Pre- and postprandial alterations of portal venous flow: evaluation with single breath-hold three-dimensional half-Fourier fast spin-echo MR imaging and a selective inversion recovery tagging pulse

PURPOSE: To evaluate the influence of food intake on portal flow using unenhanced magnetic resonance imaging (MRI). MATERIALS AND METHODS: The study population included 29 healthy subjects. A selective inversion recovery tagging pulse was used on the superior mesenteric vein (SMV) and splenic vein (SpV) to study the correlation of tagged blood in the portal vein (PV). MRI was performed before and 60-90 min after a meal. RESULTS: The flow signal from the SMV increased in 97% of the subjects after the meal. Before the meal the portal flow was dominated by flow from the SpV in 59% of the subjects, while it was dominated by flow from the SMV in 76% of the subjects after the meal. The most common distribution pattern of the flow signal from the SpV before the meal was in the central part of the main PV (55%), while it was in the left side (45%) after the meal. The most common distribution pattern of the flow signal from the SMV was in the bilateral sides of the main PV both before and after the meal (62%). CONCLUSION: This technique shows potential for evaluating pre- and postprandial alterations of flow from the SpV and SMV in the PV under physiological conditions.     

Non‐contrast‐enhanced MR portography with time‐spatial labeling inversion pulses: Comparison of imaging with three‐dimensional half‐fourier fast spin‐echo and true steady‐state free‐precession sequences

Purpose

To compare and evaluate images acquired with two different MR angiography (MRA) sequences, three‐dimensional (3D) half‐Fourier fast spin‐echo (FSE) and 3D true steady‐state free‐precession (SSFP) combined with two time‐spatial labeling inversion pulses (T‐SLIPs), for selective and non‐contrast‐enhanced (non‐CE) visualization of the portal vein.

Materials and Methods

Twenty healthy volunteers were examined using half‐Fourier FSE and true SSFP sequences on a 1.5T MRI system with two T‐SLIPs, one placed on the liver and thorax, and the other on the lower abdomen. For quantitative analysis, vessel‐to‐liver contrast (Cv‐l) ratios of the main portal vein (MPV), right portal vein (RPV), and left portal vein (LPV) were measured. The quality of visualization was also evaluated.

Results

In both pulse sequences, selective visualization of the portal vein was successfully conducted in all 20 volunteers. Quantitative evaluation showed significantly better Cv‐l at the RPVs and LPVs in half‐Fourier FSE (P < 0.0001). At the MPV, Cv‐l was better in true SSFP, but was not statistically different. Visualization scores were significantly better only at branches of segments four and eight for half‐Fourier FSE (P = 0.001 and 0.03, respectively).

Conclusion

Both 3D half‐Fourier FSE and true SSFP scans with T‐SLIPs enabled selective non‐CE visualization of the portal vein. Half‐Fourier FSE was considered appropriate for intrahepatic portal vein visualization, and true SSFP may be preferable when visualization of the MPV is required. J. Magn. Reson. Imaging 2009;29:1140–1146. © 2009 Wiley‐Liss, Inc.     

Visualization of pancreatic juice movement using unenhanced MR imaging with spin labeling: preliminary results in normal and pathophysiologic conditions

Purpose:

To visualize the movement of pancreatic juice noninvasively by using an unenhanced magnetic resonance (MR) imaging technique.

Materials and Methods:

Institutional review board approval and informed consent were obtained for this study. A flow‐out technique of time‐spatial labeling inversion pulse (SLIP) technique was applied using both nonselective and selective inversion pulses to label, or tag, pancreatic juice to move out of the region. Ten normal (eight men, two women; age range, 22–61 years; mean age, 35 years) and two pathologic conditions were examined on a commercially available 1.5 Tesla MR imager with quadrature‐detected phased‐array coils. All images were evaluated by two radiologists to assess depiction of the pancreatic juice movement or pancreatic juice reflux as compared to the pancreatic duct or the common bile duct on MRCP obtained before time‐SLIP examination.

Results:

The tagged pancreatic juice was satisfactory visualized after applying the pulse labeling. Noninvasive visualization of pancreatic juice movement, including normal pancreatic juice movement and reflux from the main pancreatic duct into the common bile duct, was possible by using the unenhanced time‐SLIP technique.

Conclusion:

Noninvasive visualization of pancreatic juice movement is possible by using the unenhanced MR imaging time‐SLIP technique. J. Magn. Reson. Imaging 2012;35:1019‐1124. © 2011 Wiley Periodicals, Inc.     

Pulmonary kinematics from tagged hyperpolarized helium‐3 MRI

Purpose:

To propose and test the feasibility of a novel method for quantifying 3D regional pulmonary kinematics from hyperpolarized helium‐3 tagged MRI in human subjects using a tailored image processing pipeline and a recently developed nonrigid registration framework.

Materials and Methods:

Following image acquisition, inspiratory and expiratory tagged ³He magnetic resonance (MR) images were preprocessed using various image filtering techniques to enhance the tag surfaces. Segmentation of the three orthogonal sets of tag planes in each lung produced distinct point‐set representations of the tag surfaces. Using these labeled point‐sets, deformation fields and corresponding strain maps were obtained via nonrigid point‐set registration. Kinematic analysis was performed on three volunteers.

Results:

Tag lines in inspiratory and expiratory images were coregistered producing a continuous 3D correspondence mapping. Average displacement and directional strains were calculated in three subjects in the inferior, mid, and superior portions of the right and left lungs. As expected, the predominant direction of displacements with expiration is from inferior to superior.

Conclusion:

Kinematic quantitation of pulmonary motion using tagged ³He MRI is feasible using the applied image preprocessing filtering techniques and nonrigid point‐set registration. Potential benefits from regional pulmonary kinematic quantitation include the facilitation of diagnosis and local assessment of disease progression. J. Magn. Reson. Imaging 2010;31:1236–1241. © 2010 Wiley‐Liss, Inc.     

Intraportal venous flow distribution: evaluation with single breath-hold ECG-triggered three-dimensional half-Fourier fast spin-echo MR imaging and a selective inversion-recovery tagging pulse.

OBJECTIVE: The purpose of this study was to evaluate the intraportal blood flow distribution from splenic and superior mesenteric veins with an unenhanced MR angiographic technique using single breath-hold ECG-triggered three-dimensional (3D) half-Fourier fast spin-echo sequence and selective inversion-recovery tagging pulse. SUBJECTS AND METHODS: Seventeen healthy volunteers were included in this prospective study. After obtaining regular single breath-hold ECG-triggered 3D half-Fourier fast spin-echo images without applying a tagging pulse, we placed the selective inversion-recovery tagging pulse on the superior mesenteric vein (TAG-A), the splenic vein (TAG-B), or on both (TAG-C) to study the inflow correlation of tagged or marked blood into the portal vein. MR images were evaluated subjectively by three reviewers. RESULTS: On MR images obtained using the TAG-A pulse to suppress the signal flow from the superior mesenteric vein into the portal vein, the most common pattern of signal loss was observed on the right half of the main portal vein (8/17 subjects). Conversely, on the MR images obtained using the TAG-B pulse, signal loss of the left half of the main portal vein was the most common pattern (11/17 subjects). Signal reduction from the splenic venous flow in the left portal vein was significantly greater than that from the superior mesenteric venous flow (p<0.05). CONCLUSION: The unenhanced MR angiographic technique using single breath-hold ECG-triggered 3D half-Fourier fast spin echo with selective inversion-recovery tagging pulse has the potential to assess the intraportal blood flow distribution from the splenic and superior mesenteric veins.     

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.     

Can MR fluoroscopic triggering technique and slow rate injection provide appropriate arterial phase images with reducing artifacts on gadoxetic acid‐DTPA (Gd‐EOB‐DTPA)‐enhanced hepatic MR imaging?

Purpose:

To evaluate whether using MR fluoroscopic triggering technique and slow rate injection improves the quality of arterial phase images in gadoxetic acid‐DTPA‐enhanced (Gd‐EOB‐DTPA) MR imaging because of proper acquisition timing and reduction of artifacts.

Materials and Methods:

Two hundred sixteen patients undergoing examination for liver diseases were retrospectively reviewed. All MR images were obtained with two Gd‐EOB‐DTPA injection protocols: (i) a combination protocol, in which the MR fluoroscopic triggering technique and slow rate injection (1 mL/s) were used; and for comparison, (ii) a conventional protocol, in which adjusted fixed scan delay and ordinary rate injection (2 mL/s) were adopted. Signal‐to‐noise ratio (SNR) of aorta, portal vein, and liver parenchyma on arterial phase images were calculated. Two blinded readers independently evaluated the obtained arterial phase images in terms of acquisition timing and degree of artifacts.

Results:

The SNRs of aorta and portal vein on arterial phase images were significantly higher in the combination protocol group (aorta/portal: 221.9 ± 91.9/197.1 ± 89.8) than that in the conventional protocol group (aorta/portal: 169.8 ± 97.4/92.7 ± 48.5) (P < 0.05). The acquisition timing for arterial phase images with the combination protocol was significantly better than that with the conventional protocol (P < 0.01). The image quality of the combination protocol was significantly higher than that of the conventional protocol (P < 0.01). The occurrence rate of moderate or severe degree of artifacts in the conventional protocol (38.0%) was more prominent than that in the combination protocol (18.5%).

Conclusion:

The combination of the MR fluoroscopic triggering technique and slow rate injection provides proper arterial phase images and reduces the artifacts in Gd‐EOB‐DTPA MR imaging. J. Magn. Reson. Imaging 2010;32:334–340. © 2010 Wiley‐Liss, Inc.     

Dynamic contrast‐enhanced magnetic resonance imaging of abdominal solid organ and major vessel: Comparison of enhancement effect between Gd‐EOB‐DTPA and Gd‐DTPA

Purpose

To evaluate the differences in enhancement of the abdominal solid organ and the major vessel on dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) obtained with gadolinium ethoxybenzyldiethylenetriamine pentaacetic acid (Gd‐EOB‐DTPA: EOB) and gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) in the same patients.

Materials and Methods

A total of 13 healthy volunteers underwent repeat assessments of abdominal MR examinations with DCE‐MRI using either Gd‐DTPA at a dose of 0.1 mmol/kg body weight or EOB at a dose of 0.025 mmol/kg body weight. DCE images were obtained at precontrast injection and in the arterial phase (AP: 25 seconds), portal phase (PP: 70 seconds), and equilibrium phase (EP: 3 minutes). The signal intensities (SIs) of liver at AP, PP, and EP; the SIs of spleen, renal cortex, renal medulla, pancreas, adrenal gland, aorta at AP; and the SIs of portal vein and inferior vena cava (IVC) at PP were defined using region‐of‐interest measurements, and were used for calculation of signal intensity ratio (SIR).

Results

The mean SIRs of liver (0.195 ± 0.140), spleen (1.35 ± 0.353), renal cortex (1.58 ± 0.517), renal medulla (0.548 ± 0.259), pancreas (0.540 ± 0.183), adrenal gland (1.04 ± 0.405), and aorta (2.44 ± 0.648) at AP as well as the mean SIRs of portal vein (1.85 ± 0.477) and IVC (1.16 ± 0.187) at PP in the EOB images were significantly lower than those (0.337 ± 0.200, 1.99 ± 0.443, 2.01 ± 0.474, 0.742 ± 0.336, 0.771 ± 0.227, 1.26 ± 0.442, 3.22 ± 1.20, 2.73 ± 0.429, and 1.68 ± 0.366, respectively) in the Gd‐DTPA images (P < 0.05 each). There was no significant difference in mean SIR of liver at PP between EOB (0.529 ± 0.124) and Gd‐DTPA (0.564 ± 0.139). Conversely, the mean SIR of liver at EP was significantly higher with EOB (0.576 ± 0.167) than with Gd‐DTPA (0.396 ± 0.093) (P < 0.001).

Conclusion

Lower arterial vascular and parenchymal enhancement with Gd‐EOB, as compared with Gd‐DTPA, may require reassessment of its dose, despite the higher late venous phase liver parenchymal enhancement. J. Magn. Reson. Imaging 2009;29:636–640. © 2009 Wiley‐Liss, Inc.     

Streamlined flow in the portal vein: demonstration with MR angiography

PURPOSE: To demonstrate whether streamlining of the portal vein flow exists by evaluating the relative distribution of blood flowing from the superior mesenteric vein (SMV) and splenic vein (SV) into the portal venous system. MATERIALS AND METHODS: Fifteen healthy adult volunteers underwent MR angiography of the main portal vein (PV) and portal vein branches after an overnight fast. Transverse two dimension time-of-flight gradient echo sequences were obtained three times, in suspended expiration and inspiration, respectively, as follows: 1) No presaturation slab, 2) presaturation slab across the SMV, 3) presaturation slab across the SV. Signal intensity (SI) measurements were obtained for all acquisitions. using regions of interest traced manually within the PV and portal branches. RESULTS: After presaturation of the SMV and SV during expiration, the overall SI average in the PV decreased by 47% +/- 8 (mean +/- SD) and 17% +/- 9, respectively. Right to left portal branch SI ratio and right-anterior to left-posterior SI ratio in the PV were 0.91 +/- 0.09 and 1.02 +/- 0.08 at baseline, respectively. They decreased significantly (P < 0.05) to 0.87 +/- 0.09 and to 0.95 +/- 0.09 after saturation of the SMV, and increased significantly to 0.95 +/- 0.08 and to 1.07 +/- 0.10 after saturation of the SV. CONCLUSION: MR angiography with selective saturation of the SMV and SV provided reproducible assessment of the respective contributions of the SMV and SV to portal flow, and allows demonstration that streamlining of splanchnic blood occurs in the portal vein of normal subjects.     

Respiratory self‐gating for free‐breathing abdominal phase‐contrast blood flow measurements

Purpose

To demonstrate the feasibility of using a free‐breathing (FB) respiratory self‐gated (RSG) approach for abdominal phase‐contrast (PC) blood flow measurements.

Materials and Methods

PC‐magnetic resonance imaging (MRI) flow measurements were performed within the right renal artery, common hepatic artery, and main portal vein during breath‐hold (BH) and FB with both signal averaging and RSG in eight healthy volunteers. The resultant images were qualitatively scored by two independent reviewers blinded to acquisition techniques. Blood flow volume and cross‐sectional vessel size measurements were compared for three techniques.

Results

The overall efficiency for the RSG‐PC sequence was 38.9% ± 4.7%. Images acquired with RSG effectively mitigated respiratory motion artifacts, which were clearly evident within FB signal‐averaged images. RSG produced similar image quality to that of BH techniques (P > 0.146) and resulted in similar vessel size measurements (P = 0.694). Flow results for both FB RSG and signal‐averaged reconstructions correlated well with BH flow measurements (r = 0.97 and 0.92, P < 0.001). However, only the RSG methods demonstrated excellent absolute agreement with BH‐PC flow measurements (P = 0.600), with signal‐averaged methods resulting in significant overestimations.

Conclusion

RSG methods can limit respiratory motion artifacts to reduce flow measurement inaccuracies during free‐breathing PC measurements in the abdomen. J. Magn. Reson. Imaging 2009;29:860–868. © 2009 Wiley‐Liss, Inc.     

Strain‐encoded cardiac MR during high‐dose dobutamine stress testing: Comparison to cine imaging and to myocardial tagging

Purpose

To investigate regional strain response during high‐dose dobutamine stress cardiac magnetic resonance imaging (DS‐CMR) using myocardial tagging and Strain‐Encoded MR (SENC).

Materials and Methods

Stress induced ischemia was assessed by wall motion analysis, by tagged CMR and by SENC in 65 patients with suspected or known CAD who underwent DS‐CMR in a clinical 1.5 Tesla scanner. Coronary angiography deemed as the standard reference for the presence or absence of CAD (≥50% diameter stenosis) in all patients.

Results

SENC and conventional tagging detected abnormal strain response in six and five additional patients, respectively, who were missed by cine images and proved to have CAD by angiography (P < 0.05 for SENC versus cine, P = 0.06 for tagging versus cine and p = NS for SENC versus tagging). On a per‐vessel level, wall motion analysis on cine images showed high specificity (95%) but moderate sensitivity (70%) for the detection of CAD. Tagging and SENC yielded significantly higher sensitivity of 81% and 89%, respectively (P < 0.05 for tagging and P < 0.01 for SENC versus wall motion analysis, and p = NS for SENC versus tagging), while specificity was equally high (96% and 94%, respectively, P = NS for all).

Conclusion

Both the direct color‐coded visualization of strain on CMR images and the generation of additional visual markers within the myocardium with tagged CMR represent useful adjuncts for DS‐CMR, which may provide incremental value for the detection of CAD in humans. J. Magn. Reson. Imaging 2009;29:1053–1061. © 2009 Wiley‐Liss, Inc.     

Portal venous system: evaluation with unenhanced MR angiography with a single-breath-hold ECG-synchronized 3D half-Fourier fast spin-echo sequence

OBJECTIVE: Eighteen healthy persons underwent unenhanced MR angiography with a breath-hold ECG-synchronized 3D half-Fourier fast spin-echo technique to evaluate the visibility of the portal vein and its branches. CONCLUSION: Our results indicated that unenhanced MR angiography with a singlebreath-hold ECG-synchronized 3D half-Fourier fast spin-echo sequence facilitates precise visualization of the anatomic features of the portal vein and its branches without the use of contrast agents.     

Preoperative detection of prostate cancer: A comparison with 11C‐choline PET, 18F‐fluorodeoxyglucose PET and MR imaging

Purpose:

To compare ¹¹C‐choline positron emission tomography (C‐PET), ¹⁸F‐fluorodeoxyglucose PET (FDG‐PET), and MR imaging in the preoperative detection of prostate cancer.

Materials and Methods:

C‐PET, FDG‐PET, and MR images were obtained in 43 consecutive patients with suspected prostate cancer, and prostate cancers were histopathologically confirmed in 26 patients. Unenhanced T1‐weighted, T2‐weighted, and gadolinium‐enhanced MR images were obtained. C‐PET and FDG‐PET were conducted 1.5 and 60 minutes after injection of 5.5 and 5.0 MBq/kg tracers, respectively. A nuclear and a genitourinary radiologist retrospectively reviewed PET and MR images at random, respectively, and assigned a confidence level for the presence of prostate cancer using a four‐point scale. Diagnostic performance was tested using the McNemar test and receiver operating characteristic curve analysis.

Results:

The sensitivity was greater (P < 0.05) with MR (88%) and C‐PET (73%) images than with FDG‐PET images (31%). The accuracy was greater (P < 0.05) with MR images (88%) than with C‐PET (67%) and FDG‐PET (53%) images. The area‐under‐curve value with MR (0.90) was greater than those with C‐PET (0.53) and FDG‐PET (0.54) images (P < 0.01).

Conclusion:

MR imaging should be primarily performed in the preoperative detection of prostate cancer. C‐PET and FDG‐PET did not improve the detection. J. Magn. Reson. Imaging 2010;31:1151–1156. © 2010 Wiley‐Liss, Inc.     

Non‐contrast‐enhanced MR angiography for selective visualization of the hepatic vein and inferior vena cava with true steady‐state free‐precession sequence and time‐spatial labeling inversion pulses: Preliminary results

Purpose

To selectively visualize the hepatic vein and inferior vena cava (IVC) using three‐dimensional (3D) true steady‐state free‐precession (SSFP) MR angiography with time‐spatial labeling inversion pulse (T‐SLIP), and to optimize the acquisition protocol.

Materials and Methods

Respiratory‐gated 3D true SSFP scans were conducted in 23 subjects in combination with two different T‐SLIPs (one placed in the thorax to suppress the arterial signal and the other in the abdomen to suppress the portal venous signal). One of the most important factors was the inversion time (TI) of abdominal T‐SLIP, and the image quality was evaluated at four different TIs of 800, 1200, 1600, and 2000 msec in terms of relative signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), and mean visualization scores.

Results

No significant difference was observed in SNR and CNR between each TI. However, IVC visualization scores were better at TIs of 1600 and 2000 msec, and overall image quality was better at TIs of 1200 and 1600 msec. Therefore, the TI of 1600 msec was considered to provide the optimal balance between IVC visualization and signal suppression of the portal vein in our protocol.

Conclusion

True SSFP scan with T‐SLIPs enabled selective visualization of the hepatic vein and IVC without an exogenous contrast agent. J. Magn. Reson. Imaging 2009;29:474–479. © 2009 Wiley‐Liss, Inc.     

Gadoxetic acid disodium-enhanced magnetic resonance imaging for biliary and vascular evaluations in preoperative living liver donors: comparison with gadobenate dimeglumine-enhanced MRI

Purpose

To compare gadoxetic acid disodium (Gd‐EOB‐DTPA)‐enhanced magnetic resonance imaging (MRI) with gadobenate dimeglumine (Gd‐BOPTA)‐enhanced MRI in preoperative living liver donors for the evaluation of vascular and biliary variations.

Materials and Methods

Sixty‐two living liver donors who underwent preoperative MRI were included in this study. Thirty‐one patients underwent MRI with Gd‐EOB‐DTPA enhancement, and the other 31 underwent MRI with Gd‐BOPTA enhancement. Two abdominal radiologists retrospectively reviewed dynamic T1‐weighted and T1‐weighted MR cholangiography images and ranked overall image qualities for the depiction of the hepatic artery, portal vein, hepatic vein, and bile duct on a 5‐point scale and determined the presence and types of normal variations in each dynamic phase. Semiquantitative analysis for bile duct visualization was also conducted by calculating bile duct‐to‐liver contrast ratios.

Results

No statistical differences were found between the two contrast media in terms of hepatic artery or bile duct image quality by the two reviewers, or in terms of portal vein image quality by one reviewer (P > 0.05). Gd‐BOPTA provided better image qualities than Gd‐EOB‐DTPA for the depiction of hepatic veins by both reviewers, and for the depiction of portal veins by one reviewer (P < 0.01). The two contrast media‐enhanced images had similar bile duct‐to‐liver contrast ratios (P > 0.05). Regarding diagnostic accuracies with hepatic vascular/biliary branching types, no significant differences were observed between the two contrast media (P > 0.05).

Conclusion

Gd‐EOB‐DTPA could be as useful as Gd‐BOPTA for the preoperative evaluation of living liver donors, and has the advantage of early hepatobiliary phase image acquisition. J. Magn. Reson. Imaging 2011;33:149–159. © 2010 Wiley‐Liss, Inc.     

Three‐dimensional plus time biventricular strain from tagged MR images by phase‐unwrapped harmonic phase

Purpose:

To validate a method called bi‐ventricular strain unwrapped phase (BiSUP) for reconstructing three‐dimensional plus time (3D+t) biventricular strain maps from phase‐unwrapped harmonic phase (HARP) images derived from tagged cardiac magnetic resonance imaging (MRI).

Materials and Methods:

A set of 30 human subjects were imaged with tagged MRI. In each study, HARP phase was computed and unwrapped in each short‐axis and long‐axis image. Inconsistencies in unwrapped phase were resolved using branch cuts manually placed with a graphical user interface. The 3D strain maps were computed independently in each imaged time frame through systole and mid diastole in each study. The BiSUP strain and displacements were compared with those estimated by a 3D feature‐based (FB) technique and a 2D+t HARP technique.

Results:

The standard deviation of the difference between strains measured by the FB and the BiSUP methods was less than 4% of the average of the strains from the two methods. The correlation between peak minimum principal strain measured using the BiSUP and HARP techniques was over 83%.

Conclusion:

The BiSUP technique can reconstruct full 3D+t strain maps from tagged MR images through the cardiac cycle in a reasonable amount of time and user interaction compared with other 3D analysis methods. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Pulmonary vein morphology by free‐breathing whole heart magnetic resonance imaging at 3 tesla versus breathhold multi‐detector computed tomography

Purpose:

To compare pulmonary vein and left atrial anatomy using three‐dimensional free‐breathing whole‐heart magnetic resonance imaging (MR) at 3 Tesla (T) and multi‐detector computed tomography (MDCT).

Materials and Methods:

Thirty‐three subjects (19 male, age 49 ± 12 years) underwent free‐breathing 3T MR and contrast‐enhanced MDCT during inspiratory breath hold. Pulmonary vein parameters (ostial areas, diameters, angles) were measured.

Results:

All pulmonary veins and anomalies were identified by 3T MR and by MDCT. The right‐sided pulmonary veins were directed more posteriorly, the right superior pulmonary vein more inferiorly, and the right inferior pulmonary vein more superiorly by 3T MR when compared with MDCT. The cross‐sectional area, perimeters and minimum diameters of right‐sided pulmonary vein ostia were significantly larger by MR, as were the maximum diameters of right and left inferior pulmonary veins. There were no significant differences between techniques in distance to first pulmonary vein branch.

Conclusion:

Pulmonary vein measurements demonstrated significant differences in angulations and dimensions when 3T MR is compared with MDCT. These differences likely represent hemodynamic and respiratory variation during free‐breathing with MR versus breath‐holding with MDCT. MR imaging at 3T during free‐breathing offers an alternate method to define pulmonary vein and left atrial anatomy without exposure to radiation. J. Magn. Reson. Imaging 2013;37:846–852. © 2012 Wiley Periodicals, Inc.     

High B‐value apparent diffusion‐weighted images from CURVE‐ball DTI

Purpose

To investigate the utility of a proposed clinical diffusion imaging scheme for rapidly generating multiple b‐value diffusion contrast in brain magnetic resonance imaging (MRI) with high signal‐to‐noise ratio (SNR).

Materials and Methods

Our strategy for efficient image acquisition relies on the invariance property of the diffusion tensor eigenvectors to b‐value. A simple addition to the conventional diffusion tensor MR imaging (DTI) data acquisition scheme used for tractography yields diffusion‐weighted images at twice and three times the conventional b‐value. An example from a neurosurgical brain tumor is shown. Apparent diffusion‐weighted (ADW) images were calculated for b‐values 800, 1600, and 2400 s/mm², and a map of excess diffusive kurtosis was computed from the three ADWs.

Results

High b‐value ADW images demonstrated decreased contrast between normal gray and white matter, while the heterogeneity and contrast of the lesion was emphasized relative to conventional b‐value data. Kurtosis maps indicated the deviation from Gaussian diffusive behavior.

Conclusion

DTI data with multiple b‐values and good SNR can be acquired in clinically reasonable times. High b‐value ADW images show increased contrast and add information to conventional DWI. Ambiguity in conventional b‐value images over whether hyperintense signal results from abnormally low diffusion, or abnormally long T₂, is better resolved in high b‐value images. J. Magn. Reson. Imaging 2009;30:243–248. © 2009 Wiley‐Liss, Inc.     

Time‐resolved MR venography of the pulmonary veins precatheter‐based ablation for atrial fibrillation

Purpose:

To evaluate time‐resolved magnetic resonance angiography (TR‐MRA) of the pulmonary venous circulation using the time‐resolved angiography with interleaved stochastic trajectories (TWIST) method and compare it with the more commonly used conventional contrast‐enhanced magnetic resonance angiography (CE‐MRA) approach in atrial fibrillation patients referred for preablation pulmonary vein mapping.

Materials and Methods:

This study was approved by the Institutional Review Board. Twenty‐six patients (15 males; age 59.6 ± 12.7 years) referred for preablation pulmonary vein mapping underwent both conventional CE‐MRA and TR‐MRA with TWIST. Imaging was performed on a 1.5 T (Magnetom Avanto, Siemens Healthcare, Erlangen, Germany) MRI scanner. Source partition and maximum intensity projection (MIP) images were evaluated retrospectively. For quantitative analysis, pulmonary vein ostium orthogonal dimensions were measured using double oblique multiplanar reformatting. The results were analyzed using paired t‐tests, Lin's concordance correlation coefficient, and Bland–Altman plots. For qualitative analysis, both source partition images and MIP images were assessed by two observers (A.P. and M.G.). The presence of common ostiums or accessory veins was recorded and analyzed using unweighted Cohen's kappa. Pulmonary vein conspicuity was scored on a scale of 1–4 (1 = poor, 2 = fair, 3 = good, 4 = excellent) and analyzed using paired t‐tests, intraclass correlation coefficients, and quadratic weighted kappa statistics.

Results:

Orthogonal venous diameters were comparable for both TR‐MRA and conventional CE‐MRA (1.34 ± 0.37 vs. 1.38 cm ± 0.36, respectively). Results of paired t‐tests, Lin's concordance correlation coefficient, and Bland–Altman analysis revealed relatively close comparison between methods. The magnitude of the mean difference for any of the statistical comparisons did not exceed 0.10 cm. The visualization of variant pulmonary vein anatomy was very similar for both techniques. Agreement between techniques was determined to be “good” to “very good” (κ = 0.78–0.85). Conspicuity scores for each pulmonary vein were also very close. Paired t‐tests, intraclass correlation coefficients, and quadratic weighted kappa statistics all revealed strong agreement between methods.

Conclusion:

TR‐MRA using TWIST produces comparable anatomic images and pulmonary venous dimensions to the more widely used CE‐MRA technique. Additionally, the TWIST technique improves arterio‐venous separation, does not need exact bolus timing, requires less gadolinium, and gives additional information on vein perfusion. J. Magn. Reson. Imaging 2013;37:127–137. © 2012 Wiley Periodicals, Inc.     

Angle‐sensitive MRI for quantitative analysis of fiber‐network deformations in compressed cartilage

Purpose

To demonstrate the feasibility of a novel experimental method to quantitatively analyze fiber‐network deformation in compressed cartilage by angle‐sensitive magnetic resonance imaging (MRI) of cartilage.

Methods

Three knee cartilage samples of an adult sheep were imaged in a high‐resolution MRI scanner at 7 T. Main fiber orientation and its “offset” from the direction perpendicular to the bone‐cartilage boundary were derived from MR images taken at different orientations with respect to B₀. Bending of the collagen fibers was determined from weight‐bearing MRI with the load (up to 1.0 MPa) applied over the whole sample surface. A “fascicle” model of the cartilage ultrastructure was assumed to analyze characteristic intensity variations in T₂‐weighted images under load.

Results

T₂‐weighted MR images showed a strong variation of the signal intensities with sample orientation. In the T₂‐weighted weight‐bearing series, regions of high signal intensity underwent shifts from the lateral to the central parts in all three cartilage samples. The bending of the collagen fibers was determined to be 27.2°, 35.4°, and 40.0° per MPa, respectively.

Conclusion

Assuming a “fascicle” model, the presented MRI method provides quantitative measures of structural adjustments in compressed cartilage. Our preliminary analysis suggests that cartilage fiber deformation includes both bending and crimping.