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.     

DWI of the spinal cord with reduced FOV single‐shot EPI

Single‐shot echo‐planar imaging (ss‐EPI) has not been used widely for diffusion‐weighted imaging (DWI) of the spinal cord, because of the magnetic field inhomogeneities around the spine, the small cross‐sectional size of the spinal cord, and the increased motion in that area due to breathing, swallowing, and cerebrospinal fluid (CSF) pulsation. These result in artifacts with the usually long readout duration of the ss‐EPI method. Reduced field‐of‐view (FOV) methods decrease the required readout duration for ss‐EPI, thereby enabling its practical application to imaging of the spine. In this work, a reduced FOV single‐shot diffusion‐weighted echo‐planar imaging (ss‐DWEPI) method is proposed, in which a 2D spatially selective echo‐planar RF excitation pulse and a 180° refocusing pulse reduce the FOV in the phase‐encode (PE) direction, while suppressing the signal from fat simultaneously. With this method, multi slice images with higher in‐plane resolutions (0.94 × 0.94 mm² for sagittal and 0.62 × 0.62 mm² for axial images) are achieved at 1.5 T, without the need for a longer readout. Magn Reson Med 60:468–473, 2008. © 2008 Wiley‐Liss, Inc.     

Fast‐spin‐echo imaging of inner fields‐of‐view with 2D‐selective RF excitations

Purpose:

To demonstrate the feasibility of two‐dimensional selective radio frequency (2DRF) excitations for fast‐spin‐echo imaging of inner fields‐of‐view (FOVs) in order to shorten acquisitions times, decrease RF energy deposition, and reduce image blurring.

Materials and Methods:

Fast‐spin‐echo images (in‐plane resolution 1.0 × 1.0 mm² or 0.5 × 1.0 mm²) of inner FOVs (40 mm, 16 mm oversampling) were obtained in phantoms and healthy volunteers on a 3 T whole‐body MR system using blipped‐planar 2DRF excitations.

Results:

Positioning the unwanted side excitations in the blind spot between the image section and the slice stack to measure yields minimum 2DRF pulse durations (about 6 msec) that are compatible with typical echo spacings of fast‐spin‐echo acquisitions. For the inner FOVs, the number of echoes and refocusing RF pulses is considerably reduced which compared to a full FOV (182 mm) reduces the RF energy deposition by about a factor of three and shortens the acquisition time, e.g., from 39 seconds to 12 seconds for a turbo factor of 15 or from 900 msec to 280 msec for a single‐shot acquisition, respectively. Furthermore, image blurring occurring for high turbo factors as in single‐shot acquisitions is considerably reduced yielding effectively higher in‐plane resolutions.

Conclusion:

Inner‐FOV acquisitions using 2DRF excitations may help to shorten acquisitions times, ameliorate image blurring, and reduce specific absorption rate (SAR) limitations of fast‐spin‐echo (FSE) imaging, in particular at higher static magnetic fields. J. Magn. Reson. Imaging 2010;31:1530–1537. © 2010 Wiley‐Liss, Inc.     

Liver fibrosis: an intravoxel incoherent motion (IVIM) study

Purpose:

To characterize longitudinal changes in molecular water diffusion, blood microcirculation, and their contributions to the apparent diffusion changes using intravoxel incoherent motion (IVIM) analysis in an experimental mouse model of liver fibrosis.

Materials and Methods:

Liver fibrosis was induced in male adult C57BL/6N mice (22–25 g; n = 12) by repetitive dosing of carbon tetrachloride (CCl₄). The respiratory‐gated diffusion‐weighted (DW) images were acquired using single‐shot spin‐echo EPI (SE‐EPI) with 8 b‐values and single diffusion gradient direction. True diffusion coefficient (D_true), blood pseudodiffusion coefficient (D_pseudo), and perfusion fraction (P_fraction) were measured. Diffusion tensor imaging (DTI) was also performed for comparison. Histology was performed with hematoxylin‐eosin and Masson's trichrome staining.

Results:

A significant decrease in D_true was found at 2 weeks and 4 weeks following CCl₄ insult, as compared with that before insult. Similarly, D_pseudo values before injury was significantly higher than those at 2 weeks and 4 weeks after CCl₄ insult. Meanwhile, P_fraction values showed no significant differences over different timepoints. For DTI, significant decrease in ADC was observed following CCl₄ administration. Fractional anisotropy at 2 weeks after CCl₄ insult was significantly lower than that before insult, and subsequently normalized at 4 weeks after the insult. Liver histology showed collagen deposition, the presence of intracellular fat vacuoles, and cell necrosis/apoptosis in livers with CCl₄ insult.

Conclusion:

Both molecular water diffusion and blood microcirculation contribute to the alteration in apparent diffusion changes in liver fibrosis. Reduction in D_true and D_pseudo values resulted from diffusion and perfusion changes, respectively, during the progression of liver fibrosis. IVIM analysis may serve as valuable and robust tool in detecting and characterizing liver fibrosis at early stages, monitoring its progression in a noninvasive manner. J. Magn. Reson. Imaging 2012;36:159–167. © 2012 Wiley Periodicals, Inc.     

Effect of shot number on the calculated apparent diffusion coefficient in phantoms and in human liver in diffusion‐weighted echo‐planar imaging

Purpose

To show the signal intensity varies with shot number in diffusion‐weighted (DW) echo‐planar imaging (EPI) and affects apparent diffusion coefficient (ADC) calculation.

Materials and Methods

This prospective study was performed on 35 adult patients and 20 volunteers. Measurements were made on a 3T scanner using a breathhold DW spin‐echo EPI (SE EPI) sequence. Three protocols were used: A) eight consecutive shots at a fixed b‐value of 0 seconds/mm² with TR = 1000 and 3000 msec; B) seven consecutive shots at b‐values = 0, 1000, 750, 500, 250, 100, 0 seconds/mm² (in that order) with TR = 3500 msec; and C) seven consecutive shots (as in B) with TR = 1000, 1750, and 7000 msec.

Results

For protocol A, signal intensity decreased significantly from the first to second shot (P<0.0001) and thereafter remained constant. For protocol B, the ADC depended on which b = 0 seconds/mm² image was used. Using the first b = 0 seconds/mm², the mean ADC was 15% higher than using the second b = 0 seconds/mm² (P<0.0001). For protocol C, the difference between ADC using the first b = 0 seconds/mm² and the second b = 0 seconds/mm² decreased as the TR increased.

Conclusion

The signal intensity can vary with shot number in SE EPI. For TR ≥ 3000 msec, steady‐state is attained after one shot. Using data acquired prior to steady‐state confounds the calculation of ADC values. J. Magn. Reson. Imaging 2009;30:547–553. © 2009 Wiley‐Liss, Inc.     

3D steady‐state diffusion‐weighted imaging with trajectory using radially batched internal navigator echoes (TURBINE)

While most diffusion‐weighted imaging (DWI) is acquired using single‐shot diffusion‐weighted spin‐echo echo‐planar imaging, steady‐state DWI is an alternative method with the potential to achieve higher‐resolution images with less distortion. Steady‐state DWI is, however, best suited to a segmented three‐dimensional acquisition and thus requires three‐dimensional navigation to fully correct for motion artifacts. In this paper, a method for three‐dimensional motion‐corrected steady‐state DWI is presented. The method uses a unique acquisition and reconstruction scheme named trajectory using radially batched internal navigator echoes (TURBINE). Steady‐state DWI with TURBINE uses slab‐selection and a short echo‐planar imaging (EPI) readout each pulse repetition time. Successive EPI readouts are rotated about the phase‐encode axis. For image reconstruction, batches of cardiac‐synchronized readouts are used to form three‐dimensional navigators from a fully sampled central k‐space cylinder. In vivo steady‐state DWI with TURBINE is demonstrated in human brain. Motion artifacts are corrected using refocusing reconstruction and TURBINE images prove less distorted compared to two‐dimensional single‐shot diffusion‐weighted‐spin‐EPI. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.     

Diffusion‐weighted imaging of the liver: Comparison of navigator triggered and breathhold acquisitions

Purpose

To compare a free breathing navigator triggered single shot echoplanar imaging (SS EPI) diffusion‐weighted imaging (DWI) sequence with prospective acquisition correction (PACE) with a breathhold (BH) DWI sequence for liver imaging.

Materials and Methods

Thirty‐four patients were evaluated with PACE‐DWI and BH DWI of the liver using b‐values of 0, 50, and 500 s/mm². There were 29 focal liver lesions in 18 patients. Qualitative evaluation was performed on a 3‐point scale ( 1 - 3 ) by two independent observers (maximum score 9). Quantitative evaluation included estimated SNR (signal to noise ratio), lesion‐to‐liver contrast ratio, liver and lesion apparent diffusion coefficients (ADCs), and coefficient of variation (CV) of ADC in liver parenchyma and focal liver lesions (estimate of noise contamination in ADC).

Results

PACE‐DWI showed significantly better image quality, higher SNR and lesion‐to‐liver contrast ratio when compared with BH DWI. ADCs of liver and focal lesions with both sequences were significantly correlated (r = 0.838 for liver parenchyma, and 0.904 for lesions, P < 0.0001), but lower with the BH sequence (P < 0.02). There was higher noise contamination in ADC measurement obtained with BH DWI (with a significantly higher SD and CV of ADC).

Conclusion

The use of a navigator echo to trigger SS EPI DWI improves image quality and liver to lesion contrast, and enables a more precise ADC quantification compared with BH DWI acquisition. J. Magn. Reson. Imaging 2009;30:561–568. © 2009 Wiley‐Liss, Inc.     

Comparison of ferucarbotran‐enhanced fluid‐attenuated inversion‐recovery echo‐planar,T2‐weighted turbo spin‐echo,T2*‐weighted gradient‐echo,and diffusion‐weighted echo‐planar imaging for detection of malignant liver lesions

Purpose:

To compare the diagnostic accuracy of superparamagnetic iron oxide (SPIO)‐enhanced fluid‐attenuated inversion‐recovery echo‐planar imaging (FLAIR EPI) for malignant liver tumors with that of T2‐weighted turbo spin‐echo (TSE), T2*‐weighted gradient‐echo (GRE), and diffusion‐weighted echo‐planar imaging (DW EPI).

Materials and Methods:

SPIO‐enhanced magnetic resonance imaging (MRI) that included FLAIR EPI, T2‐weighted TSE, T2*‐weighted GRE, and DW EPI sequences was performed using a 3 T system in 54 consecutive patients who underwent surgical exploration with intraoperative ultrasonography. A total of 88 malignant liver tumors were evaluated. Images were reviewed independently by two blinded observers who used a 5‐point confidence scale to identify lesions. Results were correlated with results of histopathologic findings and surgical exploration with intraoperative ultrasonography. The accuracy of each MRI sequence was measured with jackknife alternative free‐response receiver operating characteristic analysis. The sensitivity of each observer with each MRI sequence was compared with McNemar's test.

Results:

Accuracy values were significantly higher with FLAIR EPI sequence (0.93) than with T2*‐weighted GRE (0.80) or DW EPI sequences (0.80) (P < 0.05). Sensitivity was significantly higher with the FLAIR EPI sequence than with any of the other sequences.

Conclusion:

SPIO‐enhanced FLAIR EPI sequence was more accurate in the diagnosis of malignant liver tumors than T2*‐weighted GRE and DW EPI sequences. SPIO‐enhanced FLAIR EPI sequence is helpful for the detection of malignant liver tumors. J. Magn. Reson. Imaging 2010;31:607–616. ©2010 Wiley‐Liss, Inc.     

Contiguous‐slice zonally oblique multislice (CO‐ZOOM) diffusion tensor imaging: Examples of in vivo spinal cord and optic nerve applications

Purpose

To describe and demonstrate a new technique that allows diffusion tensor imaging of small structures such as the spinal cord (SC) and optic nerve (ON) with contiguous slices and reduced image distortions using a narrow field of view (FOV).

Materials and Methods

Images were acquired with a modified single‐shot echo‐planar imaging (EPI) sequence that contains a refocusing radio frequency (RF) pulse in the presence of the phase‐encoding (rather than slice‐select) gradient. As a result, only a narrow volume may be both excited and refocused, removing the problem of signal aliasing for narrow FOVs. Two variants of this technique were developed: cardiac gating is included in the study of the SC to reduce pulsation artifacts, whereas inversion‐recovery (IR) cerebrospinal fluid (CSF) suppression is utilized in the study of the ON to eliminate partial volume effects. The technique was evaluated with phantoms, and mean diffusivity (MD) and fractional anisotropy (FA) measurements were made in the SC and ON of two healthy volunteers.

Results

The technique provides contiguous‐slice, reduced‐FOV images that do not suffer from aliasing and have reduced magnetic susceptibility artifacts. MD and FA values determined here lie within the ranges quoted in the literature.

Conclusion

Contiguous‐slice zonally orthogonal multislice (CO‐ZOOM‐EPI is a new technique for diffusion‐weighted imaging of small structures such as the ON and SC with high resolution and reduced distortions due to susceptibility variations. This technique is able to acquire contiguous slices that may allow further nerve‐tracking analyses. J. Magn. Reson. Imaging 2009;29:454–460. © 2009 Wiley‐Liss, Inc.     

Diffusion-weighted imaging of the abdomen at 3.0 Tesla: image quality and apparent diffusion coefficient reproducibility compared with 1.5 Tesla

Purpose

To compare single‐shot echo‐planar imaging (SS EPI) diffusion‐weighted MRI (DWI) of abdominal organs between 1.5 Tesla (T) and 3.0T in healthy volunteers in terms of image quality, apparent diffusion coefficient (ADC) values, and ADC reproducibility.

Materials and Methods

Eight healthy volunteers were prospectively imaged in this HIPAA‐compliant IRB‐approved study. Each subject underwent two consecutive scans at both 1.5 and 3.0T, which included breathhold and free‐breathing DWI using a wide range of b‐values (0 to 800 s/mm²). A blinded observer rated subjective image quality (maximum score= 8), and a separate observer placed regions of interest within the liver, renal cortices, pancreas, and spleen to measure ADC at each field strength. Paired Wilcoxon tests were used to compare abdominal DWI between 1.5T and 3.0T for specific combinations of organs, b‐values, and acquisition techniques.

Results

Subjective image quality was significantly lower at 3.0T for all comparisons (P = 0.0078– 0.0156). ADC values were similar at 1.5T and 3.0T for all assessed organs, except for lower liver ADC at 3.0T using b0‐500‐600 and breathhold technique. ADC reproducibility was moderate at both 1.5T and 3.0T, with no significant difference in coefficient of variation of ADC between field strengths.

Conclusion

Compared with 1.5T, SS EPI at 3.0T provided generally similar ADC values, however, with worse image quality. Further optimization of abdominal DWI at 3.0T is needed. J. Magn. Reson. Imaging 2011;33:128–135. © 2010 Wiley‐Liss, Inc.     

Improving the performance of diffusion-weighted inner field-of-view echo-planar imaging based on 2D-selective radiofrequency excitations by tilting the excitation plane

Purpose:

To improve the performance and flexibility of diffusion‐weighted inner field‐of‐view (FOV) echo‐planar imaging (EPI) based on 2D‐selective radiofrequency (RF) excitations by 1) using higher gradient amplitudes for outer excitation lines, and 2) tilting the excitation plane such that the unwanted side excitations do not overlap with the current image slice or other slices to be acquired.

Materials and Methods:

Acquisitions with a conventional (untilted) and the improved setup were compared and inner FOV diffusion tensor measurements were performed in the human brain and spinal cord with voxel sizes of 1.0 × 1.0 × 5.0 mm³ and 0.6 × 0.6 × 5.0 mm³ on a 3 T whole‐body magnetic resonance imaging (MRI) system.

Results:

With the modified setup, the 2D‐selective RF excitations can be considerably shortened (e.g., from 26 msec to 6 msec) which 1) avoids profile distortions in the presence of magnetic field inhomogeneities, and 2) reduces the required echo time and increases the signal‐to‐noise ratio accordingly, e.g., by about 20% in the spinal cord.

Conclusion:

Tilting the excitation plane and applying variable gradient amplitudes improves the applicability of inner FOV EPI based on 2D‐selective RF excitations. J. Magn. Reson. Imaging 2012;35:984–992. © 2011 Wiley Periodicals, Inc.     

Diagnosis of cirrhosis with intravoxel incoherent motion diffusion MRI and dynamic contrast‐enhanced MRI alone and in combination: Preliminary experience

Purpose:

To report our preliminary experience with the use of intravoxel incoherent motion (IVIM) diffusion‐weighted magnetic resonance imaging (DW‐MRI) and dynamic contrast‐enhanced (DCE)‐MRI alone and in combination for the diagnosis of liver cirrhosis.

Materials and Methods:

Thirty subjects (16 with noncirrhotic liver, 14 with cirrhosis) were prospectively assessed with IVIM DW‐MRI (n = 27) and DCE‐MRI (n = 20). IVIM parameters included perfusion fraction (PF), pseudodiffusion coefficient (D*), true diffusion coefficient (D), and apparent diffusion coefficient (ADC). Model‐free DCE‐MR parameters included time to peak (TTP), upslope, and initial area under the curve at 60 seconds (IAUC60). A dual input single compartmental perfusion model yielded arterial flow (Fa), portal venous flow (Fp), arterial fraction (ART), mean transit time (MTT), and distribution volume (DV). The diagnostic performances for diagnosis of cirrhosis were evaluated for each modality alone and in combination using logistic regression and receiver operating characteristic analyses. IVIM and DCE‐MR parameters were compared using a generalized estimating equations model.

Results:

PF, D*, D, and ADC values were significantly lower in cirrhosis (P = 0.0056–0.0377), whereas TTP, DV, and MTT were significantly increased in cirrhosis (P = 0.0006–0.0154). There was no correlation between IVIM‐ and DCE‐MRI parameters. The highest Az (areas under the curves) values were observed for ADC (0.808) and TTP‐DV (0.952 for each). The combination of ADC with DV and TTP provided 84.6% sensitivity and 100% specificity for diagnosis of cirrhosis.

Conclusion:

The combination of DW‐MRI and DCE‐MRI provides an accurate diagnosis of cirrhosis. J. Magn. Reson. Imaging 2010;31:589–600. © 2010 Wiley‐Liss, Inc.     

Whole‐brain single‐shot STEAM DTI at 4 Tesla utilizing transverse coherences for enhanced SNR

Diffusion tensor imaging is an important method for noninvasively acquiring structural information of the human brain. For advanced fiber tracking, the acquisition of diffusion‐weighted (DW) images has to be performed along many different spatial directions, resulting in long scan times. Therefore, the ultra‐fast imaging method, echo‐planar imaging (EPI), is mostly used, but this technique suffers from susceptibility‐induced image artefacts and geometric distortions. These problems become even more pronounced at very high magnetic field strengths. In this regard, DW, single‐shot STEAM is an interesting and rapid imaging alternative to EPI‐based methods. DW single‐shot STEAM enables the acquisition of artefact‐free images albeit at the expense of a reduced signal‐to‐noise ratio (SNR), which can be compensated by utilizing high magnetic fields. Here, the application of DW single‐shot STEAM at 4 Tesla is demonstrated. To optimize the SNR and the resolution properties, a new variable flip‐angle computational algorithm is introduced enabling accurate signal evolution computation with a precise calculation of transverse coherences. Omission of radiofrequency (RF) spoiling results in an approximate twofold increase of the DW signal by integration of the stable refocused transverse magnetization. The advantage of the approach is shown in simulations and in vivo experiments. Magn Reson Med 61:372–380, 2009. © 2009 Wiley‐Liss, Inc.     

Ability of diffusion-weighted imaging for the differential diagnosis between chronic expanding hematomas and malignant soft tissue tumors

Purpose

To evaluate the potential of diffusion‐weighted imaging (DWI) in distinguishing chronic expanding hematomas (CEHs) from malignant soft tissue tumors.

Materials and Methods

We performed conventional MRI and DWI of six CEHs and 31 malignant soft tissue tumors from 37 patients seen between May 2000 and November 2006. DWI was obtained with a single‐shot echo‐planar imaging (EPI) sequence using a 1.5T MR imager. The mean apparent diffusion coefficient (ADC) value was also calculated. We evaluated MRI findings of CEHs and compared ADC value of CEHs with malignant soft tissue tumors.

Results

On conventional MRI, two of six CEHs were difficult to differentiate from malignant soft tissue tumors based on imaging findings. The mean ADC value of CEHs and malignant soft tissue tumors was 1.55 ± 0.121 × 10^?3 mm²/sec and 0.92 ± 0.139 × 10^?3 mm²/sec (mean ± SD), respectively. The mean ADC value of CEHs was significantly higher than that of malignant soft tissue tumors (P < 0.01). There was no overlap in the minimum ADC values among CEHs and malignant soft tissue tumors.

Conclusion

DWI is useful for differentiating between CEHs and malignant soft tissue tumors. J. Magn. Reson. Imaging 2008;28:1195–1200. © 2008 Wiley‐Liss, Inc.

     

Usefulness of diffusion-weighted imaging for differentiating between desmoid tumors and malignant soft tissue tumors

Purpose

To evaluate the usefulness of diffusion‐weighted imaging (DWI) for differentiating between desmoid tumors and malignant soft tissue tumors.

Materials and Methods

Conventional MRI and DWI were performed for 8 desmoid tumors and 74 malignant soft tissue tumors. DWI was obtained with a single‐shot echo‐planar imaging sequence using a 1.5 Tesla (T) MR imager. DW images were acquired with motion‐probing gradient pulses applied along three directions (x, y, and z axes) with three b‐factors (0, 500, and 1000 s/mm²). Two observers blinded to clinical information measured three regions of interest within the solid tumor and selected a minimum apparent diffusion coefficient () in each lesion. The mean ADC of desmoid tumors was calculated and compared with that of malignant soft tissue tumors using the Mann‐Whitney U test.

Results

The mean ADC of desmoid tumors and malignant soft tissue tumors was 1.36 ± 0.48 × 10⁻³ mm²/s and 0.88 ± 0.20 × 10⁻³ mm²/s (mean ± SD), respectively. The mean ADC of the desmoid tumors was significantly higher than that of malignant soft tissue tumors (P < 0.01).

Conclusion

DWI is considered to be useful for differentiating between desmoid tumors and malignant soft tissue tumors. In the future, further investigation in a large series is necessary. J. Magn. Reson. Imaging 2011;33:189–193. © 2010 Wiley‐Liss, Inc.

     

Magnetization transfer (MT) asymmetry around the water resonance in human cervical spinal cord

Purpose

To demonstrate the presence of magnetization transfer (MT) asymmetry in human cervical spinal cord due to the interaction between bulk water and semisolid macromolecules (conventional MT), and the chemical exchange dependent saturation transfer (CEST) effect.

Materials and Methods

MT asymmetry in the cervical spinal cord (C3/C4–C5) was investigated in 14 healthy male subjects with a 3T magnetic resonance (MR) system. Both spin‐echo (SE) and gradient‐echo (GE) echo‐planar imaging (EPI) sequences, with low‐power off‐resonance radiofrequency irradiation at different frequency offsets, were used.

Results

Our results show that the z‐spectrum in gray/white matter (GM/WM) is asymmetrical about the water resonance frequency in both SE‐EPI and GE‐EPI, with a more significant saturation effect at the lower frequencies (negative frequency offset) far away from water and at the higher frequencies (positive offset) close to water. These are attributed mainly to the conventional MT and CEST effects respectively. Furthermore, the amplitude of MT asymmetry is larger in the SE‐EPI sequence than in the GE‐EPI sequence in the frequency range of amide protons.

Conclusion

Our results demonstrate the presence of MT asymmetry in human cervical spinal cord, which is consistent with the ones reported in the brain. J. Magn. Reson. Imaging 2009;29:523–528. © 2009 Wiley‐Liss, Inc.     

Can the IVIM model be used for renal perfusion imaging?

Objective: Renal perfusion imaging may provide information about the hemodynamic significance of a renal artery stenosis and could improve noninvasive characterization when combined with angiography. It was proposed previously that diffusion sequences could provide useful perfusion indices based on the intravoxel incoherent motion (IVIM) model. Owing to motion artifacts, diffusion imaging has been restricted to relatively immobile organs like the brain. With the availability of single-shot echo-planar imaging (EPI) our purpose was to evaluate the IVIM model in renal perfusion. Methods and material: Eight volunteers underwent diffusion-sensitive magnetic resonance (MR) imaging of the kidneys using a spin echo (SE) EPI sequence. The diffusion coefficients determined by a linear regression analysis and fits to the IVIM function were calculated. Results and conclusion: Our preliminary experience does not support the possibility of obtaining perfusion information using the IVIM model in the kidneys.     

Diffusion-tensor MRI reveals the complex muscle architecture of the human forearm

Purpose:

To design a time‐efficient patient‐friendly clinical diffusion tensor MRI protocol and postprocessing tool to study the complex muscle architecture of the human forearm.

Materials and Methods:

The 15‐minute examination was done using a 3 T system and consisted of: T₁‐weighted imaging, dual echo gradient echo imaging, single‐shot spin‐echo echo‐planar imaging (EPI) diffusion tensor MRI. Postprocessing comprised of signal‐to‐noise improvement by a Rician noise suppression algorithm, image registration to correct for motion and eddy currents, and correction of susceptibility‐induced deformations using magnetic field inhomogeneity maps. Per muscle one to five regions of interest were used for fiber tractography seeding. To validate our approach, the reconstructions of individual muscles from the in vivo scans were compared to photographs of those dissected from a human cadaver forearm.

Results:

Postprocessing proved essential to allow muscle segmentation based on combined T₁‐weighted and diffusion tensor data. The protocol can be applied more generally to study human muscle architecture in other parts of the body.

Conclusion:

The proposed protocol was able to visualize the muscle architecture of the human forearm in great detail and showed excellent agreement with the dissected cadaver muscles. J. Magn. Reson. Imaging 2012;36:237–248. © 2012 Wiley Periodicals, Inc.     

Diffusion‐weighted echo‐planar magnetic resonance imaging for the assessment of tumor cellularity in patients with soft‐tissue sarcomas

Purpose

To investigate the eligibility of diffusion‐weighted imaging (DWI) for the evaluation of tumor cellularity in patients with soft‐tissue sarcomas.

Materials and Methods

Thirty consecutive patients with a total of 31 histologically‐proven soft‐tissue sarcomas prospectively underwent magnetic resonance imaging (MRI) including DWI with echo‐planar imaging (EPI) technique immediately before open biopsy (N = 1) or tumor resection (N = 30). Fourteen patients had no previous anticancer treatment, 16 had received neoadjuvant therapy. Tumor cellularity as determined from histological sections was compared with minimum apparent diffusion coefficient (ADC).

Results

Tumor cellularity correlated well with minimum ADC in a linear fashion, with a Pearson correlation coefficient of –0.88 (95% confidence interval [CI]: –0.75 to –0.96). This relationship was not influenced by prior anticancer treatment. There was only a tendency toward lower ADC in tumor with higher grading but no significant dependency (P = 0.08).

Conclusion

DWI has proven useful for the assessment of tumor cellularity in soft‐tissue sarcomas. In result, DWI may be used as a powerful noninvasive tool to monitor responses of cytotoxic treatment as reflected by changes in tumor cellularity. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.     

Robust GRAPPA‐accelerated diffusion‐weighted readout‐segmented (RS)‐EPI

Readout segmentation (RS‐EPI) has been suggested as a promising variant to echo‐planar imaging (EPI) for high‐resolution imaging, particularly when combined with parallel imaging. This work details some of the technical aspects of diffusion‐weighted (DW)‐RS‐EPI, outlining a set of reconstruction methods and imaging parameters that can both minimize the scan time and afford high‐resolution diffusion imaging with reduced distortions. These methods include an efficient generalized autocalibrating partially parallel acquisition (GRAPPA) calibration for DW‐RS‐EPI data without scan time penalty, together with a variant for the phase correction of partial Fourier RS‐EPI data. In addition, the role of pulsatile and rigid‐body brain motion in DW‐RS‐EPI was assessed. Corrupt DW‐RS‐EPI data arising from pulsatile nonlinear brain motion had a prevalence of ～7% and were robustly identified via k‐space entropy metrics. For DW‐RS‐EPI data corrupted by rigid‐body motion, we showed that no blind overlap was required. The robustness of RS‐EPI toward phase errors and motion, together with its minimized distortions compared with EPI, enables the acquisition of exquisite 3 T DW images with matrix sizes close to 512². Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.