Zeynep Firat

Diffusion Tensor Imaging and Tractography of Median Nerve: Normative Diffusion Values

OBJECTIVE The purposes of this study were to visualize the human median nerve on diffusion tensor imaging and to determine the normal fractional anisotropy (FA) value and apparent diffusion coefficient (ADC) of the normal median nerve. SUBJECTS AND METHODS The wrists of 20 healthy volunteers and of two patients with carpel tunnel syndrome were examined with a 3-T MRI system with a standard eight-channel sensitivity-encoding head coil. Diffusion tensor imaging was performed with a spin-echo echo-planar sequence. A T1-weighted sequence was performed for anatomic reference. After tractography, the FA value and ADC of the whole nerve were calculated automatically. Manual focal measurements also were obtained at the levels of the flexor retinaculum, wrist, and forearm. RESULTS We visualized the median nerve with MR diffusion tensor tractography and followed the nerve for approximately 77.5 mm. We found the normative diffusion values of the median nerve were an FA of 0.709 +/- 0.046 (SD) and an ADC of 1.016 +/- 0.129 x 10(-3) mm2/s. There was a statistically significant difference between the FA values obtained at the level of the flexor retinaculum and the values obtained from the other parts of the median nerve (p < 0.0001). We found a decrease in FA value (p < 0.01) and an increase in ADC (p < 0.05) with advancing age. CONCLUSION The normative diffusion values of the human median nerve can be used as a reference in evaluation, diagnosis, and follow-up of entrapment, trauma, and regeneration of the median nerve.

Assessment of the corticospinal tract alterations before and after resection of brainstem lesions using Diffusion Tensor Imaging (DTI) and tractography at 3 T

The purpose of the study was to investigate the role of Diffusion Tensor Imaging (DTI) and Diffusion Tensor Tractography (DTT) on the corticospinal tract alterations due to space occupying lesions in the brainstem before and after surgical resection. Pre- and post-surgical DTI data were acquired in 14 patients undergoing surgical resection of brainstem lesions. Patterns of corticospinal tract (CST) alteration on DTT were compared with the neurological exams of the patients pre- and post-operatively. DTT, especially in 3D movie format, seemed very helpful for evaluating the relationship of the lesions with the corticospinal tracts for surgical approach. None of the patients developed additional motor deficit related to surgery except one patient who presented with cerebellar ataxia after surgery. All of the patients with normal CST on DTT presented without motor deficit on neurological exam. The sensitivity, specificity, positive predictive and negative predictive values of DTT before surgery were 100%, 63.6%, 42.9% and 100%, and the corresponding values after surgery were 100%, 96%, 75% and 100% respectively. Although it has low specificity before surgery, DTT is a potentially useful technique in evaluating the effects of brainstem lesions and surgical resection on the relevant corticospinal tracts with high negative predictive value and higher specificity after surgery.

Diagnostic utility of DTI in prostate cancer

PURPOSE The aim of this study was to compare the diffusion tensor parameters of prostate cancer, prostatitis and normal prostate tissue. MATERIALS AND METHODS A total of 25 patients with the suspicion of prostate cancer were included in the study. MRI was performed with 3 T system (Intera Achieva, Philips Medical Systems, The Netherlands). T2 TSE and DTI with ss-EPI were obtained in each subject. TRUS-guided prostate biopsy was performed after the MRI examination. Images were analyzed by two radiologists using a special software system. ROIs were drawn according to biopsy zones which are apex, midgland, base and central zone on each sides of the gland. FA and ADC values in areas of cancer, chronic prostatitis and normal prostate tissue were compared using Students t-test. RESULTS Histopathological analysis revealed carcinoma in 68, chronic prostatitis in 67 and was reported as normal in 65 zones. The mean FA of cancerous tissue was significantly higher (p<0.01) than the FA of chronic prostatitis and normal gland. The mean ADC of cancerous tissue was found to be significantly lower (p<0.01), compared with non-cancerous tissue. CONCLUSION Decreased ADC and increased FA are compatible with the hypercellular nature of prostate tumors. These differences may increase the accuracy of MRI in the detection of carcinoma and to differentiate between cancer and prostatitis.

Accurate quantification of visceral adipose tissue (VAT) using water‐saturation MRI and computer segmentation: Preliminary results

To describe and evaluate the accuracy of water‐saturation MRI and a computer segmentation program for quantification of visceral adipose tissue (VAT).

The paramedian supracerebellar-transtentorial approach to the entire length of the mediobasal temporal region: an anatomical and clinical study. Laboratory investigation.

OBJECT The exploration of lesions in the mediobasal temporal region (MTR) has challenged generations of neurosurgeons to achieve an appropriate approach. To address this challenge, the extensive use of the paramedian supracerebellar-transtentorial (PST) approach to expose the entire length of the MTR, as well as the fusiform gyrus, was investigated. METHODS The authors studied the microsurgical aspects of the PST approach in 20 cadaver brains and 5 cadaver heads under the operating microscope. They evaluated the features, advantages, difficulties, and limitations of the PST approach and refined the surgical technique. They then used the PST approach in 15 patients with large intrinsic MTR tumors (6 patients), tumor in the posterior fusiform gyrus with mediobasal temporal epilepsy (MTE) (1 patient), cavernous malformations in the posterior MTR including the fusiform gyrus (2 patients), or intractable MTE with hippocampal sclerosis (6 patients) from December 2007 to May 2010. Patients ranged in age from 11 to 63 years (mean 35.2 years), and in 9 patients (60%) the lesion was located on the left side. RESULTS In all patients with neuroepithelial tumors or cavernous malformations, the lesions were completely and safely resected. In all patients with intractable MTE with hippocampal sclerosis, the anterior two-thirds of the parahippocampal gyrus and hippocampus, as well as the amygdala, were removed selectively through the PST approach. There was no surgical morbidity or mortality in this series. Three patients (20%) with high-grade neuroepithelial tumors underwent postoperative radiotherapy and chemotherapy but needed a second surgery for recurrence during the follow-up period. In all patients with MTE, antiepileptic medication could be decreased to a single drug at lower doses, and no seizure activity has occurred until this point. CONCLUSIONS The PST approach provides the surgeon precise anatomical orientation when exposing the entire length of the MTR, as well as the fusiform gyrus, for removing any lesion. This is a novel technique especially for removing tumors involving the entire MTR in a single session without damaging neighboring neural or vascular structures. This approach can also be a viable alternative for selective removal of the parahippocampal gyrus, hippocampus, and amygdala in patients with MTE due to hippocampal sclerosis.

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 3T. MATERIALS AND METHODS 27 patients with acute stroke who were admitted to the hospital during the first 24h 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 3T 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.

Diffusion tensor imaging of the kidney at 3 Tesla: normative values and repeatability of measurements in healthy volunteers

PURPOSE To evaluate the feasibility of renal diffusion tensor imaging and determine the normative fractional anisotropy and apparent diffusion coefficient values at 3 Tesla magnetic resonance imaging (MRI) using parallel imaging and free breathing technique. MATERIALS AND METHODS A total of 52 young healthy volunteers with no history of renal disease were included in the study. MRI examinations were performed with 3 Tesla MRI equipment, using six-channel phased array SENSE Torso coil. In all subjects, T2-weighted turbo spin echo and diffusion tensor imaging using single shot echo planar imaging sequences were obtained in the coronal plane with free breathing. Field of view, slice thickness, and slice gap values were identical for both sequences for anatomic correlation during analysis of diffusion tensor imaging data. Parallel imaging method was used with a SENSE factor of 2. Diffusion tensor parameters of the cortex and medulla were determined and the intra- and inter-observer measurement variances were calculated. RESULTS The mean fractional anisotropy of the medulla was significantly higher than that of the cortex, whereas the mean apparent diffusion coefficient of the medulla was lower when compared with that of the cortex. According to the two-sided paired samples Students t test, the intra- and inter-observer measurements correlated well. CONCLUSION This study shows the feasibility of renal diffusion tensor imaging and repeatibility of diffusion tensor parameter measurements in 3 Tesla MRI.

The risk of hepatocellular carcinoma in cirrhotic patients with small liver nodules on MRI

BACKGROUND AND AIM:The presence of hepatocellular carcinoma (HCC) has important implications for patients with cirrhosis. Studies have not compared the risk of cancer in cirrhotic patients with small liver nodules to cirrhotic patients without nodules. Our aim was to determine the risk of HCC in cirrhotic patients with small liver nodules on MRI compared to those without nodules.METHODS:We conducted a prospective study to determine the rate of HCC in cirrhotic patients with and without liver nodules. Cases were patients with liver nodule(s) less than 2 cm on MRI and controls were cirrhotic patients without nodules. Kaplan-Meier estimates and multivariate analysis were performed to estimate the risk of HCC in the two groups.RESULTS:A total of 310 liver transplant candidates with a mean follow-up of 663 days were included in the study and 133 underwent liver transplant during follow-up. The 1-yr incidence of HCC in the liver nodule group and control group was 11% and 0.5%, respectively, p < 0.001. The adjusted risk for HCC in the liver nodule group was 25 times higher compared to the control group, HR = 25.1 [95% CI 8.0, 78.9]. In 133 candidates who underwent transplant with and without liver nodules the rate of HCC was 11 (50%) and 4 (3.6%), respectively, p < 0.001.CONCLUSION:The incidence of HCC in patients with small liver nodules is significantly higher compared to patients with cirrhosis without liver nodules. The presence of small liver nodules warrants increased imaging surveillance for HCC.

Accuracy of magnetic resonance imaging for preoperative detection of portal vein thrombosis in liver transplant candidates

The detection of main portal vein thrombosis (PVT) on preoperative imaging of liver transplant candidates has important technical implications for the transplantation procedure. Data are scarce regarding the accuracy of magnetic resonance imaging (MRI) at detecting PVT. The aim of our study was to compare preoperative findings of the portal vein on MRI to operative findings at liver transplantation. Abdominal MRI and clinical records of 172 consecutive patients who received liver transplants between January 1999 and September 2004 were reviewed. Two radiologists independently evaluated the last abdominal magnetic resonance examinations obtained before liver transplantation, blinded to the original reading, operative findings, and clinical data. Findings on MRI were compared with intraoperative findings at transplantation. Main PVT was detected in 12 patients, in whom 8 were found to have thrombus at surgery, with 6 requiring a jump graft or thrombectomy. Sensitivity and specificity of MRI for detecting main PVT were 100% and 98%, respectively. The cause of discordance between findings on MRI and at transplantation in 2 cases was a diminutive caliber of the main portal vein that was interpreted as recanalized chronic thrombosis on MRI. In conclusion, in our study group MRI detected PVT in all liver transplant recipients requiring jump grafts at transplantation. The major reason for a false‐positive MRI was a diminutive but patent portal vein. Liver Transpl 2006.

VETOT, Volume Estimation and Tracking Over Time: Framework and Validation

We have implemented an effective and publicly available tool, VETOT, to track and quantify the evolution of tumors and organs over time. VETOT includes a framework both for registration and segmentation. We have evaluated the accuracy and reliability of different level set segmentation methods in order to validate this part of our software and evaluate its usability. In addition to the registration and segmentation frameworks, our program allows the creation of inter- and intra-patient atlases based on a common coordinate system defined by the landmarks selected during the registration process. Based on the National Library of Medicine’s Insight toolkit, this free software is extensible and provides an intuitive interface that allows very fast processing with minimum training. This paper details VETOT and our level set segmentation evaluation.