New look at renal vasculature: 7 tesla nonenhanced T1-weighted FLASH imaging

Purpose:

To investigate the feasibility of 7 Tesla (T) nonenhanced high field MR imaging of the renal vasculature and to evaluate the diagnostic potential of various nonenhanced T1‐weighted (T1w) sequences.

Materials and Methods:

Twelve healthy volunteers were examined on a 7T whole‐body MR system (Magnetom 7T, Siemens Healthcare Sector) using a custom‐built eight‐channel radiofrequency (RF) transmit/receive body coil. Subsequent to RF shimming, the following sequences were acquired (i) fat‐saturated two‐dimensional (2D) FLASH, (ii) fat‐saturated 3D FLASH, and a (iii) fat‐saturated 2D time‐of‐flight MR angiography (TOF MRA). SNR and CNR were measured in the aorta and both renal arteries. Qualitative analysis was performed with regard to vessel delineation (5‐point scale: 5 = excellent to 1 = nondiagnostic) and presence of artifacts (5‐point scale: 5 = no artifact present to 1 = strong impairment).

Results:

The inherently high signal intensity of the renal arterial vasculature in T1w imaging enabled moderate to excellent vessel delineation in all sequences. Qualitative (mean, 4.7) and quantitative analysis (SNR_mean: 53.9; CNR_mean: 28.0) demonstrated the superiority of TOF MRA, whereas 2D FLASH imaging provided poorest vessel delineation and was most strongly impaired by artifacts (overall impairment 3.7). The 3D FLASH MRI demonstrated its potential for fast high quality imaging of the nonenhanced arterial vasculature, providing homogeneous hyperintense vessel signal.

Conclusion:

Nonenhanced T1w imaging in general and, TOF MRA in particular, appear to be promising techniques for good quality nonenhanced renal artery assessment at 7 Tesla. J. Magn. Reson. Imaging 2012;36:714–721. © 2012 Wiley Periodicals, Inc.     

CE‐MRA of the lower extremities using HYPR stack‐of‐stars

Purpose

To investigate the properties of HYPR (HighlY constrained back PRojection) processing—the temporal fidelity and the improvements of spatial/temporal resolution—for contrast‐enhanced MR angiography in a pilot study of the lower extremities in healthy volunteers.

Materials and Methods

HYPR processing with a radial three‐dimensional (3D) stack‐of‐stars acquisition was investigated for contrast‐enhanced MR angiography of the lower extremities in 15 healthy volunteers. HYPR images were compared with control images acquired using a fast, multiphase, 2D Cartesian method to verify the temporal fidelity of HYPR. HYPR protocols were developed for achieving either a high frame update rate or a minimal slice thickness by adjusting the acquisition parameters. HYPR images were compared with images obtained using 3D TRICKS, a widely used protocol in dynamic 3D MRA.

Results

HYPR images showed good temporal agreement with 2D control images. In comparison with TRICKS, HYPR stack‐of‐stars demonstrated higher spatial and temporal resolution. High radial undersampling factors for each time frame were permitted, typically approximately 50 to 100 compared with fully sampled radial imaging.

Conclusion

In this feasibility study, HYPR processing has been demonstrated to improve the spatial or temporal resolution in peripheral CE‐MRA. J. Magn. Reson. Imaging 2009;29:917–923. © 2009 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.     

Respiratory motion compensated MR cholangiopancreatography at 3.0 Tesla

Purpose:

To reduce irregular respiratory motion‐induced artifacts in free‐breathing prospective navigator‐triggered three‐dimensional (3D) MR cholangiopancreatography (MRCP).

Materials and Methods:

A reference respiration model was estimated from the first‐five respiration periods during the initial navigator scan. With the navigator information acquired before and after triggering, the un‐acquired diaphragm position during the actual imaging was interpolated using the amplitude‐scaled reference model. Craniocaudal translational motion during imaging was retrospectively corrected using the estimated diaphragm position. T2‐weighted 3D MRCP data were acquired from 17 healthy volunteers. For quantitative analysis, contrast‐to‐noise ratio (CNR) and relative contrast (RC) of the biliary tree and gallbladder were compared using the paired t‐test.

Results:

The CNR and RC of the biliary tree and gallbladder were significantly higher (P < 0.05) in the maximum intensity projection images after motion compensation.

Conclusion:

The proposed algorithm can be an effective tool to reduce the irregular respiratory motion‐induced artifacts in 3D MRCP imaging. J. Magn. Reson. Imaging 2010;32:726–732. © 2010 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.     

Improved time‐of‐flight magnetic resonance angiography with IDEAL water‐fat separation

Purpose

To implement IDEAL (iterative decomposition of water and fat using echo asymmetry and least squares estimation) water‐fat separation with 3D time‐of‐flight (TOF) magnetic resonance angiography (MRA) of intracranial vessels for improved background suppression by providing uniform and robust separation of fat signal that appears bright on conventional TOF‐MRA.

Materials and Methods

IDEAL TOF‐MRA and conventional TOF‐MRA were performed in volunteers and patients undergoing routine brain MRI/MRA on a 3T magnet. Images were reviewed by two radiologists and graded based on vessel visibility and image quality.

Results

IDEAL TOF‐MRA demonstrated statistically significant improvement in vessel visibility when compared to conventional TOF‐MRA in both volunteer and clinical patients using an image quality grading system. Overall image quality was 3.87 (out of 4) for IDEAL versus 3.55 for conventional TOF imaging (P = 0.02). Visualization of the ophthalmic artery was 3.53 for IDEAL versus 1.97 for conventional TOF imaging (P < 0.00005) and visualization of the superficial temporal artery was 3.92 for IDEAL imaging versus 1.97 for conventional TOF imaging (P < 0.00005).

Conclusion

By providing uniform suppression of fat, IDEAL TOF‐MRA provides improved background suppression with improved image quality when compared to conventional TOF‐MRA methods. J. Magn. Reson. Imaging 2009;29:1367–1374. © 2009 Wiley‐Liss, Inc.     

Image analysis in time-resolved large field of view 3D MR-angiography at 3T

Purpose

To qualitatively and quantitatively evaluate the image quality in accelerated time‐resolved 3D contrast‐enhanced MR angiography (tr‐CE‐MRA) at 3T.

Materials and Methods

In all, 113 MRA were performed in 107 patients on a 3T MR system after written informed consent and approval by the ethics committee. Twenty consecutive thoracic (n = 87) or craniocervical (n = 26) 3D data volumes were acquired. The timeframes with maximum arterial and venous contrast were determined and a total of 663 arterial and venous segments were analyzed by two blinded observers. Diagnostic image quality was graded by applying a 0 (low) to 3 (excellent) scale. Additionally, local signal‐to‐noise (SNR) and contrast‐to‐noise ratios (relative CNR) were evaluated.

Results

Tr‐CE‐MRA was successfully performed in all patients. Good to excellent image quality (2.42 ± 0.31) was observed in all individuals with preserved discrimination of arteries (2.43 ± 0.48) and veins (2.20 ± 0.56). Minor image degradation due to artifacts (2.62 ± 0.25) and constantly high vascular signal and contrast were detected. There was a significant superiority of coronal orientation during thoracic MRA (P < 0.05). In 18 cases tr‐CE‐MRA provided additional information on vascular pathologies.

Conclusion

Large field of view tr‐CE‐MRA enables constantly high‐quality thoracic and craniocervical angiographies. In addition, the dynamics of tr‐CE‐MRA can offer additional information on vascular pathologies. J. Magn. Reson. Imaging 2008;28:1116–1124. © 2008 Wiley‐Liss, Inc.     

Proton resonance frequency shift-weighted imaging for monitoring MR-guided high-intensity focused ultrasound transmissions

Purpose:

To combine temperature‐related information of phase images and magnitude images acquired from an MR spoiled gradient echo sequence using a postprocessing method referred to as PRF‐shift‐weighted imaging (PRFSWI).

Materials and Methods:

Phase images are capable of detecting shifts in proton resonance frequency (PRF) caused by local changes in temperature. Magnitude images provide anatomical information for treatment planning and positioning as well as temperature‐related contrast. We used PRFSWI to produce a phase‐mask and performed multiplication on the magnitude image to increase temperature‐related contrast.

Results:

Through MRI‐guided focused ultrasound (MRIgFUS) experiments (both ex vivo and in vivo), we determined that PRFSWI is capable of enhancing the contrast of a heated area even in the initial stages of transmitting high‐intensity focused ultrasound energy.

Conclusion:

The PRFSWI images are sensitive to changes in temperature and display the heated spot directly in the magnitude images. Although the images do not provide quantitative data related to temperature, this method could be used as a complement to the phase temperature mapping method in the real‐time monitoring of MRIgFUS experiments. J. Magn. Reson. Imaging 2011;33:1474–1481. © 2011 Wiley‐Liss, Inc.     

Four-dimensional phase contrast MRI with accelerated dual velocity encoding

Purpose:

To validate a novel approach for accelerated four‐dimensional phase contrast MR imaging (4D PC‐MRI) with an extended range of velocity sensitivity.

Materials and Methods:

4D PC‐MRI data were acquired with a radially undersampled trajectory (PC‐VIPR). A dual V_enc (dV_enc) processing algorithm was implemented to investigate the potential for scan time savings while providing an improved velocity‐to‐noise ratio. Flow and velocity measurements were compared with a flow pump, conventional 2D PC MR, and single V_enc 4D PC‐MRI in the chest of 10 volunteers.

Results:

Phantom measurements showed excellent agreement between accelerated dV_enc 4D PC‐MRI and the pump flow rate (R² ≥ 0.97) with a three‐fold increase in measured velocity‐to‐noise ratio (VNR) and a 5% increase in scan time. In volunteers, reasonable agreement was found when combining 100% of data acquired with V_enc = 80 cm/s and 25% of the high V_enc data, providing the VNR of a 80 cm/s acquisition with a wider velocity range of 160 cm/s at the expense of a 25% longer scan.

Conclusion:

Accelerated dual V_enc 4D PC‐MRI was demonstrated in vitro and in vivo. This acquisition scheme is well suited for vascular territories with wide ranges of flow velocities such as congenital heart disease, the hepatic vasculature, and others. J. Magn. Reson. Imaging 2012;35:1462–1471. © 2012 Wiley Periodicals, Inc.     

Preoperative evaluation of pancreatic cancer: Comparison of gadolinium‐enhanced dynamic MRI with MR cholangiopancreatography versus MDCT

Purpose

To determine the accuracy of magnetic resonance imaging (MRI) including dynamic imaging using three‐dimensional gradient‐echo (3D‐GRE) sequences and MR cholangiopancreatograpy (MRCP) compared with that of multidetector row CT (MDCT) with regard to resectability in pancreas cancer.

Materials and Methods

From February 2004 to July 2008, 54 patients (32 men, 22 women: age range, 28–83 years; mean age, 63.1 years old) with surgically proven pancreatic carcinoma, who had undergone preoperative gadolinium‐enhanced 3D‐GRE MRI with MRCP and triple‐phase MDCT, were included in this retrospective study. Two, clinically experienced attending radiologists independently reviewed the two image sets. These readers evaluated the tumor conspicuity, presence of vascular invasion, choledochal and duodenal invasion, lymph node metastases, distant metastasis, and tumor resectability. The results were compared with the surgical and histopathologic findings using receiver operating characteristic analysis (Az) and kappa statistics.

Results

Curative resections were performed on 42 patients. Regarding the tumor conspicuity, MRI had a significantly higher Az value compared with MDCT according to both reviewers (P < 0.05). The accuracy of resectability was Az = 0.753 and 0.768 on MRI and Az = 0.829 and 0.762 on MDCT for each reviewer, and the difference in the accuracy of resectability was not significant between MRI and MDCT for either reviewer (P > 0.05). Two imaging sets showed a similar diagnostic performance in the evaluation of vascular involvement, lymph node metastasis, and distant metastasis.

Conclusion

Dynamic 3D‐GRE MRI with MRCP shows superior tumor conspicuity and similar diagnostic performance compared with MDCT in evaluating the resectability of pancreatic cancer. J. Magn. Reson. Imaging 2009;30:586–595. © 2009 Wiley‐Liss, Inc.     

Three‐dimensional dynamic time‐resolved contrast‐enhanced MRA using parallel imaging and a variable rate k‐space sampling strategy in intracranial arteriovenous malformations

Purpose

To evaluate the effectiveness of three‐dimensional (3D) dynamic time‐resolved contrast‐enhanced MRA (TR‐CE‐MRA) using a combination of a parallel imaging technique (ASSET: array spatial sensitivity encoding technique) and a time‐resolved method (TRICKS: time‐resolved imaging of contrast kinetics) and to compare it with 3D dynamic TR‐CE‐MRA using ASSET alone in the assessment of intracranial arteriovenous malformations (AVMs).

Materials and Methods

Twenty consecutive patients with angiographically confirmed AVMs were investigated using both 3D dynamic TR‐CE‐MRA techniques. Examinations were compared with respect to image quality, spatial resolution, number and type of feeders and drainers, nidus size, presence of early venous filling and temporal resolution. Digital subtraction angiography was used as standard of reference.

Results

The higher temporal and spatial resolution of 3D dynamic TR‐CE‐MRA TRICKS ASSET allowed a better assessment of intracranial vascular malformations, namely better depiction of feeders, drainers and better detection of early venous drainage. There was no significant difference between them in terms of nidus size.

Conclusion

3D dynamic TR‐CE‐MRA combining parallel imaging and a time‐resolved method with subsecond and submillimeter resolution could become the first‐line investigation technique in both diagnosis and follow‐up of intracranial AVMs. J. Magn. Reson. Imaging 2009;29:7–12. © 2008 Wiley‐Liss, Inc.     

MR angiography of the cerebral perforating arteries with magnetization prepared anatomical reference at 7T: Comparison with time‐of‐flight

Purpose

To develop a magnetic resonance imaging (MRI) protocol that visualizes both the perforating arteries and the related anatomy in a single acquisition at 7T.

Material and Methods

T₁‐weighted magnetization prepared imaging (MPRAGE) was empirically modified for use as angiography method at 7T. The resulting sequence depicts the vasculature simultaneously with the surrounding anatomical structures, and is referred to as “magnetization prepared anatomical reference MRA” (MPARE‐MRA). The method was compared to time‐of‐flight (TOF) MRA in seven healthy subjects. The conspicuity of the perforating arteries and the contrast between gray and white matter were evaluated both quantitatively by contrast‐to‐noise (CNR) measurements, and qualitatively by two radiologists who scored the images.

Results

The contrast‐to‐noise ratio (CNR) between blood and background was 28 ± 9 for MPARE‐MRA and 35 ± 16 for TOF‐MRA, indicating good conspicuity of the vessels. CNR values were: internal capsule (IC) vs. caudate head (CH): 4.2 ± 0.7; IC vs. putamen: 3.5 ± 0.6; white matter vs. gray matter: 9.7 ± 2.5.

Conclusion

The benefits of ultra‐high‐field MRI can transform MPRAGE into a new angiography method to image small vessels and associated parenchyma at the same time. This technique can be used to study the correlation between tissue damage and vascular pathology. J. Magn. Reson. Imaging 2008;28:1519–1526. © 2008 Wiley‐Liss, Inc.     

Time‐resolved three‐dimensional magnetic resonance digital subtraction angiography without contrast material in the brain: Initial investigation

Purpose

To evaluate a novel magnetic resonance (MR) angiography (MRA) of three‐dimensional (3D) MR digital subtraction angiography (MRDSA) without contrast material, which is essentially 3D true steady‐state free precession (SSFP) with selected inversion recovery (IR) pulse using multiple cardiac phase acquisitions with a short increment delay in the assessment of normal cranial arteries, as a feasibility study before clinical use.

Materials and Methods

Serial MRA images using 3D MRDSA without contrast material were acquired from 10 healthy volunteers. Visualization of normal cranial arteries with time‐spatial labeling inversion pulse (Time‐SLIP) MRDSA was qualitatively compared with the conventional MRA method, 3D time‐of‐flight (TOF)‐MRA.

Results

In all volunteers, serial 3D MRDSAs containing hemodynamic information were successfully imaged. The results of visualization of the branches of the cranial arteries with Time‐SLIP MRDSA were comparable to those of 3D TOF‐MRA. The mean scores ± standard deviations for normal cerebral arteries (internal carotid arteries, middle cerebral arteries, anterior cerebral arteries, posterior cerebral arteries, and basilar arteries) were 2.4 ± 0.5, 2.3 ± 0.5, 2.0 ± 0.7, 2.3 ± 0.7, and 2.5 ± 0.7, respectively.

Conclusion

Time‐SLIP 3D MRDSA is a simple method for obtaining hemodynamic information. Although more MR sequence improvement is needed, it can play an important role in assessing cranial arteries without contrast material. J. Magn. Reson. Imaging 2009;30:214–218. © 2009 Wiley‐Liss, Inc.     

Practical signal-to-noise ratio quantification for sensitivity encoding: application to coronary MR angiography

Purpose:

To develop and evaluate a practical method for the quantification of signal‐to‐noise ratio (SNR) on coronary MR angiograms (MRA) acquired with parallel imaging.

Materials and Methods:

To quantify the spatially varying noise due to parallel imaging reconstruction, a new method has been implemented incorporating image data acquisition followed by a fast noise scan during which radiofrequency pulses, cardiac triggering and navigator gating are disabled. The performance of this method was evaluated in a phantom study where SNR measurements were compared with those of a reference standard (multiple repetitions). Subsequently, SNR of myocardium and posterior skeletal muscle was determined on in vivo human coronary MRA.

Results:

In a phantom, the SNR measured using the proposed method deviated less than 10.1% from the reference method for small geometry factors (≤2). In vivo, the noise scan for a 10 min coronary MRA acquisition was acquired in 30 s. Higher signal and lower SNR, due to spatially varying noise, were found in myocardium compared with posterior skeletal muscle.

Conclusion:

SNR quantification based on a fast noise scan is a validated and easy‐to‐use method when applied to three‐dimensional coronary MRA obtained with parallel imaging as long as the geometry factor remains low. J. Magn. Reson. Imaging 2011;33:1330–1340. © 2011 Wiley‐Liss, Inc.     

Non‐contrast renal artery MRA using an inflow inversion recovery steady state free precession technique (Inhance): Comparison with 3D contrast‐enhanced MRA

Purpose:

To assess the performance of a three‐dimensional (3D) non‐contrast respiratory‐triggered steady state free precession (SSFP) pulse sequence for detection of renal artery stenosis.

Materials and Methods:

A total of 64 patients who had non‐contrast MR angiography (NC MRA) and 3D contrast‐enhanced MRA (CE MRA) performed during the same exam and three patients who had NC MRA followed by conventional catheter angiography within one month of the MRI exam were included in this retrospective study. Two blinded readers evaluated NC MRA images for the presence of significant renal artery stenosis and also rated their diagnostic confidence and evaluated the images for artifact. A similar analysis was performed for CE MRA images by two additional blinded readers, and discrepancies were resolved by consensus reading.

Results:

The 67 patients had 168 main and accessory renal arteries, with significant (>50%) stenosis in 34 arteries on CE MRA or conventional angiography. The two NC MRA readers had sensitivity and specificity for detection of significant stenosis of 94%/82% and 82%/87% respectively on a per renal artery basis.

Conclusion:

There was good agreement between CE MRA and NC MRA for detection of significant renal artery stenosis. This technique should prove useful in evaluating patients with suspected renovascular hypertension who are unable to undergo CE MRA. J. Magn. Reson. Imaging 2010;31:1411–1418. © 2010 Wiley‐Liss, Inc.     

Flow‐sensitive 4D MRI of the thoracic aorta: Comparison of image quality,quantitative flow,and wall parameters at 1.5 T and 3 T

Purpose:

To evaluate the effect of field strength on flow‐sensitive 4D magnetic resonance imaging (MRI) of the thoracic aorta. A volunteer study at 1.5 T and 3 T was conducted to compare phase‐contrast MR angiography (MRA) and 3D flow visualization quality as well as quantification of aortic hemodynamics.

Materials and Methods:

Ten healthy volunteers were examined by flow‐sensitive 4D MRI at both 1.5 T and 3 T MRI with identical imaging parameters (TE/TR = 6/5.1 msec, spatial/temporal resolution ≈2 mm/40.8 msec). Analysis included assessment of image quality of derived aortic 3D phase contrast (PC) angiography and 3D flow visualization (semiquantitative grading on a 0–2 scale, two blinded observers) and quantification of blood flow velocities, net flow per cardiac cycle, wall shear stress (WSS), and velocity noise.

Results:

Quality of 3D blood flow visualization (average grading = 1.8 ± 0.4 at 3 T vs. 1.1 ± 0.7 at 1.5 T) and the depiction of aortic lumen geometry by 3D PC‐MRA (1.7 ± 0.5 vs. 1.2 ± 0.6) were significantly (P < 0.01) improved at 3 T while velocity noise was significantly higher (P < 0.01) at 1.5 T. Velocity quantification resulted in minimally altered (0.05 m/s, 3 mL/cycle and 0.01 N/m²) but not statistically different (P = 0.40, P = 0.39, and P = 0.82) systolic peak velocities, net flow, and WSS for 1.5 T compared to 3 T.

Conclusion:

Flow‐sensitive 4D MRI at 3 T provided improved image quality without additional artifacts related to higher fields. Imaging at 1.5 T MRI, which is more widely available, was also feasible and provided information on aortic 3D hemodynamics of moderate quality with identical performance regarding quantitative analysis. J. Magn. Reson. Imaging 2012;36:1097–1103. © 2012 Wiley Periodicals, Inc.     

Comprehensive MR evaluation of renal disease: Added clinical value of quantified renal perfusion values over single MR angiography

Purpose:

To evaluate the diagnostic accuracy of quantified renal perfusion parameters in identifying and differentiating renovascular from renal parenchymal disease.

Materials and Methods:

In all, 27 patients underwent renal perfusion measurements on a 3.0 T magnetic resonance imaging (MRI) system. Imaging was performed with a saturation recovery TurboFLASH sequence (TR/TE 177/0.93 msec, flip angle 12°, 5 slices/sec). All patients also underwent high‐resolution MR angiography (MRA) (TR/TE 3.1/1.09, flip angle 23°, spatial resolution 0.9 × 0.8 × 0.9 mm³). MR perfusion measurements were analyzed with a two‐compartment model, quantifying the plasma flow (F_P)—a characteristic renal first‐pass perfusion parameter. A receiver‐operator characteristic analysis was used to determine the optimal threshold value for distinguishing normal and abnormal plasma flow values. Utilizing this cutoff, sensitivity and specificity of solitary MR perfusion measurements, MRA, and a diagnostic strategy combining the two were evaluated.

Results:

Quantified MR perfusion values yielded a sensitivity of 100% and a specificity of 85% utilizing the optimal plasma flow threshold value of 150 mL/100 mL/min, whereas single MRA achieved a sensitivity of 51.9% and a specificity of 90%. Combining both methods enabled improved detection of renovascular and renoparenchymal disease with a sensitivity of 96.3% and specificity of 90%.

Conclusion:

In distinction to MRA, quantified MR perfusion measurements allow for the detection of pure renal parenchymal disorders. The combination of MRA with these perfusion measurements suggests an algorithm by which parenchymal and renovascular diseases may be reliably distinguished and the hemodynamic significance of the latter reliably determined. J. Magn. Reson. Imaging 2010;31:125–133. © 2009 Wiley‐Liss, Inc.     

Magnetic resonance imaging findings of the mass-forming type of autoimmune pancreatitis: comparison with pancreatic adenocarcinoma

Purpose:

To determine the characteristic magnetic resonance imaging (MRI) features of mass‐forming autoimmune pancreatitis (AIP), which allow its differentiation from pancreatic adenocarcinoma (PAC).

Materials and Methods:

MR images of 37 patients with either pathologically proven, mass‐forming AIPs (n = 9) or PACs (n = 28) were retrospectively reviewed. The pancreatic MR protocol included unenhanced images, contrast‐enhanced dynamic images, diffusion‐weighted imaging (DWI), and MR‐cholangiopancreatography (MRCP). Two reviewers analyzed the MR images regarding the number, location, morphologic features, and enhancement degree and pattern of the lesions as well as secondary changes of the pancreatic parenchyma, the biliary and pancreatic ducts. The size and apparent diffusion coefficient (ADC) values of the lesions were measured.

Results:

Although sensitivities were low (28.6%–44.4%), specificities of multiplicity, capsule‐like rim enhancement, and skipped stricture of the biliary or pancreatic duct in mass‐forming AIP were high (100%). Sensitivities and specificities of irregular or geographic shape, delayed enhancement, and a low ADC value <1.26 × 10^?3 mm²/s in mass‐forming AIP were favorable (71.4%–83.3% and 78.5%–89.3%).

Conclusion:

Although to differentiate mass‐forming AIP from pancreatic cancer is difficult, the combination of MRI findings including contrast‐enhanced dynamic images, MRCP, and DWI can be a help. J. Magn. Reson. Imaging 2012;36:188–197. © 2012 Wiley Periodicals, Inc.

     

Imaging of the wrist at 1.5 Tesla using isotropic three-dimensional fast spin echo cube

Purpose:

To compare three‐dimensional fast spin echo Cube (3D‐FSE‐Cube) with conventional 2D‐FSE in MR imaging of the wrist.

Materials and Methods:

The wrists of 10 volunteers were imaged in a 1.5 Tesla MRI scanner using an eight‐channel wrist coil. The 3D‐FSE‐Cube images were acquired in the coronal plane with 0.5‐mm isotropic resolution. The 2D‐FSE images were acquired in both coronal and axial planes for comparison. An ROI was placed in fluid, cartilage, and muscle for SNR analysis. Comparable coronal and axial images were selected for each sequence, and paired images were randomized and graded for blurring, artifact, anatomic details, and overall image quality by three blinded musculoskeletal radiologists.

Results:

SNR of fluid, cartilage and muscle at prescribed locations were higher using 3D‐FSE‐Cube, without reaching statistical significance. Fluid–cartilage CNR was also higher with 3D‐FSE‐Cube, but not statistically significant. Blurring, artifact, anatomic details, and overall image quality were significantly better on coronal 3D‐FSE‐Cube images (P < 0.001), but significantly better on axial 2D‐FSE images compared with axial 3D‐FSE‐Cube reformats (P < 0.01).

Conclusion:

Isotropic data from 3D‐FSE‐Cube allows reformations in arbitrary scan planes, which may make multiple 2D acquisitions unnecessary, and improve depiction of complex wrist anatomy. However, axial reformations suffer from blurring, likely due to T2 decay during the long echo train, limiting overall image quality in this plane. J. Magn. Reson. Imaging 2011;33:908–915. © 2011 Wiley‐Liss, Inc.     

Non‐invasive visualization of basilar artery perforators with 7T MR angiography

Purpose:

To visualize the perforating arteries originating from basilar artery (BA) by using ultra‐high resolution 7T MR angiography (MRA) and optimizing MR parameters as well as radio frequency (RF) coils, which may provide important information for neurosurgery and understanding diseases of the pons, but was unable to clearly visualize with conventional MRA techniques.

Materials and Methods:

Seven healthy volunteers (five males and two females, age [mean ± SD] = 28.71 ± 7.54 years) were scanned using optimized MR parameters to obtain images of pontine arteries (PAs) originating from the main trunk of BA. Two different volume coils and a phased array coil were designed and compared for this study. The images obtained at 7T MRA were compared with those at 1.5T and 3T MRA.

Results:

The results showed that PA imaging at 7T MRI consistently provided clearly identifiable vessels, which were difficult to visualize in MR angiograms obtained at 1.5T and 3T MRIs. Volume RF coils had higher sensitivity for the center of the brain, which enhanced PA imaging compared to phased array coil. The average number of PA branches in all seven subjects observable by 7T MRA was 7.14 ± 2.79, and the visualized PA branches were found to mainly propagating on the surface of the pons.

Conclusion:

We have demonstrated that ultra‐high resolution 7T MRA could delineate the PAs using optimized imaging parameters and volume RF coils compared to commercially available 1.5T and 3T MRIs. J. Magn. Reson. Imaging 2010;32:544–550. © 2010 Wiley‐Liss, Inc.