Turgut Tali

A catheter tracking method using reverse polarization for MR-guided interventions

To conduct interventional procedures in MRI, reliable visualization of interventional devices such as catheters is necessary. For this purpose, the use of inductively‐coupled radio frequency (ICRF) coils has been proposed. Without a wired connection, the signal around the ICRF coil is amplified, enabling catheters to be visualized. The wireless connection allows easy handling of catheters, in some pulse sequences, however, it might be difficult to differentiate the catheters from anatomical background information. In this work, a novel ICRF coil visualization method, which allows separation of the catheter and the anatomical information by using the reverse and forward polarization modes of a coil, is proposed. This method allows images of the anatomy and the catheter to be combined into a color‐coded image. First, an ICRF coil with decoupling diodes was constructed; we call this a receive‐coupled RF (RCRF) coil. The RF safety profile of the RCRF coil is shown to be better than the ICRF coil. Second, to demonstrate the feasibility of this method, a receive‐only birdcage coil without a hybrid coupler was constructed and then connected to a scanner as a two‐channel phased‐array coil. MR signals acquired from two channels were added after phase adjustments to create the reverse and forward polarization mode images. The reverse polarization mode image contained signal only from the RCRF coil, but the forward polarization mode displayed both anatomical information and the RCRF coil. The performance of this novel tracking method was tested in phantom and animal experiments. Color‐coded images demonstrate the feasibility of the method to track catheters using RCRF coils. Magn Reson Med 58:1224–1231, 2007.

Diffusion-weighted imaging of the appendicular skeleton with a non-Carr-Purcell-Meiboom-Gill single-shot fast spin-echo sequence.

OBJECTIVE The objective of our study was to prospectively evaluate the signal-to-noise ratio (SNR) improvement in diffusion-weighted imaging (DWI) of the appendicular skeleton with the use of a newly developed non-Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo (SSFSE) sequence and to evaluate its effect on apparent diffusion coefficient (ADC) measurements. SUBJECTS AND METHODS DWI of the bone was performed in 32 patients with an echo-planar imaging (EPI)-based sequence followed by a non-CPMG SSFSE technique. SNR and ADC values were measured over a lesion-free right femoral head. A score was assigned for each set of images to assess image quality. When a bone lesion was present, contrast-to-noise ratio (CNR) and ADC were also measured. Paired Students t tests were used for statistical analysis. RESULTS The mean (+/- SD) SNR values were 9.89 +/- 2.20 and 81.68 +/- 4.87 for EPI and non-CPMG SSFSE DWI, respectively. SNR values associated with the non-CPMG SSFSE technique were found to be significantly higher than those measured with the EPI-based DWI technique (p < 0.01). Mean ADCs of the bone were 0.57 +/- 0.20 and 0.29 +/- 0.15 x 10(-3) mm2/s, respectively, for EPI and non-CPMG SSFSE DWI. Image quality scores were higher for the non-CPMG SSFSE DWI technique (p < 0.05) than for the EPI-based DWI technique. Overall lesion CNR was found to be higher in DWI performed with the non-CPMG SSFSE technique. CONCLUSION The non-CPMG SSFSE technique provides a significant improvement over the currently used EPI-based DWI technique and has the potential to be a powerful tool in imaging the appendicular skeleton.

Staging of hip avascular necrosis: is there a need for DWI?

Background No comprehensive study has been performed to stage avascular necrosis of the hip using diffusion-weighted imaging (DWI). Purpose To determine apparent diffusion co-efficient (ADC) alterations in hip avascular necrosis (AVN) and to determine variations of ADC values according to stages of disease. Material and Methods The study is approved by our institutional review board and local ethical committee. Written informed consent was present for each subject. Thirty-five femoral heads of 21 cases affected by AVN were included in the study. Control group consisted of both femoral heads of 10 healthy volunteers. The hips affected by AVN were staged according to Ficat and Arlet classification system from I to IV. All cases underwent to routine hip magnetic resonance imaging (MRI) and DWI performed with a single-shot fast spin echo sequence at a b value of 600 s/mm2. The ADC values were calculated automatically by placing ROIs on AVN lesions in affected patients and both femoral heads of control group. The median ADC value obtained from femoral heads of control group and that from AVN lesions were compared by Mann-Whitney U test. The median ADC values of AVN lesions at different stages were compared by Kruskal-Wallis test. Results The median ADC value of normal bone measured in control group was 185.5 ± 133.2 x 10−6 mm2/s. The median ADC value measured in hip avascular necrosis lesions was 988.0 ± 332.7 x 10−6 mm2/s. ADC values in hip AVN lesions were statistically significantly higher than normal bone marrow (P < 0.01). The median ADC values of hips with avascular necrosis at stage I, II, III, IV were 817.5 ± 172.1 x 10−6 mm2/s, 902.0 ± 181.0 x 10−6 mm2/s, 1200.0 ± 363.2 x 10−6 mm2/s and 1024.0 ± 324.0 x 10−6 mm2/s, respectively. There was no statistically significant difference among AVN lesions at stages I, II, III and IV (P > 0.05). Conclusion Although DWI is a promising imaging tool that provides valuable diagnostic information in hip AVN, it fails to distinguish between different stages, and therefore is of limited value.

Giant Vertebral Notochordal Rest: Magnetic Resonance and Diffusion Weighted Imaging Findings

A giant vertebral notochordal rest is a newly described, benign entity that is easily confused with a vertebral chordoma. As microscopic notochordal rests are rarely found in adult autopsies, the finding of a macroscopic vertebral lesion is a new entity with only seven previously presented cases. We report here radiological findings, including diffusion weighted images, of a patient with a giant notochordal remnant confined to the L5 vertebra, with an emphasis on its distinction from a chordoma.

Rosai-Dorfman disease with epidural and spinal bone marrow involvement: magnetic resonance imaging and diffusion-weighted imaging features.

Sinus histiocytosis with massive lymphadenopathy (SHML), or Rosai-Dorfman disease, is a rare histiocytic disorder that typically presents with chronic, self-limiting cervical lymphadenopathy. Although this disease mainly affects histiocytes, there are a few reports of bone marrow infiltration. Diffusion-weighted imaging (DWI) is a promising technology in differentiating between various bone marrow pathologies. We here present conventional magnetic resonance imaging and DWI features of a patient with SHML and bone marrow involvement.

T2-weighted vs. intrathecal contrast-enhanced MR cisternography in the evaluation of CSF rhinorrhea

Background Endoscopic surgical approach is being more widely used in the treatment of cerebrospinal fluid (CSF) rhinorrhea. Accurate localization of CSF fistulas prior to surgery is essential in increasing the success of dural repair and in decreasing negative or recurrent explorations. Purpose To evaluate and compare intrathecal contrast medium-enhanced magnetic resonance cisternography (CEMRC) with T2-weighted MR cisternography (T2MRC) in identifying the presence and site of CSF rhinorrhea. Material and Methods Sixty patients with suspected CSF rhinorrhea underwent MR cisternography including intrathecally enhanced fat-suppressed T1WI in three orthogonal planes and T2WI in the coronal plane. Both set of images were reviewed by two blinded radiologists for the presence and location of CSF leakage. Imaging data were compared with surgical findings and/or beta-2 transferrin testing. Results With surgery proven CSF leakage in 20 instances as reference, CEMRC detected 18 (90%), whereas T2MRC reported only 13 (65%) correctly. Overall, sensitivity, specificity, positive predictive value, and negative predictive value in detecting CSF fistulas were 92%, 80%, 76%, and 93% for CEMRC, and 56%, 77%, 64%, and 71% for T2MRC, respectively. Conclusion The minimally invasive CEMRC is an effective method with higher sensitivity and specificity than T2MRC in the evaluation of CSF fistulas.

pASL versus DSC perfusion MRI in lateralizing temporal lobe epilepsy.

Background Accurate lateralization of the epileptogenic focus in temporal lobe epilepsy (TLE) is crucial. Pulsed arterial spin labeling (pASL) has the capability of quantifying local relative cerebral blood flow (rCBF) by measuring the inflow of electromagnetically labeled arterial blood into the target area, and can be used in the presurgical workup of refractory TLE. Purpose To evaluate pASL in detecting mesial temporal lobe (mTL) perfusion asymmetry for the lateralization of the epileptogenic focus in patients with refractory TLE and to compare it with dynamic susceptibility contrast enhanced (DSC) magnetic resonance imaging (MRI) technique. Material and Methods This study was approved by the local ethical committee, and written informed consent was obtained in each patient. Thirty-six patients with medically refractory TLE and 11 healthy volunteer was enrolled in this study. Following brain MRI, pASL and DSC perfusion were performed in all subjects at 3T. rCBF measurements with two different perfusion MRI technique were compared between the patient and healthy volunteers. Lateralization based on perfusion asymmetry index (AI) were also evaluated and compared with clinical lateralization. Results rCBF ratios measured in healthy volunteers by two different perfusion technique did not show any statistically significant difference. In TLE patients rCBF ratio of the ipsilateral (affected) side was found to be significantly lower than the contralateral (unaffected) side with both technique. The AI in the patient group was 8.86 ± 3.88 with pASL and 8.39 ± 4.06 with DSC. Correlation coefficient between clinical laterality and perfusion AI were 0.86 for pASL and 0.83 for DSC. Conclusion pASL can successfully detect interictal asymmetry in patients with TLE and can readily be combined with routine structural assessment for lateralization, providing an alternative to DSC perfusion.

A comprehensive neuropsychological mapping battery for functional magnetic resonance imaging.

Existing batteries for FMRI do not precisely meet the criteria for comprehensive mapping of cognitive functions within minimum data acquisition times using standard scanners and head coils. The goal was to develop a battery of neuropsychological paradigms for FMRI that can also be used in other brain imaging techniques and behavioural research. Participants were 61 healthy, young adult volunteers (48 females and 13 males, mean age: 22.25 ± 3.39 years) from the university community. The battery included 8 paradigms for basic (visual, auditory, sensory-motor, emotional arousal) and complex (language, working memory, inhibition/interference control, learning) cognitive functions. Imaging was performed using standard functional imaging capabilities (1.5-T MR scanner, standard head coil). Structural and functional data series were analysed using Brain Voyager QX2.9 and Statistical Parametric Mapping-8. For basic processes, activation centres for individuals were within a distance of 3-11 mm of the group centres of the target regions and for complex cognitive processes, between 7 mm and 15 mm. Based on fixed-effect and random-effects analyses, the distance between the activation centres was 0-4 mm. There was spatial variability between individual cases; however, as shown by the distances between the centres found with fixed-effect and random-effects analyses, the coordinates for individual cases can be used to represent those of the group. The findings show that the neuropsychological brain mapping battery described here can be used in basic science studies that investigate the relationship of the brain to the mind and also as functional localiser in clinical studies for diagnosis, follow-up and pre-surgical mapping.

Pathological Laughing As a Manifestation in a Clinically Isolated Brainstem Syndrome: A Case Report

The prevalence of pathological laughing and crying in multiple sclerosis (MS) is 10%. It has been speculated that the anatomical lesion responsible for the pathological laughing is located in the pontine base, prefrontal cortex, and cerebellum. We report an 18‐year‐old male patient presenting with pathological laughing and hypomania. In his neurological examination, he had a euphoric effect with ataxic walking and dysarthria speech. He had a bilateral conjugated gaze limitation, with a prominent bilateral horizontal nystagmus on left gaze, dysmetria, dysdiadokokinesia, and remarkable dysfunction in a heel‐to‐shin test on the left. The IgG index in cerebrospinal fluid was normal with an oligoclonal band was present. In cranial MRI, there was a lesion on central pons which was hypointense in T1 images with contrast enhancement and hyperintense in T2 and flair images. Also another lesion in right brachium pontis which did not contrast enhancement but was hyperintense on T2 and flair images was present. There was an elevation of myoinositol/creatine ratio and choline and a reduction of NAA in proton MR spectroscopy. MR spectroscopic evaluation of the patient demonstrated the demyelination process. There has been no report of patients in whom pathological laughter was the presenting symptom of clinically isolated brainstem syndrome.

Evaluation of Aqueductal Patency in Patients with Hydrocephalus: Three-Dimensional High-Sampling-Efficiency Technique (SPACE) versus Two-Dimensional Turbo Spin Echo at 3 Tesla

Objective To compare the accuracy of diagnosing aqueductal patency and image quality between high spatial resolution three-dimensional (3D) high-sampling-efficiency technique (sampling perfection with application optimized contrast using different flip angle evolutions [SPACE]) and T2-weighted (T2W) two-dimensional (2D) turbo spin echo (TSE) at 3-T in patients with hydrocephalus. Materials and Methods This retrospective study included 99 patients diagnosed with hydrocephalus. T2W 3D-SPACE was added to the routine sequences which consisted of T2W 2D-TSE, 3D-constructive interference steady state (CISS), and cine phase-contrast MRI (PC-MRI). Two radiologists evaluated independently the patency of cerebral aqueduct and image quality on the T2W 2D-TSE and T2W 3D-SPACE. PC-MRI and 3D-CISS were used as the reference for aqueductal patency and image quality, respectively. Inter-observer agreement was calculated using kappa statistics. Results The evaluation of the aqueductal patency by T2W 3D-SPACE and T2W 2D-TSE were in agreement with PC-MRI in 100% (99/99; sensitivity, 100% [83/83]; specificity, 100% [16/16]) and 83.8% (83/99; sensitivity, 100% [67/83]; specificity, 100% [16/16]), respectively (p < 0.001). No significant difference in image quality between T2W 2D-TSE and T2W 3D-SPACE (p = 0.056) occurred. The kappa values for inter-observer agreement were 0.714 for T2W 2D-TSE and 0.899 for T2W 3D-SPACE. Conclusion Three-dimensional-SPACE is superior to 2D-TSE for the evaluation of aqueductal patency in hydrocephalus. T2W 3D-SPACE may hold promise as a highly accurate alternative treatment to PC-MRI for the physiological and morphological evaluation of aqueductal patency.