Biomedical subjects

P Erhart

Publications and source records attributed to P Erhart.

At least 19 recordsLinked to original sources

PubMed2001

Temperature quantification using the proton frequency shift technique: In vitro and in vivo validation in an open 0.5 tesla interventional MR scanner during RF ablation.

Open magnetic resonance (MR) scanners allow MR-guided targeting of tumors, as well as temperature monitoring of radio frequency (RF) ablation. The proton frequency shift (PFS) technique, an accurate and fast imaging method for temperature quantification, was used to synthesize thermal maps after RF ablation in an open 0.5 T MR system under ex vivo and in vivo conditions. Calibration experiments with 1.5% agarose gel yielded a chemical shift factor of 0.011 +/- 0.001 ppm/ degrees C (r2 = 0.96). Three gradient echo (GRE) pulse sequences were tested for thermal mapping by comparison with fiberoptic thermometer (Luxtron Model 760) readings. Temperature uncertainty decreased from high to low bandwidths (BW): +/-5.9 degrees C at BW = 15.6 kHz, +/-1.4 degrees C at BW = 3.9 kHz, and +/-0.8 degrees C at BW = 2.5 kHz. In vitro experiments (N = 9) in the paraspinal muscle yielded a chemical shift factor of 0.008 +/- 0.001 ppm/ degrees C. Temperature uncertainty was determined as +/-2.7 degrees C (BW = 3.9 kHz, TE = 19.3 msec). The same experiments carried out in the paraspinal muscle (N = 9) of a fully anesthetized pig resulted in a temperature uncertainty of +/-4.3 degrees C (BW = 3.9 kHz, TE = 19.3 msec), which is higher than it is in vitro conditions (P < 0.15). Quantitative temperature monitoring of RF ablation is feasible in a 0.5 T open-configured MR scanner under ex vivo and in vivo conditions using the PFS technique.

Animals↗

PubMed1999

Single-loop coil concepts for intravascular magnetic resonance imaging.

Compared with other coil designs that have been investigated for intravascular use, the single-loop coil can be designed with a very small diameter for insertion into small vessels and with a longitudinal extent over several centimeters for multislice imaging. If it designed to be expandable inside the target vessel, then it combines these features with increased signal-to-noise ratio (SNR) and penetration depth. Expandable single-loop coils that are capable of meeting these requirements were developed and integrated into two different commercial catheter-based delivery systems: a self-expandable, single-loop made from NiTinol and a single-loop coil mounted on an inflatable balloon. The influence of a small-diameter coaxial cable for remote tuning and matching on the coil performance was investigated. Calculations showed the dependence of the signal on the separation between the conductors. The comparison of both catheter approaches in in vitro flow experiments and in an in vivo pig experiment revealed the influence of pulsatile flow on image quality during intravascular imaging with these designs.

Animals↗

PubMed1998

Tissue-independent MR tracking of invasive devices with an internal signal source.

An improved MR tracking coil design is described that provides more robust tracking performance. It is shown theoretically and experimentally that a coil equipped with an internal spin source increases the signal-to-noise ratio in comparison to a coil system without internal source. The tracking behavior is stable even in air, which is important for laparoscopic work, in which the device has to be placed inside the inflated abdomen. Two types of coil windings were tested: one with the windings perpendicular to the coil axis and the other one with the windings tilted relative to this axis. The experiments showed no significant effect on the signal-to-noise ratio between the two types. The improved MR-tracking coil design with internal source was successfully used in cholecystostomies and in laparoscopic interventions; both procedures were performed on swine.

Animals↗

PubMed1998

[Active instrumental guidance in interventional MR tomography: introduction to a new concept].

PURPOSE: An active MR-based guidance system for visualisation of invasive instruments is described. METHODS: The principle of MR tracking is based on the integration of a miniaturised coil into the tip of the instrument itself. A phantom experiment was designed to demonstrate the localising accuracy of this technique. In addition, biocompatibility and warming effects were evaluated. Preliminary intravascular applications that were performed in animal experiments under MR guidance included embolisation, vascular occlusion as well as transjugular intrahepatic punctures. Percutaneous biopsies, cholecystostomies and laparoscopic applications were also evaluated with MR tracking. RESULTS: Phantom experiments confirmed an excellent localisation accuracy of MR tracking compared top conventional radiography. At a field strength of 0.5 T, the temperature increase remained below 2 degrees C. Results of phantom experiments revealed a potential of significant heating dependent on the sequence parameters employed. MR tracking allowed a robust, simultaneously biplanar visualisation of the instrument tips in real time. Based on MR "road map" images, various intravascular and percutaneous interventions were successfully performed in vivo under MR guidance. CONCLUSIONS: MR tracking is a flexible concept permitting monitoring in the guidance of instruments in an MR environment. Various preliminary in vitro and in vivo experiments demonstrate safety, localisation accuracy and feasibility of this biplanar localisation technique in real time.

Biopsy, Needle↗

PubMed1997

Imaging temperature changes in an interventional 0.5 T magnet: in-vitro results.

BACKGROUND AND OBJECTIVE: To evaluate the ability of monitoring laser induced temperature changes in an open, interventional 0.5 T magnet, adopting fast T1-weighted sequences. MATERIALS AND METHODS: A fast gradient echo- (FGRE) and a fast spoiled gradient echo-sequence (FSPGR), both enabling an image update every 2.5 s, were investigated for their ability to visualize laser tissue effects at 5 Watt. Laser induced temperature was fluorooptically measured and correlated with signal intensity (SI) changes depicted by magnetic resonance imaging (MRI). MRI-lesions were compared with macroscopic findings. RESULTS: SI changes on FGRE images appeared as early as 15 s following the onset of laser application and were significantly more pronounced than those seen on FSPGR images (p < .0001). A correlation of r = 0.94 (FGRE) and r = 0.92 (FSPGR) between temperature and SI loss was established. Owing to a steeper slope, the FGRE sequence was considered more sensitive to temperature changes. The areas of macroscopic tissue change correlated with those of SI loss, but lesion size was generally underestimated by MRI. CONCLUSION: Laser monitoring is possible with rapid image updates in a midfield (0.5 T) interventional MRI environment using fast gradient echo sequence designs.

Animals↗

PubMed1997

Guidewire antennas for MR fluoroscopy.

Before MRI can be used for guiding vascular interventions, the problem of dependably visualizing guidewires must be solved. Ideally, the position and curvature of the tip of the guidewire should be visible to facilitate steering through the vascular system. In this paper, various antennas are described that can be incorporated into a guidewire tip. These antennas allow the guidewire to be visualized with high contrast. Computer simulation and experimental evidence are presented showing the value of adding a passive MR signal source, with a short T1, internal to the coil. The internal source increases the available signal, narrows the apparent width of the guidewire, and allows the use of fast imaging sequences.

Blood Vessels↗

PubMed1997

Magnetic resonance-guided laparoscopic interstitial laser therapy of the liver.

BACKGROUND: There is a necessity for an imaging method during laparoscopy to get a three-dimensional access to the target. In this study we evaluated laparoscopic interstitial laser therapy of the liver under magnetic resonance imaging guidance. METHODS: Five domestic pigs underwent laparoscopy in an open-configuration magnetic resonance system. Under simultaneous real-time magnetic resonance imaging interstitial laser therapy was applied to the liver. Magnetic resonance images, macroscopic aspects of the lesions, and light microscopic findings were compared. RESULTS: The interventions could be safely performed. There was no image artifact caused by instruments or by the carbon dioxide. Dynamic gadolinium-enhanced imaging proved to significantly predict the macroscopic volume of the laser lesions. CONCLUSIONS: Magnetic resonance-guided laparoscopic interstitial laser therapy of the liver combines the advantages of minimal invasive surgery and magnetic resonance imaging. Further development should focus on laparoscopic instruments and temperature sensitive sequences.

Animals↗

PubMed1997

Comparison of mRAST and CAP with skin end point titration for Alternaria tenuis and dermatophagoides pteronyssinus.

There has been a recent explosion of new in vitro tests for the diagnosis of allergies. At present there is no general agreement on which type of in vitro test is best. Recently our hospital switched in vitro testing from the modified radioallergosorbent system (mRAST) to the Pharmacia CAP system (CAP). While changing in vitro testing techniques, 47 patients were tested with both the mRAST and CAP tests. Comparisons were made between the mRAST and CAP results of Alternaria tenuis and Dermatophagoides pteronyssinus allergens. These results were then compared with the results of patients who also underwent intradermal skin testing based on end point titration techniques.

Allergens↗

PubMed1997

Intravascular MR imaging of atherosclerotic plaque: ex vivo analysis of human femoral arteries with histologic correlation.

PURPOSE: To assess the potential role of intravascular magnetic resonance (MR) imaging with receiver coils mounted to an inflatable balloon in characterizing atherosclerotic plaque. MATERIALS AND METHODS: Twelve human harvested segmental femoral arteries with atherosclerotic changes were studied with a 5-F imaging balloon catheter equipped with a single-loop wire receiver coil. Imaging was performed with an open-configuration 0.5-T (n = 6) or a 1.5-T (n = 6) MR system, with T1- and T2-weighted sequences. Histologic analysis was the reference standard, and MR images were analyzed with regard to vessel wall thickness, plaque area, and components. RESULTS: Images acquired at 1.5 T were characterized by better in-plane resolution (117 x 104 microm). Resolution at 0.5 T (234 x 178 microm) was sufficient to discriminate the wall layers. On T2-weighted images, adventitia, media, and thickened intima could be discriminated. T1-weighted images did not permit differentiation between wall layers. There was good correlation between MR and histologic measurements of wall thickness (r = .97) and plaque area (r = .98). Plaque characterization was possible on T2-weighted images. Calcified plaque was identified as areas of low signal intensity (134 +/- 98) and could be differentiated from fibrous structures containing collagen (1,968 +/- 680) or fatty components (762 +/- 394). CONCLUSION: Intravascular MR imaging on the basis of the balloon catheter design enables differentiation of wall layers and plaque components.

Aged↗

PubMed1997

Active biplanar MR tracking for biopsies in humans.

OBJECTIVE: The purpose of this study was to assess the potential of active biplanar MR needle tracking in a 0.5-T open-configuration MR system. A needle design characterized by an integrated internal signal source was used. To evaluate the performance of this new technique in vivo as well as in vitro, procedures were performed on patients. CONCLUSION: The results of this study prove that the biplanar tracking concept can be applied in a clinical environment. The applicability of biplanar tracking is further enhanced by integrating an internal signal source.

Adult↗

PubMed1997

Real-time monitoring of laser diskectomies with a superconducting, open-configuration MR system.

OBJECTIVE: The objective of our study was to assess the ability of a 0.5-T superconducting, open-configuration MR system to guide laser diskectomies. The study was performed ex vivo on six human cadavers as well as in vivo on three patients. CONCLUSION: The macroscopic size of necrosis correlated well with the monitored temperature spread (r2 = .76-.85). After MR-guided introduction of the laser fiber into the targeted disk space, temperature spread was visualized in all subjects.

Adolescent↗

PubMed1996

Biopsy needle susceptibility artifacts.

Understanding the appearance of thin metallic structures in magnetic resonance imaging is important for evaluating the potential role of MRI in guiding and monitoring percutaneous interventions. As most MR compatible instruments are made from materials with a susceptibility different from water, their visibility is enhanced beyond what is expected on the grounds of displaced water alone. Unfortunately, this artifactually enhanced visibility is not constant, but instead depends on a variety of factors. This article presents computer simulations of the image distortion resulting from magnetic susceptibility differences between a needle and the surrounding tissue. The simulations show not only an artifact size that is dependent on needle composition, orientation, and pulse sequence, but also a corresponding shift of the artifact center away from the actual center of the needle. These effects place limits on the accuracy of MRI-guided needle tip placement.

Artifacts↗

PubMed1996

[Interactive stereotaxic interventions in superconducting, open 0.5-Tesla MRI tomography].

PURPOSE: Evaluation of an interactive, stereotactic biopsy device integrated in an open superconductive 0.5 tesla MR-scanner with a vertical gap. MATERIAL AND METHODS: In addition to "in-vitro" experiments performed on a plexiglas phantom with holes of varying diameters (5-20 mm) biopsies on eleven patients (7 women, 4 men; average age 55 years) were performed in the interventional MR-system. Lesions in the abdomen (n = 6), muscle (n = 1), thyroid (n = 3) and breast (n = 1) were targeted with 18-20 G aspiration biopsy needles of 5-15 cm length. The intervention was interactively guided by a fast T1-weighted 2-D gradient echo sequence. RESULTS: All of the 15 and 20 mm holes of the phantom, but only 83% of the 10 and 5 mm holes were hit. No complications occurred during the MR-guided patient procedures. All lesions (mean size 3.5 cm, distance from the skin 2 cm to 10 cm) were biopsied successfully. The fast image acquisition in combination with the stereotactic technique enables interactive control of the needle. CONCLUSIONS: Stereotactic, interactively controlled biopsies in the interventional MR are technical feasible. However, the range of meaningful indications for MR-guided biopsies is limited.

Abdominal Neoplasms↗

PubMed1996

[Minimally invasive surgery with MRI imaging].

The main shortcoming of conventional laparoscopic procedures is the lack of a truely three-dimensional view. The development of a open-configured MR-imaging system (0.5 Tesla, General Electric, USA) with free access to the patient, allows the performance of minimal invasive procedures under MR-guidance. Advantages inherent to minimal invasive surgery can now be combined with the ideal tissue discrimination and the temperature sensitivity of MR-imaging. This new method can be used for diagnostic as well as for therapeutic interventions, especially interstitial therapy of inoperable metastases of parenchymal organs.

Humans↗

PubMed1996

[Magnetic resonance controlled minimal invasive surgery: initial results and perspectives].

The development of an open-configured MR-imaging system opens new perspectives in minimal invasive surgery. The combination of laparoscopy and real-time MR imaging allows the guidance of diagnostic interventions as well as interstitial therapies of parenchymal organs. In the near future, tumor diagnosis, therapy and follow-up can be done using the same technique.

Equipment Design↗

PubMed1991

[Therapy of organic brain syndrome with nicergoline given once a day].

In a double-blind, active-controlled study 30 patients with mild to moderate multiinfarct dementia diagnosed according to DSM III definition were treated by either 20 mg nicergoline or 4.5 mg co-dergocrine mesilate once daily during eight weeks. Therapeutic effects on symptoms of the organic brain syndrome were quantitatively measured by standardized psychological and psychometric methods evaluating cognitive and thymopsychic functions. Main criteria, which were tested by inferential analysis, were SCAG total score (Sandoz Clinical Assessment Geriatric Scale), SCAG overall impression and the AD Test (alphabetischer Durchstreichtest). Other results were assessed by descriptive statistics. Both treatments resulted in a statistically significant improvement in most of the tested functions. The effects of 4.5 mg co-dergocrine mesilate s.i.d. were in accordance with published results. Although differing slightly with respect to individual results 20 mg of nicergoline once daily showed the same efficacy on the whole.

Aged↗

PubMed1990

[The usefulness of event-related negativity in demonstrating the therapeutic effects of nootropic drugs using cerebrolysin as an example].

This study investigated the usefulness of the Contingent Negative Variation (CNV) in the assessment of therapeutic efficacy of a nootropic substance, Cerebrolysin. A total of 41 geriatric patients with the diagnosis of moderate organic brain syndrome of different etiology were included in this randomized placebo-controlled double-blind study. After ten Cerebrolysin- plus multi-vitamins-Infusions, the treatment group of 27 patients showed a significant CNV-amplitude increase as compared to pre-treatment values. In the placebo group of 14 patients CNV-amplitudes even decreased after ten Infusions with multi-vitamins alone. These findings were interpreted in line with the vigilance model of nootropic drug effects as a vigilance-increasing effect of Cerebrolysin, i.e. as an increased neuronal performance readiness. The results confirmed the usefulness of the CNV method by providing an EEG-index of nootropic drug effects.

Aged↗

PubMed1981

Thalamic degeneration.

A man of 61 died after an illness of 20 years duration. The clinical picture displayed progressive dementia, loss of memory, apathy, inertia, emotional lability, temporal and local disorientation, visual hallucination and apraxia. Neuropathological findings predominated in the thalamus and displayed extensive nerve cell loss and gliosis in the anterior, medial, and posterior formations, whereas the lateral formations were somewhat better preserved. The lateral amygdala were severely affected. The cortex showed widespread moderate damage in the third or fourth layer which are interpreted as transneuronal degeneration. In addition moderate atrophy of the vestibular nuclei, the inferior olives and the cerebellum was noted. This case seems to be one of the very rare examples of isolated thalamic degeneration according to Martin (1975).

Atrophy↗