Biomedical subjects

J S Lewin

Publications and source records attributed to J S Lewin.

At least 19 recordsLinked to original sources

PubMed2006

CT assessment of vocal cord medialization.

BACKGROUND AND PURPOSE: Unilateral vocal cord paralysis (UVCP) occurs after iatrogenic injury or disease process and is associated with dysphonia and aspiration. Various surgical options are available for treatment of UVCP, including vocal cord medialization thyroplasty and injection laryngoplasty. These augmentative procedures improve phonation and airway protection. Our purpose was to demonstrate the CT appearance of implants used for the treatment of UVCP. METHODS: Twelve patients treated surgically for UVCP were studied with helical CT. The vocal cords were augmented by using Silastic implants (n = 7), polytetrafluoroethylene (Gore-Tex) implants (n = 2), Teflon injections (n = 2), or fat injection (n = 1). Augmented vocal cords were characterized by size, shape, and Hounsfield units (HU). Two other patients with failed medialization thyroplasty were evaluated for the position of the extruded implant relative to the paralyzed vocal cord. RESULTS: The 7 Silastic implants were triangular and hyperattenuated (293.4 +/- 90.4 HU). The 2 Gore-Tex implants were heterogeneous with lobulated medial margins and were hyperattenuating (320 and 414 HU). The injected materials demonstrated ovoid/masslike configurations: the 2 Teflon injections were hyperattenuated (107 and 429 HU), and the fat injection was hypoattenuated (-102 HU). Inferior displacement of the implant was demonstrated relative to the true vocal cord in 2 patients with failed Silastic thyroplasties. CONCLUSION: CT can distinguish various types of vocal cord augmentation. Silastic implants are recognized by their characteristic triangular configuration. The Gore-Tex implants had unique heterogeneous attenuation with lobulated medial margins. Fat and Teflon injections both appear ovoid/masslike. Teflon injection should not be mistaken for tumor.

Adipose Tissue↗

PubMed2003

Magnetic resonance-guided biliary drainage in a patient with malignant obstructive jaundice and thrombocytopenia.

In a patient suffering from malignant obstructive jaundice and thrombocytopenia, magnetic resonance imaging (MRI) was used to guide percutaneous transhepatic biliary drainage, to avoid blind puncture of the bile ducts using fluoroscopy. The first puncture approach was successful, and an MRI-visible guide wire and drainage catheter were inserted successfully within 35 min. The course after the intervention was uneventful, and the patient's fever and itching improved. MRI guidance facilitated optimal procedure planning and high puncture accuracy.

Cholestasis↗

PubMed2001

Inhibition of prostate carcinogenesis in TRAMP mice by oral infusion of green tea polyphenols.

Development of effective chemopreventive agents against prostate cancer (CaP) for humans requires conclusive evidence of their efficacy in animal models that closely emulates human disease. The autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) model, which spontaneously develops metastatic CaP, is one such model that mimics progressive forms of human disease. Employing male TRAMP mice, we show that oral infusion of a polyphenolic fraction isolated from green tea (GTP) at a human achievable dose (equivalent to six cups of green tea per day) significantly inhibits CaP development and increases survival in these mice. In two separate experiments, the cumulative incidence of palpable tumors at 32 weeks of age in 20 untreated mice was 100% (20 of 20). In these mice, 95% (19 of 20), 65% (13 of 20), 40% (8 of 20), and 25% (5 of 20) of the animals exhibited distant site metastases to lymph nodes, lungs, liver, and bone, respectively. However, 0.1% GTP (wt/vol) provided as the sole source of drinking fluid to TRAMP mice from 8 to 32 weeks of age resulted in (i) significant delay in primary tumor incidence and tumor burden as assessed sequentially by MRI, (ii) significant decrease in prostate (64%) and genitourinary (GU) (72%) weight, (iii) significant inhibition in serum insulin-like growth factor-I and restoration of insulin-like growth factor binding protein-3 levels, and (iv) marked reduction in the protein expression of proliferating cell nuclear antigen (PCNA) in the prostate compared with water-fed TRAMP mice. The striking observation of this study was that GTP infusion resulted in almost complete inhibition of distant site metastases. Furthermore, GTP consumption caused significant apoptosis of CaP cells, which possibly resulted in reduced dissemination of cancer cells, thereby causing inhibition of prostate cancer development, progression, and metastasis of CaP to distant organ sites.

Administration, Oral↗

PubMed2001

Radial keyhole sequences for low field projection reconstruction interventional MRI.

Interventional magnetic resonance imaging (IMRI) is a rapidly emerging application for MRI in which diagnostic and therapeutic procedures are performed with MR image guidance. Real-time or near-real-time image acquisition and relative insensitivity to motion are essential for most intraoperative, therapeutic, and diagnostic procedures performed under MR guidance. The purpose of this work was to demonstrate the development and utility of two alternative rapid acquisition strategies during IMRI that are analogous to computed tomography fluoroscopy or keyhole MRI in a radial rather than rectilinear coordinate frame. The two strategies discussed here, interleaved projection reconstruction and continuous projection reconstruction, are compared and the feasibility of their application in experimental interventional applications is studied. J. Magn. Reson. Imaging 2001;13:142-151.

Animals↗

PubMed2001

How does alteration of hepatic blood flow affect liver perfusion and radiofrequency-induced thermal lesion size in rabbit liver?

The purpose of this study was to test the hypothesis that decreasing liver perfusion in rabbits results in an increase in thermal lesion size and that these effects can be accurately monitored using magnetic resonance imaging (MRI). We additionally tested the hypothesis that the increase in thermal lesion size would depend on the particular vessel or vessels occluded (hepatic artery, portal vein, or both). Using an Institutional Animal Care and Use Committee approved protocol, 20 New Zealand white rabbits were randomly assigned to four treatment groups (five in each group): control and ligation of portal vein (PV), hepatic artery (HA), or both PV and HA (HAPV). Surgical ligation of the appropriate vessel was performed under general anesthesia. Immediately after ligation, the rabbits were placed in a 0.2-T open MR system, and an 18-G copper radiofrequency (RF) electrode with a 2-cm exposed tip was inserted into the liver. RF was applied for 10 minutes with the tip temperature maintained at 90 degrees +/- 2 degrees C. Before and after ablation, perfusion data were obtained for 90 seconds using 30 3-second sequential single oblique-slice fast imaging with steady-state progression (FISP) acquisitions after injection of gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) via the inferior vena cava. Postablation scanning included axial and oblique turbo spin-echo (TSE) T2-weighted (T2w), STIR, and Gd-enhanced T1w sequences. Lesion size was determined perpendicular to the RF electrode using software calipers on the imager. The rabbits were sacrificed after completion of the post-therapy scans, and their livers were harvested for histologic analysis. The liver showed a mean increase in signal amplitude (SA) of 76% 24 seconds after Gd contrast injection in the control group. After contrast injection, the SA increased to a mean of only 66% in the group with ligated hepatic arteries, with no difference in the time to peak compared with the control group. No significant SA increase over baseline could be found in the groups with ligated PV or ligated PV and HA. T2-weighted images demonstrated the highest lesion-to-liver contrast-to-noise ratios (CNRs; mean -5.5) on postprocedure images, followed by STIR images (mean -2.2) in the control group. The lesions were poorly delineated on the Gd-enhanced images. Average maximum lesion sizes (mean +/- 95% confidence interval) were 22 +/- 4.3 mm after ligation of PV, 22 +/- 2.6 mm after ligation of both PV and HA, 14 +/- 2.0 mm after ligation of HA, and 13 +/- 1.9 mm in the control group. We accept the hypothesis that the diameter of the region of coagulation necrosis achieved by standardized RF ablation in the liver increases with reduced organ perfusion and that this effect can be accurately monitored using MRI. The major factor influencing the size of the coagulation area is the portal venous flow. Occlusion of the hepatic artery alone does not significantly increase lesion size. T2w sequences are best suited for postprocedure imaging due to the high lesion-to-liver CNR in rabbits with normal hepatic perfusion. J. Magn. Reson. Imaging 2001;13:57-63.

Animals↗

PubMed2001

Two-step navigatorless correction algorithm for radial k-space MRI acquisitions.

A new way to correct magnetic resonance image artifacts resulting from view-dependent phase variations and view-dependent variations in rigid body object translation is presented by exploiting basic properties of the trajectory of radial k-space acquisitions. Simulations, phantom studies, and in vivo experiments are used to demonstrate the feasibility and the utility of this method. While somewhat analogous to navigator echo correction, in which special gradients are interleaved into the imaging sequence so echoes at the center of k-space can be acquired prior to or after collection of the image data, the current method does not require additional new gradient structures within the pulse sequence or increases in scan time. The new method uses the phase information from all collected radial k-space data points rather than only the navigator echo, which permits correction of multiple sources of view-dependent phase variation in the image data. The resultant effect is improved image quality in radial MRI acquisitions. Magn Reson Med 45:277-288, 2001.

Algorithms↗

PubMed2001

Further experience with Botox injection for tracheoesophageal speech failure.

BACKGROUND: Some patients fail to acquire tracheoesophageal (TE) speech after laryngectomy because of pharyngeal constrictor hypertonicity. Botox injection relieves hypertonicity, but there are little objective data regarding outcomes, duration of effect, and reinjection rates. METHODS: Hypertonicity was identified by means of insufflation testing and confirmed videofluoroscopically in 23 unsuccessful TE speakers. Each patient received an EMG-guided Botox injection. Additional injections were offered if the first injection failed to produce fluent speech. RESULTS: Overall, 20 of 23 patients (87%) achieved fluent TE speech production after Botox injections; 5 after additional injections. Two patients declined further intervention, and 1 failed to achieve fluent TE speech production even after 3 Botox injections. The longest sustained effect was 37 months, the shortest was 5 months for 1 patient who required reinjection of Botox to maintain her TE speech production. CONCLUSIONS: Botox injection relieves constrictor hypertonicity in selected cases of TE speech failure with little need for reinjection to maintain long-term speech success.

Botulinum Toxins, Type A↗

PubMed2001

A multielement RF coil for MRI guidance of interventional devices.

Accurate localization of minimally invasive devices is critical to the success of interventional procedures. Device orientation and tip position are two of the most important pieces of information needed to define device location for magnetic resonance imaging (MRI)-guided interventional procedures. While a single one-element micro coil incorporated into an interventional device has proven to be effective in some applications, it can only supply tip position information. However, multiple positions on the device are necessary to also determine its orientation. For this purpose, a novel single micro coil design with three separate winding elements that provides both the device orientation and tip position is described in this study. Definition of MR scan planes, by using the device orientation and the target tissue location, permits automatic tracking of the insertion of the device. Furthermore, devices that include this coil design are permitted to bend to a limited extent. This makes the micro coil design appropriate for many flexible interventional devices. Reliable near-real-time tracking of three points on an interventional device is demonstrated on a 0.2T MRI system with modest gradient performance. Phantom and in vivo animal experiments are used to demonstrate the utility of this new coil design.

Animals↗

PubMed2001

The value of diffusion-weighted imaging for prediction of lasting deficit in acute stroke: an analysis of 134 patients with acute neurologic deficits.

Acute stroke is one of the three major causes of death and disability in the United States. Now that new, and possibly effective therapy is becoming available, accurate, rapid diagnosis is important to provide timely treatment, while avoiding the risk of complications from unnecessary intervention. Our objective was to test the hypothesis that use of echo-planar (EPI) diffusion-weighted imaging (DWI) is more accurate than conventional T2 weighted MRI in predicting progression to stroke in patients with acute ischemic neurologic deficits. We studied 134 patients presenting with acute neurologic deficits to a community hospital emergency room with both conventional MRI and DWI within 72 h of the onset of the acute deficit. We found DWI significantly more sensitive to permanent neurologic deficit at discharge (sensitivity 0.81) than conventional MRI (sensitivity 0.41). When available, DWI should be considered for routine use in patients being imaged for acute stroke.

Adult↗

PubMed2001

MR imaging-guided radiofrequency thermal ablation in the porcine brain at 0.2 T.

The aim of this study was to test the hypotheses that (a) MR imaging-guided radiofrequency (RF) thermal ablation is safe and feasible in porcine brain using an open C-arm-shaped low-field MR system, and that (b) induced thermal lesion size can be predicted using low-field MR imaging. Magnetic resonance-guided RF ablation was performed in the cerebral frontal lobes of six pigs. An 18-G monopolar RF electrode was inserted into the porcine brain using MR image guidance and RF was then applied for 10 min. After post-procedure imaging (T2-weighted, T1-weighted before and after gadodiamide administration), the pigs were killed and the brains were used for pathologic examination. Successful RF electrode placement was accomplished in all cases without complications; total magnet time ranged from 73 to 189 min. The thermal lesion size varied from 10 to 12 mm perpendicular to the electrode track and was easily visualized on T2-weighted and enhanced T1-weighted images. Enhanced T1-weighted imaging demonstrated the highest brain-to-RF thermal lesion contrast-to-noise ratio with an average of 1.5 +/- 1.6. Enhanced T1-weighted imaging never underestimated pathologic lesion diameter with a mean difference of 2.3 +/- 1.0 mm and a radiologic/pathologic correlation of 0.69. Magnetic resonance imaging-guided RF thermal ablation is feasible and safe in the porcine brain using an open MR low-field system. Induced-thermal lesion size can best be monitored using enhanced T1-weighted images. In the future, RF ablation under low-field MR guidance may offer an alternative treatment option for primary and secondary brain tumors.

Animals↗

PubMed2001

Experience with the chin tuck maneuver in postesophagectomy aspirators.

Aspiration is a common finding in the postesophagectomy barium swallow that often necessitates premature termination of the study prior to complete evaluation of the gastric conduit. More importantly, aspiration may play a significant role in the high incidence of postoperative pulmonary complications in this population. The chin tuck maneuver is a postural technique that reduces and often eliminates aspiration in swallowing-impaired patients. To evaluate the ability of the chin tuck maneuver to prevent aspiration during radiographic examination of the gastric conduit, the technique was used in 21 esophagectomy patients who aspirated during a swallowing evaluation combining the barium swallow and videofluoroscopy. Aspiration was eliminated in 81% of aspirators using the chin tuck maneuver. The results of this study demonstrate that the chin tuck maneuver is a simple technique that should be attempted in patients who aspirate postesophagectomy during radiographic imaging studies that require multiple swallows of contrast materials. Combining the barium swallow with the videofluoroscopic evaluation of swallowing provides objective documentation of both the structural integrity of the gastric conduit and swallowing function in patients after esophagectomies who are at high risk for postoperative morbidity.

Aged↗

PubMed2001

[Comparison of susceptibility artefacts of different radiofrequency electrodes at O.2 T. Influence of electrode positioning, pulse sequence and image reconstruction methods].

PURPOSE: Interventional MRI procedure monitoring requires small but accurate susceptibility artifacts of the instruments used. In this investigation, susceptibility artifacts of different RF-electrode designs were compared using a variety of pulse sequences and k-space acquisition methods. METHODS: 4 different 18-gauge RF-electrodes (with three single electrodes made of stainless steel, copper, inconal, and a triple-clustered electrode configuration made of inconal) were placed in a 0.2 T MR-scanner perpendicular to the main magnetic field. Pulse sequences used included: TSE T2, FISP, true-FISP, PSIF, and a temperature sensitive ES-GRE sequence. In addition to the 2D Cartesian k-space trajectory with Fourier transformation (2DFT), projection reconstruction (PR) was used with the FISP, true-FISP and PSIF sequences. RESULTS: The best tip accuracy was achieved with the combination of inconal electrodes and TSE T2. The usefulness of the tested sequences was found to be: TSE T2 > PSIF > FISP/true-FISP > ES-GRE. In general 2DFT provided better or equal tip accuracy than PR. The apparent shaft width was smaller using the copper electrode compared to the inconal electrode. However, the "match shaped" tip artifact of the copper probe led to a higher error in tip accuracy. CONCLUSIONS: TSE-T2 sequences and Cartesian 2DFT acquisitions should be used for accurate tip positioning at 0.2 T. Further, artifact size of the electrode shaft prevents the use of inconal for temperature sensitive sequences. Copper electrodes can be used for these purposes, although copper is not considered to be biocompatible at present.

Artifacts↗

PubMed2001

Segmented k-space and real-time cardiac cine MR imaging with radial trajectories.

The authors developed and evaluated two cine magnetic resonance (MR) imaging sequences with a radial rather than a rectilinear k-space coordinate frame: segmented k space and real-time true fast imaging with steady-state precession, or FISP. The two radial k-space segmentation (or view sharing) techniques, which were interleaved or continuous, were compared, and the feasibility of their application in cardiac cine MR imaging was explored in phantom and volunteer studies. Images obtained with the radial sequences were compared with those obtained with two-dimensional Fourier transform, or 2DFT, sequences currently used in cine MR imaging. Temporal resolution of 55 msec was achieved with the real-time radial sequences, which allowed acquisition of almost 19 high-quality images per second.

Adult↗

PubMed2001

Initial angiographic appearance of intracranial vascular occlusions in acute stroke as a predictor of outcome of thrombolysis: initial experience.

PURPOSE: To determine whether the initial angiographic morphology and location of intracranial arterial occlusions in acute stroke are reliable predictors of success of thrombolysis. MATERIALS AND METHODS: Thirty-three intracranial occlusions were studied in 32 patients who underwent intraarterial thrombolysis with urokinase within 6 hours from clinical onset of stroke symptoms. The initial angiographic appearance of each occlusion was categorized as cutoff, tapered, meniscus, tram-track, or tandem. Following thrombolysis, outcomes were classified as complete, partial, or no recanalization. RESULTS: Complete recanalization was accomplished in 17 of the 33 lesions, partial recanalization in nine, and no effect in seven. Tram-track (n = 3) and tapered (n = 7) lesions demonstrated the highest rates of at least partial recanalization (100% and 86%, respectively), whereas cutoff lesions (n = 13) demonstrated the lowest rate (69%). Intracranial hemorrhage was associated with higher doses of urokinase. Complete recanalization success rates were 60% for M1 lesions (n = 10), 43% for M2 or A2 lesions (n = 14), and 33% for M3 lesions (n = 3). Vertebrobasilar lesion (n = 5) success rates for complete and at least partial recanalization were 80% and 100%, respectively. CONCLUSION: Relationships were found to exist between the success rate of recanalization and initial angiographic lesion location and morphology, which represent important trends; however, further studies with a larger sample size are needed.

Adolescent↗

PubMed2001

Perfusion-modulated MR imaging-guided radiofrequency ablation of the kidney in a porcine model.

OBJECTIVE: This study was performed to test the hypothesis that temporary renal ischemia will result in increased thermal lesion size during radiofrequency thermal ablation in the kidney. MATERIALS AND METHODS: Twelve kidneys were treated in six pigs that were placed under general anesthesia in the MR suite, using a 0.2-T open C-shaped MR imaging system. A 4-cm-long, 14-mm-diameter balloon catheter was placed into the aorta using a transfemoral approach, and the balloon was positioned proximal to the renal arteries via guidance with MR imaging. A 2-cm exposed-tip MR-compatible 17-gauge radiofrequency electrode was placed into one kidney under MR fluoroscopy using fast imaging with steady-state free precession (FISP) sequences. Thermal ablation was performed with the electrode tip temperature maintained at 90 +/- 2 degrees C for 10 min. This procedure was repeated in the contralateral kidney. The balloon was inflated during one ablation. Postablation images were obtained, the pigs were sacrificed, and both kidneys of each animal were harvested for pathologic correlation. RESULTS: Technical success was achieved in all animals. The lesion measured 14.2 +/- 2.2 mm (mean +/- standard deviation) for the ischemic kidney versus 8.0 +/- 2.6 mm in the normally perfused kidney (p = 0.00002). No significant complications were noted. In all images, thermal lesions displayed low signal intensity with a sharp rim of high signal intensity best visualized using short tau inversion recovery (STIR) sequences with a mean accuracy of 1.3 +/- 1.2 mm when compared with pathologic findings and a mean contrast-to-noise ratio of 4.9 +/- 2.5. CONCLUSION: We accept the hypothesis that temporary renal ischemia leads to a significantly increased radiofrequency ablation lesion size. We conclude that catheter-based balloon perfusion reduction is feasible, that the procedure does not lead to major complications, and that it can be performed using MR imaging as the sole imaging modality.

Animals↗

PubMed2001

Intraoperative MR systems. Low-field approaches.

Numerous different concepts in low- and mid-field intervention have been described and applied for percutaneous intervention and intraoperative MR imaging, and each has demonstrated usefulness in specific applications. As the use of interventional methods under MR imaging expands, the imaging systems used for intervention will continue to evolve. More than likely, different system designs will be advocated for different interventional applications. The ultimate choice of interventional system will depend on each institution's optimal balance among the types of procedures to be performed, the required image quality, and the financial constraints.

Aged↗

PubMed2001

Optimizing brain tumor resection. Low-field interventional MR imaging.

In this article, the authors describe their strategy for intraoperative MR image guidance of tumor resection at low-field (0.2 T) strength. It is their opinion that intraoperative imaging is most useful in assessing the resection of intrinsic, infiltrating brain tumors; boundaries of the tumor cannot be clearly distinguished with the surgeon's eyes, and therefore, this discussion predominantly applies to the surgical resection of gliomas.

Brain Neoplasms↗

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↗