PubMed Health⌕ Search

Biomedical subjects

J S Lewin

Publications and source records attributed to J S Lewin.

At least 19 recordsLinked to original sources
PubMed2000

Experience with Barton button and peristomal breathing valve attachments for hands-free tracheoesophageal speech.

BACKGROUND: Tracheostoma breathing valves permit hands-free tracheoesophageal (TE) speech production; however, few laryngectomees routinely use them because of problems with attachment. METHODS: We retrospectively reviewed the charts of 45 TE speakers to determine the success rate and factors associated with successful breathing valve use based on attachment. All patients attempted to use a tracheostoma breathing valve with either a standard or customized peristomal housing, or a standard or customized Barton button. Device selection was based on inspection of the patient's neck and peristomal contour. Six to eight consecutive hours of attachment defined success. RESULTS: Overall, 9% of subjects succeeded with any peristomal attachment as compared to 68% with either a standard (57%) or customized (85%) Barton button. Smooth stomal contour, a contiguous stomal lip, and correct button length were important for successful Barton button use. CONCLUSIONS: Standard or customized Barton buttons offer excellent alternatives to peristomal housing attachments for hands-free TE speech in select patients.

Equipment Design↗
PubMed2000

Intraoperative magnetic resonance image guidance in neurosurgery.

Recently, there has been a burgeoning interest in the use of image-guided navigation to improve the safety and effectiveness of neurosurgical procedures. The intraoperative use of magnetic resonance imaging (MRI) provides the most accurate guidance available. This report discusses the hardware and software improvements that have made intraoperative MRI a reality and describes the use of this technology for neurosurgical intraoperative guidance.

Brain Neoplasms↗
PubMed2000

Thermal lesion conspicuity following interstitial radiofrequency thermal tumor ablation in humans: a comparison of STIR, turbo spin-echo T2-weighted, and contrast-enhanced T1-weighted MR images at 0.2 T.

The purpose of this study was to compare the contrast between radiofrequency (RF) thermal liver lesions and surrounding tissue in T2-weighted turbo spin-echo sequences (TSE T2), short TI inversion recovery techniques (STIR), and contrast-enhanced (CE) T1-weighted spin-echo images. Nineteen RF thermal ablations were performed on eight patients with metastatic liver tumors. After ablation, contrast-to-noise ratios (CNRs) were calculated between mean signal amplitudes from three regions of interest (ROI) (lesion, surrounding edema, and normal tissue) using TSE T2-weighted, STIR, and contrast-enhanced T1-weighted (CE T1) sequences for each lesion. CNRs between the thermal lesion and normal liver tissue for both TSE T2-weighted (mean 0.9) and STIR (2.0) images were significantly lower than for CE T1-weighted (8.4) images (t-test, alpha = 0.05). However, CNRs between edema rim and the core of the thermal lesion for both TSE T2-weighted (8.1) and STIR images (7.2) were not significantly different (t-test, alpha = 0.05) from CNRs between lesion and normal tissue for CE T1-weighted images (8.4), nor was the CNR between edema rim and normal tissue for both TSE T2-weighted (10.3) and STIR (9.8) images. Although the edema was not visible on CE T1-weighted images, 18 of 19 lesions (94.7%) were surrounded by a hyperintense rim on TSE T2-weighted or STIR images. Both TSE T2-weighted and STIR sequences represent valid techniques for repeatable assessment of RF thermal lesions.

Adult↗
PubMed2000

An optical system for wireless detuning of parallel resonant circuits.

A new optical method of detuning parallel resonant circuits is described. This method involves the integration of a photoresistor in parallel with the inductor and capacitor of a parallel resonant circuit, in this case a magnetic resonance imaging (MRI) receiver coil. A fiberoptic cable extending the length of the interventional device is used in conjunction with an external light source to deliver light to the photoresistor. Exposing the photoresistor to light changes its bulk resistance and greatly lowers the Q of the parallel resonant circuit, effectively detuning it. By combining this optical detuning scheme with inductive coupling of the interventional device-mounted microcoils to a standard MRI coil, a completely wireless device for active device tracking has been created. This new device improves on current technology by simplifying device complexity and reducing patient risk by eliminating the need for electrical connections between the device-mounted microcoils to the MR receiver channel.

Equipment Design↗
PubMed2000

Active MR guidance of interventional devices with target-navigation.

This project incorporated a novel inductive coupling structure of three micro coils into an invasive device tip to determine both its tip position and orientation. Moreover, with the introduction of a new target-navigation technique the MR scan plane was defined automatically by the invasive device orientation and target tissue location. A time domain multiplexing technique was applied for simultaneous MR imaging and device tracking. Using these techniques, the acquired MR images always showed both the invasive device and its target tissue. Thus, roadmap images and their potential misregistration errors were avoided. A graphical user interface (GUI) was also designed to assist interventional physicians in monitoring and guiding the insertion of the interventional device. Ex vivo phantom and in vivo animal experiments were performed to test this new technique. The methods developed in this project provide a new active technique for interventional device guidance using MRI. Magn Reson Med 44:56-65, 2000.

Animals↗
PubMed2000

Percutaneous magnetic resonance image-guided biopsy and aspiration in the head and neck.

OBJECTIVE/HYPOTHESIS: To test the hypotheses that 1) magnetic resonance imaging (MRI)-guided biopsy and aspiration with an open 0.2-T system (Magnetom Open, Siemens, Erlangen, Germany) in the head and neck is feasible and successful and 2) procedure times can be sufficiently short to be well tolerated by the patient. METHODS: Sixty-one MRI-guided procedures were performed in 47 patients (ages, 6 mo-88 y) in the head and neck, including the mucosal sites and masticator and parapharyngeal spaces (n = 23), parotid space (n = 6), submandibular space (n = 2), cervical vertebral column/paraspinal tissues (n = 8), skull base (n = 3), larynx or hypopharynx (n = 3), and infrahyoid nodal chains and surrounding tissues (n = 16). A clinical C-arm imaging system was used, supplemented by an in-room radiofrequency-shielded liquid crystal monitor, rapid gradient echo sequences for needle guidance, and MRI-compatible anesthesia, monitoring, and surgical lighting equipment. Tissue sampling included fine-needle aspiration (n = 58) and cutting-needle core biopsy (n = 27), with 24 patients undergoing both procedures. Procedures were evaluated for success of needle placement, procedure time, and complications. RESULTS: Successful needle placement was accomplished in all cases without complication, with tissue sufficient for pathological diagnosis obtained for all but five patients with an average of 2.1 passes per patient. For fine-needle aspiration, average instrument time was 7.8 minutes per pass, and average cutting-needle core biopsy time was 9.2 minutes. CONCLUSIONS: Interactive MRI guidance for needle biopsy and aspiration of deep head and neck lesions is feasible, successful, and safe. Procedure times are sufficiently short to be well tolerated by the patient.

Adolescent↗
PubMed2000

Semiautomatic 3-D image registration as applied to interventional MRI liver cancer treatment.

We evaluated semiautomatic, voxel-based registration methods for a new application, the assessment and optimization of interventional magnetic resonance imaging (I-MRI) guided thermal ablation of liver cancer. The abdominal images acquired on a low-field-strength, open I-MRI system contain noise, motion artifacts, and tissue deformation. Dissimilar images can be obtained as a result of different MRI acquisition techniques and/or changes induced by treatments. These features challenge a registration algorithm. We evaluated one manual and four automated methods on clinical images acquired before treatment, immediately following treatment, and during several follow-up studies. Images were T2-weighted, T1-weighted Gd-DTPA enhanced, T1-weighted, and short-inversion-time inversion recovery (STIR). Registration accuracy was estimated from distances between anatomical landmarks. Mutual information gave better results than entropy, correlation, and variance of gray-scale ratio. Preprocessing steps such as masking and an initialization method that used two-dimensional (2-D) registration to obtain initial transformation estimates were crucial. With proper preprocessing, automatic registration was successful with all image pairs having reasonable image quality. A registration accuracy of approximately equal to 3 mm was achieved with both manual and mutual information methods. Despite motion and deformation in the liver, mutual information registration is sufficiently accurate and robust for useful applications in I-MRI thermal ablation therapy.

Algorithms↗
PubMed1999

An MRI study of adolescent patients with either schizophrenia or bipolar disorder as compared to healthy control subjects.

BACKGROUND: There are few imaging studies in adolescent patients with either schizophrenia or bipolar disorder. Such studies are of interest because adolescents may have a more severe illness and neurodevelopmental events may have a greater role in their pathophysiology. METHODS: We compared 20 patients with schizophrenia and 15 patients with bipolar disorder (10 to 18 years) to 16 normal adolescents on magnetic resonance imaging (MRI) measures of intracranial volume and ventricular and sulcal enlargement. Two planned comparison contrasts were employed, one comparing the two patient groups to each other (contrast 1), and one comparing both patient groups combined to control subjects (contrast 2). RESULTS: None of the contrast 1 comparisons (schizophrenia vs bipolar) were statistically significant. Contrast 2 comparisons (control subjects vs patients) were statistically significant for intracranial volume (reduced in patients) as well as frontal and temporal sulcal size (increased in patients). CONCLUSIONS: The patient groups were not statistically significantly different from each other on any measure. The combined patient groups were different from control subjects on intracranial volume and frontal and temporal sulcal size. Also, there was evidence for ventricular enlargement, after removal of a control subject with an extreme value. These findings indicate that the same abnormalities noted in adult populations are present in adolescents.

Adolescent↗
PubMed1999

Three-dimensional magnetic resonance-based morphometrics and ventricular dysmorphology in schizophrenia.

BACKGROUND: Recent methodological refinements in magnetic resonance (MR) imaging have led to brain averaging and morphometric approaches that are sensitive to subtle anatomical distinctions in schizophrenia. METHODS: Using a novel morphometric technique for surface analysis, 48 selected landmarks of the rendered ventricular system were extracted and compared between the ventricles of 20 patients with schizophrenia and 20 normal subjects. RESULTS: There was no significant difference in ventricular shape between groups, but significant (p = .015) and highly localized shape deformity was detected at the foramen of Monro and at the proximal temporal horn of the lateral ventricle of male (but not female) patients relative to controls. CONCLUSIONS: Three-dimensional MR-based morphometrics complements established volumetric approaches and can detect minute shape deformities that may be associated with schizophrenia.

Adolescent↗
PubMed1999

Biochemoprevention for dysplastic lesions of the upper aerodigestive tract.

OBJECTIVES: To evaluate the efficacy and secondarily the toxic effects of biochemopreventive therapy (high-dose isotretinoin [13-cis-retinoic acid], alpha-tocopherol, and interferon alfa) in the reversal of advanced premalignant lesions of the upper aerodigestive tract and to correlate the therapeutic events with modulation of biomarkers. DESIGN: Prospective, nonrandomized chemoprevention trial. SETTING: Tertiary cancer care referral center and ambulatory care. PARTICIPANTS: Thirty-six patients with advanced premalignant lesions of the upper aerodigestive tract, without cancer during the 2 years before the intervention, with evaluable lesions, and without retinoid therapy for 3 months before the trial. INTERVENTION: Administration of oral isotretinoin (100 mg/m2 per day), oral alpha-tocopherol (1200 IU/d), and subcutaneous interferon alfa (3 megaunits per square meter twice weekly) for 12 months, with serial biopsies and clinical examination at 0, 6, 12, and 18 months from study start. MAIN OUTCOME MEASURES: Clinical and histologic responses to the intervention. RESULTS: Of the 36 patients, evaluation was possible in 30 for response at 6 months and in 21 at 12 months. At 6 months, there were 10 pathologic complete responses and 7 partial responses; at 12 months, 7 complete and 3 partial responses. A striking difference in response was observed in favor of laryngeal lesions (9/19 [47%] complete response rate at 6 months and 7/14 [50%] at 12 months vs 1/11 [9%] and 0/7 [0%], respectively, for oral lesions). Toxic effects were acceptable and did not exceed grade 3. CONCLUSION: Biochemoprevention is a promising biologic approach for laryngeal dysplasia and needs to be investigated further.

Adult↗
PubMed1999

Temperature measurement using echo-shifted FLASH at low field for interventional MRI.

We investigated the feasibility of using echo-shifted fast low-angle shot (FLASH) for temperature-monitored thermo-therapeutic procedures in a 0.2 T interventional magnetic resonance (MR) scanner. Based on the proton resonance frequency shift technique, modified echo-shifted FLASH has sufficiently high signal-to-noise ratio to provide accurate temperature maps with short scan times, i.e., 5 seconds in phantoms (TR = 20.5 msec; effective TE = 30 msec; one echo shift; NSA = 2) and ex vivo experiments (TR = 19.4 msec; effective TE = 28.9 msec; one echo shift; NSA = 2) and 3 seconds (TR = 19.4 msec; effective TE = 28.9 msec, one echo shift; NSA 1) for an in vivo case. The proton resonance frequency shifts with temperature observed in a 0.2 T MR scanner using this sequence were -0.0072 ppm/degrees C (temperature uncertainty = +/-2.5 degrees C) for polyacrylamide phantoins and -0.0086 ppm/degrees C (temperature uncertainty = +/- 1 degrees C) for ex vivo bovine liver. These experiments demonstrated that echo-shifted FLASH is a viable method for low-field temperature monitoring despite the decreased signal and decreased phase sensitivity compared with its counterpart in a 1.5 T MR imaging system. The improved temporal resolution of temperature images, now possible in low-field interventional MR systems using echo-shifted FLASH, will allow clinicians more accurate monitoring of interstitial ablation in MR-guided interventional procedures.

Animals↗
PubMed1999

MRI-guided radiofrequency thermal ablation of implanted VX2 liver tumors in a rabbit model: demonstration of feasibility at 0.2 T.

Successful radiofrequency (RF) thermal ablation was performed on VX2 tumors implanted in 23 rabbit livers under magnetic resonance (MR) guidance using a C-arm-shaped low-field 0.2 T system. RF application and immediate postprocedure MRI of all animals was performed [T2-weighted, turbo short tau inversion recovery (STIR), T1-weighted before and after gadopentetate dimeglumine administration). Follow-up MRI with a superparamagnetic iron oxide (SPIO) contrast medium was performed in nine rabbits at 2 weeks and in four rabbits at 1 month post RF ablation. All livers were harvested for pathologic examination. T2-weighted and turbo-STIR images demonstrated the highest tumor-to-RF-thermal lesion contrast-to-noise ratios (CNRs; means 4.5 and 3.8, respectively) on postprocedure images; this was redemonstrated at 2- and 4-week follow-up imaging. T2-weighted imaging never overestimated pathologic lesion size by more than 2 mm, and the radiologic-pathologic correlation coefficient was not less than 0.90. In conclusion, MRI-guided RF thermal ablation in implanted liver tumor is feasible using a C-arm-shaped low-field 0.2 T system. The thermal lesion size can be most accurately monitored with T2-weighted and turbo-STIR images.

Animals↗
PubMed1999

Fast T(2)-weighted imaging by PSIF at 0.2 T for interventional MRI.

Rapid T(2) weighted (T(2)W) images would facilitate physicians being able to distinguish normal tissues, vessels, tumors, and thermal lesions from therapeutic devices throughout interventional MRI procedures commonly performed in open low-field scanners (e.g., 0.2 T). Conventional diagnostic MRI techniques have not been successful at low-field strength for fast T(2)W imaging during the guidance phase of interventional MRI (I-MRI) procedures. FISP and true-FISP methods yield T(1)/T(2)-weighted images and do not always provide sufficient contrast for device guidance or lesion assessment. As such, a variant of PSIF (a gradient reversed form of FISP) which collects the T(2)-weighted spin echo of the SSFP signal was developed and implemented at 0.2 T for use in I-MRI procedures. The sequence has a balanced readout gradient to reduce motion sensitivity. Asymmetric sampling toward the end of the TR cycle reduces T(2)* decay of the spin echo component in the SSFP signal. The sequence gives one image in 5-7 s in vivo with adequate SNR and T(2) contrast for interventional applications. Patient studies showed that the PSIF sequence variant demarcates many tumors not detectable by either FISP or true-FISP. Results from animal experiments suggested that it has potential to monitor thermal lesions during interstitial thermal ablation procedures. Magn Reson Med 42:335-344, 1999.

Animals↗
PubMed1999

Improved device definition in interventional magnetic resonance imaging using a rotated stripes keyhole acquisition.

Keyhole acquisition techniques have been used to reduce image acquisition times primarily in contrast agent studies and via simulation in interventional MRI procedures. More recent simulations have suggested that improved definition of an interventional device [e.g., biopsy needles, radio frequency (RF) electrodes] could be achieved by rotating the keyhole pattern in k-space so that the read out direction lies perpendicular to the device orientation in real space. This study seeks to validate the earlier predictions of improved efficacy of a rotated stripes keyhole acquisition in actual in vitro and in vivo interventional MR imaging procedures. A true-FISP sequence was modified to perform central stripes keyhole (as known as conventional keyhole) acquisitions after a full initial reference data set was acquired. The gradients of this sequence were then modified to rotate the k-space definition and the keyhole stripes by 10 degrees, 20 degrees, 30 degrees, 45 degrees, and 60 degrees from their conventional k-space orientation. Acquisitions were performed during insertion of interventional devices in phantom and in vivo RF ablation procedures, using the modified sequence selected which placed the phase encoding axis at parallel and perpendicular orientations to the devices. Resulting images were compared between the two orientations for needle width and tip accuracy. Apparent needle width was thinner and tip position more accurately determined for placement of phase encoding parallel to the needle in all cases. Rotated keyhole imaging provides the required temporal advantage of conventional keyhole imaging along with a near optimal definition of an interventional device when the phase encoding is oriented parallel to the direction of the needle motion. Magn Reson Med 42:554-560, 1999.

Animals↗
PubMed1999

[Keyhole-true FISP: fast T2-weighted imaging for interventional MRT at 0.2 T].

PURPOSE: The aim of this study is to introduce a fast, T2 weighted true FISP keyhole sequence implemented on an open C arm low field magnetic resonance (MR) scanner for interventional procedure guidance. METHOD: Following the acquisition of a reference data set using a true FISP (fast Imaging with Steady Precision) sequence, only the 32 central raw data lines (keyhole) are acquired in a fluoroscopic-like mode enabling continuous image reconstruction and update. The keyhole true-FISP sequence was tested in animal experiments and used in MR-guided interventions in 10 patients. RESULTS: The described true FISP keyhole sequence is characterized by an image frame rate of 2.5 images per second and a T2-like contrast. Due to system constraints with respect to the reconstruction, the actual displaying of images was delayed by up to 180 ms. CONCLUSIONS: The use of the described keyhole sequence enabled a fluoroscopy-like guidance of interventional devices in an open, low-field system.

Animals↗
PubMed1999

Low-flow vascular malformations in the head and neck: safety and feasibility of MR imaging-guided percutaneous sclerotherapy--preliminary experience with 14 procedures in three patients.

Fourteen percutaneous sclerotherapy procedures with magnetic resonance (MR) imaging guidance were performed in three patients with low-flow vascular malformations. All targeted vascular malformation compartments were filled with sclerosing agent without complications in a mean procedural time of 29 minutes. Follow-up imaging demonstrated reduction in size of the treated portions in all patients. In conclusion, sclerotherapy with MR imaging guidance can be performed safely and allows monitoring of injection.

Adult↗