Single-shot Spin-echo Echo-planar Imaging Research Articles

Motion Correction of Multi-b-value Diffusion-weighted Imaging in the Liver

Motion artifacts are a significant source of error in the acquisition and quantification of parameters from multi-b-value diffusion-weighted imaging (DWI). The objective of this article is to present a reliable method to reduce motion-related artifacts during free-breathing at higher b-values when signal levels are low. Twelve patients referred for magnetic resonance imaging of the liver underwent a clinical magnetic resonance imaging examination of the abdominal region that included DWI. Conventional single-shot spin-echo echo planar imaging acquisitions of the liver during free breathing were repeated in a "time-resolved" manner during a single acquisition to obtain data for multi-b-value analysis, alternating between low and high b-values. Image registration using a normalized mutual information similarity measure was used to correct for spatial misalignment of diffusion-weighted volumes caused by motion. Registration error was estimated indirectly by comparing the normalized root-mean-square error (NRMSE) values of data fitted to the biexponential intra-voxel incoherent motion model before and after motion correction. Regions of interest (ROIs) were selected in the liver close to the surface of the liver and close to internal structures such as large bile ducts and blood vessels. For the 12 patient datasets, the mean NRMSE value for the motion-corrected ROIs (0.38 ± 0.16) was significantly lower than the mean NRMSE values for the non-motion-corrected ROIs (0.41 ± 0.13) (P < .05). In cases where there was substantial respiratory motion during the acquisition, visual inspection verified that the algorithm markedly improved alignment of the liver contours between frames. The proposed method addresses motion-related artifacts to increase robustness in multi-b-value acquisitions.

Correction: Quantification of Hepatic Iron Concentration in Chronic Viral Hepatitis: Usefulness of T2-weighted Single-Shot Spin-Echo Echo-Planar MR Imaging

Correction: Quantification of Hepatic Iron Concentration in Chronic Viral Hepatitis: Usefulness of T2-weighted Single-Shot Spin-Echo Echo-Planar MR Imaging

EADC Values in Diagnosis of Renal Lesions by 3.0 T Diffusion-Weighted Magnetic Resonance Imaging: Compared with the ADC Values

Exponential apparent diffusion coefficient (EADC) is an indicator of diffusion-weighted imaging (DWI) and reflects the pathological changes of tissues quantitatively. However, no study has been investigated in the space-occupying kidney disease using EADC values. This study aims to evaluate the diagnostic role of EADC values at a high magnetic field strength (3.0 T) in kidney neoplastic lesions, compared with that of the ADC values. Ninety patients with suspected renal tumors (including 101 suspected renal lesions) and 20 healthy volunteers were performed MRI scanning. Diffusion-weighted imaging was performed with a single-shot spin-echo echo-planar imaging (SE-EPI) sequence at a diffusion gradient of b = 500 s/mm2. We found renal cell carcinoma (RCC) can be distinguished from angiomyolipoma, and clear cell carcinoma can be distinguished from non-clear cell carcinoma by EADC value. There was significant difference in overall EADC values between renal cell carcinoma (0.150 ± 0.059) and angiomyolipoma (0.270 ± 0.108) when b value was 500 s/mm2. When receiver operating characteristic (ROC) was higher than 0.192, the sensitivity and specificity of EADC value of renal cell carcinoma were 84.6 and 81.1 %, respectively. In conclusion, EADC map shows the internal structure of the kidney tumor more intuitively than the ADC map dose, and is also in line with the observation habits of the clinicians. EADC can be used as an effective imaging method for tumor diagnosis.

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. © 2012 Wiley Periodicals, Inc.

Su1240 Magnetic Resonance Elastography (MRE) of the Pancreas, a Feasibility Study in Healthy Volunteers

Background: MRE is a non-invasive advanced imaging technique utilizing wave propagation to characterize the In Vivo mechanical properties of tissue, including stiffness, in organs such as the liver. MRE of the pancreas has not been thoroughly studied, but could provide a non-invasive tool for assessing pancreatic pathology such as pancreatitis, solid and cystic pancreatic masses. Aims: To determine the feasibility of MRE of the pancreas and establish normal ranges for tissue density of the normal pancreas. Methods: IRB approval was obtained. Stage 1: MRE of the pancreas was performed in 12 healthy volunteers with a 2-D gradientecho (GRE) sequence. An acoustic driver (AD) system delivered 40 HZ vibrations into the abdomen via a plastic drum secured via an elastic belt and powered pneumatically by a speaker located outside of the scan room. In an attempt to optimize wave propagation, the AD was placed over the liver, pancreas and left flank with the patient supine, and over the mid back with patient prone. MR elastograms were generated using an inversion algorithm to yield quantitative images of tissue stiffness in kilopascals (kPa). Stage 2: 3-D MRE was performed in 12 healthy volunteers using a flow-compensated single-shot spin-echo planar imaging (EPI) acquisition with motion encoding performed sequentially in the X, Y, and Z directions. Processing of the measured 3D displacement field was performed by first calculating the 3D vector curl of the displacement field and then using a 3D local frequency estimation (LFE) algorithm to calculate the tissue stiffness from the curl data. The pancreas was manually segmented using the MRE magnitude images and the mean stiffness in kilopascals (kPa) was recorded. Results: Stage 1: With the 2D MRE technique, there was poor pancreatic wave propagation at all AD locations including patient supine and prone for all 12 volunteers. This precluded accurate mean shear pancreatic stiffness calculation. Stage 2: With 3D MRE technique (image 1), 10 of 12 volunteers had adequate pancreatic wave propagation, with calculated mean shear hepatic stiffness of 1.04 ± 0.25 kPa (range 0.861.25 kPa). Of the 2 with poor wave propagation, one had BMI >30 kg/m2, and one had an atrophic pancreas. Conclusions: MRE of the pancreas is feasible, but requires 3D image sequencing to obtain adequate elastograms to calculate tissue stiffness. Further refinements in the technology are required to obtain consistent elastograms, including for patients with obesity or pancreatic atrophy. Ongoing investigations include determining the variation in stiffness within regions of the pancreas and to compare the normal pancreas with the spectrum of pancreatic diseases including pancreatic cancer, pancreatic cysts, acute and chronic pancreatitis.

Quantification of Hepatic Iron Concentration in Chronic Viral Hepatitis: Usefulness of T2-weighted Single-Shot Spin-Echo Echo-Planar MR Imaging

ObjectiveTo investigate the usefulness of single-shot spin-echo echo-planar imaging (SSEPI) sequence for quantifying mild degree of hepatic iron stores in patients with viral hepatitis.MethodsThis retrospective study included 34 patients with chronic viral hepatitis/cirrhosis who had undergone histological investigation and magnetic resonance imaging with T2-weighted gradient-recalled echo sequence (T2-GRE) and diffusion-weighted SSEPI sequence with b-factors of 0 s/mm2 (T2-EPI), 500 s/mm2 (DW-EPI-500), and 1000 s/mm2 (DW-EPI-1000).The correlation between the liver-to-muscle signal intensity ratio, which was generated by regions of interest placed in the liver and paraspinous muscles of each sequence image, and the hepatic iron concentration (µmol/g dry liver), which was assessed by spectrophotometry, was analyzed by linear regression using a spline model. Akaike information criterion (AIC) was used to select the optimal model.ResultsMean ± standard deviation of the hepatic iron concentration quantified by spectrophotometry was 24.6±16.4 (range, 5.5 to 83.2) µmol/g dry liver. DW-EPI correlated more closely with hepatic iron concentration than T2-GRE (R square values: 0.75 for T2-EPI, 0.69 for DW-EPI-500, 0.62 for DW-EPI-1000, and 0.61 for T2-GRE, respectively, all P<0.0001). Using the AIC, the regression model for T2-EPI generated by spline model was optimal because of lowest cross validation error.ConclusionT2-EPI was sensitive to hepatic iron, and might be a more useful sequence for quantifying mild degree of hepatic iron stores in patients with chronic viral hepatitis.

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

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. The 15-minute examination was done using a 3 T system and consisted of: T(1) -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. Postprocessing proved essential to allow muscle segmentation based on combined T(1) -weighted and diffusion tensor data. The protocol can be applied more generally to study human muscle architecture in other parts of the body. 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.

Liver fibrosis: An intravoxel incoherent motion (IVIM) study

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. Liver fibrosis was induced in male adult C57BL/6N mice (22-25 g; n = 12) by repetitive dosing of carbon tetrachloride (CCl(4) ). 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. A significant decrease in D(true) was found at 2 weeks and 4 weeks following CCl(4) 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 CCl(4) insult. Meanwhile, P(fraction) values showed no significant differences over different timepoints. For DTI, significant decrease in ADC was observed following CCl(4) administration. Fractional anisotropy at 2 weeks after CCl(4) 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 CCl(4) insult. 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.

The Role Of Diffusion-Weighted Mr Imaging And Adc Values In The Diagnosis Of Gastric Tumors

The aim of this study was to investigate the role of diffusion-weighted MR imaging (DWI) in the diagnosis of gastric tumors by means of measuring the apparent diffusion coefficient (ADC) values of these lesions, and making a comparison with the endoscopic biopsy results. Seventy patients having gastric tumor constituted the case group. For the control group 30 healthy individuals were included. Abdominal MRI examinations were performed with a 1,5 Tesla unit. DWI examinations were obtained by single shot spin echoplanar imaging. The ADC was measured based on the tissue of the gastric tumoral entities and normal gastric mucosa in the control group. Mean ADC values were 0,84 +/- 0,17 x 10(-3) mm2/s and 1,79 +/- 0,08 x 10 mm2/s in gastric tumor group and in control group, respectively, being statistically significant (p<0.05).There was no significance among ADC values of adenocarcinoma subgroups. The comparison of the ADC values in the adenocarcinoma and lymphoma cases were also found to be statistically significant. DWI is beneficial in the diagnosis of malignant gastric lesions by the aid of ADC measurements. Although ADC quantification seems to be invaluable in the evaluation of histopathologic subgroups of adenocarcinoma, it can help in the diagnosis of gastric lymphoma.

Differentiation of Malignant From Benign Pheochromocytomas With Diffusion-Weighted and Dynamic Contrast-Enhanced Magnetic Resonance at 3.0 T

To retrospectively evaluate the usefulness of the apparent diffusion coefficients (ADCs) and dynamic contrast-enhanced magnetic resonance (MR) imaging for differentiation of malignant from benign pheochromocytomas at 3.0-T MR. The Institutional Review Board approved this retrospective study, and informed consent was waived. Forty patients with pheochromocytomas underwent diffusion-weighted (DW) MR imaging in addition to T1- and T2-weighted sequences, chemical shift imaging techniques, and dynamic contrast-enhanced MR imaging at 3.0-T MR imaging system. In each patient, precontrast single-shot spin-echo echo-planar DW imaging was performed with b values of 0 and 800 seconds/mm². In each patient, 3-dimensional fat-saturated T1-weighted dynamic contrast-enhanced MR imaging was performed at baseline (precontrast), during the arterial phase, and 1, 2, 3, and 5 minutes after contrast injection. Diagnosis was based on pathologic findings in surgical specimens. Independent samples t test was used to compare ADCs of benign and malignant pheochromocytomas. Receiver operating characteristic curve analysis was used to test the ability of ADCs in differentiating malignant from benign pheochromocytomas. Differences in dynamic contrast-enhanced patterns between malignant and benign pheochromocytomas were analyzed. Pathologic diagnoses revealed that 29 pheochromocytomas (three from both adrenal glands of the same patient) were benign and 13 were malignant. With b values of 0 and 800 seconds/mm², mean ± SD ADC of malignant pheochromocytomas ([1.175 ± 0.132] × 10⁻³ mm²/s) was larger than that of benign ones ([0.918 ± 0.124] × 10⁻³ mm²/s), and the difference was significant (P < 0.001). Apparent diffusion coefficients obtained with b values of 0 and 800 seconds/mm² were effective for distinguishing malignant from benign pheochromocytomas (area under the receiver operating characteristic curve, 0.906): A threshold value of 1.016 × 10⁻³ mm²/s permitted distinction with high sensitivity (93.3%) and specificity (77.8%). In dynamic contrast-enhanced MR imaging, malignant pheochromocytomas got peak signal intensity earlier (at arterial phase) than benign ones (at 1 minute after contrast injection). In our limited study, ADCs in DW imaging with b values of 0 and 800 seconds/mm and dynamic contrast-enhanced pattern of malignant pheochromocytomas were significantly different from that of benign ones, suggesting that DW imaging and dynamic contrast-enhanced MR imaging may be useful in preoperative characterization and prognosis of pheochromocytomas, especially for those without obvious metastasis and vascular invasion.

Diffusion-Weighted MR Imaging before and after Contrast Enhancement with Superparamagnetic Iron Oxide for Assessment of Hepatic Metastasis

PurposeThe purpose of our study was to validate diffusion-weighted MRI (DWI) before and after superparamagnetic iron oxide (SPIO) injection for assessment of hepatic metastases.Materials and MethodsEighty-six hepatic metastases (size range, 0.3-4.7 cm; mean, 1.5 cm) verified pathologically or by follow-up imaging studies in 22 consecutive patients (17 men and 5 women; 44-83 years; mean age, 60 years) during a 13-month period were enrolled. Hepatic MRI, including DWI (b-factors=50, 400, 800 s/mm2) with breath-holding technique of single-shot spin-echo echo-planar imaging (TR/TE=1000/69 ms, average=2) before and after SPIO administration, were retrospectively reviewed by two independent radiologists with a 5-point scale confidence score for each hepatic lesion on pre-contrast DWI (pre-DWI), SPIO-enhanced DWI (SPIO-DWI), and SPIO-enhanced T2*-weighted imaging (SPIO-T2*wI).ResultsFor all lesions, SPIO-T2*wI showed significantly higher confidence score in the diagnosis of hepatic metastases than pre-contrast or SPIO-DWI regardless of the size of b-factors (p<0.05) with only one exception; using b-factor=50 s/mm2, the score of SPIO-T2*wI was still higher than SPIO-DWI but there was no statistical significance given by observer 1 (p=0.730). For the subcentimeter lesions (n=37), SPIO-T2*wI showed the highest score, and using b-factor=50 or 400 s/mm2 SPIO-DWI showed similar confidence scores to SPIO-T2*wI by both observers (p>0.05). Pre-DWI using b-factor=50 sec/mm2 was also comparable with SPIO-T2*wI by observer 1 (p=0.060).ConclusionPre-DWI has a limited value for the assessment of hepatic metastases, however, the repetition of DWI after SPIO injection using small b-factors could complement SPIO-T2*wI, especially for subcentimeter lesions.

Evaluation ofT2values and apparent diffusion coefficient of the masseter muscle by clenching

The aim of this study was to evaluate the changes in T2 values and apparent diffusion coefficient (ADC) in the masseter muscle by clenching in healthy volunteers. 37 volunteers were enrolled in the study. We measured bite force using pressure-sensitive paper and a T2 map. The ADC map was obtained at rest, during clenching, immediately after and 5 min after clenching. The spin-echo sequence was used to calculate T2, and single-shot spin-echo echo planar imaging was used to calculate the ADC. The motion-probing gradients (MPGs) were applied separately along the posterior-to-anterior (PA), right-to-left (RL) and superior-to-inferior (SI) directions, with b values of 0, 300 and 600 s mm(-2) in each direction. ADC-PA, ADC-RL, and ADC-SI values were obtained, and we calculated the ADC-iso for the mean diffusivity. There were no significant differences between the stronger and weaker sides of bite force before, during or 5 min after clenching for T2 and ADC. The bite force had little effect on these parameters; thus, we used the average of the two sides for the following analyses. Time course analysis of ADC-iso, ADC-PA, ADC-RL and ADC-SI demonstrated a marked increase after clenching and a rapid decrease immediately after clenching, although they did not completely return to the initial values; however, the change in ADC-RL was significantly greater than those in ADC-PA or ADC-SI (P<0.001 each). The changes in T2 were similar to those of ADC, although not as marked. ADC (especially ADC-RL) was altered by contraction of the masseter muscle.

The value of apparent diffusion coefficient values of cerebellar and the middle cerebellar peduncles in differential diagnosis of multiple system atrophy and Parkinson disease

Objective To evaluate the apparant diffusion coefficient (ADC) values of cerebellar and the middle cerebellar peduncles in the differential diagnosis of multiple system atrophy (MSA) and Parkinson disease (PD). Methods Conventional MRI and DWI were performed in 18 clinically proved MSA patients with 7 cases of early cases (early-stage MSA group), 19 PD patients (PD group) and 18 agematched normal controls (the control group). DWI was performed using a single shot-spin echo-echo planar imaging sequences, and ADC values were measured in the ROIs (0. 16 cm2) of the bilateral cerebellum, the middle cerebellar peduncles and cerebral white matter. Then one way ANOVA test was used for statistical analysis. Results Of the 18 MSA patients, 11 had MR abnormalities, 8 had hot-cross bun sign in the pens on T2-weighted images, 11 patients had pontine, cerebellar and medulla oblongata atrophy, 10 patients had atrophy of the middle cerebellar peduncles, 2 patients had hyperintense rim of the putamen and putaminal atrophy on T2-weighted images. The ADC values in the middle cerebellar peduncles were significantly increased in the MSA group[ (0. 98 ±0. 07) × 103 mm2/s] and early-stnge MSA group [ (0. 95 ±0. 05) ×103 mm2/s] as compared to PD group [ (0. 77 ±0. 04) × 103 mm2/s] and control group[ (0. 78 ±0. 04) ×103 mm2/s]. There was statistical significant difference among them (F = 91.049,55. 301, P ＜ 0.01 ).There was no overlap in the distribution of ADC values of the middle cerebellar peduncles among the MSA group [ (0.86-1.13 ) × 103 mm2/s ], early-stage MSA group [ (0. 86-1.02 ) × 103 mm2/s ] and PD group [ (0. 68-0. 84) × 103 mm2/s] and the control group [ (0. 69-0. 82) × 103 mm2/s]. The ADC values in the cerebellum were significantly increased in the MSA group[ (0. 95 ±0. 09) × 103 mm2/s] and early-stage MSA group [ (0. 92 ±0. 07) × 103 mm2/s] as compared to PD group [ (0. 78 ±0. 05) × 103 mm2/s] and control group[ (0. 79 ± 0. 05 ) × 103 mm2/s ]. Statistically significant difference was found among them (F =39. 274,18. 623 ,P ＜0. 01 ). There was overlap in the distribution of ADC values of the cerebellum [ MSAgroup(0. 80-1.10) × 103 mm2/s,early stage MSA group (0. 80-0. 99) × 103 mm2/s,PD group(0. 72-0. 90) × 103 mm2/s,control group (0. 71-0. 87) × 103 mm2/s]. There was no significant difference among the ADC values of MSA group, MSA group(early stages) and PD group and the control group in the cerebral white matter( P ＞ 0. 05 ). Conclusions ADC values in the cerebellum and the middle cerebellar peduncles have very important significance in differential diagnosis between MSA and PD. Key words: Multiple system atrophy; Parkinson disease; Diffusion magnetic resonance imaging

Diffusion tensor imaging in the cervical spinal cord

There are discrepancy between MR findings and clinical presentations. The compressed cervical cord in patients of the spondylotic myelopathy may be normal on conventional MRI when it is at the earlier stage or even if patients had severe symptoms. Therefore, it is necessary to take a developed MR technique--diffusion tensor imaging (DTI)--to detect the intramedullary lesions. Prospective MR and DTI were performed in 53 patients with cervical compressive myelopathy and twenty healthy volunteers. DTI was performed along six non-collinear directions with single-shot spin echo echo-planar imaging (EPI) sequence. Intramedullary apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in four segments (C2/3, C3/4, C4/5, C5/6) for volunteers, in lesions (or the compressed cord) and normal cord for patients. DTI original images were processed to produce color DTI maps. In the volunteers' group, cervical cord exhibited blue on the color DTI map. FA values between four segments had a significant difference (P < 0.01), with the highest FA value (0.85 ± 0.03) at C2/3 level. However, ADC value between them had no significant difference (P > 0.05). For patients, only 24 cases showed hyperintense on T2-weighted image, while 39 cases shown patchy green signal on color DTI maps. ADC and FA values between lesions or the compressed cord and normal spinal cord of patients had a significant difference (both P < 0.01). FA value at C2/3 cord is the highest of other segments and it gradually decreases towards the caudal direction. Using single-shot spin echo EPI sequence and six non-collinear diffusion directions with b value of 400 s mm(-2), DTI can clearly show the intramedullary microstructure and more lesions than conventional MRI.

In vivo magnetic resonance elastography of human brain at 7 T and 1.5 T

To investigate the feasibility of quantitative in vivo ultrahigh field magnetic resonance elastography (MRE) of the human brain in a broad range of low-frequency mechanical vibrations. Mechanical vibrations were coupled into the brain of a healthy volunteer using a coil-driven actuator that either oscillated harmonically at single frequencies between 25 and 62.5 Hz or performed a superimposed motion consisting of multiple harmonics. Using a motion sensitive single-shot spin-echo echo planar imaging sequence shear wave displacements in the brain were measured at 1.5 and 7 T in whole-body MR scanners. Spatially averaged complex shear moduli were calculated applying Helmholtz inversion. Viscoelastic properties of brain tissue could be reliably determined in vivo at 1.5 and 7 T using both single-frequency and multifrequency wave excitation. The deduced dispersion of the complex modulus was consistent within different experimental settings of this study for the measured frequency range and agreed well with literature data. MRE of the human brain is feasible at 7 T. Superposition of multiple harmonics yields consistent results as compared to standard single-frequency based MRE. As such, MRE is a system-independent modality for measuring the complex shear modulus of in vivo human brain in a wide dynamic range.

Renal Cell Carcinoma: Diffusion-weighted MR Imaging for Subtype Differentiation at 3.0 T

To assess the usefulness of apparent diffusion coefficients (ADCs) for characterizing renal cell carcinoma (RCC) subtypes at 3.0 T. The Institutional Review Board approved this retrospective study, and informed consent was waived. Eighty-three patients underwent diffusion-weighted (DW) magnetic resonance (MR) imaging of 85 renal masses. In each patient, precontrast single-shot spin-echo echo-planar DW imaging was performed with b values of 0 and 500 and 0 and 800 sec/mm(2) by using a 3.0-T MR imaging system. Differences in ADCs between the RCC lesions and uninvolved renal parenchyma were tested by using a paired-samples t test. One-way analysis of variance was used to compare ADCs of the various RCC subtypes. Receiver operating characteristic (ROC) curve analysis was used to test the ability of ADCs in differentiating clear cell from non-clear cell RCCs. Pathologic diagnoses of the 85 tumors (median diameter, 4.4 cm) in the 83 patients (54 men, 29 women; age range, 23-75 years; mean age, 49.4 years) were clear cell RCC for 49 tumors, papillary RCC for 22 tumors, and chromophobic RCC for 14 tumors. With b values of 0 and 500 sec/mm(2), clear cell RCCs showed a significantly higher mean ADC (1.849 × 10(-3) mm(2)/sec) than papillary (1.087 × 10(-3) mm(2)/sec) and chromophobic (1.307 × 10(-3) mm(2)/sec) RCCs (P < .001); however, the difference between papillary and chromophobic RCCs was not significant (P = .068). With b values of 0 and 800 sec/mm(2), clear cell RCC showed the largest mean ADC (1.698 × 10(-3) mm(2)/sec) of the three subtypes, and the difference between each pair of subtypes was significant (P < .001). ADCs obtained with b values of 0 and 800 sec/mm(2) were more effective for distinguishing clear cell from non-clear cell RCC (area under the ROC curve, 0.973): A threshold value of 1.281 × 10(-3) mm(2)/sec permitted distinction with high sensitivity (95.9%) and specificity (94.4%). DW imaging with b values of 0 and 800 sec/mm(2) allows sensitive and specific differentiation of clear cell, papillary, and chromophobic RCCs, suggesting that DW imaging may be useful in the preoperative characterization of RCC.

Diffusion-Weighted MRI of Malignant Pleural Mesothelioma: Preliminary Assessment of Apparent Diffusion Coefficient in Histologic Subtypes

The purpose of this study was to prospectively assess, in the evaluation of patients with suspected malignant pleural mesothelioma (MPM), apparent diffusion coefficient (ADC) values derived from diffusion-weighted images obtained with a free-breathing single-shot spin-echo echo-planar imaging sequence and to correlate the ADC values with the three histologic subtypes of MPM. Sixty-two patients with a known pleural abnormality and clinical findings suggestive of MPM underwent diffusion-weighted 3-T MRI and ADC calculation. The pathologic diagnosis was confirmed by surgical procedure. ADC values were correlated with the histologic subtypes of MPM. Statistical analysis was performed with analysis of variance and the Student's t test. Fifty-seven patients had MPM. Forty of the tumors were epithelioid, 11 were biphasic, and six were sarcomatoid. The other five patients had pleural thickening (two patients), metastatic adenocarcinoma (one patient), chronic inflammation (one patient), and malignant lymphoma (one patient). Because of image distortion, the diffusion-weighted images and ADC maps were not satisfactory for assessment in seven cases. The ADC values of MPM were 1.31 +/- 0.15 x 10(-3) mm(2)/s for the epithelioid, 1.01 +/- 0.11 x 10(-3) mm(2)/s for the biphasic, and 0.99 +/- 0.07 x 10(-3) mm(2)/s for the sarcomatoid subtypes of MPM. The ADC of the epithelioid subtype was statistically significantly higher than that of the sarcomatoid subtype (p < 0.05). The ADC in the two cases of benign plaque was 0.85 +/- 0.17 x 10(-3) mm(2)/s. The ADC values of epithelioid mesothelioma are higher than those of sarcomatoid mesothelioma. There is no significant difference between the ACD values of biphasic and those of sarcomatoid MPM.

Human cervical spinal cord funiculi: Investigation with magnetic resonance diffusion tensor imaging

To use spinal cord diffusion tensor imaging (DTI) for investigating human cervical funiculi, acquire axial diffusion magnetic resonance imaging (MRI) data with an in-plane resolution sufficient to delineate subquadrants within the spinal cord, obtain corresponding DTI metrics, and assess potential regional differences. Healthy volunteers were studied with a 3 T Siemens Trio MRI scanner. DTI data were acquired using a single-shot spin echo EPI sequence. The spatial resolution allowed for the delineation of regions of interest (ROIs) in the ventral, dorsal, and lateral spinal cord funiculi. ROI-based and tractography-based analyses were performed. Significant fractional anisotropy (FA) differences were found between ROIs in the dorsal and ventral funiculi (P = 0.0001), dorsal and lateral funiculi (P = 0.015), and lateral and ventral funiculi (P = 0.0002). Transverse diffusivity was significantly different between ROIs in the ventral and dorsal funiculi (P = 0.003) and the ventral and lateral funiculi (P = 0.004). Tractography-based quantifications revealed DTI parameter regional differences that were generally consistent with the ROI-based analysis. Original contributions are: 1) the use of a tractography-based method to quantify DTI metrics in the human cervical spinal cord, and 2) reported DTI values in various funiculi at 3 T.

Diffusion-weighted magnetic resonance imaging for pretreatment prediction and monitoring of treatment response of patients with locally advanced breast cancer undergoing neoadjuvant chemotherapy

Background. For patients with locally advanced breast cancer (LABC) undergoing neoadjuvant chemotherapy (NACT), the European Guidelines for Breast Imaging recommends magnetic resonance imaging (MRI) to be performed before start of NACT, when half of the NACT has been administered and prior to surgery. This is the first study addressing the value of flow-insensitive apparent diffusion coefficients (ADCs) obtained from diffusion-weighted (DW) MRI at the recommended time points for pretreatment prediction and monitoring of treatment response. Materials and methods. Twenty-five LABC patients were included in this prospective study. DW MRI was performed using single-shot spin-echo echo-planar imaging with b-values of 100, 250 and 800 s/mm2 prior to NACT, after four cycles of NACT and at the conclusion of therapy using a 1.5 T MR scanner. ADC in the breast tumor was calculated from each assessment. The strength of correlation between pretreatment ADC, ADC changes and tumor volume changes were examined using Spearman’s rho correlation test. Results. Mean pretreatment ADC was 1.11 ± 0.21 × 10–3 mm2/s. After 4 cycles of NACT, ADC was significantly increased (1.39 ± 0.36 × 10–3 mm2/s; p=0.018). There was no correlation between individual pretreatment breast tumor ADC and MR response measured after four cycles of NACT (p=0.816) or prior to surgery (p=0.620). Conclusion. Pretreatment tumor ADC does not predict treatment response for patients with LABC undergoing NACT. Furthermore, ADC increase observed mid-way in the course of NACT does not correlate with tumor volume changes.

Role of diffusion-weighted magnetic resonance imaging in the diagnosis of extrahepatic cholangiocarcinoma

To determine the clinical value of diffusion-weighted imaging (DWI) for the diagnosis of extrahepatic cholangiocarcinoma (EHCC) by comparing the diagnostic sensitivity of DWI and magnetic resonance cholangiopancreatography (MRCP). Magnetic resonance imaging examination was performed in 56 patients with suspected EHCC. T1-weighted imaging, T2-weighted imaging, MRCP and DWI sequence, DWI using single-shot spin-echo echo-planar imaging sequence with different b values (100, 300, 500, 800 and 1000 s/mm(2)), were performed. All cases were further confirmed by surgery or histopathological diagnosis. Two radiologists jointly performed the analysis of the DWI and MRCP images. Apparent diffusion coefficient (ADC) value and signal-noise ratio were calculated for EHCC. Sensitivity, specificity, accuracy, positive predictive value and negative predictive value were tested using DWI with a b value of 500 s/mm(2) and MRCP images, respectively. Histopathological diagnosis confirmed that among the 56 cases, 35 were EHCC (20 hilar and 15 distal extrahepatic), 16 were cholangitis, and 5 were calculus of bile duct. Thirty-three out of the 35 EHCC cases were detected by DWI. EHCC exhibited differential levels of high signal intensity in DWI and low signal intensity in the ADC map. The mean value for ADC was (1.31 +/- 0.29) x 10(-3) mm(2)/s. The detection rate of EHCC was significantly higher by DWI (94.3%) than by MRCP (74.3%) (P < 0.05). There was a significant difference in sensitivity (94.3% vs 74.3%), specificity (100% vs 71.4%), accuracy (96.4% vs 73.2%), positive predictive value (100% vs 81.3%), and negative predictive value (91.3% vs 62.5%) between DWI and MRCP in diagnosing EHCC. DWI has a high sensitivity for the detection of EHCC as it shows the EHCC lesion more unambiguously than MRCP does. DWI can also provide additional clinically important information in EHCC patients when added to routine bile duct MR imaging protocols.