Biomedical subjects

J R Reichenbach

Publications and source records attributed to J R Reichenbach.

At least 37 records · Page 2Linked to original sources

PubMed2001

Vacuum-assisted resection of malignant tumors with and without subsequent radiofrequency ablation: feasibility of complete tumor treatment tested in an animal model.

PURPOSE: To evaluate the feasibility of vacuum-assisted tumor excision with and without RF ablation for the minimally invasive treatment of small tumors. MATERIALS AND METHODS: Twenty VX2 tumors were implanted bilaterally into the spine muscle of 10 rabbits. Tumor excision was performed after tumor sizes reached 10 mm (12-27 d incubation) with use of a vacuum-assisted biopsy device. Three or four directed vacuum-assisted biopsies were performed in angle steps of 30 degrees. In 10 tumors, ultrasound (US)-guided radiofrequency (RF) ablation (8 min, 60 W) was subsequently performed with use of a cooled-tip electrode system. Follow-up US was performed at 3-4-day intervals for as long as 3 weeks after excision/RF ablation. Autopsy and histopathologic analysis were performed. RESULTS: The duration of vacuum excision ranged from 12 to 45 minutes (25 min +/- 7). Histologically tumor-free margins in the outer round of the core biopsy specimens were found in only four of 20 cases (20%). Maximum lesion sizes during RF ablation ranged from 18 to 25 mm (20 mm +/- 2.6). Histologic examination of the excision specimens documented tumor-free margins in only three tumors (30%) among the excision-only group and only one (10%) among the combined excision/ablation group. Local recurrences occurred in eight of 10 cases (80%) after vacuum excision alone, whereas recurrence after combined excision and RF ablation occurred only in two of 10 cases (20%; P <.05). CONCLUSIONS: Local tumor resection with use of vacuum-assisted biopsy is feasible and promising as a minimally invasive therapy for the treatment of small focal breast neoplasms. Combined excision and RF ablation techniques may reduce the rate of local recurrence considerably.

Animals↗

PubMed2001

Percutaneous radiofrequency (RF) thermal ablation of rabbit tumors embedded in fat: a model for RF ablation of breast tumors.

RATIONALE AND OBJECTIVES: To develop an experimental tumor model for RF ablation of breast tumors surrounded by fat and to investigate the minimally invasive treatment of such tumors by saline-enhanced RF ablation monitored by ultrasound (US). METHODS: Twenty-eight VX2 tumors were implanted into the retroperitoneum of 14 rabbits and monitored by B-mode US at regular intervals of 2 to 3 days. Saline-enhanced RF ablation (25-mm tip length) was performed 16 days after tumor implantation (10-minute treatment time, 28 W, 15 mL/h infusion of 0.9% NaCl, which was increased to 30 mL/h in cases of an impedance increase). Thermal lesion growth was monitored by B-mode US. Treatment was considered complete if no relapse was detectable histopathologically after a follow-up period of up to 3 weeks. RESULTS: All tumor implantations were successful, reaching sizes from 5 to 38 mm 16 days after implantation. Tumors >20 mm showed central necrosis on US. Smaller tumors without signs of necrosis required greater needle perfusion to maintain constant needle-to-tissue impedance. Local relapses occurred in 14 of 27 tumors (51.8%), all with tumors >20 mm. In 12 cases, they were already detected sonographically. In 2 cases, "islands" of vital tumor were detected only during histopathological assessment. CONCLUSIONS: VX2 tumors are implantable into hypovascular adipose tissue with a high success rate and may be used as a model for RF ablation of breast tumors. B-mode US is not suitable for guiding RF ablation of tumors embedded in fat. The method appears to be more successful with smaller tumors.

Adipose Tissue↗

PubMed2001

Contrast-enhanced near-infrared laser mammography with a prototype breast scanner: feasibility study with tissue phantoms and preliminary results of imaging experimental tumors.

RATIONALE AND OBJECTIVES: Near-infrared (NIR) optical mammography without contrast has a low specificity. The application of optical contrast medium may improve the performance. The concentration-dependent detectability of a new NIR contrast medium was determined with a prototype optical breast scanner. In vivo imaging of experimental tumors was performed. METHODS: The NIR contrast agent NIR96010 is a newly synthesized, hydrophilic contrast agent for NIR mammography. A concentration-dependent contrast resolution was determined for tissue phantoms consisting of whole milk powder and gelatin. A central part of the phantoms measuring 2 x 2 cm2 without contrast was replaced with phantom material containing 1 micromol/L to 25 nmol/L NIR96010. The composite phantoms were measured with a prototype NIR breast scanner with lasers of lambda1 = 785 nm and lambda2 = 850 nm wavelength. Intensity profiles and standard deviations of the transmission signal in areas with and without contrast were determined by linear fit procedures. Signal-to-noise ratios and spatial resolution as a function of contrast concentration were determined. Near-infrared imaging of five tumor-bearing SCID mice (MX1 breast adenocarcinoma, tumor diameter 5-10 mm) was performed before and after intravenous application of 2 micromol/kg NIR96010. RESULTS: Spectrometry showed an absorption maximum of the contrast agent at 755 nm. No spectral shifts occurred in protein-containing solution. Signal-to-noise ratio in the transmission intensity profiles ranged from 1.1 at 25 nmol/L contrast to 28 at 1 micromol/L. At concentrations <40 nmol/L, no differentiation from the background was possible. The transitional area between the contrast-free edge of the phantom and the central contrast-containing part appeared in the profiles as a steep increase with a width of 4.2 +/- 1.8 mm. The experimental tumors were detectable in nonenhanced images as well as contrast-enhanced images, with better delineation after contrast administration. In postcontrast absorption profiles, a 44.1% +/- 11.3% greater absorption increase was seen in tumor tissue compared with normal tissue. CONCLUSIONS: The laser wavelength lambda1 of the prototype laser mammography device was not situated at maximum absorption of the contrast agent NIR96010 but on the descending shoulder of the absorption spectrum. This implies a 20% signal loss for contrast detection. Despite the nonideal measurement conditions, concentrations as low as 40 nmol/L were detectable in vitro. In vivo, all tumors were detectable in color-coded nonenhanced scans as well as in contrast-enhanced scans, with better delineation after contrast administration.

Alkenes↗

PubMed2001

Apparent diffusion coefficient decreases and magnetic resonance imaging perfusion parameters are associated in ischemic tissue of acute stroke patients.

Perfusion-and diffusion-weighted magnetic resonance imaging scans are thought to allow the characterization of tissue at risk of infarction. The authors tested the hypothesis that the apparent diffusion coefficient (ADC) decrease should be associated with the severity of the perfusion deficit in ischemic tissue of acute stroke patients. Perfusion-and diffusion-weighted scans were performed in 11 patients with sudden onset of neurologic deficits within the last 6 hours and T2-weighted magnetic resonance imaging scans were obtained after 6 days. Parameter images of the maximum of the contrast agent concentration, time to peak, relative cerebral blood volume, relative cerebral blood flow, and relative mean transit time were computed from the perfusion-weighted data. A threshold function was used to identify tissue volumes with stepwise ADC decreases. An onionlike distribution of successively decreasing ADC values was found, with the lowest ADC in the center of the ischemic region. Correspondingly, tissue perfusion decreased progressively from the periphery toward the ischemic core. This effect was most pronounced in the time-to-peak maps, with a linear association between ADC decrease and time-to-peak increase. Apparent diffusion coefficient values decreased from the periphery toward the ischemic core, and this distribution of ADC values was strongly associated with the severity of the perfusion deficit.

Adult↗

PubMed2000

Hemodynamic assessment of acute stroke using dynamic single-slice computed tomographic perfusion imaging.

BACKGROUND: Stroke management would benefit from a broadly available imaging tool that detects perfusion deficits in patients with acute stroke. OBJECTIVE: To determine the role of dynamic, single-slice computed tomographic (CT) perfusion imaging (CTP) in the assessment of acute middle cerebral artery stroke. DESIGN AND PATIENTS: Imaging with CTP and CT within the first 6 hours of symptom onset and before the start of treatment in a consecutive clinical series of 22 patients (mean age, 68.3 years; 14 women; studied within 143 +/- 96 minutes of stroke onset). SETTING: A stroke unit in a university hospital. MAIN OUTCOME MEASURES: Area of the perfusion deficit (nAP(0)) from time-to-peak maps, hemispheric lesion area from follow-up CT (HLA(F)), final infarct volume, and stroke recovery (National Institutes of Health Stroke Scale scores). RESULTS: Eighteen patients had perfusion deficits in the middle cerebral artery territory and corresponding hypoattenuation in follow-up CT. Three patients with normal CTP findings showed lacunar infarctions or normal findings on follow-up CT. In 1 patient, CTP did not reveal a territorial deficit above the imaging slice. The overall sensitivity and specificity of CTP for the detection of perfusion deficits in patients with proven territorial infarction (n = 18) on follow-up CT were 95% and 100%, respectively. The nAP(0) was significantly correlated with the National Institutes of Health Stroke Scale score at admission (P<.003) and the HLA(F) (P<.001). Different stroke patterns were identified in patients with follow-up CTP (n = 10): (1) initial perfusion deficit and partial nutritional reperfusion (nAP(0)>HLA(F); n = 6), (2) initial perfusion deficit and nonnutritional reperfusion (nAP( 0)>/=HLA(F); n = 2), and (3) initial perfusion deficit without reperfusion (nAP(0)>/=HLA(F); n = 2). CONCLUSIONS: Computed tomographic perfusion imaging detects major perfusion deficits in the middle cerebral artery territory. Because CTP is broadly available, it may play a role in acute stroke management. Arch Neurol. 2000;57:1161-1166

Acute Disease↗

PubMed2000

Comparison of artifacts produced from carbon fiber and titanium alloy needles at 1.5 T MR imaging.

A novel coaxial carbon fiber-based biopsy needle set was investigated in phantom experiments and compared with a commercially available, magnetic resonance (MR)-compatible titanium alloy set using MR imaging at 1.5 T. Image artifacts observed with different MR sequences were assessed. It was found that the carbon fibers produced distinctly smaller image artifacts compared with the titanium needle. Depending on the type of MR sequence, the relative range of artifact size ratios between the carbon and titanium needles was between 0.7 (spin-echo sequence) and 0.4 (gradient-echo sequence) with the needles oriented perpendicular to the main magnetic field. Carbon fiber composites are promising materials for the design and construction of MR-compatible instruments.

Artifacts↗

PubMed2000

31P magnetic resonance spectroscopy in fibromyalgic muscle.

OBJECTIVE: To measure inorganic phosphate (Pi), phosphocreatine (PCr), ATP and phosphodiesters (PDE) in fibromyalgic muscle tissue by (31)P magnetic resonance spectroscopy. METHODS: A 1.5 Tesla scanner with a P 100 surface coil was used to examine 15 patients (mean age 49.9+/-14.3 yr) with fibromyalgia, according to the American College of Rheumatology criteria, and 17 healthy controls (mean age 30.2+/-5.8 yr). RESULTS: Compared with the controls, there were increases in the levels of PDE (+22%, P = 0.032) and Pi (+19%, P = 0.019) in the spectra of fibromyalgia patients, but there was no difference in pH. CONCLUSION: The metabolic differences we found may have been related to weakness and fatigue in the fibromyalgia patients, but they do not fully explain the fibromyalgia symptoms.

Adenosine Triphosphate↗

PubMed2000

Saline-enhanced radiofrequency ablation of breast tissue: an in vitro feasibility study.

RATIONALE AND OBJECTIVES: The feasibility of radiofrequency (RF) ablation for the treatment of breast tumors was investigated in vitro. The best parameters for ablation of breast tissue were chosen. METHODS: Saline-enhanced RF ablation was performed in human breast tissue specimens and cow udder tissue. Temperature profiles were measured depending on RF power (20, 28, 36 W) and NaCl infusion rate (15, 30, 60 mL/h) using eight thermocouples. Lesion development was monitored by ultrasound. Thermolysis efficiency was measured by tissue weight determinations before and after ablation. RESULTS: After RF ablation of tissue samples, 73.6% turned into a fat/saline emulsion. Ultrasound monitoring showed a cone-shaped hyperechoic area during the first 2 minutes of RF ablation, followed by an irregular expansion of the area. Time-dependent spatial temperature curves were more homogeneous at low infusion rates (15 mL/h). Peak temperatures up to 160 degrees C were measured. CONCLUSIONS: Controlled RF ablation of breast tissue is feasible. The irregular expansion of RF lesions in fatty breast tissue is due to liquefied fat. Low saline interstitial infusion rates result in better control of lesioning.

Animals↗

PubMed1999

Sub-millimeter fMRI at 1.5 Tesla: correlation of high resolution with low resolution measurements.

Functional magnetic resonance imaging of the visual cortex with an in-plane resolution of 0.4 x 0.4 mm2 was performed using a simple visual stimulus resulting in clear maps of activation. A collapsing filter was used to compare these high-resolution images with low-resolution images collected during the same session. A good correspondence between the high- and low-resolution functional maps was found with respect to the center of localization of activation. However, only 20% of the size of activated areas in the low-resolution experiment was observed at high resolution, which was partly caused by the difference in signal-to-noise ratio. The high-resolution images produce signal changes much higher than the low-resolution images due to reduced partial volume effects. Additionally, the high-resolution functional maps were compared with detailed anatomical and venous information. The activated areas were predominantly observed at venous vessels within the sulci with a diameter on the order of the pixel size.

Adult↗

PubMed1999

High-resolution, multiple gradient-echo functional MRI at 1.5 T.

A multiple gradient echo, high resolution imaging method is proposed to better visualize different sources of activation in functional magnetic resonance imaging (fMRI) experiments. Eight echoes are collected from 30 ms to 205 ms with an echo spacing of 25 ms. All echoes show significant activation, but each echo reveals its own pattern of activation. From this variability, it appears that large vessel contributions can be separated from small vessel contributions using a fuzzy cluster analysis across echo times. The results demonstrate the importance of a multiple gradient echo data acquisition approach in localizing various vascular contributions to brain activation in fMRI.

Adult↗

PubMed1999

High-resolution MR venography of cerebral arteriovenous malformations.

The purpose of this study was to evaluate the diagnostic potential of a high-resolution magnetic resonance (MR) venography technique in patients with cerebral arteriovenous malformations (AVMs). A high-resolution 3D gradient echo sequence was used with a long echo time TE to obtain venous information down to sub-pixel sized vessel diameters of several hundred microns. The method is based on the paramagnetic property of deoxyhemoglobin, and the resulting developing phase difference between veins and brain parenchyma at long echo times which leads to signal cancellation. The reconstructed venograms were compared with time-of-flight (TOF)-MR angiography using qualitative and quantitative criteria with the conventional digital subtraction angiography serving as the reference gold standard. In 17 patients with angiographically proven cerebral AVMs, the method indicates its potential in clinical applications. Venography was able to detect all AVMs whereas TOF-MRA failed in three patients. In the delineation of venous drainage patterns MR venography was superior to TOF-MRA, however, the method failed in the detection of about half of the main feeding arteries, as expected. Due to susceptibility artifacts at air/tissue boundaries and interference with paramagnetic hemosiderin, venography was limited with respect to the delineation of the exact nidus sizes and shapes in ten patients with AVMs located close to the skull base or having suffered from previous bleeding. Although the visualization of draining veins represents an important prerequisite in the surgical and radiosurgical treatment planning of cerebral AVMs, application of high resolution MR venography may be limited in the diagnostic work-up in some of these patients. On the other hand, it may be of special importance in the early detection and assessment of small AVMs that are difficult to diagnose with other MR methods.

Adolescent↗

PubMed1998

In vivo measurement of changes in venous blood-oxygenation with high resolution functional MRI at 0.95 tesla by measuring changes in susceptibility and velocity.

High-resolution functional imaging experiments at 0.95 Tesla have been performed to determine the changes in oxygen saturation in pial veins during motor activation by measuring both flow and susceptibility changes in the blood. Averaging across subjects, mean values for the change of the oxygenation level, deltaY = 0.16 +/- 0.08 (n = 7) and deltaY = 0.13 +/- 0.09 (n = 4), were obtained from the susceptibility sensitive and the flow sensitive acquisitions, respectively. The results suggest that the increase in blood flow is largely uncoupled from the oxygen consumption. The quoted errors reflect mainly the intersubject variability. In addition, low-resolution echo planar imaging (EPI) measurements were performed on the same volunteers to quantify signal intensity changes. Using the measured change in oxygenation, the observed signal changes in the EPI experiments can be attributed to a 5% venous blood volume.

Adolescent↗

PubMed1998

High-resolution venography of the brain using magnetic resonance imaging.

The purpose of this study was to evaluate a non-flow related magnetic resonance imaging method to visualize small veins independent of arteries in the human brain. A long TE, high-resolution 3D gradient echo MR acquisition was used to highlight venous information. The method is based on the paramagnetic property of deoxyhemoglobin and the resulting phase difference between veins and brain parenchyma at long echo times. The MR magnitude images were masked with a phase mask filter to enhance small structure visibility. Venous information down to sub-pixel vessel diameters of several hundred microns is visible. Venous data are displayed in an angiographic manner using a minimum intensity projection algorithm. Both superficial veins and deep white matter veins are visible. The method has been successfully applied in volunteers. Preliminary results in patients with cerebral arteriovenous malformations indicate its potential in clinical applications. The proposed method is easy to implement and does not require administration of a contrast agent or application of specially designed rf pulses to highlight the veins. Rather it exploits the intrinsic magnetic properties (BOLD-effect) and the prolonged T2* of venous blood. The method may be of diagnostic potential in the assessment of arteriovenous malformations or other vascular venous lesions.

Adolescent↗

PubMed1998

Functional magnetic resonance imaging of the basal ganglia and cerebellum using a simple motor paradigm.

Activation of cortical and subcortical motor areas of the brain, including primary motor cortex, supplementary motor area, basal ganglia and cerebellum, were successfully investigated in seven right-handed, normal volunteers during a simple, rapid, thumb flexion-extension task using functional magnetic resonance imaging. A multi-slice echo-planar imaging sequence was used to cover the entire brain. A signal increase varying from 2% to 6% was observed for the different regions involved in the motor task. Moving the non-dominant thumb was associated with a more bilateral activation pattern in both putamen and cerebellar regions. This study demonstrates the capability of functional magnetic resonance imaging to delineate simultaneously many activated brain areas that are commonly thought to be involved in the performance of motor tasks.

Adult↗

PubMed1998

Comparison of functional MR-venography and EPI-BOLD fMRI at 1.5 T.

Functional magnetic resonance imaging (fMRI) of the brain using blood oxygenation level dependent (BOLD) contrast relies on the changes of paramagnetic deoxyhemoglobin concentration, which affects brain parenchyma and draining venous vessels. These changes in deoxyhemoglobin concentration in venous vessels can also be monitored using a high-resolution susceptibility-based MR-venography technique. Four volunteers participated in the study in which functional MR-venograms were compared with conventional echo-planar imaging (EPI)-BOLD-fMRI. In all cases, small venous vessels could be identified close to the areas of activation detected by conventional fMRI. In the venograms, task performance (finger tapping) resulted in a loss of venous vessel contrast compared to the resting state, which is consistent with a local decrease of deoxyhemoglobin concentration. MR-venography allows a direct visualization of the BOLD-effect at high spatial resolution. In combination with conventional fMRI, this technique may help to separate the contribution of brain parenchyma and venous vessels in fMRI studies.

Brain↗

PubMed1997

1H T1 and T2 measurements of the MR imaging contrast agents Gd-DTPA and Gd-DTPA BMA at 1.5T.

We report in vitro T1 and T2 relaxation studies for the open-chain complexes Gd-DTPA and Gd-DTPA BMA. Measurements were performed on phantoms containing aqueous and plasma solutions of different concentrations by MR imaging in a 1.5T superconducting whole-body scanner. Longitudinal relaxation times T1 were evaluated from serial turbo-FLASH experiments for concentrations less than 1 mM, whereas for larger concentrations the values were obtained from a standard inversion recovery (IR) sequence. Transverse relaxation times T2 were determined using multi-echo spin-echo MRI protocols. The T1 and T2 relaxivities of the nonionic Gd-DTPA BMA are similar to those of the Gd-DTPA. The temperature dependencies of the relaxivities were determined over a temperature interval ranging from 21 to 50 degrees C and were found to be slightly different for the two contrast agents. In the case of Gd-DTPA BMA a larger deviation of the expected temperature behavior of the relaxivities was observed as compared with Gd-DTPA. Deviations from a strictly linear dependence of relaxation times on temperature were found at lower concentrations in aqueous solutions. In plasma solutions a high T1/T2 ratio was observed for low concentrations, which decreased monotonically with increasing concentrations.

Contrast Media↗

PubMed1997

Small vessels in the human brain: MR venography with deoxyhemoglobin as an intrinsic contrast agent.

To assess a magnetic resonance (MR) imaging method for depicting small veins in the brain, a three-dimensional, long echo time, gradient-echo sequence that depended on the paramagnetic property of deoxyhemoglobin was used. Veins with diameters smaller than a pixel were depicted. This MR imaging method is easy to implement and may prove helpful in the evaluation of venous diseases.

Brain↗

PubMed1996

Commutator filter: a novel technique for the identification of structures producing significant susceptibility inhomogeneities and its application to functional MRI.

A robust postprocessing method to detect regions of magnetic field change is presented. High resolution gradient echo data is acquired to create a complex baseline image. From this image, two low resolution images are obtained by applying a low pass filter on the magnitude image and the complex image, respectively. Subtraction of the magnitude of the filtered complex image from the filtered magnitude image gives a new image called a commutator image in which regions of susceptibility-induced field variation are greatly enhanced. Results on phantoms and applications to visualize paramagnetic venous blood vessels in the human brain are presented. The use of this technique on a 3D gradient echo data set represents a new approach to obtain an MR venogram. The application of this method to blood oxygenation level dependent (BOLD) functional brain MR imaging is demonstrated and the important role susceptibility plays in this model is verified.

Algorithms↗