.g., due to coupling with the body coil or surface coils), on the other hand, are dephased and reduced in signal intensity. Since the approach requires no a priori knowledge of the microcoil orientation with respect to the main magnetic field, data from several orthogonal dephasing gradients are acquired and analyzed in real time. One of several selection algorithms is employed to identify the “best” data for use in the coil localization algorithm. This approach was tested in flow phantoms and animal models, with several multiplexing schemes, including the Hadamard and zero‐phase reference approaches. It was found to provide improved MR tracking of untuned microcoils. It also dramatically improved MR tracking robustness in low signal‐to‐noise‐ratio conditions and permitted tracking of microcoils that were inductively coupled to the body coil. Magn Reson Med 63:1398–1403, 2010. © 2010 Wiley‐Liss, Inc.     

Breathhold time‐resolved three‐directional MR velocity mapping of aortic flow in patients after aortic valve‐sparing surgery

Purpose

To evaluate the utility of breathhold time‐resolved three‐directional MR velocity mapping for quantifying the restoration of normal flow patterns in patients after aortic valve‐sparing surgery.

Materials and Methods

Breathhold time‐resolved three‐directional MR velocity mapping was performed on 13 patients with aortic valve‐sparing surgery. Ten healthy volunteers and 12 patients with ascending aortic aneurysm underwent the same MR examination for comparison. Aortic laminar flow, turbulent flow, and the presence of vortical flow in the sinuses of Valsalva were semiquantitatively assessed and statistically compared between the three groups of subjects.

Results

The average score of laminar flow in the ascending aorta for patients with surgery was not significantly different from that of volunteers (P = 0.210), but was significantly greater than that of patients with aneurysm (P < 0.01). The average score of turbulent flow in patients with surgery was significantly smaller than that of patients with aneurysm (P < 0.01). The presence of systolic vortical flow in the sinuses of Valsalva for patients with surgery was not significantly different from that of healthy volunteers (P = 0.405) and patients with aneurysm (P = 0.238).

Conclusion

Breathhold time‐resolved three‐directional MR velocity mapping allows for quantifying flow patterns in the aortic root and ascending aorta. Normal laminar flow in the ascending aorta and vortical flow in the sinuses of Valsalva can be restored in patients after aortic valve‐sparing surgery. J. Magn. Reson. Imaging 2009;29:569–575. © 2009 Wiley‐Liss, Inc.     

Gadoxetic acid‐enhanced MRI versus multiphase multidetector row computed tomography for evaluating the viable tumor of hepatocellular carcinomas treated with image‐guided tumor therapy

Purpose:

To compare the diagnostic performance of gadoxetic acid‐enhanced MRI with that of multi‐phase 40‐ or 64‐multidetector row computed tomography (MDCT) to evaluate viable tumors of hepatocellular carcinomas (HCCs) treated with image‐guided tumor therapy.

Materials and Methods:

A total of 108 patients with 162 HCCs (56 lesions with viable tumor and 106 without viable tumor) treated by means of transcatheter arterial chemoembolization or radiofrequency ablation were retrospectively included in this study. All patients underwent multi‐phase CT at 40‐ or 64‐MDCT and gadoxetic acid‐enhanced MRI using 3.0 Tesla (T). Two observers independently and randomly reviewed the CT and MR images of the treated lesions. The diagnostic performance of two techniques for the evaluation of the viable tumors in the treated lesions was assessed with a receiver operating characteristic (ROC) analysis.

Results:

For each observer, the areas under the ROC curve were 0.953 and 0.969 for MRI, and 0.870 and 0.888 for MDCT (P < 0.05). The diagnostic accuracies (96.3% for each observer) and sensitivities (92.9% and 96.4%) of MRI in two observers were significantly higher than those (82.7% and 80.9%, 53.6% for each observer, respectively) of MDCT (P < 0.001). The negative predictive values (96.3% and 98.1%) of MRI in two observers were significantly higher than those (80.0% and 79.5%) of MDCT (P < 0.001). For each observer, specificities and positive predictive values did not differ significantly between the two techniques (P > 0.05).

Conclusion:

Gadoxetic acid‐enhanced MRI shows better diagnostic performance than that of MDCT for evaluating the viable tumors of HCCs treated with image‐guided tumor therapy. J. Magn. Reson. Imaging 2010;32:629–638. © 2010 Wiley‐Liss, Inc.     

Reduced field‐of‐view single‐shot fast spin echo imaging using two‐dimensional spatially selective radiofrequency pulses

Purpose:

To demonstrate reduced field‐of‐view (RFOV) single‐shot fast spin echo (SS‐FSE) imaging based on the use of two‐dimensional spatially selective radiofrequency (2DRF) pulses.

Materials and Methods:

The 2DRF pulses were incorporated into an SS‐FSE sequence for RFOV imaging in both phantoms and the human brain on a 1.5 Tesla (T) whole‐body MR system with the aim of demonstrating improvements in terms of shorter scan time, reduced blurring, and higher spatial resolution compared with full FOV imaging.

Results:

For phantom studies, scan time gains of up to 4.2‐fold were achieved as compared to the full FOV imaging. For human studies, the spatial resolution was increased by a factor of 2.5 (from 1.7 mm/pixel to 0.69 mm/pixel) for RFOV imaging within a scan time (0.7 s) similar to full FOV imaging. A 2.2‐fold shorter scan time along with a significant reduction of blurring was demonstrated in RFOV images compared with full FOV images for a target spatial resolution of 0.69 mm/pixel.

Conclusion:

RFOV SS‐FSE imaging using a 2DRF pulse shows advantages in scan time, blurring, and specific absorption rate reduction along with true spatial resolution increase compared with full FOV imaging. This approach is promising to benefit fast imaging applications such as image guided therapy. J. Magn. Reson. Imaging 2010;32:242–248. © 2010 Wiley‐Liss, Inc.     

Dual‐echo arteriovenography imaging with 7T MRI

Purpose:

To implement a dual‐echo sequence MRI technique at 7T for simultaneous acquisition of time‐of‐flight (TOF) MR angiogram (MRA) and blood oxygenation level‐dependent (BOLD) MR venogram (MRV) in a single MR acquisition and to compare the image qualities with those acquired at 3T.

Materials and Methods:

We implemented a dual‐echo sequence with an echo‐specific k‐space reordering scheme to uncouple the scan parameter requirements for MRA and MRV at 7T. The MRA and MRV vascular contrast was enhanced by maximally separating the k‐space center regions acquired for the MRA and MRV and by adjusting and applying scan parameters compatible between the MRA and MRV. The same imaging sequence was implemented at 3T. Four normal subjects were imaged at both 3T and 7T. MRA and MRV at 7T were reconstructed both with and without phase‐mask filtering and were compared quantitatively and qualitatively with those at 3T with phase‐mask filtering.

Results:

The depiction of small cortical arteries and veins on MRA and MRV at 7T was substantially better than that at 3T, due to about twice higher contrast‐to‐noise ratio (CNR) for both arteries (164 ±57 vs. 77 ± 26) and veins (72 ± 8 vs. 36 ± 6). Even without use of the phase‐masking filtering, the venous contrast at 7T (65 ± 7) was higher than that with the filtering at 3T (36 ± 6).

Conclusion:

The dual‐echo arteriovenography technique we implemented at 7T allows the improved visualization of small vessels in both the MRA and MRV because of the greatly increased signal‐to‐noise ratio (SNR) and susceptibility contrast, compared to 3T. J. Magn. Reson. Imaging 2010;31:255–261. © 2009 Wiley‐Liss, Inc.