The utility of high b-value DWI in evaluation of ischemic stroke at 3 T

Purpose

The utility of DWI with high b-value in ischemic stroke is still unsettled. The purpose of this study is to compare high b-value (3000) and standard b-value (1000) diffusion-weighted images in patients with ischemic stroke at 3 T.

Materials and methods

27 patients with acute stroke who were admitted to the hospital during the first 24 h after symptom onset were included in this study. All patients had a brain MRI study with stroke protocol including standard (b = 1000) DWI and high b-value (b = 3000) DWI sequences at 3 T MR scanner.Number and localization of the lesions were assessed MR signal intensities (SI), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), contrast ratio (CR) and apparent diffusion coefficient (ADC) values of the lesions and normal parenchyma on DWI with b = 1000 and b = 3000 sequences were measured.

Results

All patients with acute stroke revealed hyperintense lesions due to restricted diffusion on DWI with both b-values. However, lesions of restricted diffusion were more conspicuous in b = 3000 value DWI than b = 1000, and additional 4 ischemic lesions were detected on b = 3000 DWI. SNR, CNR, SI and also ADC values in both stroke area and normal parenchyma were lower at b = 3000 than the value at b = 1000. At b = 3000, CR was significantly greater than b = 1000 images.

Conclusions

Although quantitative analysis shows higher SI, SNR and CNR values with standard b-value (b = 1000) diffusion-weighted imaging, using higher b-value may still be beneficial in detecting additional subtle lesions in patients whose clinical findings are not correlated with standard b-value DWI in stroke.     

Effect of gadolinium chelate contrast agents on diffusion weighted MR imaging of the liver, spleen, pancreas and kidney at 3 T

Purpose

To retrospectively test the null hypotheses that the qualitative appearance of DWI and the signal intensity values in DWI and corresponding ADC values of the liver, spleen, pancreas and kidneys are identical before and after the administration of gadolinium.

Materials and methods

Following IRB approval, DWI was acquired in 50 patients (25 male; mean age 54.9 years) prior to and after contrast administration, using single-shot echo planar imaging with b-values of 50 s/mm² and 800 s/mm² at 3 T. Binomial analysis was used to determine which image set was more significantly preferred in conveying the diffusion information. Pre- and post-gadolinium DWI and ADC values of corresponding regions of each organ were analyzed using standardized signal intensity measurements.

Results

Pre-contrast DWI images of the liver, spleen, and pancreas were preferred 52%, 49%, and 58%, respectively, with none of the differences being statistically significant. DWI of the kidneys was preferred on pre-contrast images in 83% (p < 0.001). In the liver and spleen, contrast caused a significant increase in the post-contrast DWI signal intensity values at b = 50 (p < 0.02) and b = 800 (p < 0.05) but had no statistically significant effect on the ADC value (p > 0.40). Pancreatic DWI signal intensity and ADC values pre- and post-contrast were also not significantly different (p = 0.489). In the renal parenchyma, significant decrease in the values of DWI at b = 50 (p < 0.01) and b = 800 (p < 0.01) as well as ADC (p < 0.02) was demonstrated following gadolinium administration.

Conclusion

Intravenous gadolinium administration does not make a statistically significant difference in the qualitative appearance or ADC measurements of the liver, spleen, or pancreas when comparing pre-contrast to post-contrast DWI. In the kidneys, however, ADC values are significantly lower post-contrast with the pre-contrast diffusion weighted images also being qualitatively preferred.     

Evaluation of short-term response of high intensity focused ultrasound ablation for primary hepatic carcinoma: Utility of contrast-enhanced MRI and diffusion-weighted imaging

Objective

To explore the significance of contrast-enhanced MRI (CE-MRI) and diffusion-weighted imaging (DWI) in evaluating the short-term response of high intensity focused ultrasound (HIFU) ablation for primary hepatic carcinoma (PHC).

Methods

Thirty-nine lesions in the livers of 27 patients were performed HIFU ablation. Conventional MRI sequences, CE-MRI and DWI were performed 1 week before HIFU and 1 week, 3 months after the therapy, respectively. The short-term responses of HIFU for all lesions were evaluated with MRI.

Results

28 of the 39 lesions (28/39, 71.8%) showed complete necrosis with no enhancement 1 week and 3 months after HIFU. The apparent diffusion coefficient (ADC) values 1 week and 3 months after HIFU were significantly higher than those 1 week before treatment (p < 0.05). The tumor recurrence was detected in 7 of the 39 lesions (7/39, 17.9%) which had no significant enhancement 1 week after HIFU. On the 3 months follow-up, focal nodules were found on the inner aspects of the treated areas. The ADC values had no significant difference between 1 week before and after treatment (p > 0.05), however, they were significantly higher 3 months after HIFU (p < 0.05). The tumor residuals were detected in 4 of the 39 lesions (4/39, 10.3%) showing enhancement 1 week after treatment and increased size 3 months after HIFU. The ADC values had no significant difference among 1 week before HIFU, 1 week and 3 months after treatment (p > 0.05).

Conclusion

CE-MRI and DWI can be employed to evaluate the short-term response of HIFU ablation for PHC and to guide the patient management.     

The utility of diffusion-weighted MR imaging in differentiation of uterine adenomyosis and leiomyoma

Purpose

To investigate the value of diffusion-weighted MR imaging (DWI), especially apparent diffusion coefficient (ADC) in the differentiation of uterine adenomyosis and leiomyoma.

Materials and methods

17 patients with uterine leiomyoma and 22 patients with uterine adenomyosis underwent diffusion-weighted imaging (DWI) in addition to routine MR imaging. The ADC values, as well as ADC D-value (defined as the ADC value of high signal intensive foci minus the ADC value of lesion tissues the difference in value), were measured and compared to investigate whether they could help in the differentiation of uterine adenomyosis and leiomyoma. Histopathologic examination was conducted as the golden standard.

Results

For high signal intensive foci within the lesions, uterine adenomyosis demonstrated significantly lower mean ADC value than uterine leiomyoma (1.582 vs. 2.122 × 10⁻³ mm²/s, P = 0.001). For lesion tissues, uterine adenomyosis demonstrated significantly higher mean ADC value than uterine leiomyoma (1.214 vs. 0.967 × 10⁻³ mm²/s, P = 0.001). However, there was overlap between uterine adenomyosis and leiomyoma in both measurements. Mean ADC D-value was significantly lower in uterine adenomyosis than in uterine leiomyoma (0.369 vs. 1.096 × 10⁻³ mm²/s, P = 0.000). ADC D-value had no overlap between uterine adenomyosis and leiomyoma.

Conclusion

DWI can be applied for the further differentiation of uterine adenomyosis and leiomyoma, in addition to routine MR imaging. ADC D-value may be a more useful tool than ADC value in the differentiation.     

Value of diffusion-weighted MR imaging in the differentiation between benign and malignant cervical lymph nodes

Purpose

To evaluate echo-planar diffusion-weighted MR imaging (DWI) in the differentiation between benign and malignant cervical lymph nodes.

Materials and methods

35 consecutive patients with 55 enlarged (>10 mm) cervical lymph nodes underwent MR imaging at 1.5-T. DWI was performed using a single-shot echo-planar (SSEPI) MR imaging sequence with b values (b: diffusion factor) of 0, 500 and 1000 s/mm². Apparent diffusion coefficient (ADC) maps were reconstructed for all patients and ADC values were calculated for each lymph node. Imaging results were correlated with histopathologic findings after neck dissection or surgical biopsy, findings in PET/CT or imaging follow-up. Mann-Whitney test was used for statistical analysis and a receiver operating characteristic (ROC) curve analysis was performed.

Results

Cervical lymph node enlargement was secondary to metastases from squamous cell carcinomas [n = 25], non-Hodgkin’s lymphoma [n = 6], reactive lymphadenitis [n = 20], cat scratch lymphadenitis [n = 2] and sarcoidosis [n = 2]. The mean ADC values (×10⁻³ mm²/s) were 0.78 ± 0.09 for metastatic lymph nodes, 0.64 ± 0.09 for lymphomatous nodes and 1.24 ± 0.16 for benign cervical lymph nodes. ADC values of malignant lymph nodes were significantly lower than ADC values of benign lymph nodes. 94.3% of lesions were correctly classified as benign or malignant using a threshold ADC value of 1.02 × 10⁻³ mm²/s.

Conclusion

According to our first experience, DWI using a SSEPI sequence allows reliable differentiation between benign and malignant cervical lymph nodes.     

T2-enhanced tensor diffusion trace-weighted image in the detection of hyper-acute cerebral infarction: Comparison with isotropic diffusion-weighted image

Background and purpose

Although isotropic diffusion-weighted imaging (isoDWI) is very sensitive to the detection of acute ischemic stroke, it may occasionally show diffusion negative result in hyper-acute stroke. We hypothesize that high diffusion contrast diffusion trace-weighted image with enhanced T2 may improve stroke lesion conspicuity.

Methods

Five hyper acute stroke patients (M:F = 0:5, average age = 61.8 ± 20.5 y/o) and 16 acute stroke patients (M:F = 11:5, average age = 67.7 ± 12 y/o) were examined six-direction tensor DWIs at b = 707 s/mm². Three different diffusion-weighted images, including isotropic (isoDWI), diffusion trace-weighted image (trDWI) and T2-enhanced diffusion trace-weighted image (T2E_trDWI), were generated. Normalized lesion-to-normal ratio (nLNR) and contrast-to-noise ratio (CNR) of three diffusion images were calculated from each patient and statistically compared.

Results

The trDWI shows better nLNR than isoDWI on both hyper-acute and acute stroke lesions, whereas no significant improvement in CNR. Nevertheless, the T2E_trDWI has statistically superior CNR and nLNR than those of isoDWI and trDWI in both hyper-acute and acute stroke.

Conclusions

We concluded that tensor diffusion trace-weighted image with T2 enhancement is more sensitive to stroke lesion detection, and can provide higher lesion conspicuity than the conventional isotropic DWI for early stroke lesion delineation without the need of high-b-value technique.     

Comparison of the diagnostic performances of diffusion parameters in diffusion weighted imaging and diffusion tensor imaging of breast lesions

Purpose

To evaluate the diagnostic efficiency of the diffusion parameters measured by conventional diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) for discrimination of malignant breast lesions from benign lesions and the normal breast.

Materials and methods

The study included 52 women with 55 breast lesions (30 malignant, 25 benign). DTI and DWI were performed complementary to dynamic contrast MRI at 3T. Apparent diffusion coefficient (ADC) of DWI, mean diffusivity (MD) and fractional anisotropy (FA) values of DTI were measured for lesions and contralateral breast parenchyma in each patient. We used b factors of 0, 50, 850, 1000 and 1500 s/mm² for DWI and b 0 and 1000 s/mm² for DTI. ADC, MD and FA values were compared between malignant and benign lesions, and the normal parenchyma by univariate and multivariate analyses.

Results

Diffusion parameters showed no difference according to menopausal status in the normal breast. ADC and MD values of the malignant lesions were significantly lower than benign lesions and normal parenchyma (p = 0.001). The FA showed no statistical significance. With the cut-off values of ≤1.23 × 10⁻³ mm²/s (b 0–1000 s/mm²) and ≤1.12 × 10⁻³ mm²/s (b 0–1500 s/mm²), ADC showed 92.85% and 96.15% sensitivity; 72.22% and 73.52% PPV, respectively. With a cut-off value of ≤1.27 × 10⁻³ mm²/s (b 1000 s/mm²), MD was 100% sensitive with a PPV of 65.90%. Comparing the diagnostic performance of the parameters in DTI with DWI, we obtained similar efficiency of ADC with b values of 0,1000 and 0,1500 s/mm² and MD with a b value of 0, 1000 s/mm² (AUC = 0.82 ± 0.07).

Conclusion

ADC of DWI and MD of DTI values provide significant discriminative factors for benign and malignant breast lesions. FA measurement was not discriminative. Supported with clinical and dynamic contrast MRI findings, DWI and DTI findings provide significant contribution to the final radiologic decision.     

Role of PROPELLER diffusion weighted imaging and apparent diffusion coefficient in the diagnosis of sellar and parasellar lesions

Objective

To evaluate the role of the apparent diffusion coefficient (ADC) using periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) diffusion weighted imaging (DWI) in the differentiation between sellar and parasellar mass lesions.

Materials and methods

The study protocol was approved by our institutional review board. We retrospectively studied 60 patients with sellar and parasellar lesions who had undergone PROPELLER DWI on a 3-T MR imager. Conventional MRI findings were expressed as the ratio of signal intensity (SI) in the lesions to the normal white matter and the degree of contrast enhancement. ADC values were calculated as the minimum (ADC-MIN), mean (ADC-MEAN), and maximum (ADC-MAX). All patients underwent surgery and all specimens were examined histologically. Logistic discriminant analysis was performed by using the SI ratios on T1- and T2-weighted images (T1-WI, T2-WI), the degree of enhancement, and absolute ADC values as independent variables.

Results

ADC-MIN of hemorrhagic pituitary adenomas was lower than of the other lesions with similar appearance on conventional MRI (non-hemorrhagic pituitary adenomas, craniopharyngiomas, Rathke's cleft cysts; accuracy 100%); the useful cut-off value was 0.700 × 10⁻³ mm²/s. ADC-MAX of meningiomas was lower than of non-hemorrhagic pituitary adenomas (accuracy 90.3%; p < 0.01). ADC-MIN of craniopharyngiomas was lower than of Rathke's cleft cysts (accuracy 100%; p < 0.05).

Conclusion

As PROPELLER DWI is less sensitive to susceptibility artifacts than single-shot echoplanar DWI, it is more useful in the examination of sellar and parasellar lesions. Calculation of the ADC values helps to differentiate between various sellar and parasellar lesions.     

Combined diffusion-weighted and dynamic contrast-enhanced imaging of patients with acute osteoporotic vertebral fractures

Objectives

To evaluate the potential and to analyze parameter correlations of combined quantitative diffusion-weighted MRI (DWI) and high-temporal-resolution dynamic contrast-enhanced MRI (DCE-MRI) in vertebral bone marrow (vBM) of patients with osteoporosis and acute vertebral compression fractures, providing additional information for a better understanding of the physiological background of parameter changes.

Materials and methods

20 patients with acute osteoporotic fractures were examined with DWI and DCE-MRI at 1.5 T. DCE-MRI was performed with a 2D saturation-recovery turbo-FLASH sequence, acquiring 300 dynamics with a temporal resolution of 1 s. For DWI measurements, a DW HASTE sequence with b-values from 100 to 600 s/mm² was applied. In each patient, ROIs were drawn manually in the fractures and in normal appearing vertebrae. For DCE-MRI, the concentration-time curves of these ROIs were analyzed using a two-compartment tracer-kinetic model in the lesions, providing separate estimates of perfusion and permeability, and a one-compartment model in normal vBM, providing only a mixed representation of perfusion and permeability in terms of a mixed flow parameter K^trans and the extracellular volume (ECV). In the case of DWI, attenuation curves were fitted to a monoexponential decay model to determine the apparent diffusion coefficient (ADC).

Results

Mean perfusion parameters and ADCs were significantly (p < 0.001) different in the fractures compared to adjacent normal appearing vertebrae (K^trans: 7.81 mL/100 mL/min vs. 14.61 mL/100 mL/min, ECV: 52.84 mL/100 mL vs. 4.61 mL/100 mL, ADC: 1.71 × 10^-3 mm²/s vs. 0.57 × 10^-3 mm²/s). ADCs showed a significant correlation with the ECV.

Conclusion

The quantitative analysis of DWI and DCE-MRI could distinguish osteoporotic fractures from normal appearing vertebrae. A significant correlation found between ECV and ADCs might be able to explain the cause for the increased diffusivity in osteoporotic fractures. Since the other perfusion parameters do not correlate with the ADC, they provide additional pathophysiological information not accessible with DWI.     

Diffusion-weighted imaging of breast tumors: Differentiation of benign and malignant tumors

Objective

The aim of this study was to evaluate the role of diffusion-weighted images (DWI) in the differentiation between benign and malignant breast tumors.

Patients and methods

This study included 62 females with focal breast lesions according to mammography or sonomamography. All patients underwent dynamic contrast enhanced MRI (DCE-MRI), and DWI of the breast. The mean apparent diffusion coefficient (ADC) values were calculated for all lesions and were correlated with the final histopathological results. The sensitivity and specificity of DWI in the differentiation between benign and malignant breast tumors were calculated.

Results

Seventy-eight lesions were detected in the examined 62 patients included in this study. Fifty one lesions were benign and 27 lesions were malignant according to the final histopathological results. (25/27) lesions were correctly diagnosed by ADC as malignant lesions with mean ADC value (0.92 ± 0.23 × 10⁻³ mm²/s) which was significantly lower than the mean ADC value for benign tumors (1.46 ± 0.48 × 10⁻³ mm²/s) and was correctly diagnosed in (50/51) lesions. The sensitivity and specificity of DWI in the differentiation between benign and malignant breast tumors were 92.6% and 98%, respectively.

Conclusion

DWI offers a useful method for differentiation of benign and malignant breast lesions with high sensitivity and specificity. Being a short unenhanced scan DWI can be safely added to the standard breast MRI protocol.     

Intracerebral metastasis showing restricted diffusion: Correlation with histopathologic findings

Objective

We aimed to detect the frequency of restricted diffusion in intracerebral metastases and to find whether there is correlation between the primary tumor pathology and diffusion-weighted MR imaging (DWI) findings of these metastases.

Material and methods

87 patients with intracerebral metastases were examined with routine MR imaging and DWI. 11 hemorrhagic metastatic lesions were excluded. The routine MR imaging included three plans before and after contrast enhancement. The DWI was performed with spin-echo EPI sequence with three b values (0, 500 and 1000), and ADC maps were calculated. 76 patients with metastases were grouped according to primary tumor histology and the ratios of restricted diffusion were calculated according to these groups. ADCmin values were measured within the solid components of the tumors and the ratio of metastases with restricted diffusion to that which do not show restricted diffusion were calculated. Fisher's exact and Mann-Whitney U tests were used for the statistical analysis.

Results

Restricted diffusion was observed in a total of 15 metastatic lesions (19, 7%). Primary malignancy was lung carcinoma in 10 of these cases (66, 6%) (5 small cell carcinoma, 5 non-small cell carcinoma), and breast carcinoma in three cases (20%). Colon carcinoma and testicular teratocarcinoma were the other two primary tumors in which restricted diffusion in metastasis was detected. There was no statistical significant difference between the primary pathology groups which showed restricted diffusion (p > 0.05). ADCmin values of solid components of the metastasis with restricted diffusion and other metastasis without restricted diffusion also showed no significant statistical difference (0.72 ± 0.16 × 10⁻³ mm²/s and 0.78 ± 21 × 10⁻³ mm²/s respectively) (p = 0.325).

Conclusion

Detection of restricted diffusion on DWI in intracerebral metastasis is not rare, particularly if the primary tumor is lung or breast cancer. However we found that there is no correlation between the metastasis showing restricted diffusion and primary pathology. Prospective studies with larger groups and more information are necessary regarding the correlation between the primary tumor histopathology and the ADC values of metastasis with restricted diffusion.     

Role of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) in differentiating between benign and malignant breast lesions

Objective

To assess the role of DWI and ADC in differentiating between benign and malignant breast lesions.

Materials and methods

51 patients (age range 24–66 years; mean age 48 years) were included in our study. MRI was done using bilateral fat-suppressed T2- weighted fast spin-echo, STIR, axial T1-weighted fast spin-echo. DWI series were acquired using echo planar imaging pulse sequences incorporated with diffusion gradients and finally dynamic contrast enhancement study was done.

Results

Sixty three lesions were detected in 51 patients included in our study. Twenty one lesions were malignant, three lesions were intermediate and twenty two lesions were fibroadenoma according to the final histopathological study and seventeen lesions were breast cysts. A total of 21 lesions showed lower ADC values than benign lesions and were in the range of 0.76–1.29 × 10⁻³ mm²/s and were diagnosed as malignant breast lesions. The sensitivity and specificity for DWI in the differentiating malignant from benign breast lesions were calculated and showed 95.4% and 97.5%, respectively.

Conclusion

DWI is easy to obtain in short scan time and easy to evaluate, and ADC values can differentiate between benign and malignant breast lesions with high sensitivity and specificity.     

Diffusion weighted imaging and estimation of prognosis using apparent diffusion coefficient measurements in ischemic stroke

Objective

Estimation of the prognosis of infarction by using diffusion weighted imaging (DWI) and quantitative apparent diffusion coefficient (ADC) measurements.

Methods

23 patients having acute stroke symptoms with verified infarction in magnetic resonance imaging (MRI) were included in this study. Their MRI studies were performed between 6 and 12 h after the onset of their symptoms and were repeated on the fifth day. The infarction volumes were calculated by using DWI and the patients were divided into two groups as the ones having an expansion in the infarction area (group 1, n = 16) and the others having no expansion in the infarction area (group 2, n = 7). Quantitative ADC values were estimated. The groups were compared in terms of the ADC values on ADC maps obtained from DWI, performed during the between 6 and 12 h from the onset of the symptoms, referring to the core of the infarction (ADC_IC), ischemic penumbra (ADC_P) and the nonischemic parenchymal tissue (ADC_N). P values < 0.05 were accepted to be statistically significant.

Results

During the between 6 and 12 h mean infarction volume calculated by DWI was 23.3 cm³ for group 1 patients (ranging from 1.1 to 68.6) and this was found to be 40.3 cm³ (ranging from 1.8 to 91.5) on the fifth day. For the group 2 patients these values were found to be 42.1 cm³ (ranging from 1 to 94.7) and 41.9 (ranging from 1 to 94.7) for the same intervals respectively. A significant statistical result was failed to be demonstrated between the mean ADC_IC and ADC_N values (p = 0.350 and p = 0.229 respectively). However the comparison of the ADC_P values between the groups was found to be highly significant (p < 0.001). When the differences between the ADC_P and ADC_IC and ADC_N and ADC_P were compared the results proved to be statistically significant (p = 0.038 and p < 0.001 respectively).

Conclusions

We believe that ADC results that would be obtained from the core and the penumbra of the infarction area will be beneficial in the estimation of the infarction prognosis and in the planning of a treatment protocol.     

Role of diffusion weighted MRI in differentiating typical from atypical meningiomas at 1.5 and 3T MRI

Purpose

Atypical and malignant meningiomas are considered to have a higher rate of recurrence and show aggressive behavior compared to benign variety. The purpose of our study was to study the role of diffusion weighted imaging and determination of apparent diffusion coefficient (ADC) values and ADC ratios to differentiate typical meningiomas from atypical/malignant variety at 1.5 and 3T MRI.

Materials and methods

A total of 94 adult patients (48 patients at 3T and 46 patients at 1.5T) with pathologically proven meningiomas were retrospectively evaluated on conventional and diffusion weighted MRI. The signal intensity of the lesions on DW imaging was evaluated. ADC values and ADC ratios were calculated from lesion and contralateral normal white matter.

Results

94 lesions comprising of 66 benign and 28 atypical meningiomas were evaluated. The mean ADC values at 3T MRI were 0.82 ± 0.12 × 10⁻³ in benign (typical) meningiomas and 0.68 ± 0.10 × 10⁻³ in atypical meningiomas. At 1.5T, the mean ADC values of benign meningiomas were 0.83 ± 0.11 × 10⁻³ and 0.70 ± 0.09 × 10⁻³ in atypical meningiomas. The mean ADC ratios were 1.08 ± 0.17 and 0.85 ± 0.15 for benign and atypical meningiomas respectively. There was a statistically significant difference between the mean ADC ratios and the mean ADC values of typical and atypical meningiomas (P < 0.001) at both 1.5T and 3T MRI.

Conclusion

DWI with calculation of apparent diffusion coefficient (ADC) values and ADC ratios has a potential role in differentiating benign from atypical meningiomas at both 1.5 and 3T MRI. The differences in mean ADC values between benign and atypical meningiomas were similar at both 1.5 and 3T MRI.     

Cerebral diffusion tensor imaging in tuberous sclerosis

Purpose

The purpose of this study was to investigate the features of the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in cortical tubers and white-matter lesions in patients with tuberous sclerosis (TS) using diffusion tensor imaging (DTI).

Materials and methods

Conventional magnetic resonance imaging (MRI) and DTI were performed in 14 patients with clinically established TS. Based on these DT images, ADC and FA maps were generated. The ADC values in 32 cortical tubers, and the ADC and FA values in 18 white-matter lesions were measured and compared with those of the corresponding contralateral regions.

Results

Compared with the corresponding contralateral regions, cortical tubers of TS patients had significantly higher ADC values (P < 0.001); white-matter lesions had significantly higher ADC values (P < 0.001) and significantly lower FA values (P < 0.001).

Conclusion

DTI is a useful tool for demonstrating changes in cortical tubers and white-matter lesions resulting from TS.     

Simple quantitative measurement based on DWI to objectively judge DWI-FLAIR mismatch in a canine stroke model

PURPOSE

Diffusion-weighted imaging (DWI) - fluid attenuated inversion recovery (FLAIR) mismatch was proven useful to time the onset of wake-up stroke; however, identifying the status of FLAIR imaging has been mostly subjective. We aimed to evaluate the value of relative DWI signal intensity (rDWI), and relative apparent diffusion coefficient (rADC) in identifying the FLAIR status in the acute period.

METHODS

Autologous clot was used to embolize left middle cerebral artery in 20 dogs. Magnetic resonance imaging was performed 3–6 hours and 24 hours after embolization. DWI-FLAIR mismatch was defined as hyperintense signal detected on DWI, but not on FLAIR. The mean values of rDWI or rADC of FLAIR− and FLAIR+ lesions were compared and the critical cutoff values of rDWI and rADC for identifying the FLAIR status were determined.

RESULTS

Stroke models were successfully established in all animals. DWI+ lesions were found in all 20 dogs from three hours, while FLAIR+ lesions were found in three, 11, 16, 19, and 20 dogs at five time points after embolization, respectively. The mean rDWI values were significantly different between FLAIR− and FLAIR+ lesions (P < 0.001), but rADC values were not (P = 0.73). Using rDWI=1.90 as the threshold value, excellent diagnostic efficacy was achieved (AUC, 0.88; sensitivity, 0.77; specificity, 0.88). However, rADC appeared not useful (AUC, 0.48; sensitivity, 0.52; specificity, 0.58) in identifying the FLAIR status.

CONCLUSION

In our embolic canine stroke model, rDWI was useful to identify FLAIR imaging status in the acute period, while rADC was not.Diffusion-weighted imaging (DWI) - fluid attenuated inversion recovery (FLAIR) mismatch refers to the situation where an ischemic lesion is detected on DWI in the absence of a corresponding lesion on FLAIR imaging. Recently, several studies indicated that DWI-FLAIR mismatch might aid to predict whether the stroke onset time is within 4.5 hours or not (1–6). Furthermore, this mismatch pattern, which is based on the detection time difference between DWI and FLAIR imaging, would help to time the stroke lesions in patients with unclear onset time. This information is important for clinicians to select the optimal treatment, because more ischemic stroke patients would benefit from thrombolytic therapy (7). However, in previous studies, assessment of FLAIR imaging has been subjective. An objective, simple, and quantitative measurement to help judge the status of FLAIR imaging is yet to be found.DWI can detect a hyperacute ischemic lesion as soon as 30 minutes after stroke, and it is viewed as a sensitive and effective tool to detect ischemic stroke events (8, 9). Meanwhile, several studies observed that the relative signal intensity (SI) of lesions on DWI could be a reliable parameter to demonstrate the secondary pathologic process after ischemic stroke (10). Therefore, we hypothesized that, quantitative parameters derived from DWI, such as relative DWI signal intensity (rDWI) and relative ADC value (rADC), might be useful to evaluate the status of FLAIR imaging.In this study, we aimed to determine the value of rDWI and rADC in evaluating the status of FLAIR imaging, based on our embolic canine ischemic stroke model, considering different temporal evolution of the volume of ischemic lesions demonstrated on DWI and FLAIR imaging.     

The role of MR diffusion in differentiation of malignant and benign hepatic focal lesions

Aim

To determine if focal liver masses could be differentiated as benign or malignant by DWI and ADC maps.

Methods and materials

Sixty focal liver lesions were scanned using 1.5 T MRI. DWI was performed with b 0, b 500 and b 1000 gradients with ADC measurements. Comparison of mean ADC values between each benign and malignant lesion was done. Reference standard of diagnosis was obtained by correlating DWI with histopathologic findings and imaging follow-up. The accuracies of DWI and ADC values were assessed with the Student’s t test, and cut-off values were determined with receiver operating characteristic curve analysis.

Results

When ADC value of 1.0 × 10⁻³ mm²/s was used as a threshold value for differentiation of malignant tumors from benign lesions, sensitivity was 90.3%, specificity 78.57% and accuracy 86.7%. The best result was obtained with the use of ADC cut off value (at b 500) of 1.5 × 10⁻³ mm²/s and ADC cut off value (at b 1000) of 1.0 × 10⁻³ mm²/s, with 90.3% sensitivity, 92.86% specificity, 91.1% accuracy, 96.6% positive predictive value and 81.3% negative predictive value.

Conclusion

DWI and ADC map is a useful tool in differential diagnosis of malignant from benign liver lesions.     

Diffusion tensor imaging with cerebrospinal fluid suppression and signal-to-noise preservation using acquisition combining fluid-attenuated inversion recovery and conventional imaging: Comparison of fiber tracking

Objective

To propose an acquisition scheme suitable for fiber tractography without cerebrospinal fluid contamination while retaining high signal-to-noise ratio.

Materials and methods

Diffusion tensor imaging (DTI) data at b = 0 and 1000 s/mm² were acquired using conventional spin-echo echo-planar imaging (TR/TE = 4000/69, NEX = 4, scan time 2:14) plus one additional fluid-attenuated inversion recovery (FLAIR) b = 0 set obtained at TI = 2200, TR = 6000, and NEX = 6 (scan time 1:36). The FLAIR images were intensity-adjusted to match the conventional b = 0 images according to the white matter signals. Five healthy adults were scanned, with tractography performed from conventional b = 1000 and FLAIR b = 0 images using the EZ-tracing algorithm. Total traced volumes were statistically compared among conventional DTI, FLAIR DTI, and the “combined DTI” methods at three different slice thicknesses. The fiber consistency index was derived for five repeated scans to assess possible false tracts.

Results

Whole-brain traced volumes from FLAIR DTI and combined DTI were 9.7% (p < 0.001) and 17.0% (p < 0.0001) greater than from conventional DTI, respectively (paired Student t-test). Fiber consistency was similar for all three acquisition techniques (p > 0.2), suggesting insignificant difference in false tracking. Compared with conventional DTI, the increase in total traced volume for FLAIR DTI diminished with decreasing slice thickness, whereas the tractography advantage for combined DTI became increasingly prominent at thinner slices.

Conclusions

The combined DTI technique is capable of improving tractography with higher signal-to-noise ratio at shorter scan time than FLAIR DTI. Its superiority at thin-slice acquisitions makes it particularly suitable for high-resolution clinical applications.     

Capillary telangiectasias of the pons. Does diffusion-weighted MR increase diagnostic accuracy?

Background and Purpose

Capillary telangiectasias are benign lesions of the brainstem which are sometimes difficult to distinguish from other lesions in standard MRI. The purpose of this study was to evaluate if diffusion-weighted imaging (DWI) could help to improve diagnostic accuracy.

Methods

148 MR examinations of patients with pontine lesions were evaluated retrospectively and revealed capillary telangiectasia (n = 18), presumed microvascular disease (n = 20), encephalitis disseminata (n = 21), pontine myelinolysis (n = 16), tumor (n = 20), acute infarction (n = 20), subacute infarction (n = 13) and chronic infarction (n = 20).All patients were examined using identical measurement parameters for DWI, Fluid attenuated inversion recovery, T2-weighted turbo spin-echo, and T1-weighted spin-echo before and after application of contrast agent in transverse orientation.

Results

All capillary telangiectasias showed low signal intensity in DWI and significant contrast enhancement after application of gadolinium. Hypointense signal on DWI was very rare for the remaining lesions: only 1 pontine myelinolysis, 1 tumor, 4 subacute infarctions, and 19 chronic infarctions also revealed low signal intensity on DWI. The combination of high signal intensity on T1-weighted post-contrast images and low signal intensity on DWI was found for all capillary telangiectasias, but only for 1/20 tumor and for 4/13 subacute infarctions. These lesions could be differentiated by their clinical course and/or MRI follow-up examinations.The results of the visual assessment were confirmed by quantitative evaluation.

Conclusion

DWI seems to be a useful adjunct for the diagnosis of capillary telangiectasias which will facilitate the differential diagnosis concerning tumorous, inflammatory and ischemic lesions.     

Intravoxel incoherent motion (IVIM) in evaluation of breast lesions: Comparison with conventional DWI

Objectives

To obtain perfusion as well as diffusion information in normal breast tissues and breast lesions from intravoxel incoherent motion (IVIM) imaging with biexponential analysis of multiple b-value diffusion-weighted imaging (DWI) and compare these parameters to apparent diffusion coefficient (ADC) obtained with monoexponential analysis in their ability to discriminate benign lesions and malignant tumors.

Materials and methods

In this prospective study, informed consent was acquired from all patients. Eighty-four patients with 40 malignant tumors, 41 benign lesions, 30 simple cysts and 39 normal breast tissues were imaged at 1.5 T utilizing contrast-enhanced magnetic resonance imaging (MRI) and DWI using 12 b values (range: 0–1000 s/mm²). Tissue diffusivity (D), perfusion fraction (f) and pseudo-diffusion coefficient (D*) were calculated using segmented biexponential analysis. ADC (b = 0 and 1000 s/mm²) was calculated with monoexponential fitting of the DWI data. D, f, D* and ADC values were obtained for normal breast tissues, simple cysts, benign lesions and malignant tumors. Receiver operating characteristic analysis was performed for all DWI parameters.

Results

There was good interobserver agreement on the measurements between the 2 observers. D values were significantly different among malignant tumors, benign lesions, simple cysts and normal breast tissues (P = 0.000) and it was the same result for f, D* and ADC values. Further comparisons of these 4 parameters between every single pair were as the following. D and ADC values of malignant tumors were significantly smaller than those of benign lesions, simple cysts and normal tissues (P = 0.000, respectively). The f value of malignant tumors was significantly higher than that of benign lesions, simple cysts and normal breast tissues (P = 0.001, P = 0.000, and P = 0.000). D and ADC values demonstrated higher sensitivity and specificity in differentiating benign lesions and malignant tumors, with area under the curve (AUC) of 0.952 and 0.945, respectively, while f and D* with the lower AUC of 0.723 and 0.630, respectively. Combining f and D values had a sensitivity up to 98.75%.

Conclusion

DWI response curves in malignant tumors, benign lesions and normal fibroglandular tissues are found to be biexponential fit in comparison with the monoexponential fit for simple cysts. IVIM provides separate quantitative measurement of D for cellularity and f and D* for vascularity and is helpful for differentiation between benign and malignant breast lesions.