Diagnosis of liver metastases: Can diffusion-weighted imaging (DWI) be used as a stand alone sequence?

Objectives

To evaluate if diffusion-weighted MRI (DWI) can replace gadolinium-enhanced MRI (Gd-MRI) for diagnosing liver metastases. The diagnostic accuracy of both techniques alone and in combination are compared.

Materials and methods

Sixty-eight patients with histologically proven primary extrahepatic tumors were included in this retrospective study. Lesions included 62 metastases and 130 benign lesions. Three image sets (unenhanced T1 and T2/gadolinium enhanced T1 (Gd-MRI), DWI and combination of both) were reviewed independently by 3 observers. The areas under the receiver operating characteristic curves (A_z), sensitivity and specificity for the 3 image sets were compared. The standard of reference was either histopathology or multi-modality and clinical follow-up.

Results

Pooled data showed higher diagnostic accuracy for the combined set (A_z = 0.93) compared to Gd-MRI (p = 0.001) and DWI (p < 0.0001). No difference was found between the performance of Gd-MRI and DWI (p = 0.09). Sensitivity for the combined set was higher than Gd-MRI (p = 0.0003) and DWI (p = 0.0034). Specificity for DWI was lower than Gd-MRI (p < 0.0001) and the combined set (p < 0.0001).

Conclusion

The diagnostic performance of DWI is equal to that of Gd-MRI. DWI alone can be used in patients where gadolinium contrast administration is not allowed. Combination of Gd-MRI and DWI significantly increases diagnostic accuracy.     

Sandwich sign of Borrmann type 4 gastric cancer on diffusion-weighted magnetic resonance imaging

Objective

To assess the appearance of Borrmann type 4 (BT-4) gastric cancer on diffusion-weighted magnetic resonance imaging (DWI) and to investigate the potential of qualitative and quantitative DW images analysis to differentiate BT-4 gastric cancer from poorly distended normal stomach wall.

Materials and methods

DWI was performed on 23 patients with BT-4 gastric cancer and 23 healthy volunteers. The signal characteristics and correlated histopathological basis of the cancers on DWI were investigated. The contrast-to-noise ratios (CNR) of cancer were compared between DWI and T1WI/T2WI_. The thickness and apparent diffusion coefficient (ADC) of cancer and normal stomach wall were compared.

Results

All of the gastric cancers displayed hyperintensity compared to the nearby normal gastric wall on DWI. A three-layer sandwich sign that demonstrated high signal intensity in the inner and outer layer, and low signal intensity in the intermediate layer was observed in 69.6% of cancers on DWI. The low signal intensity represents the muscularis propria through the comparison with pathology, and it is postulated that scattering distribution of the cancer cells in this layer causes less damage and subsequently less restriction of water movement, which causes the low signal intensity on DWI. The CNR obtained with DWI was higher than that with T1WI and T2WI (P < 0.001). The mean ADC value of BT-4 gastric cancer was significantly lower than the poorly distended normal stomach wall (1.12 ± 0.23 × 10⁻³ mm²/s vs. 1.93 ± 0.22 × 10⁻³ mm²/s, P < 0.01).

Conclusion

DWI can highlight the signals of BT-4 gastric cancer which may present a characteristic three-layer sandwich sign, and ADC values are helpful in the discrimination of gastric cancer from poorly distended stomach wall.     

Detection and classification of focal liver lesions in patients with colorectal cancer: retrospective comparison of diffusion-weighted MR imaging and multi-slice CT

Objectives

To compare the diagnostic performance of diffusion-weighted MR imaging (DWI) with multi-slice CT (MS-CT) in the detection and classification of focal liver lesions in patients with colorectal cancer.

Methods

In a retrospective study 68 patients who underwent DWI at 1.5 T (b-values of 50, 300 and 600 s/mm²) and contrast-enhanced MS-CT were analysed by two radiologists blinded to the clinical results. Imaging results were correlated with intraoperative surgical and ultrasound findings (n = 24), imaging follow-up or PET (n = 44). Sensitivity of DWI and MS-CT in detection of focal liver lesions was compared on a per-lesion and a per-segment basis. Receiver operator-characteristic (ROC) curves to determine the diagnostic performance and the sensitivities of correctly identifying liver metastases on a segmental base were calculated.

Results

For lesion detection, DWI was significantly superior to MS-CT both on a per-lesion (difference in sensitivities for reader 1 and 2 22.65% and 19.06%, p < 0.0001) and a per-segment basis (16.86% and 11.76%, p < 0.0001). Especially lesions smaller than 10 mm were better detected with DWI compared to MS-CT (difference 41.10% and 29.45%, p < 0.0001). ROC-analysis showed superiority for lesions classification (p < 0.0001) of DWI (AUC: 0.949 and 0.951) as compared to MS-CT (AUC: 0.879 and 0.892, p < 0.0001 and p = 0.005). DWI was able to filter out metastatic segments with a higher sensitivity (88.2 and 86.5%) compared to MS-CT (68.0 and 67.4%, p < 0.0001 and p = 0.005, respectively).

Conclusion

Compared to MS-CT DWI is both more sensitive in the detection of liver lesions and more accurate in determining the extent of metastatic disease in patients with colorectal cancer and therefore might help to optimize therapeutic management in those patients.     

MRI of fat necrosis of the breast: the "black hole" sign at short tau inversion recovery

Objective

To describe MRI features of fat necrosis of the breast.

Materials and methods

Twenty-five lesions in 16 patients were retrospectively analyzed. MRI was performed due to equivocal findings at conventional imaging after surgical treatment of cancer (n = 14) or during anticoagulant therapy (n = 1), after focal mastitis treated with ductal resection (n = 1). In the 15 patients with previous surgery MRI was performed after a median interval of 24 months, using short tau inversion recovery (STIR) and contrast-enhanced dynamic T1-weighted sequences. Signal-to-noise ratio (SNR) inside the lesion and surrounding healthy fat was calculated on both STIR and unenhanced T1-weighted images. Maximal lesion diameter was measured on STIR images. All lesions had final clinical and imaging assessment in favor of fat necrosis and negative clinical and imaging follow-up (21–40 months; median 24 months).

Results

At STIR sequence, fat necrosis appeared as a “black hole”, being markedly hypointense (median SNR = 29) compared with surrounding fat (median SNR = 95) (P < 0.001), while no significant difference was found at unenhanced T1-weighted sequence. No significant correlation with time from treatment was found. Of 25 lesions, 15 showed ring enhancement, with continuous increase (n = 10), plateau (n = 2), or wash-out curve (n = 3). The 11 enhancing lesions in the 8 patients with previous radiation therapy showed an initial enhancement higher than that of the 4 enhancing lesions in the 2 patients who did not, although the difference was not significant (P = 0.104).

Conclusion

Fat necrosis of the breast exhibits a “black hole” sign on STIR images, allowing for an easier diagnosis in clinical practice.     

Quantitative perfusion computed tomography measurements of cerebral hemodynamics: correlation with digital subtraction angiography identified primary and secondary cerebral collaterals in internal carotid artery occlusive disease

Background

The aim of the present study was to assess hemodynamic variations in symptomatic unilateral internal carotid artery occlusion (ICAO) patients with primary collateral flow via circle of Willis or secondary collateral flow via ophthalmic artery and/or leptomeningeal collaterals.

Methods

Thirty-eight patients with a symptomatic unilateral ICAO were enrolled in the study. Based on digital subtraction angiography (DSA) findings, patients were classified into 2 groups: primary collateral (n = 14) and secondary collateral (n = 24) groups. Collateral flow hemodynamics were investigated with perfusion computed tomography (PCT) by measuring the cerebral blood flow (CBF), cerebral blood volume (CBV) and time to peak (TTP) in the hemispheres ipsilateral and contralateral to ICAO. Based on the measurements, the ipsilateral to contralateral ratio for each parameter was calculated and compared.

Results

Irrespective of the collateral patterns, ipsilateral CBF was not significantly different from that of the contralateral hemisphere (P = 0.285); ipsilateral CBV and TTP was significantly increased compared with those of the contralateral hemisphere (P = 0.000 and P = 0.000 for CBV and TTP, respectively). Furthermore, patients with secondary collaterals had significantly larger ipsilateral-to-contralateral ratios for both CBV (rCBV, P = 0.0197) and TTP (rTTP, P = 0.000) than those of patients with only primary collaterals. These two groups showed no difference in ipsilateral-to-contralateral ratio for CBF (rCBF, P = 0.312).

Conclusion

Patients with symptomatic unilateral ICAO in our study were in an autoregulatory vasodilatation status. Moreover, secondary collaterals in ICAO patients were correlated with ipsilateral CBV and delayed TTP that suggested severe hemodynamic impairment, presumably increasing the risk of ischemic events.     

MR spectroscopy of liver in overweight children and adolescents: investigation of ¹H T₂ relaxation times at 3T

Objective

The objective was to investigate T₂ relaxation values and to optimize hepatic fat quantification using proton MR spectroscopy (¹H MRS) at 3 T in overweight and obese children and adolescents.

Subjects

The study included 123 consecutive children and adolescents with a body mass index above the 97th percentile according to age and sex.¹H MR spectroscopy was performed at 3.0 T using point resolved spectroscopy sequence with series TE. T₂ relaxation values and hepatic fat content corrected for the T₂ relaxation effects were calculated.

Results

T₂ values for water ranged from 22 ms to 42 ms (mean value 28 ms) and T₂ values for fat ranged from 36 ms to 99 ms (mean value 64 ms).Poor correlation was observed: (1) between T₂ relaxation times of fat and T₂ relaxation times of water (correlation coefficient r = 0.038, P = 0.79); (2) between T₂ relaxation times of fat and fat content (r = 0.057, P = 0.69); (3) between T₂ relaxation times of water and fat content (r = 0.160, P = 0.26).Correlation between fat peak content and the T₂ corrected fat content decreased with increasing echo time TE: r = 0.97 for TE = 45, r = 0.93 for TE = 75, r = 0.89 for TE = 105, P < 0.0001.

Conclusion

¹H MRS at 3 T is an effective technique for measuring hepatic fat content in overweight and obese children and adolescents. It is necessary to measure T₂ relaxation values and to correct the spectra for the T₂ relaxation effects in order to obtain an accurate estimate of the hepatic fat content.     

Diffusion weighted MR imaging in patients with HCC and liver cirrhosis after administration of different gadolinium contrast agents: Is it still reliable?

Purpose

Diffusion weighted imaging (DWI) is an emerging technique for abdominal MR and usually performed before intravenous contrast injection. Recent studies performed in patients with normal liver function have shown that DWI can be performed after gadolinium administration. Aim of this study was to compare DWI before and after administration of different gadolinium compounds in patients with HCC and liver cirrhosis.

Materials and methods

15 patients with known HCC and liver cirrhosis underwent liver MRI at 1.5 T (Magnetom Avanto, Siemens) including DWI on day 1 before and after administration of gadobutrol (Gadovist^®) and on day 2 after administration of EOB-Gadolinium-DTPA (Primovist^®). Signal to noise ratios (SNR) and contrast to noise ratios (CNR) of HCC lesions were determined for all DWI data sets. Furthermore, ADC values were compared using a Wilcoxon test. A p-value <0.05 indicated statistically significant differences.

Results

There were no statistically significant differences regarding SNR pre-contrast (mean: 48.1), after gadobutrol (mean: 47.7) or after EOB-Gadolinium-DTPA (mean: 50.0; values for b = 50 s/mm²). Similarly, no significant differences were found for CNR (average values:34.4 vs. 32.3 vs. 30.7; b = 50 s/mm²) nor for ADC-values (mean: 1.5 vs. 1.4 vs. 1.5 × 10⁻³ mm²/s) of HCC.

Conclusion

There is no significant difference regarding DWI in patients with cirrhosis before and after contrast injection. Hence, it is reliable to run DWI after gadolinium either as an alternative for unsuccessful pre-contrast DWI or as a gap filler to spare time in EOB-Gadolinium-DTPA imaging.     

Diffusion-weighted MR imaging for detection of extrahepatic cholangiocarcinoma

Objectives

To measure the sensitivity of diffusion-weighted imaging (DWI) and determine the most appropriate b value for DWI; to explore the correlation between the apparent diffusion coefficient (ADC) value and the degree of extrahepatic cholangiocarcinoma differentiation.

Methods

Preoperative diffusion-weighted imaging and magnetic resonance examinations were performed for 31 patients with extrahepatic cholangiocarcinoma. Tumor ADC values were measured, and the signal-to-noise ratio, contrast-to-noise ratio, and signal-intensity ratio between the diffusion-weighted images with various b values as well as the T2-weighted images were calculated. Pathologically confirmed patients were pathologically graded to compare the ADC value with different b values of tumor at different degrees of differentiation, and the results were statistically analyzed by using the Friedman test.

Results

A total of 29 cases of extrahepatic cholangiocarcinoma were detected by DWI. As the b value increased, tumor signal-to-noise ratio and contrast-to-noise ratio between the tumor and normal liver gradually decreased, but the tumor signal-intensity ratio gradually increased. When b = 800 s/mm², contrast-to-noise ratio between tumor and normal liver, tumor signal-intensity ratio, and tumor signal-to-noise ratio of diffusion-weighted images were all higher than those of T2-weighted images; the differences were statistically significant (P < 0.05). As the b value increased, the tumor ADC value gradually declined. As the degree of differentiation decreased, the tumor ADC value declined.

Conclusion

The b value of 800 s/mm² was the best in DWI of extrahepatic cholangiocarcinoma; the lesion ADC value declined as the degree of cancerous tissue differentiation decreased.     

Diffusion weighted MRI and 18F-FDG PET/CT in non-small cell lung cancer (NSCLC): Does the apparent diffusion coefficient (ADC) correlate with tracer uptake (SUV)?

Introduction

To investigate the potential correlation of the apparent diffusion coefficient assessed by diffusion-weighted MRI (DWI) and glucose metabolism determined by the standardized uptake value (SUV) at 18F-FDG PET/CT in non-small cell lung cancer (NSCLC).

Materials and methods

18F-FDG PET/CT and DWI (TR/TE, 2000/66 ms; b-values, 0 and 500 s/mm²) were performed in 41 consecutive patients with histologically verified NSCLC. Analysing the PET-CT data calculation of the mean (SUV_mean) and maximum (SUV_max) SUV was performed. By placing a region-of-interest (ROI) encovering the entire tumor mean (ADC_mean) and minimum ADC (ADC_min) were determined by two independent radiologists. Results of 18F-FDG PET-CT and DWI were compared on a per-patient basis. For statistical analysis Pearson's correlation coefficient, Bland–Altman and regression analysis were assessed.

Results

Data analysis revealed a significant inverse correlation of the ADC_min and SUV_max (r = −0.46; p = 0.032). Testing the correlation of the ADC_min and SUV_max for each histological subtype separately revealed that the inverse correlation was good for both adenocarcinomas (r = −0.47; p = 0.03) and squamouscell carcinomas (r = −0.71; p = 0.002), respectively. No significant correlation was found for the comparison of ADC_min and SUV_mean (r = −0.29; p = 0.27), ADC_mean vs. SUV_mean (r = −0.28; p = 0.31) or ADC_mean vs. SUV_max (r = −0.33; p = 0.23). The κ-value of 0.88 indicated a good agreement between both observers.

Conclusion

This preliminary study is the first to verify the relation between the SUV and the ADC in NSCLC. The significant inverse correlation of these two quantitative imaging approaches points out the association of metabolic activity and tumor cellularity. Therefore, DWI with ADC measurement might represent a new prognostic marker in NSCLC.     

Association of degree and type of edema in posterior reversible encephalopathy syndrome with serum lactate dehydrogenase level: initial experience

Purpose

Posterior reversible encephalopathy syndrome (PRES) is a clinicoradiologic entity characterized by headache, blurred vision and seizures with typical parieto-occipital predominantly vasogenic edema, occasionally with cytotoxic edema. The association between the degree and type of edema in PRES with biochemical parameter, especially serum lactate dehydrogenase, has not been determined.

Material and methods

Thirty-five patients with typical clinical symptoms and characteristic MR imaging findings of PRES were included in this study. The extent of brain edema was graded on the anatomical distribution by 2 observers blinded to patients’ clinical record, as well as the type of brain edema determined on DWI and ADC map. The levels of biochemical parameters were correlated with the degree of edema and compared between different types of edema.

Results

Serum LDH concentrations between patients with cytotoxic edema and with vasogenic components were not statistically different (NWU test, U = 93.0, Z = 1.818, P = 0.069). Only serum lactate dehydrogenase (LDH) concentration was significantly correlated with the score of brain edema distribution (Spearman's rho correlation, r = 0.721, P = 0.00). No relationship was found between other biochemical parameters and the degree and type of brain edema.

Conclusion

Increased serum LDH level, which plays an essential role in endothelial injury, may be a potential risk factor for the development of edema in PRES.     

Multiphase contrast-saline mixture injection with dual-flow in 64-row MDCT coronary CTA

Purpose

To explore the feasibility of multiphase contrast–saline mixture with dual-flow injection technique for visualization of right ventricular (RV) cavity and interventricular septum (IVS) in 64-row multidetector computed tomography (MDCT) coronary angiography.

Materials and methods

Twenty-four patients underwent coronary CT angiography (CTA) imaging with 64-row MDCT. In twelve patients (group A), 60 ml contrast medium (CM) bolus was followed by 40 ml saline, and in the other twelve patients (group B), 50 ml CM bolus was followed by 50 ml contrast–saline mixture at 60:40 ratio. The CM, saline and contrast–saline mixture flow rate were all 5.0 ml/s. Two experienced radiologists measured the CT values of ascending aorta, descending aorta, pulmonary artery and RV, rated the uniformity of RV cavity, the visualization of coronary arteries and IVS independently.

Results

By Kappa test, agreement between the two radiologists was 0.93 and 0.86 concerning the CT value measurements and the grades of the three indexes, respectively. By t-test, the mean CT values of ascending aorta and descending aorta of the two groups had no statistical difference (t = 1.459, P > 0.05; t = 1.619, P > 0.05); while the mean CT values of pulmonary artery and RV cavity had statistical differences (t = 8.316, P < 0.05; t = 10.372, P < 0.05). By two-related rank sum test, according to the visualization of coronary arteries and the uniformity of RV cavity, there were no statistical differences (U = 66.00, P > 0.05; U = 54.00, P > 0.05); while according to the visualization of IVS, group B was better than group A (U = 8.00, P < 0.05).

Conclusion

In coronary CTA, a contrast–saline mixture after CM bolus can provide clear visualization of RV and IVS and LV without impairing coronary CTA image.     

Correlation of measurements from diffusion weighted MR imaging and FDG PET/CT in GIST patients: ADC versus SUV

Purpose

We investigated the correlation relationship between ADCs measured by MRI and SUVs measured by PET/CT of lesions on GIST (gastrointestinal stromal tumor) patients to verify if MR is able to replace or serve as an alternative to PET/CT in GIST staging and treatment monitoring.

Materials and methods

Between September 2010 and January 2011, five patients with histologically proven metastatic GIST in Queen Mary Hospital, Hong Kong were enrolled into our study. All patients underwent both MRI and PET/CT scans at prognosis. Pearson's correlations of twenty-nine lesions were conducted between 5 pairs of ADCs and SUVs values.

Results

Lesions in the liver, peritoneum or bowel loops were found by PET/CT and no extra-abdominal lesion was identified. All twenty-nine lesions are identifiable by MRI with sensitivity of 100%. Significant inverse correlation were found between ADC_mean and SUV_mean (P = 0.006), ADC_mean and SUV_max (P = 0.010), ADC_min and SUV_max (P = 0.014), ADC_min and SUV_mean (P = 0.026), rADC_min and rSUV_max (P = 0.047).

Conclusion

DWI is comparable to PET/CT in visually detecting the GIST lesions’ location. Significant inverse correlations were found between ADCs from DWIBS and SUVs from PET/CT on data of GIST patients. This finding demonstrates that DWI is potentially capable of offering similar information for diagnosis and treatment response evaluating in GIST's patients as PET/CT does. Furthermore, ADC_min, which is determined by single pixel, is not as reliable as ADC_mean, which is weighted average value of the whole lesion volume.     

Diffusion weighted imaging of liver lesions suspect for metastases: Apparent diffusion coefficient (ADC) values and lesion contrast are independent from Gd-EOB-DTPA administration

Purpose

Gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) enhanced liver MRI is widely used for detection and differentiation of focal liver lesions. Diffusion weighted imaging (DWI) including apparent diffusion coefficient (ADC) measurements is increasingly utilised as a fast and, with limitations, quantitative method for liver lesion detection and characterisation. Herein we investigate whether the administration of Gd-EOB-DTPA affects DWI.

Materials and methods

31 consecutive patients referred to standardised liver MRI (1.5 T, Gd-EOB-DTPA, 0.025 mmol/kg) were retrospectively reviewed. All underwent a breathhold DWI sequence before and after contrast agent administration (EPI-DWI, TR/TE (effective): 2100/62 ms, b-values: 0 and 800 s/mm²). Patients with previously treated liver lesions were excluded. Signal intensity of lesion, parenchyma and noise on DWI images as well as the ADC value were measured after identification by two observers in consensus using manually placed regions of interest. The reference standard was imaging follow-up determined separately by two radiologists. Data analysis included signal-to-noise (SNR) ratio and contrast-to-noise ratio (CNR) calculations, comparisons were drawn by employing multiple Bonferroni corrected Wilcoxon signed-rank tests.

Results

50 malignant and 39 benign lesions were identified. Neither SNR, CNR nor ADC values showed significant differences between pre- and postcontrast DWI. Both pre- and postcontrast ADC values differed significantly between benign and malignant lesions (P < 0.001).

Conclusion

We did not identify a significant influence of Gd-EOB-DTPA on DWI of liver lesions. This allows for individual tailoring of imaging protocols according to clinical needs.     

Assessment of liver tumor response by high-field (3T) MRI after radiofrequency ablation: Short- and mid-term evolution of diffusion parameters within the ablation zone

Purpose

To compare the apparent diffusion coefficient (ADC) values of malignant liver lesions on diffusion-weighted MRI (DWI) before and after successful radiofrequency ablation (RF ablation).

Materials and methods

Thirty-two patients with 43 malignant liver lesions (23/20: metastases/hepatocellular carcinomas (HCC)) underwent liver MRI (3.0 T) before (<1 month) and after RF ablation (at 1, 3 and 6 months) using T2-, gadolinium-enhanced T1- and DWI-weighted MR sequences. Jointly, two radiologists prospectively measured ADCs for each lesion by means of two different regions of interest (ROIs), first including the whole lesion and secondly the area with the visibly most restricted diffusion (MRDA) on ADC map. Changes of ADCs were evaluated with ANOVA and Dunnett tests.

Results

Thirty-one patients were successfully treated, while one patient was excluded due to focal recurrence. In metastases (n = 22), the ADC in the whole lesion and in MRDA showed an up-and-down evolution. In HCC (n = 20), the evolution of ADC was more complex, but with significantly higher values (p = 0.013) at 1 and 6 months after RF ablation.

Conclusion

The ADC values of malignant liver lesions successfully treated by RF ablation show a predictable evolution and may help radiologists to monitor tumor response after treatment.     

PET/CT scanning guided intensity-modulated radiotherapy in treatment of recurrent ovarian cancer

Objective

This study was undertaken to evaluate the clinical contribution of positron emission tomography using ¹⁸F-fluorodeoxyglucose and integrated computer tomography (FDG-PET/CT) guided intensity-modulated radiotherapy (IMRT) for treatment of recurrent ovarian cancer.

Materials and methods

Fifty-eight patients with recurrent ovarian cancer from 2003 to 2008 were retrospectively studied. In these patients, 28 received PET/CT guided IMRT (PET/CT–IMRT group), and 30 received CT guided IMRT (CT–IMRT group). Treatment plans, tumor response, toxicities and survival were evaluated.

Results

Changes in GTV delineation were found in 10 (35.7%) patients based on PET–CT information compared with CT data, due to the incorporation of additional lymph node metastases and extension of the metastasis tumor. PET/CT guided IMRT improved tumor response compared to CT–IMRT group (CR: 64.3% vs. 46.7%, P = 0.021; PR: 25.0% vs. 13.3%, P = 0.036). The 3-year overall survival was significantly higher in the PET–CT/IMRT group than control (34.1% vs. 13.2%, P = 0.014).

Conclusions

PET/CT guided IMRT in recurrent ovarian cancer patients improved the delineation of GTV and reduce the likelihood of geographic misses and therefore improve the clinical outcome.     

Clinical usefulness of the visibility of the transcerebral veins at 3T on T2*-weighted sequence in acute stroke patients

Objectives

The objective of this work was to investigate the clinical usefulness of the visibility of the transcerebral veins (VTV) in acute ischemic stroke patients at 3 T.

Methods

Sixty consecutive carotid artery territory stroke patients were included retrospectively. Two readers categorized the VTV on T2*-weighted sequence at 3 T for each hemisphere, and asymmetry of this sign was assessed between each hemisphere by an asymmetry index (AI) using a three-item scale. The VTV and AI were correlated with clinical and radiological covariates. Particular interest was focused on patients for whom initial diffusion-weighted imaging alone was inconclusive.

Results

VTV were detected in the stroke hemisphere in 58.3% (n = 35) and in the contralateral side in 10% (n = 6, p < 0.0001). Asymmetry of the VTV between ischemic and contralateral hemispheres was present in 53.3% (n = 32). Intracranial artery occlusion, final infarct volume and symptomatic hemorrhagic transformation were correlated with a higher AI at baseline (ρ = 0.563, ρ = 0.291, and ρ = 0.285, p < 0.05, respectively). Three hyperacute stroke patients with subtle DWI high signal intensity at admission demonstrated VTV.

Conclusions

The pathological value of the VTV seems to reside in its asymmetry between hemispheres, as it was correlated with important clinical parameters. This study also suggests that the VTV could be a supportive finding in stroke diagnosis, especially when DWI is unreliable.     

Comparison of acquired diffusion weighted imaging and computed diffusion weighted imaging for detection of hepatic metastases

Objective

To compare the accuracy of acquired diffusion weighted imaging (DWI) (b = 1000 s/mm²) with that of computed DWI (b = 1000 s/mm²) for the detection of hepatic metastases.

Methods

Two hundred and sixty patients underwent abdominal magnetic resonance imaging (MRI) at 3.0 T for the evaluation of hepatic metastasis, including T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), heavily T2WI, DWI with b-values of 0, 500, 1000 s/mm², and three-dimensional dynamic contrast-enhanced MRI with gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA), and 190 patients were included in the final study. Computed DWI (=1000 s/mm²) was synthesized from lower b-values (b = 0 and 500 s/mm²). Two groups were assigned and compared: group A (acquired DWI) and group B (computed DWI). Diagnostic performance using each imaging set was evaluated by receiver operating characteristic (ROC) curve analysis.

Results

A total of 76 hepatic metastases were confirmed. The area under the ROC curve (Az) of group A was larger than that of group B (Observer 1; 0.919–0.915, Observer 2; 0.926–0.901), but there were no significant differences (observer 1, P = 0.500; observer 2, P = 0.190). There were 5 metastases visualized in group A, but these were difficult to detect in group B. However, there were 2 metastases that were better visualized in group B than in group A.

Conclusion

There were no significant differences between acquired DWI and computed DWI in the detection of hepatic metastasis.     

Utility of chemical shift and diffusion-weighted imaging in characterization of hyperattenuating adrenal lesions at 3.0T

Objective

The purpose of our study was to evaluate the value of chemical shift imaging (CSI) and diffusion weighted imaging (DWI) at 3.0 T MRI in adrenal hyperattenuating lesions.

Methods

Fifty-one hyperattenuating adrenal lesions in 40 patients were evaluated. Signal intensity index (SII), adrenal to spleen ratio (ASR) and apparent diffusion coefficient (ADC) were used as quantitative analysis parameters.

Results

The mean SII, ASR and ADC values were: benign pheochromocytomas (n = 22), 7.04%; 0.96, 1.15 × 10⁻³ mm²/s; lipid-poor adenomas (n = 18), 33.77%, 0.71, 1.07 × 10⁻³ mm²/s; malignant tumors (n = 7), 11.24%; 1.00; 0.92 × 10⁻³mm²/s. There were significant differences between the lipid-poor adenomas and nonadenomas for SII and ASR, and there were significant differences between the benign and the malignant tumor ADC values. The optimal diagnostic threshold point of SII and ASR for lipid-poor adenomas was 11.96%, 0.83, the sensitivity and specificity were 88.9%, 97.5% and 97%, 83.3%. The optimal diagnostic threshold point of ADC value for benign lesions and malignant tumors was 1.04 × 10⁻³ mm²/s, the sensitivity and specificity were 61.4% and 85.7%.

Conclusion

Quantitative analysis of chemical shift MRI and DWI can help to characterize the hyperattenuating adrenal lesions, especially in differentiatiation between the lipid-poor adenomas, the benign pheochromocytomas, and the malignant tumors.     

High b-value diffusion-weighted MR imaging of normal brain at 3T

Introduction

The purpose of this study was to determine the normative apparent diffusion coefficient (ADC) values at 3 T using high b-value (3000 s/mm²) diffusion-weighted images (DWI) and compare the signal characteristics of the high b value with standard b-value (1000 s/mm²) DWI.

Methods

Institutional review board approval was obtained for this prospective study which included 20 volunteers (10 M, 10 F, mean age: 38.7 ± 14.9) without any known clinical disease or radiological findings. All brain examinations were performed with 3 T MR by using similar parameters of b1000 and b3000 DWI sequences. DWI and ADC maps were obtained. Signal intensity, noise, signal to noise ratio (SNR), contrast to noise (CNR), contrast ratio (CR), and ADC values of bilateral posterior limb of internal capsule, frontal white matter, parietal gray matter, pons, thalamus, splenium of corpus callosum were measured on b1000 and b3000 DW images.

Results

In all anatomic locations, MR signal intensity, SNR and ADC values of b3000 images were significantly lower than MR signal intensity, SNR and ADC values of b1000 images (p < 0.001). The CNR and CR values at the posterior limb of internal capsule and pons were significantly increased on b3000 images (p < 0.001) and decreased in the other regions measured.

Conclusion

The ADC values calculated from standard b-value DWI were significantly higher than those calculated from high b-value DWI. These results agree with the previous studies. In the regions where CNR values increase with high b value, b3000 DWI images may provide additional clinical information.     

Renal and perirenal space involvement in acute pancreatitis: An MRI study

Objectives

To study the prevalence and characteristics of renal and perirenal space involvement and its relation to the severity of acute pancreatitis (AP) using MRI.

Methods

115 patients with AP who underwent MRI with the clinical kidney function test were retrospectively analyzed in this study. MRI sequences included conventional and diffusion weighted imaging (DWI) sequences. The renal and perirenal space involvement in AP was noted on MRI. The renal apparent diffusion coefficient (ADC) on DWI was measured for each kidney. The severity of AP on MRI was graded using MR severity index (MRSI). The relationships among the renal and perirenal space involvement on MRI, the renal ADC, MRSI and the results of the kidney function test were analyzed.

Results

In the 115 patients with AP, the renal and perirenal space abnormalities detected included renal parenchymal abnormalities (0.8%), abnormalities of the renal collecting system (2.6%), renal vascular abnormalities (1.7%), thickened renal fascia (99%), perirenal stranding (62%) and perirenal fluid collection (40%). The prevalence of perirenal space abnormalities was correlated with the severity of AP based on MRSI (P < 0.05). The renal ADC values were lower in patients with abnormal kidney function than in those without kidney injury (P < 0.05). The prevalence of kidney function abnormalities was 9.4%, 32% and 100% in mild, moderate, and severe AP cases, respectively (P = 0.00).

Conclusion

Perirenal space involvement is much more than renal parenchymal involvement in AP. The prevalence of perirenal space involvement in AP on MRI has a positive correlation with the severity of AP according to MRSI.