Rapid isotropic diffusion mapping without susceptibility artifacts: whole brain studies using diffusion-weighted single-shot STEAM MR imaging.

A subsecond magnetic resonance imaging (MRI) technique for isotropic diffusion mapping is described which, in contrast to echo-planar imaging (EPI), is insensitive to resonance offsets, i.e., tissue susceptibility differences, magnetic field inhomogeneities, and chemical shifts. It combines a diffusion-weighted (DW) spin-echo preparation period and a high-speed stimulated echo acquisition mode (STEAM) MRI sequence and yields single-shot images within measuring times of 559 msec (80 echoes). Here, diffusion encoding involved one scan without DW, three DW scans with b = 490 sec mm(-2), and three DW scans with b = 1000 sec mm(-2) (orthogonal gradient orientations). An automated on-line evaluation resulted in isotropic DW images as well as ADC maps (trace of the diffusion tensor). Experiments at 2.0 T covered the brain of healthy subjects in 20 contiguous sections of 6 mm thickness and 2.0 x 2.0 mm(2) in-plane resolution within a total measuring time of 78 sec. High-resolution studies at 1.0 x 1.0 mm(2) (interpolated from 2.0 x 1.0 mm(2) acquisitions) were obtained within 5 min 13 sec using four averages. In comparison with EPI, DW single-shot STEAM MRI exhibits only about half the SNR, but completely avoids regional signal losses, high intensity artifacts, and geometric distortions.     

Peritumoral brain regions in gliomas and meningiomas: investigation with isotropic diffusion-weighted MR imaging and diffusion-tensor MR imaging

PURPOSE: To retrospectively measure the diffusion-weighted (DW) imaging characteristics of peritumoral hyperintense white matter (WM) and peritumoral normal-appearing WM, as seen on T2-weighted magnetic resonance (MR) images of infiltrative high-grade gliomas and meningiomas. MATERIALS AND METHODS: Seventeen patients with biopsy-proved glioma and nine patients with imaging findings consistent with meningioma and an adjacent hyperintense region on T2-weighted MR images were examined with DW and diffusion-tensor MR imaging. Apparent diffusion coefficients (ADCs) were measured on maps generated from isotropic DW images of enhancing tumor, hyperintense regions adjacent to enhancing tumor, normal-appearing WM adjacent to hyperintense regions, and analogous locations in the contralateral WM corresponding to these areas. Fractional anisotropy (FA) was measured in similar locations on maps generated from diffusion-tensor imaging data. Changes in ADC and FA in each type of tissue were compared across tumor types by using a two-sample t test. P <.05 indicated statistical significance. RESULTS: Mean ADCs in peritumoral hyperintense regions were 1.309 x 10(-3) mm2/sec (mean percentage of 181% of normal WM) for gliomas and 1.427 x 10(-3) mm2/sec (192% of normal value) for meningiomas (no significant difference). Mean ADCs in peritumoral normal-appearing WM were 0.723 x 10(-3) mm2/sec (106% of normal value) for gliomas and 0.743 x 10(-3) mm2/sec (102% of normal value) for meningiomas (no significant difference). Mean FA values in peritumoral hyperintense regions were 0.178 (43% of normal WM value) for gliomas and 0.224 (65% of normal value) for meningiomas (P =.05). Mean FA values for peritumoral normal-appearing WM were 0.375 (83% of normal value) for gliomas and 0.404 (100% of normal value) for meningiomas (P =.01). CONCLUSION: The difference in FA decreases in peritumoral normal-appearing WM between gliomas and meningiomas was significant, and the difference in FA decreases in peritumoral hyperintense regions between these tumors approached but did not reach significance. These findings may indicate a role for diffusion MR imaging in the detection of tumoral infiltration that is not visible on conventional MR images.     

Diffusion MRI findings in Wilson's disease.

Six patients having Wilson's disease were studied with diffusion MRI in order to characterize cerebral lesions. Diffusion MRI was obtained using the spin-echo, echo-planar sequence with a gradient strength of 30 mT/m. The trace protocol was used in the axial imaging plane. Heavily diffusion-weighted (b=1000s/mm(2)) images, and the ADC (apparent diffusion coefficient) values from automatically generated ADC maps were studied. The ADC values of the normal brain parenchyma were available in 17 age-matched cases for comparison (ADC values, 0.85+/-0.11 x 10(-3)mm(2)/s). In Wilson's disease two distinct diffusion MRI patterns were observed by quantitative evaluations of the ADC maps; cytotoxic edema-like (ADC values, 0.52+/-0.03 x 10(-3)mm(2)/s), and vasogenic edema-like (ADC values, 1.42+/-0.17 x 10(-3)mm(2)/s) patterns. Diffusion imaging appears to be a promising sequence to evaluate the changes in the brain tissue in Wilson's disease at least by revealing two different patterns.     

Pituitary macroadenomas: preoperative evaluation of consistency with diffusion-weighted MR imaging--initial experience

PURPOSE: To prospectively evaluate use of diffusion-weighted (DW) magnetic resonance (MR) images and apparent diffusion coefficient (ADC) maps for determination of the consistency of macroadenomas. MATERIALS AND METHODS: The study protocol was approved by the institutional ethics committee, and informed consent was obtained from all patients. Twenty-two patients with pituitary macroadenoma (10 men, 12 women; mean age, 54 years +/- 17.09 [standard deviation]; range, 21-75 years) were examined. All patients underwent MR examination, which included T1-weighted spin-echo and T2-weighted turbo spin-echo DW imaging with ADC mapping and contrast material-enhanced T1-weighted spin-echo imaging. Regions of interest (ROIs) were drawn in the macroadenomas and in normal white matter on DW images, ADC maps, and conventional MR images. Consistency of macroadenomas was evaluated at surgery and was classified as soft, intermediate, or hard. Histologic examination was performed on surgical specimens of macroadenomas. Mean ADC values, signal intensity (SI) ratios of tumor to white matter within ROIs on conventional and DW MR images, and degree of enhancement were compared with tumor consistency and with percentage of collagen content at histologic examination by using analysis of variance for linear trend. RESULTS: The mean value of ADC in the soft group was (0.663 +/- 0.109) x 10(-3) mm(2)/sec; in the intermediate group, (0.842 +/- 0.081) x 10(-3) mm(2)/sec; and in the hard group, (1.363 +/- 0.259) x 10(-3) mm(2)/sec. Statistical analysis revealed a significant correlation between tumor consistency and ADC values, DW image SI ratios, T2-weighted image SI ratios, and percentage of collagen content (P < .001, analysis of variance). No other statistically significant correlations were found. CONCLUSION: Findings in this study suggest that DW MR images with ADC maps can provide information about the consistency of macroadenomas.     

High b-value diffusion-weighted MRI of normal brain

PURPOSE: As MR scanner hardware has improved, allowing for increased gradient strengths, we are able to generate higher b values for diffusion-weighted (DW) imaging. Our purpose was to evaluate the appearance of the normal brain on DW MR images as the diffusion gradient strength ("b value") is increased from 1,000 to 3,000 s/mm2. METHOD: Three sets of echo planar images were acquired at 1.5 T in 25 normal subjects (mean age 61 years) using progressively increasing strengths of a diffusion-sensitizing gradient (corresponding to b values of 0, 1,000, and 3,000 s/mm2). All other imaging parameters remained constant. Qualitative assessments of trace images were performed by two neuroradiologists, supplemented by quantitative measures of MR signal and noise in eight different anatomic regions. RESULTS: As gradient strength increased from b = 1,000 to 3,000, both gray and white matter structures diminished in signal as expected based on their relative diffusion coefficients [calculated average apparent diffusion coefficient (ADC) values: gray matter = 8.5 x 10(-4) mm2/s, white matter = 7.5 x 10(-4) mm2/s]. The signal-to-noise ratios for the b = 1,000 images were approximately 2.2 times higher than for the b = 3,000 images (p < 0.0001). As the strength of the diffusion-sensitizing gradient increased, white matter became progressively hyperintense to gray matter. Relative to the thalamus, for example, the average MR signal intensity of white matter structures increased by an average of 27.5%, with the densely packed white matter tracts (e.g., middle cerebellar peduncle, tegmentum, and internal capsule) increasing the most. CONCLUSION: Brain DW images obtained at b = 3,000 appear significantly different from those obtained at b = 1,000, reflecting expected loss of signal from all areas of brain in proportion to their ADC values. Consequently, when all other imaging parameters are held constant, b = 3,000 DW images appear significantly noisier than b = 1,000 images, and white matter tracts are significantly more hyperintense than gray matter structures.     

Uterine fibroids: diffusion-weighted MR imaging for monitoring therapy with focused ultrasound surgery--preliminary study

PURPOSE: To prospectively determine the feasibility of using diffusion-weighted (DW) imaging and apparent diffusion coefficient (ADC) mapping before (baseline) and after treatment and at 6-month follow-up to monitor magnetic resonance (MR) image-guided focused ultrasound surgical ablation of uterine fibroids. MATERIALS AND METHODS: Informed consent was obtained from patients before treatment with our study protocol, as approved by the institutional review board, and the study complied with the Health Insurance Portability and Accountability Act. Fourteen patients (mean age, 46 years +/- 5 [standard deviation]) who underwent DW imaging were enrolled in this study, and 12 of 14 completed the inclusive MR examination with DW imaging at 6-month follow-up. Treatment was performed by one radiologist with a modified MR image-guided focused ultrasound surgical system coupled with a 1.5-T MR imager. Pre- and posttreatment and 6-month follow-up MR images were obtained by using phase-sensitive T1-weighted fast spoiled gradient-recalled acquisition, T1-weighted contrast material-enhanced, and DW imaging sequences. Total treatment time was 1-3 hours. Trace ADC maps were constructed for quantitative analysis. Regions of interest localized to areas of hyperintensity on DW images were drawn on postcontrast images, and quantitative statistics were obtained from treated and nontreated uterine tissue before and after treatment and at 6-month follow-up. Statistical analysis was performed with analysis of variance. Differences with P < .05 were considered statistically significant. RESULTS: T1-weighted contrast-enhancing fibroids selected for treatment had no hyperintense or hypointense signal intensity changes on the DW images or ADC maps before treatment. Considerably increased signal intensity changes that were localized within the treated areas were noted on DW images. Mean baseline ADC value in fibroids was 1504 mm(-6)/sec2 +/- 290. Posttreatment ADC values for nontreated fibroid tissue (1685 mm(-6)/sec2 +/- 468) differed from posttreatment ADC values for fibroid tissue (1078 mm(-6)/sec2 +/- 293) (P = .001). A significant difference (P < .001) between ADC values for treated (1905 mm(-6)/sec2 +/- 446) and nontreated (1437 mm(-6)/sec2 +/- 270) fibroid tissue at 6-month follow-up was observed. CONCLUSION: DW imaging and ADC mapping are feasible for identification of ablated tissue after focused ultrasound treatment of uterine fibroids.     

Lung carcinoma: diffusion-weighted mr imaging--preliminary evaluation with apparent diffusion coefficient

PURPOSE: To prospectively evaluate diffusion-weighted (DW) magnetic resonance (MR) imaging with a split acquisition of fast spin-echo signals for diffusion imaging (SPLICE) sequence for tissue characterization of lung carcinomas by using apparent diffusion coefficients (ADCs). Materials and METHODS: An institutional review board approved this study; informed consent was obtained from patients. Thirty patients (nine women, 21 men; mean age, 68.0 years) with lung carcinoma underwent DW MR imaging with the SPLICE sequence. ADC of each lung carcinoma was calculated from DW MR images obtained with low and high b values. ADCs of lung carcinomas were statistically compared among histologic types. Nine surgically excised lung carcinomas were evaluated for correlation between ADCs and tumor cellularities. Analysis of variance was used to determine changes in ADCs and histologic lung carcinoma types. Spearman rank correlation was calculated between ADCs and tumor cellularities. RESULTS: ADCs for lung carcinomas were 1.63 x 10(-3) mm(2)/sec +/- 0.5 (mean +/- standard deviation) for squamous cell carcinoma, 2.12 x 10(-3) mm(2)/sec +/- 0.6 for adenocarcinoma, 1.30 x 10(-3) mm(2)/sec +/- 0.4 for large-cell carcinoma, and 2.09 x 10(-3) mm(2)/sec +/- 0.3 for small-cell carcinoma. ADC of adenocarcinoma was significantly higher than that of squamous cell carcinoma and large-cell carcinoma (P < .05). ADCs were 1.59 x 10(-3) mm(2)/sec +/- 0.5 and 1.70 x 10(-3) mm(2)/sec +/- 0.4 for moderately and poorly differentiated squamous cell carcinoma, respectively. ADCs were 2.52 x 10(-3) mm(2)/sec +/- 0.4 and 1.44 x 10(-3) mm(2)/sec +/- 0.3 for well- and poorly differentiated adenocarcinoma, respectively. ADC of well-differentiated adenocarcinoma was significantly higher than that of moderately and poorly differentiated squamous cell carcinoma and poorly differentiated adenocarcinoma (P < .05). With the Spearman rank test, ADCs of lung carcinomas correlated well with tumor cellularities (Spearman coefficient, -0.75; P < .02). CONCLUSION: ADCs of lung carcinomas overlap, but ADCs of well-differentiated adenocarcinoma appear to be higher than those of other histologic lung carcinoma types.     

Tuberous sclerosis: diffusion MRI findings in the brain

Diffusion MRI has mainly been used for detection of acute ischemia, and for distinction of cytotoxic and vasogenic edema. We applied diffusion MRI in patients with tuberous sclerosis in order to evaluate diffusion imaging characteristics of parenchymal changes. Five children with known tuberous sclerosis were included in this study. The MRI examinations were performed on a 1.5-T MR unit. Diffusion MRI was obtained using the echo-planar imaging sequence. Apparent diffusion coefficient (ADC) values from the abnormal brain parenchyma were calculated directly from automatically generated ADC maps. Seven normal children were available for comparison. In this control group the mean ADC value of the normal white matter was 0.84 +/- 0.12 x 10(-3) mm(2)/s. In tuberous sclerosis patients the mean ADC value of the white matter hamartomas ( n=20) was apparently high (1.52 +/- 0.24 x 10(-3) mm(2)/s) compared with that of normal white matter. The ADC value of calcified hamartomas was "zero". The ADC value within a giant cell tumor was 0.89 x 10(-3) mm(2)/s, similar to that of normal cerebral white matter. The ADC maps were superior to b=1000 s/mm(2) (true diffusion) images with respect to lesion evaluation, and they provided mathematical information on tissue integrity. With respect to detection of the exact numbers and sizes of the parenchymal hamartomas fluid-attenuated inversion recovery images were superior to ADC maps. It is believed that diffusion MRI can be useful in evaluation of various parenchymal changes associated with tuberous sclerosis. Further studies on tuberous sclerosis, and on various brain lesions, would provide increasing data on this relatively new MRI sequence.     

Diffusion-weighted MRI in the evaluation of renal lesions: preliminary results

The purpose of this study was to evaluate the capability and the reliability of diffusion-weighted MRI in the evaluation of normal kidney and different renal lesions. 39 patients (10 normal volunteers and 29 patients with known renal lesions) underwent MRI of the kidneys by using a 1.5 T superconducting magnet. Axial fat suppressed turbo spin echo (TSE) T(2) and coronal fast field echo (FFE) T(1) or TSE T(1) weighted images were acquired for each patient. Diffusion-weighted (DW) images were obtained in the axial plane during breath-hold (17 s) with a spin-echo echo planar imaging (SE EPI) single shot sequence (repetition time (TR)=2883 ms, echo time (TE)=61 ms, flip angle=90 degrees ), with b value of 500 s mm(-2). 16 slices were produced with slice thickness of 7 mm and interslice gap of 1 mm. An apparent diffusion coefficient (ADC) map was obtained at each slice position. The ADC was measured in an approximately 1 cm region of interest (ROI) within the normal renal parenchyma, the detected renal lesions and the collecting system if dilated. ADC values in normal renal parenchyma ranged from 1.72 x 10(-3) mm(2) s(-1) to 2.65 x 10(-3) mm(2) s(-1), while ADC values in simple cysts (n=13) were higher (2.87 x 10(-3) mm(2) s(-1) to 4.00 x 10(-3) mm(2) s(-1)). In hydronephrotic kidneys (n=6) the ADC values of renal pelvis ranged from 3.39 x 10(-3) mm(2) s(-1) to 4.00 x 10(-3) mm(2) s(-1). In cases of pyonephrosis (n=3) ADC values of the renal pelvis were found to be lower than those of renal pelvis of hydronephrotic kidneys (0.77 x 10(-3) mm(2) s(-1) to 1.07 x 10(-3) mm(2) s(-1)). Solid benign and malignant renal tumours (n=7) showed ADC values ranging between 1.28 x 10(-3) mm(2) s(-1) and 1.83 x 10(-3) mm(2) s(-1). In conclusion diffusion-weighted MR imaging of the kidney seems to be a reliable way to differentiate normal renal parenchyma and different renal diseases. Clinical experience with this method is still preliminary and further studies are required.     

Diffusion-weighted MRI: role in detecting abdominopelvic internal fistulas and sinus tracts

Purpose:

To retrospectively determine the incremental value of diffusion‐weighted MR‐imaging (DW‐MRI) to T2‐weighted (T2w) images in diagnosis of internal fistulas (IFs) and sinus tracts (STs).

Materials and Methods:

Fourteen patients with 25 IFs and STs arising from the small bowel ( 20 ), colon ( 4 ) and biliary tract ( 1 ) were included. Two independent observers reviewed T2w images, T2w+DW‐MRI images and T2w+contrast enhanced T1‐weighted (CE T1w) images at three sessions to detect IF/ST based on a confidence scale of five. Sensitivity and confidence score of each session was compared.

Results:

10/25 (40%) and 9/25 (36%) IFs and STs were detected on T2w images by observer 1 and 2, respectively. Both observers detected 19/25 (76%) and 24/25(96%) IFs and STs on T2w+DW‐MRI and T2w+CE T1w images, respectively. Detection rate and confidence score improved significantly by combining T2w images with DW‐MRI or CE T1w images (reader 1 + 2: P ≤ 0.01). There was no significant difference between the IF/ST detection rate of T2w+DW‐MRI and T2w+CE T1 image combinations. Confidence scores with T2w+CE T1w images were significantly greater than DW‐MRI+T2w images (reader 1:P = 0.01; reader 2: P = 0.03).

Conclusion:

DW‐MRI showed additional value to T2w imaging for diagnosis of IF and ST. DW‐MRI can be a useful adjunct, especially for patients with renal failure. J. Magn. Reson. Imaging 2012;35:125‐131. © 2011 Wiley Periodicals, Inc.     

Canavan disease: diffusion magnetic resonance imaging findings

A 15-month-old boy with Canavan disease is reported in whom a restricted diffusion pattern on diffusion magnetic resonance imaging (MRI) (high signal on b = 1,000 mm2/s images and low apparent diffusion coefficient [ADC] values) was evident in the affected regions of the brain, including the peripheral white matter, globi pallidi, thalami, brainstem, dorsal pons, and dentate nuclei. The ADC values at these regions ranged from 0.42 to 0.56 x 10(-3) mm2/s compared with the normal ADC values from the uninvolved deep frontal white matter (0.68-0.92 x 10(-3) mm2/s). The known histopathologic features in Canavan disease include edematous and gelatinous brain tissue associated with diffuse vacuolization. Considering these and the diffusion MRI findings in this patient, it is likely that existence of a gel (gelatinous) state rather than the usual sol state of water molecules in the affected brain regions accounted for the restricted diffusion pattern in Canavan disease.     

Evaluation of normal brain development by prenatal MR imaging

PURPOSE: The aim of this study was to describe the normal pattern of development and maturation of the foetal brain with respect to gestational age as assessed with magnetic resonance imaging (MRI) and to provide an overview of the possibilities of the technique. MATERIALS AND METHODS: Foetal cerebral MRI was performed on 56 pregnant women between 19 and 37 weeks of gestation. Half-Fourier single-shot turbo spin-echo (HASTE), true fast imaging with steady precession (FISP), T1-weighted fast low angle shot (FLASH) two-dimensional (2D) and diffusion-weighted (DW) sequences with apparent diffusion coefficient (ADC) were obtained. Biometric parameters and developmental areas of the cerebral cortex were correlated to gestational age by using the Spearman rank correlation test. RESULT: We found a negative correlation between the germinal matrix/biparietal diameter ratio and gestational age and a positive correlation between the germinal and cortical matrix when expressed as external intraocular diameter ratio (R=0.452, p=0.02). The cortical mantle was correlated with biometric parameters, such as the biparietal diameter and the frontooccipital diameter, and with gestational age. The interhemispheric fissure, the parietooccipital fissure and the sylvian fissure were detectable by the 22nd week. In the grey matter, the mean ADC values varied from 1.76 x 10(-3) mm(2)/s (at week 19) to 0.89 x 10(-3) mm(2)/s (at week 37), whereas in the white matter, the values varied from 2.03 x 10(-3) mm(2)/s (at week 19) to 1.25 x 10(-3) mm(2)/s (at week 37). CONCLUSIONS: MRI provides a reliable valuation of brain maturation during pregnancy.     

Diffusion-weighted imaging in the setting of diffuse cortical laminar necrosis and hypoxic-ischemic encephalopathy

BACKGROUND AND PURPOSE: As is the case for CT scans, MR images may occasionally appear deceptively normal unless proper windowing is used. We sought to illustrate the necessity for proper windowing and for assessing the gray-white matter differentiation on diffusion-weighted (DW) images in the setting of hypoxic-ischemic encephalopathy. METHODS: Six comatose patients (age range, 34-56 years) underwent MR imaging in the early phase (range, 1-5 days) after severe anoxic insult. T2-weighted, turbo fluid-attenuated inversion-recovery, and DW images were obtained in all six patients, with contrast-enhanced T1-weighted images obtained in four and apparent diffusion coefficient (ADC) maps in five of the six patients. RESULTS: At presentation, each of the six patients had symmetric, uniform hyperintensity in the cortex (mean ADC, 0.35 x 10(-3) mm(2)/s) relative to the white matter (mean ADC, 0.91 x 10(-3) mm(2)/s) on DW images. Each also had a poor outcome: brain death in four patients and a permanent vegetative state in two patients. CONCLUSION: The appearance of the MR images in the setting of diffuse cortical laminar necrosis can be deceptive to the unwary radiologist. The key to correct interpretation is proper windowing and the marked gray-white matter differentiation on spin-echo images but best seen on properly windowed DW images in the early subacute phase. This appearance also implies an extremely poor outcome, either a permanent vegetative state or brain death.     

Clinical usefulness of diffusion-weighted imaging using low and high b-values to detect rectal cancer.

PURPOSE: The purpose of this study was to assess the potential role of diffusion-weighted imaging (DWI) using low and high b-values to detect rectal cancer. METHODS: The subjects were 15 patients diagnosed endoscopically with rectal cancer (m in 1 patient, sm in 0, mp in 3, ss in 7, se in 1, a in 3) and 20 patients diagnosed endoscopically with colon cancer and no other lesions (control group). Magnetic resonance imaging was performed using a 1.5T system. DWI was performed in the axial plane using echo planar imaging sequence (repetition time/echo time 1200/66, field of view 306x350 mm, reconstruction matrix 156x256, pixel size 2.0x1.4x8.0 mm) and acquired with 2 b-values (50 and 800 s/mm2). Low and high b-value DW images were analyzed visually. A lesion was positive by detection of a focal area of high signal in the rectum in high b-value images. The apparent diffusion coefficient (ADC) values of areas of high signal in high b-value images were calculated from the low and high b-value images. RESULTS: High b-value images enabled visualization of all 15 rectal cancers. In the control group, 13 cases were classified as negative and 7 cases as positive for rectal cancer. Sensitivity for detection of rectal cancer was 100% (15/15), and specificity was 65% (13/20). The mean ADC values in 7 patients with false-positive lesions and in 15 patients with rectal cancer were 1.374x10(-3) mm2/s (standard deviation [SD]: 0.157) and 1.194x10(-3) mm2/s (SD: 0.152), respectively (P=0.026). CONCLUSION: DWI with low and high b-values may be used to screen for rectal cancer.     

Diffusion-weighted imaging in the follow-up of treated high-grade gliomas: tumor recurrence versus radiation injury

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) MR imaging is a means to characterize and differentiate morphologic features, including edema, necrosis, and tumor tissue, by measuring differences in apparent diffusion coefficient (ADC). We hypothesized that DW imaging has the potential to differentiate recurrent or progressive tumor growth from treatment-induced damage to brain parenchyma in high-grade gliomas after radiation therapy. METHODS: We retrospectively reviewed follow-up conventional and DW MR images obtained starting 1 month after completion of radiation treatment with or without chemotherapy for histologically proved high-grade gliomas. Eighteen patients with areas of abnormal enhancing tissue were identified. ADC maps were calculated from echo-planar DW images, and mean ADC values and ADC ratios (ADC of enhancing lesion to ADC of contralateral white matter) were compared with final diagnosis. Recurrence was established by histologic examination or by clinical course and a combination of imaging studies. RESULTS: Recurrence and nonrecurrence could be differentiated by using mean ADC values and ADC ratios. ADC ratios in the recurrence group showed significantly lower values (mean +/- SD, 1.43 +/- 0.11) than those of the nonrecurrence group (1.82 +/- 0.07, P <.001). Mean ADCs of the recurrent tumors (mean +/- SD, 1.18 +/- 0.13 x 10(-3) mm/s(2)) were significantly lower than those of the nonrecurrence group (1.40 +/- 0.17 x 10(-3) mm/s(2), P <.006). CONCLUSION: Assessment of ADC ratios of enhancing regions in the follow-up of treated high-grade gliomas is useful in differentiating radiation effects from tumor recurrence or progression.     

Monitoring of gustatory stimulation of salivary glands by diffusion-weighted MR imaging: comparison of 1.5T and 3T

BACKGROUND AND PURPOSE: Our aim was to compare different field strengths monitoring physiologic changes due to oral stimulation of parotid glands by using diffusion-weighted (DW) echo-planar imaging (EPI). MATERIALS AND METHODS: Twenty-seven healthy volunteers were examined with a DW-EPI sequence at 1.5T and 3T before and after oral stimulation with commercially available lemon juice. The b factors used were 0, 500, and 1000 s/mm(2). Apparent diffusion coefficient (ADC) maps were evaluated with a manually placed region of interest including the entire parotid gland. For comparison of results, a Student t test was used on the basis of the mean of the volunteer median values. To compare both field strengths, we calculated the Pearson correlation coefficient (r). RESULTS: DW-EPI MR imaging visualized the parotid glands of all volunteers. With 1.5T, the mean ADC before stimulation was 1.12 x 10(-3) mm(2)/s +/- 0.08 x 10(-3) mm(2)/s. After stimulation with lemon juice, the ADC increased to 1.18 x 10(-3) mm(2)/s +/- 0.09 x 10(-3) mm(2)/s. For 3T, the ADC before stimulation was 1.14 x 10(-3) mm(2)/s +/- 0.04 x 10(-3) mm(2)/s, with an increase to 1.17 x 10(-3) mm(2)/s +/- 0.05 x 10(-3) mm(2)/s after stimulation. For both field strengths, the increase in ADC after stimulation was significant (P < .001). High correlations between both field strengths were found pre- and poststimulation (r = 0.955, and 0.936, respectively). CONCLUSION: DW-EPI MR imaging allows monitoring of physiologic changes due to oral stimulation of parotid glands by using DW imaging with high correlation between 1.5T and 3T.     

In vivo diffusion tensor imaging of the human prostate.

This study demonstrates the feasibility of in vivo prostate diffusion tensor imaging (DTI) in human subjects. We implemented an EPI-based diffusion-weighted (DW) sequence with seven-direction diffusion gradient sensitization, and acquired DT images from six subjects using cardiac gating with a phased-array prostate surface coil operating in a linear mode. We calculated two indices to quantify diffusion anisotropy. The direction of the eigenvector corresponding to the leading eigenvalue was displayed by means of a color-coding scheme. The average diffusion values of the prostate peripheral zone (PZ) and central gland (CG) were 1.95 +/- 0.08 x 10(-3) mm2 s and 1.53 +/- 0.34 x 10(-3) mm2 s, respectively. The average fractional anisotropy (FA) values for the PZ and CG were 0.46 +/- 0.04 and 0.40 +/- 0.08, respectively. The diffusion ellipsoid in prostate tissue was anisotropic and approximated a prolate model, as shown in the color maps of the anisotropy. Consistent with the tissue architecture, the prostate fiber orientations were predominantly in the superior-inferior (SI) direction for both the PZ and CG. This study shows the feasibility of in vivo DTI and establishes normative DT values for six subjects.     

DCE and DW MRI in monitoring response to androgen deprivation therapy in patients with prostate cancer: a feasibility study

Androgen deprivation therapy (ADT) is a key primary treatment for advanced and metastatic prostate cancer and is an important neoadjuvant before radiotherapy. We evaluated 3.0 T dynamic contrast-enhanced MRI and diffusion-weighted (DW) MRI in monitoring ADT response. Twenty-three consecutive patients with prostate cancer treated by primary ADT were included. Imaging was performed at baseline and 3 months posttreatment with ADT. After 3 months therapy there was a significant reduction in all dynamic contrast-enhanced MRI parameters measured in tumor regions of interest (K(trans), k(ep), v(p), IAUGC-90); P < 0.001. Areas of normal-appearing peripheral zone showed no significant change; P = 0.285-0.879. Post-ADT, there was no significant change in apparent diffusion coefficient values in tumors, whilst apparent diffusion coefficient values significantly decreased in areas of normal-appearing peripheral zone, from 1.786 × 10(-3) mm(2) /s to 1.561 × 10(-3) mm(2) /s; P = 0.007. As expected the median Prostate-Specific Antigen (PSA) significantly reduced from 30 ng/mL to 1.5 ng/mL posttreatment, and median prostate volume dropped from 47.6 cm(3) to 24.9 cm(3) ; P < 0.001. These results suggest that dynamic contrast-enhanced MRI and diffusion-weighted MRI offer different information but that both could prove useful adjuncts to the anatomical information provided by T2-weighted imaging. dynamic contrast-enhanced as a marker of angiogenesis may help demonstrate ADT resistance and diffusion-weighted imaging may be more accurate in determining presence of tumor cell death versus residual tumor.     

Diffusion-weighted and conventional MR imaging findings of neuroaxonal dystrophy

BACKGROUND AND PURPOSE: Neuroaxonal dystrophy is a rare progressive disorder of childhood characterized by mental deterioration and seizures. The diffusion-weighted and conventional MR imaging findings are reported for six cases. METHODS: Six patients aged 19 months to 9 years with proved neuroaxonal dystrophy (one with the infantile form, five juvenile forms) underwent imaging at 1.5 T. Echo-planar diffusion-weighted images were acquired with a trace imaging sequence in five patients and with a three-gradient protocol (4000/110) in one. Images obtained with a b value of 1000 s/mm2 and corresponding apparent diffusion coefficient (ADC) maps were studied. ADCs from lesion sites and normal regions (pons and temporal and occipital lobes) were evaluated. RESULTS: A hyperintense cerebellum (a characteristic of the disease) was evident on fluid-attenuated inversion recovery images in all cases. Four patients had associated cerebral changes. Diffusion-weighted images, especially ADC maps, showed an elevated diffusion pattern in the cerebellum in the five juvenile cases (normal images at b = 1000 s/mm2, ADCs of 1.30-2.60 x 10(-3) mm2/s). A restricted diffusion pattern was evident in the infantile case (hyperintensity at b = 1000 s/mm2, low ADCs of 0.44-0.55 x 10(-3) mm2/s). ADCs were normal in the pons and temporal and occipital lobes (0.64-1.00 x 10(-3) mm2/s). CONCLUSION: An elevated cerebellar diffusion pattern is a predominant feature of juvenile neuroaxonal dystrophy. Coexistent elevated and restricted diffusion patterns were evident in different brain regions in different forms of the disease. Dystrophic axons likely account the restricted diffusion, whereas spheroid formation (swelling) and abnormal myelination result in elevated diffusion.     

High-b-value diffusion-weighted MR imaging of hyperacute ischemic stroke at 1.5T

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) imaging at b = 2000 s/mm(2) offers theoretical advantages over DW imaging at b = 1000 s/mm(2) for detection of hyperacute ischemic stroke. The purpose of this study was to determine whether b = 2000 images are better than b = 1000 images for detecting and estimating the extent of diffusion change within 6 hours after stroke onset. METHODS: We compared DW images obtained with a b value of 1000 s/mm(2) (TR/TE/NEX, 7500/71/1) with those obtained with a b value of 2000 s/mm(2) (TR/TE/NEX, 7500/83/2) in 94 patients examined within 6 hours of clinically suspicious hyperacute ischemic stroke (57 men, 37 women; mean age +/- SD, 62 years +/- 8; age range, 47-80 years; mean time interval +/- SD, 206 +/- 90 min). Three observers performed qualitative analysis of DW images and reached a consensus about lesion conspicuity, lesion extent, and image artifact. In the quantitative analysis of 34 patients with lesions in the territory of the middle cerebral artery, the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and volume of ischemic lesion were measured and findings of the b = 1000 and b = 2000 images were compared. RESULTS: The sensitivity and specificity of b = 1000 and b = 2000 images were calculated as 94% (80/85)/ 100% (9/9) and 98% (83/85)/ 100% (9/9), respectively, relative to the presence or absence of infarction on the follow-up T2-weighted images. In three patients, hyperintense lesions were depicted only on b = 2000 images. On qualitative analysis, lesions were more conspicuous and larger on b = 2000 images in 23 and 11 patients, respectively. On quantitative analysis, as the b value increased, the mean lesion volume increased by 47% (22.1 +/- 27.9 mL at b = 1000 s/mm(2) versus 32.5 +/- 36.5 mL at b = 2000 s/mm(2), P < .001, n = 34). As the b value increased, mean SNR decreased both in the lesion and in the contralateral normal area by 17% and 28%, respectively, but the mean CNR increased by 23% (8.7 +/- 6.4 at b = 1000 s/mm(2) versus 10.7 +/- 6.5 at b = 2000 s/mm(2), P < .001, n = 34). CONCLUSION: DW images acquired with a b value of 2000 s/mm(2) were better than DW images acquired with a b value of 1000 s/mm(2) for the detection and estimation of the extent of diffusion change in patients examined within 6 hours of ischemic stroke onset.