Biomedical subjects

T Kahn

Publications and source records attributed to T Kahn.

177 records · Page 10Linked to original sources

PubMedDate not supplied

In vivo MRI thermometry using a phase-sensitive sequence: preliminary experience during MRI-guided laser-induced interstitial thermotherapy of brain tumors.

The purpose of this study was the application of the proton-resonance-frequency method to monitor laser-induced interstitial thermotherapy (LITT) in a patient with an astrocytoma WHO II. A phase-sensitive two-dimensional (2D) fast low-angle shot (FLASH) sequence was used to determine the temperature-related phase shifts during LITT. Temperature maps were displayed during therapy with a temporal resolution of 20 seconds. Irradiation was discontinued as soon as the 60 to 65 degrees C isotherm reached the margin of the tumor. A contrast-enhanced MRI study performed immediately after therapy showed a good correlation of the size of an enhancing rim around the lesion with the 60 to 65 degrees C isotherm. The preliminary results of our study indicate that MRI guidance of LITT may be improved by temperature quantification based on the proton-resonance-frequency method.

Astrocytoma↗

PubMedDate not supplied

Is demyelination a feature of maple syrup urine disease?

To determine whether disturbance of myelination is a pathophysiologic feature in patients with treated maple syrup urine disease (MSUD), neurophysiologic studies were performed in 10 MSUD patients ages 4-16 years. Afferent and efferent pathways were studied by visual evoked potentials, somatosensory evoked potentials, motor evoked potentials, stance-stabilizing reflexes, and peripheral nerve conduction velocity. Magnetic resonance imaging was used to detect possible cerebral white matter abnormalities. Visual evoked potentials were normal in all patients. There was only slight prolongation of central afferent and efferent conduction times and the long latency component of the stance-stabilizing reflexes. Peripheral nerve conduction studies revealed reduced sensory nerve conduction velocity in 3 patients. The neurophysiologic findings were not consistently correlated to the neurologic outcome of the patients. Magnetic resonance imaging did not reveal major abnormalities and demonstrated bilateral periventricular high intensity periventricular signals on T2-weighted images in 4 of 10 patients. It is concluded that dysmyelination is not a major pathophysiologic feature in patients with MSUD.

Adolescent↗

PubMedDate not supplied

The concept of the GPOH-HD 2003 therapy study for pediatric Hodgkin's disease: evolution in the tradition of the DAL/GPOH studies.

Today it is possible to cure more than 90 % of children and adolescents with Hodgkin's disease with a combination of radiotherapy and chemotherapy. Since the DAL-HD 82 study, the main scientific focus has been on avoiding late effects such as the OPSI syndrome, late complications involving the heart, lungs, thyroid and/or gonads particularly sterility in men and premature onset of menopause in women, and the prevention of secondary malignancies. The GPOH-HD 2003 study will introduce FDG-PET to the initial diagnostic program and the assessment of response to therapy in order to evaluate further possibilities for reducing therapy. In this context, the central review of all clinical and radiological findings, systematically done since the DAL-HD 90 study, will be increasingly relevant in maintaining standardised stage classification and therapy group assignment which was established by the preceding studies. Continuing in the direction of the earlier studies, the indications for radiotherapy will be restricted even further. In the early stages (treatment group 1) patients with CR or a negative FDG-PET at the end of chemotherapy will receive no radiotherapy in order to reduce the risk of a secondary malignancy. In a randomized comparison, procarbazine will be replaced by dacarbazine in the COPP cycles to determine whether sterility in men and premature onset of menopause in women can be avoided by elimination of procarbazine while retaining the same clinical efficacy. Finally, relapse therapy is to be tailored according to the time of relapse, the initial therapy group, and the patient's response to the relapse therapy with more patients receiving autologous transplantation in order to further improve the results of relapse treatment.

Antineoplastic Combined Chemotherapy Protocols↗

PubMedDate not supplied

MR measurement of spinal CSF flow with the RACE technique.

The purpose of our study was the application and validation of a phase-sensitive pulse sequence that allowed real time CSF flow measurement without need for electrocardiographic (ECG) synchronization. After excitation of a slice perpendicular to the axis of the spine, projective data were obtained with a gradient echo sequence [contrast enhanced Fourier acquired steady-state technique (CE-FAST)] without spin warp gradient [real time acquisition and evaluation of motion technique (RACE)], allowing one-dimensional spatial resolution across the region of interest with a total sampling time of 20-30 ms. The sequence was calibrated with a spinal CSF phantom with oscillatory fluid motion. The calculated mean pulsation amplitudes of 20 healthy volunteers in the cervical region were 16 mm (range 9-36 mm), in the thoracic region 11 mm (5-21 mm), and in the lumbar region 3 mm (1-6 mm). The technique was capable of demonstrating physiologic alterations of CSF flow during respiratory maneuvers and may provide a tool to evaluate the altered CSF dynamics resulting from spinal block, inflammatory processes, or hemorrhage.

Adolescent↗

PubMedDate not supplied

Selective MR angiography and intracranial collateral blood flow.

This study evaluates the usefulness of MR angiography (MRA) in analyzing the individual collateral flow dynamics and anatomy of the circle of Willis in patients with high-grade extracranial carotid stenosis or occlusion. Selective MRA of the carotid or vertebrobasilar territory was performed by means of presaturation of up to three of the brain-supplying arteries at the level of the middle or lower neck (angled presaturation slabs). Results obtained with selective and nonselective arterial MRA in 45 consecutive patients were compared with findings at transcranial Doppler ultrasonography and intraarterial angiography, the latter serving as the "gold standard." Sensitivity of selective MRA in detecting intracranial collateral circulation via the anterior and posterior communicating artery was 95 and 97%, respectively; sensitivity in depicting extracranial to intracranial transorbital flow was lower (67%). Nonselective arterial MRA was 100% sensitive in detecting a nonfilling of the horizontal (A1) segment of the anterior cerebral artery and in identifying an origin of the posterior cerebral artery from the intracranial carotid artery. Visibility of the posterior communicating artery at MRA predicted for pathological collateral flow via this vessel in all cases. We conclude that selective and nonselective MRA of the cerebral arteries as used here is the most powerful noninvasive method to demonstrate collateral circulation via the basal communicating arteries and to identify hemodynamically relevant anatomic variants of the circle of Willis.

Adult↗

PubMedDate not supplied

MRI-guided laser-induced interstitial thermotherapy of cerebral neoplasms.

OBJECTIVE: Laser-induced interstitial thermotherapy (LITT) using a neodymium:yttrium aluminum garnet (Nd: YAG) laser is a new therapeutic approach in the treatment of brain tumors. The purpose of our study was to determine the value of MRI in monitoring LITT. MATERIALS AND METHODS: Eight patients with intracerebral tumors were treated with LITT. The light guide was inserted via an applicator sheath that was implanted stereotaxically with CT guidance. The laser irradiation was performed within the MR unit and monitored by repetitive measurements of a T1-weighted 2D-FLASH sequence. RESULTS: During therapy in all patients, typical changes of signal intensity were seen. A gradually increasing central zone of high signal intensity was surrounded by an increasing peripheral area of reduced signal intensity. The diameter of an enhancing rim at the outer border of the peripheral area after Gd-DTPA was considered as the total lesion size. The lesion size as determined on 2D-FLASH scans during LITT accounted for 88-100% (mean 93.5%) of total lesion size on T1-weighted images after Gd-DTPA acquired immediately after therapy. On T2-weighted images the signal intensities of the two zones were vice versa. Follow-up studies showed a decrease of total lesion size (15-87%). CONCLUSION: Our results demonstrate that MRI is feasible and effective in monitoring LITT. However, the role of LITT in the therapeutic workup of brain tumors still has to be defined in future clinical studies.

Adult↗

PubMedDate not supplied

MRI of the brain in Wilson disease: T2 signal loss under therapy.

Repeat examinations in a de novo patient with Wilson disease revealed an expansion of decreased signal intensities in the basal ganglia on T2-weighted imaging after initiation of copper trapping therapy. Since marked clinical improvement was associated with continued urinary copper excretion, iron depositioning in exchange for copper might explain these findings.

Adult↗

PubMedDate not supplied

Factors influencing flow-induced signal loss in MR angiography: an in vitro study.

OBJECTIVE: Signal loss due to poststenotic turbulence is one remaining limitation in the clinical use of MRA. The objective of this study was to determine the factors influencing poststenotic signal loss (PSL) in a stenotic tube system. MATERIALS AND METHODS: With use of a two-dimensional gradient echo sequence (FLASH), the influence of (a) the degree of stenosis (50, 75, and 91% cross-sectional area reduction), (b) flow velocity (12, 47, 71, and 94 cm/s), (c) TE (3, 6, 13, and 20 ms), and (d) flip angle (5, 10, 20, ... , 90 degrees) on the length of PSL was measured in a nonpulsatile stenotic tube system. To quantify the effect of first-order gradient motion refocusing (GMR), the signal intensity ratio from flow-compensated and -uncompensated images was calculated. For statistical analysis, multiple regression analysis and unpaired Student t test were used. RESULTS: In the flow model used, the length of PSL increased significantly with the degree of stenosis (beta ST' = 0.483 mm/%, beta ST" = 0.447 mm/%, p < 0.0001), flow velocity (beta v' = 0.297 s, beta v" = 0.213 s, p < 0.0001), and TE (beta TE = 1.88 mm/ms, p < 0.0001), respectively, whereas no correlation emerged for varying flip angles (beta alpha = 0.0214, p = 0.29). First-order GMR reduced significantly PSL in through-plane measurements (p < 0.0001). Maximal signal-enhancing effects of first-order GMR were observed 1-3 cm distal to the stenosis. CONCLUSION: Flow model parameters (i.e., degree of stenosis, flow velocity) markedly influenced the length of PSL that could be compensate for by use orf shortened TEs and first-order GMR. Varying flip angles had no significant influence on PSL.

Acrylic Resins↗

PubMedDate not supplied

Laser-induced thermal lesions in the human brain: short- and long-term appearance on MRI.

PURPOSE: The purpose of our study was to investigate with MRI the development of thermal lesions in the human brain up to almost 4 years after laser-induced interstitial thermotherapy (LITT). METHOD: Eighteen patients with brain tumors who underwent LITT entered the study. RESULTS: In all patients the acute lesion comprised five concentric zones that showed reverse signal intensities on T1- versus T2-weighted images. Lesion development over time was uniform in 89% of the lesions. In two cases variations were observed. CONCLUSION: The results of our MR follow-up studies showed that post-LITT, laser-induced lesions will shrink exponentially after an initial expansion without any pseudocystic effects.

Adult↗

PubMedDate not supplied

Topography and identification of the inferior precentral sulcus in MR imaging.

Sagittal MR imaging was used to investigate cerebral sulci bordering the functionally important areas on the lateral suprasylvian surface. The aim of the study was to identify characteristic relationships of the inferior precentral sulcus to nearby sulci and gyri. MR findings in 20 healthy volunteers were compared with those in 62 intact postmortem hemispheres. MR techniques are described for the direct identification of the anterior ascending ramus of the sylvian fissure and the inferior precentral sulcus. These sulci, which border Broca's area and the primary motor area, can be reliably identified with sagittal MR. Four different types of sulcus topography were recognized. Most frequently, the inferior precentral sulcus is the sulcus posterior to the anterior ascending sylvian ramus (95% in the MR study, 87% in the anatomic study). Occasionally, an additional sulcus is interposed (5%, 10%), or an ascending ramus is absent (0%, 3%). Identification of these landmarks is important for the exact preoperative localization of cortical lesions as well as for the intraoperative interpretation of individual sulcus patterns.

Adult↗

PubMedDate not supplied