Evaluation of the role of magnetization transfer imaging in prostate: a preliminary study

Results of the preliminary study on the evaluation of the role of magnetization transfer imaging (MTI) of prostate in men who had raised prostate-specific antigen (PSA) (>4 ng/ml) or abnormal digital rectal examination (DRE) are reported. MT ratio (MTR) was calculated for 20 patients from the hyper- (normal) and hypo-intense regions (area suspicious of malignancy as seen on T2-weighted MRI) of the peripheral zone (PZ) and the central gland (CG) at 1.5 T. In addition, MTR was calculated for three healthy controls. Mean MTR was also calculated for the whole of the PZ (including hyper- and hypo-intense area) in all patients. Out of 20 patients, biopsy revealed malignancy in 12 patients. Mean MTR value (8.29+/-3.49) for the whole of the PZ of patients who were positive for malignancy on biopsy was statically higher than that observed for patients who were negative for malignancy (6.18+/-3.15). The mean MTR for the whole of the PZ of controls was 6.18+/-1.63 and is similar to that of patients who were negative for malignancy. Furthermore, for patients who showed hyper- (normal portion) and hypo-intense (region suspicious of malignancy) regions of the PZ, the MTR was statistically significantly different. These preliminary results reveal the potential role of MT imaging in the evaluation of prostate cancer.     

Diffusion-weighted MRI in prostate cancer -- comparison between single-shot fast spin echo and echo planar imaging sequences

Diffusion-weighted (DW) MRI at 1.5 T was carried out in two groups of patients. MRI data were correlated with the biopsy and histopathology (where available). The performance of two sequences -- a single-shot FSE (14 patients) and a single-shot EPI (15 patients) -- was compared. Average ADC values from the normal peripheral zone (PZ), central gland (CG) and the tumour [prostate carcinoma (PCa)] were calculated from b values of 0 and 600. Tukey-Kramer test was used for statistical analysis. EPI produced higher values of ADC (10(-3) mm(2)/s) than FSE sequence: 1.992+/-0.208 vs. 1.573+/-0.270 in PZ (P<.001), 1.518+/-0.126 vs. 1.373+/-0.179 in CG and 1.214+/-0.254 vs. 0.993+/-0.158 in PCa (P<.01). In conclusion, both EPI and FSE sequences showed differences in ADC between normal PZ, CG and PCa; however, EPI produced significantly higher ADC values than FSE.     

Three-dimensional magnetic resonance spectroscopic imaging of histologically confirmed brain tumors

The goal of this study was to determine whether presurgical metabolite levels measured by 3D MR Spectroscopic Imaging (MRSI) can accurately detect viable cancer within human brain tumor masses. A total of 31 patients (33 exams, 39 pathology correlations) with brain tumors were studied prior to surgical biopsy and/or resection. The 3D MRSI was obtained with a spatial resolution of 0.2 to 1 cc throughout the majority of the mass and adjacent brain tissue using PRESS-CSI localization. Levels of choline, creatine and NAA were estimated from the locations of the resected tissue and normalized to normal appearing brain tissue. The data were correlated with subsequent histologic analysis of the biopsy tissue samples. Although there were large variations in the metabolite ratios, all regions of confirmed cancer demonstrated significant choline levels and a mean choline/NAA ratio of 5.84 + 2.58 with the lowest value being 1.3. This lowest value is greater than 4 standard deviations above the mean (0.52 +/- 0.13) found in 8 normal volunteers. The choline signal intensities in confirmed cancers were significantly elevated compared to normal appearing brain tissue with a mean ratio of 1.71 +/- 0.69. Spectra with no significant metabolite levels were observed in the non-enhancing necrotic core of the tumor masses. The results of this study indicate that 3D MRSI of brain tumors can detect abnormal metabolite levels in regions of viable cancer and grades and can differentiate cancer from necrosis and/or normal brain tissue.     

Short echo time in vivo prostate ¹H-MRSI

Visualization of short echo time (TE) metabolites in prostate magnetic resonance spectroscopic imaging is difficult due to lipid contamination and pulse timing constraints. In this work, we present a modified pulse sequence to permit short echo time (TE=40ms) acquisitions with reduced lipid contamination for the detection of short TE metabolites. The modified pulse sequence employs the conformal voxel MRS (CV-MRS) technique, which automatically optimizes the placement of spatial saturation planes to adapt the excitation volume to the shape of the prostate, thus reducing lipid contamination in prostate magnetic resonance spectroscopic imaging (MRSI). Metabolites were measured and assessed using a modified version of LCModel for analysis of in vivo prostate spectra. We demonstrate the feasibility of acquiring high quality spectra at short TEs, and show the measurement of short TE metabolites, myo-inositol, scyllo-inositol, taurine and glutamine/glutamate for both single and multi-voxel acquisitions. In single voxels experiments, the reduction in TE resulted in 57% improvement in the signal-to-noise ratio (SNR). Additional 3D MRSI experiments comparing short (TE=40 ms), and long (TE=130 ms) TE acquisitions revealed a 35% improvement in the number of adequately fitted metabolite peaks (775 voxels over all subjects). This resulted in a 42 ± 24% relative improvement in the number of voxels with detectable citrate that were well-fitted using LCmodel. In this study, we demonstrate that high quality prostate spectra can be obtained by reducing the TE to 40 ms to detect short T2 metabolites, while maintaining positive signal intensity of the spin-coupled citrate multiplet and managing lipid suppression.     

Apparent diffusion coefficient (ADC) measurements may be more reliable and reproducible than lesion volume on diffusion-weighted images from patients with acute ischaemic stroke-implications for study design

Early ischemic change after stroke can be demonstrated with diffusion-weighted imaging (DWI) and quantified by measuring the apparent diffusion coefficient (ADC) and/or lesion volume. We examined the reliability and reproducibility of lesion volume and ADC measurement on DWI images, and discuss the implications for clinical studies. Using 38 DWI scans from 15 stroke patients, two observers (a physicist and a neuroscience graduate) blind to each other, recorded the lesion volume on DWI sequences, measured the ADC values in this volume and calculated the ratio of ischemic: control ADC (ADCr). One observer repeated his measurements blind to his first, and also examined the effect on lesion volume and ADC of deliberately varying by only one pixel, the outline of the visible boundary of the lesion. The inter and intra-rater reliability were worse for lesion volume than ADC or ADCr measurements: lesion volume, inter-rater coefficient of variation (CoV) 85 +/- 130%, intra-rater CoV 20+/-SD80% (p < 0.05); ADC inter-rater CoV 7.7 +/- SD 19%, intra-rater CoV 0.2 +/- SD 12% (p = NS); and ADCr inter-rater CoV 8 +/- SD27%, intra-rater CoV 0.8 +/- SD73% (p = NS). Altering the position of the outline tracing of the lesion boundary by one pixel altered the measured volumes by 22 +/- SD25% (p < 0.05), but ADC values were altered by only 2.9 +/- SD4.9% and ADCr by 2.7 +/- SD4.8% (p = NS). ADC and ADCr values are more reliable and reproducible than DWI lesion size in acute ischemic stroke because altering where the lesion boundary is measured has a much greater impact on lesion volume than on the ADC or ADCr. This effect is greatest in large lesions.     

3-D echo planar (1)HMRS imaging in MS: metabolite comparison from supratentorial vs. central brain

To determine if metabolite ratios as measured by 3-dimensional echo planar spectroscopy imaging (3D-EPSI) from central brain regions of interest (ROI) centered at the corpus callosum reflect imaging metrics of large volumes of supratentorial brain (STB) from patients with multiple sclerosis. METHODS: 48 MS patients with relapsing-remitting, secondary progressive, and primary progressive disease underwent a 3D-EPSI sequence covering large volumes of STB. Metabolite ratios were first estimated from all voxels within a STB mask using a linear regression of N-acetylaspartate (NAA) over Creatine (Cr), NAA over choline (Cho) and Cho over Cr. Secondly, spectroscopic voxels from a central brain (CB) ROI centered at the corpus callosum were selected within the STB. Ratios were compared using Bland-Altman regression analysis and Spearman's correlation coefficients between STB versus central brain. Ratios from studied ROIs were correlated with the EDSS and compared to normal controls. RESULTS: Very strong correlations ranging from 0.884 and 0.938 (p < 0.0001) were found for all metabolite ratios between STB versus central brain. NAA/Cr ratios were similarly and negatively correlated with the EDSS across all ROIs, trends ranging from -0.257 to -0.314 (p < 0.1). NAA/Cr from all MS patients was similarly decreased compared to controls across all ROIs (p < 0.01). CONCLUSION: Metabolite ratios from a central brain ROI were statistically equivalent and highly correlated with ratios from the STB. The study of NAA/Cr using (1)HMRS from a central brain ROI centered at the corpus callosum seems to be representative of brainwide axonal changes in patients with MS.     

The imaging appearance of Creutzfeldt-Jakob disease caused by the E200K mutation

The E200K mutation on chromosome 20 can cause familial Creutzfeldt-Jakob disease (CJD). Patients with this mutation are clinically similar to those with sporadic CJD, but their imaging features are not well documented. We report here the quantitative and qualitative evaluation of the magnetic resonance (MR) imaging characteristics of this unique group of patients using three-dimensional spoiled gradient recalled (SPGR) echo images, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) measurements, MR spectroscopy and a fluid-attenuated inversion recovery (FLAIR) sequence. The SPGR and ADC data were analyzed with SPM99. ANCOVA and regression models were used for a region-of-interest (ROI) analysis of ADC and metabolic ratios. CJD patients had a decreased fraction of gray matter and an increased fraction of cerebrospinal fluid (P=.001) in the cortex and cerebellum and increased ADC values in the cortex (P<.001). Focal decreases of ADC were found in the putamen via ROI analysis (548+/-83 vs. 709+/-9 microm(2)/s, P=.02). N-acetyl aspartate (NAA) was generally reduced, with the NAA/Cho ratio lowest in the cingulate gyrus. Qualitative assessment revealed hyperintensities on FLAIR, DWI or both in the putamen (three out of four patients), caudate (three out of four patients) and thalamus. These results provide a framework for future study of patients with genetically defined familial CJD.     

Apparent diffusion coefficient of line scan diffusion image in normal prostate and prostate cancer—comparison with single-shot echo planner image

Purpose

This retrospective study was designed to evaluate the apparent diffusion coefficient (ADC) of line scan diffusion images (LSDI) in normal prostate and prostate cancer. Single-shot echo planner images (SS-EPI) were used for comparison.

Materials and Methods

Twenty prostate tumors were examined by conventional MRI in 14 patients prior to radical prostatectomy. All patients were examined with a 1.5-T MR imager (Signa CV/i ver. 9.1 GE Medical System Milwaukee, WI, USA). Diffusion-weighted MR imaging (DWI) using LSDI was performed with a pelvic phased-array coil, with b values of 5 and 800 s/mm². DWI using SS-EPI was performed with a body coil, with b values of 0 and 800 s/mm². The ADCs of each sequence for 14 normal prostate and 20 prostate cancers were histopathologically assessed. Signal-to-noise ratio (SNR) on DWI was estimated and compared for each sequence.

Results

The mean ADCs (±S.D.) of normal peripheral zones (PZ), transition zones (TZ) and cancer (in 10⁻³ mm²/s) that used LSDI were 1.42±0.12, 1.23±0.10 and 0.79±0.19, respectively. Those that used SS-EPI were 1.76±0.26, 1.38±0.20 and 1.05±0.27, respectively. Using unpaired t test (P<.05), we found a significant difference in each sequence between normal tissue (both PZ and TZ) and the cancer. Paired t test (P<.05) also registered a significant difference between LSDI and SS-EPI. Mean SNR for DWI using LSDI was 16.49±5.03, while the DWI using SS-EPI was 18.85±9.26. The difference between the SNR of each sequence was not statistically significant by paired t test.

Conclusion

We found that ADCs using LSDI and SS-EPI showed similar tendencies in the same patients. However, in all regions, LSDI ADCs had smaller standard deviations than SS-EPI ADCs.     

Elliptical magnetic resonance spectroscopic imaging with GRAPPA for imaging brain tumors at 3 T

Magnetic Resonance Spectroscopic Imaging (MRSI) is a technique for imaging spatial variation of metabolites and has been very useful in characterizing biochemical changes associated with disease as well as response to therapy in malignant pathologies. This work presents a self-calibrated undersampling to accelerate 3D elliptical MRSI and an extrapolation-reconstruction algorithm based on the GRAPPA method. The accelerated MRSI technique was tested in three volunteers and five brain tumor patients. Acceleration allowed larger spatial coverage and consequently, less lipid contamination in spectra, compared to fully sampled acquisition within the same scantime. Metabolite concentrations measured from the accelerated acquisitions were in good agreement with measurements obtained from fully sampled MRSI scans.     

Diffusion-weighted magnetic resonance imaging for early response assessment of chemoradiotherapy in patients with nasopharyngeal carcinoma

Purpose

To prospectively evaluate the feasibility of diffusion-weighted magnetic resonance imaging (DWI) for monitoring early treatment response to chemoradiotherapy (CRT) of nasopharyngeal carcinoma (NPC).

Materials and methods

Thirty-one patients with stage III and IV NPC were enrolled in this study from February 2012 to November 2012．T2-weighted and DWI sequences with diffusion factor of 0 and 800mm²/s were performed using a 3.0 T Philips Achieva TX scanner at baseline and 3 days, 20 days (after the first cycle of chemotherapy), 50 days (6 days after radiotherapy initiation) after neoadjuvant chemotherapy (NAC) initiation. The diameter of each primary lesion and target metastatic lymph node before and after the first cycle of NAC was measured and classified into stable disease (SD), partial response (PR) or completed response (CR) based on RECIST 1.1. The apparent diffusion coefficient (ADC) values and changes compared to baseline at each time point were compared between responders (CR and PR) and non-responders (SD). The rates of residual at the end of CRT were compared between these two groups.

Results

A significant increase in ADC was observed at each stage of therapy (P=.001) in lesions of primary and metastatic. The ADC values (ADC), ADC changes (ΔADC) and percentage ADC changes (Δ%ADC) of day 20 in responders were significantly higher than in non-responders for both primary lesions (p=.005, p=.006, p=.008, respectively) and metastatic lymph nodes (p=.002, p=.002, p=.003). Non-responders showed a higher rate of residual for both primary lesions (p=.008) and metastatic lymph nodes (p=.024) than responders.

Conclusions

DW MR imaging allows for detecting early treatment response of NPC. Patients with high ADC values and large ADC increase early after NAC initiation tended to respond better to CRT. Thus, accessing the curative effect of NAC in advanced NPC provides the opportunity to adjust following CRT regimen.     

Proton MR spectroscopy features of normal appearing white matter in neurofibromatosis type 1

To determine whether differences exist between neurofibromatosis type 1 (NF1) patients with or without focal lesions and healthy normal volunteers in the metabolite ratios of normal appearing white matter, 27 patients with NF1 (with parenchymal lesion, MR positive, n: 17; without parenchymal lesions, MR negative, n: 10) and 20 healthy volunteers underwent MRI and short TE (31 ms) proton MR spectroscopy (MRS). In 17 patients with parenchymal lesions, 61 focal lesions were detected by MRI. MRS was performed from normal appearing frontal and posterior parietal white matter (FWM and PWM) in NF1 and from control groups. NAA/Cr, Cho/Cr and MI/Cr ratios were calculated. Significant increase in Cho/Cr and MI/Cr ratios were found in FWM and PWM in MR negative and positive groups when compared to control group. NAA/Cr ratio in MR positive group was significantly decreased in FWM compared to control group. There were no significant differences between FWM and PWM in all metabolite ratios of MR negative group. MI/Cr ratio in MR positive group was significantly elevated in PWM compared to FWM. Metabolite changes detected by MRS could indicate demyelination and gliosis in normal appearing white matter in all NF1 patients, and additionally neuroaxonal damage in the FWM of NF1 patients with focal lesions. For that reason, in the clinical evaluation and follow-up of these patients MRS features of normal appearing white matter should be considered in addition to focal lesions.     

A comparative assessment of preclinical chemotherapeutic response of tumors using quantitative non-Gaussian diffusion MRI

BackgroundDiffusion-weighted MRI (DWI) signal attenuation is often not mono-exponential (i.e. non-Gaussian diffusion) with stronger diffusion weighting. Several non-Gaussian diffusion models have been developed and may provide new information or higher sensitivity compared with the conventional apparent diffusion coefficient (ADC) method. However the relative merits of these models to detect tumor therapeutic response is not fully clear.MethodsConventional ADC, and three widely-used non-Gaussian models, (bi-exponential, stretched exponential, and statistical model), were implemented and compared for assessing SW620 human colon cancer xenografts responding to barasertib, an agent known to induce apoptosis via polyploidy. Bayesian Information Criterion (BIC) was used for model selection among all three non-Gaussian models.ResultsAll of tumor volume, histology, conventional ADC, and three non-Gaussian DWI models could show significant differences between control and treatment groups after four days of treatment. However, only the non-Gaussian models detected significant changes after two days of treatment. For any treatment or control group, over 65.7% of tumor voxels indicate the bi-exponential model is strongly or very strongly preferred.ConclusionNon-Gaussian DWI model-derived biomarkers are capable of detecting tumor earlier chemotherapeutic response of tumors compared with conventional ADC and tumor volume. The bi-exponential model provides better fitting compared with statistical and stretched exponential models for the tumor and treatment models used in the current work.     

Role of apparent diffusion coefficient values for the differentiation of viable and necrotic areas of breast cancer and its potential utility to guide voxel positioning for MRS in the absence of dynamic contrast-enhanced MRI data

We carried out retrospective analysis of apparent diffusion coefficient (ADC) values in 48 infiltrating ductal breast cancer patients who had dynamic contrast-enhanced magnetic resonance imaging (DCEMRI; Group I) and in 53 patients (Group II) for whom DCEMRI data were not available. Twenty-three patients of Group I showed no necrosis (Group Ia), while in 25 patients, both viable (nonnecrotic) and necrotic tumor areas (Group Ib) were observed on DCEMRI. T1-weighted, fat-suppressed and short inversion recovery images were used to identify the viable and necrotic tumor areas in Group II patients, and necrosis was not seen in 11 patients (Group IIa), while 42 (Group IIb) showed both viable and necrotic tumor areas. The ADCs of the necrotic area of Group Ib (1.79±0.30 ×10(-3) mm(2)/s) and Group IIb (1.83±0.40 ×10(-3) mm(2)/s) patients were similar and significantly higher (P<.01) compared to the ADCs of the viable tumor area of Group Ia (0.96±0.21 ×10(-3) mm(2)/s) and Group IIa (0.90±0.17 ×10(-3) mm(2)/s) patients. Proton MR spectroscopy (MRS) data were also available in these patients, and the ADC values were retrospectively determined from the voxel from which MR spectrum was obtained. These values were compared with the ADC obtained for the viable and necrotic areas of the tumor. ADC of the MRS voxel was similar to that obtained for the viable tumor area in patients of both groups. This interesting observation reveals the potential utility of using ADC values to identify viable tumor area for positioning of voxel for MRS in the absence of DCEMRI data.     

Diagnosis of relevant prostate cancer using supplementary cores from magnetic resonance imaging-prompted areas following multiple failed biopsies

Objectives

To establish the value of MRI in targeting re-biopsy for undiagnosed prostate cancer despite multiple negative biopsies and determine clinical relevance of detected tumors.

Materials and Methods

Thirty-eight patients who underwent MRI after 2 or more negative biopsies due to continued clinical suspicion and later underwent TRUS-guided biopsy supplemented by biopsy of suspicious areas depicted by MRI were identified. Diagnostic performance of endorectal 3T MRI in diagnosing missed cancer foci was assessed using biopsy results as the standard of reference. Ratio of positive biopsies using systematic versus MRI-prompted approaches was compared. Gleason scores of detected cancers were used as surrogate for clinical relevance.

Results

Thirty-four percent of patients who underwent MRI before re-biopsy had prostate cancer on subsequent biopsy. The positive biopsy yield with systematic sampling was 23% versus 92% with MRI-prompted biopsies(p < 0.0001). Seventy-seven percent of tumors were detected exclusively in the MRI-prompted zones. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy of MRI to provide a positive biopsy were 92%, 60%, 55%, 94% and 71%, respectively. The anterior gland and apical regions contained most tumors; 75% of cancers detected by MRI-prompted biopsy had Gleason score ≥ 7.

Conclusions

Clinically relevant tumors missed by multiple TRUS-guided biopsies can be detected by a MRI-prompted approach.     

Correlation of proton MR spectroscopy and diffusion tensor imaging

Proton magnetic resonance spectroscopy ((1)H-MRS) provides indices of neuronal damage. Diffusion tensor imaging (DTI) relates to water diffusivity and fiber tract orientation. A method to compare (1)H-MRS and DTI findings was developed, tested on phantom and applied on normal brain. Point-resolved spectroscopy (T(R)/T(E)=1500/135) was used for chemical shift imaging of a supraventricular volume of interest of 8 x 8 x 2 cm(3) (64 voxels). In DTI, a segmental spin-echo sequence (T(R)/T(E)=5500/91) was used and slices were stacked to reproduce the slab used in MRS. The spatial distributions of choline and N-acetylaspartate (NAA) correlated to mean fractional anisotropy and apparent diffusion coefficient (ADC) for the inner 6 x 6=36 voxels defined in MRS, most notably NAA and ADC value (r=-.70, P<.00001; correlation across four subjects, 144 data pairs). This is the first association of neuron metabolite contents in volunteers with structure as indicated by DTI.     

Diffusion-weighted MRI: influence of intravoxel fat signal and breast density on breast tumor conspicuity and apparent diffusion coefficient measurements

Promising recent investigations have shown that breast malignancies exhibit restricted diffusion on diffusion-weighted imaging (DWI) and may be distinguished from normal tissue and benign lesions in the breast based on differences in apparent diffusion coefficient (ADC) values. In this study, we assessed the influence of intravoxel fat signal on breast diffusion measures by comparing ADC values obtained using a diffusion-weighted single shot fast spin-echo sequence with and without fat suppression. The influence of breast density on ADC measures was also evaluated. ADC values were calculated for both tumor and normal fibroglandular tissue in a group of 21 women with diagnosed breast cancer. There were systematic underestimations of ADC for both tumor and normal breast tissue due to intravoxel contribution from fat signal on non–fat-suppressed DWI. This ADC underestimation was more pronounced for normal tissue values (mean difference=40%) than for tumors (mean difference=27%, P<.001) and was worse in women with low breast tissue density vs. those with extremely dense breasts (P<.05 for both tumor and normal tissue). Tumor conspicuity measured by contrast-to-noise ratio was significantly higher on ADC maps created with fat suppression and was not significantly associated with breast density. In summary, robust fat suppression is important for accurate breast ADC measures and optimal lesion conspicuity on DWI.     

Comparison of accuracy of intravoxel incoherent motion and apparent diffusion coefficient techniques for predicting malignancy of head and neck tumors using half-Fourier single-shot turbo spin-echo diffusion-weighted imaging

Purpose

To evaluate the use of the intravoxel incoherent motion (IVIM) technique in half-Fourier single-shot turbo spin-echo (HASTE) diffusion-weighted imaging (DWI), and to compare its accuracy to that of apparent diffusion coefficient (ADC) to predict malignancy in head and neck tumors.

Patients and methods

HASTE DW images of 33 patients with head and neck tumors (10 benign and 23 malignant) were evaluated. Using the IVIM technique, parameters (D, true diffusion coefficient; f, perfusion fraction; D*, pseudodiffusion coefficient) were calculated for each tumor. ADC values were measured over a range of b values from 0 to 1000 s/mm². IVIM parameters and ADC values in benign and malignant tumors were compared using Student's t test, receiver operating characteristics (ROC) analysis, and multivariate logistic regression modeling.

Results

Mean ADC and D values of malignant tumors were significantly lower than those of benign tumors (P < 0.05). Mean D* values of malignant tumors were significantly higher than those of benign tumors (P < 0.05). There was no significant difference in mean f values between malignant and benign tumors (P > 0.05). The technique of combining D and D* was the best for predicting malignancy; accuracy for this model was higher than that for ADC.

Conclusions

The IVIM technique may be applied in HASTE DWI as a diagnostic tool to predict malignancy in head and neck masses. The use of D and D* in combination increases the diagnostic accuracy in comparison with ADC.     

Considerations in applying 3D PRESS H-1 brain MRSI with an eight-channel phased-array coil at 3 T

The purpose of this study was to assess the benefits of a 3 T scanner and an eight-channel phased-array head coil for acquiring three-dimensional PRESS (Point REsolved Spectral Selection) proton (H-1) magnetic resonance spectroscopic imaging (MRSI) data from the brains of volunteers and patients with brain tumors relative to previous studies that used a 1.5 T scanner and a quadrature head coil. Issues that were of concern included differences in chemical shift artifacts, line broadening due to increased susceptibility at higher field strengths, changes in relaxation times and the increased complexity of the postprocessing software due to the need for combining signals from the multichannel data. Simulated and phantom spectra showed that very selective suppression pulses with a thickness of 40 mm and an overpress factor of at least 1.2 are needed to reduce chemical shift artifact and lipid contamination at higher field strengths. Spectral data from a phantom and those from six volunteers demonstrated that the signal-to-noise ratio (SNR) in the eight-channel coil was more than 50% higher than that in the quadrature head coil. For healthy volunteers and eight patients with brain tumors, the SNR at 3 T with the eight-channel coil was on average 1.5 times higher relative to the eight-channel coil at 1.5 T in voxels from normal-appearing brains. In combination with the effect of a higher field strength, the use of the eight-channel coil was able to provide an increase in the SNR of more than 2.33 times the corresponding acquisition at 1.5 T with a quadrature head coil. This is expected to be critical for clinical applications of MRSI in patients with brain tumors because it can be used to either decrease acquisition time or improve spatial resolution.     

Diffusion-weighted imaging of local recurrent prostate cancer after radiation therapy: comparison with 22-core three-dimensional prostate mapping biopsy

Accurate localization of local recurrence within the prostate gland is important to perform focal salvage therapy effectively with minimal complications. The purpose of this study was to evaluate the usefulness of diffusion-weighted imaging (DWI) in the detection and localization of prostate cancer recurrence in patients with biochemical failure after definitive radiation therapy using 22-core three-dimensional prostate mapping biopsy (3D-PMB) as a standard reference. Ten patients who underwent magnetic resonance imaging and 22-core 3D-PMB were retrospectively analyzed. For visual assessment of DWI, the prostate was divided into 22 regions corresponding to 3D-PMB. Two diagnostic radiologists determined the presence of abnormal high signal intensity in each region on DWI, and the results of DWI were compared with those of 3D-PMB. Of the 220 regions, 16 regions in six patients were positive for cancer on 3D-PMB, and 30 regions in six patients were judged as positive on DWI. On a patient-by-patient basis, sensitivity and specificity were 100% (6/6) and 100% (4/4), respectively. On a region-by-region basis, sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 69% (11/16), 91% (185/204), 37% (11/30), 97% (185/190) and 89% (196/220), respectively. For discrepant localization between DWI and pathology, DWI-positive and pathology-positive regions tended to be adjacent to each other. In conclusion, DWI is a useful tool for the detection and localization of recurrent prostate cancer in patients with biochemical failure after radiation therapy and may be helpful in the planning of focal salvage therapy.     

Can diffusion-weighted imaging be used as a reliable sequence in the detection of malignant pulmonary nodules and masses?

Recent developments in diffusion-weighted magnetic resonance imaging (DWI) make it possible to image malignant tumors to provide tissue contrast based on difference with the diffusion of water molecules among tissues, which can be measured by the apparent diffusion coefficient (ADC) value. We aimed to assess the diagnostic accuracy of DWI for benign/malignant discrimination of pulmonary nodules/masses with a meta-analysis. The MEDLINE, EMBASE, Cancerlit and Cochrane Library database, from January 2001 to August 2011, were searched for studies evaluating the diagnostic accuracy of DWI for benign/malignant discrimination of pulmonary nodules. We determined sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LRP and LRN), and constructed summary receiver operating characteristic SROC) curves. Across 10 studies (545 patients), there was no evidence of publication bias (P= .22, bias=−19.19). DWI had a pooled sensitivity of 0.84 (95% CI, 0.76–0.90) and a pooled specificity of 0.84 (95% CI, 0.64–0.94). Overall, LRP was 5.3 (95% CI, 2.1–13.0) and LRN was 0.19 (95% CI, 0.12–0.30). In patients with high pretest probabilities, DWI enabled confirmation of malignant pulmonary lesion; in patients with low pretest probabilities, DWI enabled exclusion of malignant pulmonary lesion. Worst-case-scenario (pretest probability, 50%) posttest probabilities were 84% and 16% for positive and negative DWI results, respectively. Diffusion-weighted magnetic resonance imaging can be used to differentiate malignant from benign pulmonary lesions. High-quality prospective studies regarding DWI in the evaluation of pulmonary nodules are still needed to be conducted.