Biomedical subjects

Patrick Asbach

Publications and source records attributed to Patrick Asbach.

10 recordsLinked to original sources

PubMed2006

Behavior of metal implants used in ENT surgery in 7 Tesla magnetic resonance imaging.

Magnetic resonance imaging (MRI) has become increasingly important as an imaging technique in cross-sectional imaging of head and neck diseases. To investigate whether MRI examinations can be performed without risk in patients with metal implants even at higher field strengths, we examined different materials in 7 Tesla MRI. Implants near sensory organs like the middle ear or eye are of particular interest here. Using the 7 Tesla research MRI for small animals, we tested implants made of various metals like titanium, gold, gold/platinum, platinum/iridium, gold-plated silver, PTFE and stainless steel for heating, translocation and rotation according to a standardized protocol. A fiber optic temperature probe measured the heating of the implant before, during and after MRI scanning. None of the implants showed significant heating. The gold-plated stainless steel ventilation tube was the only implant to markedly change its position already in the Petri dish. Of the remaining implants, a trachea support ring, a nose dilatator and the wire from the ventilation tubes moved during vibration of the Petri dish. With exception of two implants, all implants changed positions in the water bath. In the swim test, the gold implants showed the least movement of all the implants. In this study, the properties of the non-ferromagnetic implant materials differed in the 7 Tesla MRI. Stainless steel ventilation tubes, the trachea support ring and the nose dilatator were not suited for the 7 Tesla MRI system, because they changed their position during MRI. In the case of ventilation tubes with a steel wire, the wire should be removed before MRI to prevent injury to the external auditory canal. There was a tendency for the pure gold implants to move less in the 7 Tesla MRI than all other tested materials. General statements cannot be made about the MRI suitability of different implants. Every implant should be individually examined to confirm its definitive MRI compatibility. Particularly, middle ear implants warrant special attention here due to their closeness to the oval window.

Equipment Failure Analysis↗

PubMed2006

Respiratory-triggered MRCP applying parallel acquisition techniques.

PURPOSE: To evaluate the influence of parallel imaging on the image quality of respiratory triggered magnetic resonance cholangiopancreatography (MRCP). MATERIALS AND METHODS: A total of 30 consecutive patients underwent MRCP applying a respiratory triggered T2-weighted (T2w) turbo spin-echo (TSE) sequence without and with parallel imaging (acceleration factor of 2). Acquisition times of both sequences were recorded. Quantitative evaluation included measurement of a contour sharpness index of two segments of the pancreaticobiliary tree as well as calculation of the relative contrast between ductal structures and organ parenchyma at four different segments. The qualitative evaluation was performed by two independent radiologists who graded overall image quality, depiction of eight segments of the pancreaticobiliary tree, and the frequency of artifacts. RESULTS: The application of parallel imaging significantly (P<0.05) reduced the acquisition time of the respiratory triggered MRCP sequence by 37.7% (six minutes and two seconds+/-one minute and 26 seconds vs. three minutes and 46 seconds+/-58 seconds). The quantitative and qualitative evaluation revealed no statistically significant differences between the two sequences (P>0.05). The frequency of artifacts was at the same level for both sequences as well. CONCLUSION: The application of parallel imaging for respiratory triggered MRCP significantly reduces the acquisition time without relevant influence on image quality.

Adult↗

PubMed2006

In vivo determination of hepatic stiffness using steady-state free precession magnetic resonance elastography.

OBJECTIVE: The objective of this study was to introduce an magnetic resonance elastography (MRE) protocol based on fractional motion encoding and planar wave acquisition for rapid measurements of in vivo human liver stiffness. MATERIALS AND METHODS: Vibrations of a remote actuator membrane were fed by a rigid rod to the patient's surface beneath the right costal arch resulting in axial shear deflections of the liver. Data acquisition was performed using a balanced steady-state free precession (bSSFP) sequence incorporating oscillating gradients for motion sensitization. Tissue vibrations of frequency fv = 51 Hz were tuned by twice the sequence repetition time (1/fv = 2TR). Twenty axial images acquired by time-resolved through-plane wave encoding were used for planar elasticity reconstruction. The MRE data acquisition was achieved within 4 breathholds of 17 seconds each. The method was applied to 12 healthy volunteers and 2 patients with diffuse liver disease (fibrosis grade 3). RESULTS: MRE data acquisition was successful in all volunteers and patients. The elastic moduli were measured with values between 1.99 +/- 0.16 and 5.77 +/- 0.88 kPa. Follow-up studies demonstrated the reproducibility of the method and revealed a difference of 0.74 +/- 0.47 kPa (P < 0.05) between the hepatic stiffness of 2 healthy male volunteers. CONCLUSION: bSSFP combined with fractional MRE enables rapid measurement of liver stiffness in vivo. The used actuation principle supports a 2-dimensional analysis of the strain wave field captured by axial wave images. The measured data indicate individual variations of hepatic stiffness in healthy volunteers.

Adult↗

PubMed2005

Magnetic resonance cholangiopancreatography using a free-breathing T2-weighted turbo spin-echo sequence with navigator-triggered prospective acquisition correction.

PURPOSE: The objective of this study was to evaluate the image quality of a respiratory-triggered T2-weighted (T2w) turbo spin-echo (TSE) sequence for magnetic resonance cholangiopancreatography (MRCP) using a new method for respiratory triggering by tracking the motion of the right diaphragm [prospective acquisition correction (PACE) technique]. MATERIALS AND METHODS: Fifty consecutive patients underwent MRCP imaging applying breath-hold half-Fourier single-shot TSE sequences and the respiratory-triggered T2w TSE sequence. Qualitative evaluation grading the depiction of eight segments of the pancreaticobiliary tree and the frequency of artifacts was performed. Quantitative evaluation included calculation of the relative contrast (RC) between fluid-filled ductal structures and organ parenchyma at four segments. RESULTS: A significantly higher (P<.01) RC was measured for the respiratory-triggered T2w TSE sequence [maximum intensity projection (MIP)] for all of the four investigated segments (one of four segments for the MIP) of the pancreaticobiliary tree, as well as a significant (P<.01) improvement of visualization of all ductal segments compared with the breath-hold sequences. The frequency of artifacts was significantly lower (P<.01) compared with the breath-hold sequences. CONCLUSION: Respiratory-triggered MRCP using a T2w TSE sequence with PACE significantly improves image quality and may be included into the routine MRCP sequence protocol.

Adult↗

PubMed2005

Magnetic resonance imaging of the upper abdomen using a free-breathing T2-weighted turbo spin echo sequence with navigator triggered prospective acquisition correction.

PURPOSE: To evaluate a free-breathing navigator triggered T2-weighted turbo spin-echo sequence with prospective acquisition correction (T2w-PACE-TSE) for MRI of the upper abdomen in comparison to a conventional T2-weighted TSE (T2w-CTSE), a single-shot TSE (T2w-HASTE), and a T1-weighted gradient-echo sequence (T1w-FLASH). MATERIALS AND METHODS: A total of 40 consecutive patients were examined at 1.5 T using free-breathing T2w-PACE-TSE, free-breathing T2w-CTSE, and breath-hold T2w-HASTE and T1w-FLASH acquisition. Images were evaluated qualitatively by three radiologists regarding motion artifacts, liver-spleen contrast, depiction of intrahepatic vessels, the pancreas and the adrenal glands, and overall image quality on a four-point scale. Quantitative analysis of the liver-spleen contrast was performed. RESULTS: Depiction and sharpness of intrahepatic vessels were rated significantly better (P < 0.01) using T2w-PACE-TSE compared to T2w-CTSE and T2w-HASTE sequences. Significantly higher contrast values were measured for T2w-PACE-TSE images compared to T2w-CTSE, T2w-HASTE, and T1w-FLASH images (P < 0.01). Mean examination time of the T2w-PACE-TSE was 7.91 minutes, acquisition time of the T2w-CTSE sequence was 4.52 minutes. CONCLUSION: Prospective acquisition correction is an efficient method for reducing respiratory movement artifacts in T2w-TSE imaging of the upper abdomen. Compared to T2w-CTSE and T2w-HASTE sequences recognition of anatomical details and contrast can be significantly improved.

Abdomen↗

PubMed2005

The ependymal "Dot-Dash" sign: an MR imaging finding of early multiple sclerosis.

BACKGROUND AND PURPOSE: Corpus callosum lesions are of specific interest in the evaluation of suspected multiple sclerosis in brain MR imaging. Using thin-section sagittal fluid-attenuated inversion recovery images, researchers have shown that the finding of "subcallosal striations" correlates significantly with the diagnosis of multiple sclerosis. Using the same MR imaging technique, we describe a finding of ependymal irregularity that we call the "Dot-Dash" sign, which we believe to be associated with early multiple sclerosis. METHODS: Sagittal 2-mm fast fluid-attenuated inversion recovery images were obtained in 70 patients. Thirty-five patients had multiple sclerosis according to the Poser criteria, and 35 were age-matched controls. The images were reviewed in a blinded fashion by an experienced neuroradiologist for the presence or absence of the Dot-Dash sign. RESULTS: The correlation between the Dot-Dash sign and definite clinical multiple sclerosis is highly significant (P < .001), with a sensitivity of 91.4% and a specificity of 65.7%. In the age group of < or =50 years, the sensitivity was 95.7% and the specificity, 71.9%. CONCLUSION: The Dot-Dash sign of ependymal irregularity on thin-section sagittal fluid-attenuated inversion recovery images is an early marker for multiple sclerosis, which is particularly useful in the younger patient. This finding appears to be more sensitive for early lesion detection than any other multiple sclerosis imaging finding yet described in the literature.

Adolescent↗

PubMed2003

A telemedicine guideline for the practice of teleconsultation.

UNLABELLED: To establish a guideline for the use of teleconsultation, which is one of the most important applications in telemedicine beeing perfomed very frequently in daily medical practice in almost any field of medicine. EVIDENCE: The recommendations are based on expert knowledge, because of the lack of evidence based data in the telemedical scientific literature. In addition, scientific articles of the highest level of evidence available published between 1970 and 1999 were reviewed. DEVELOPEMENT AND CONSENUS PROCESS: A guideline draft was prepared using the attributes of clinical practice guidelines developed by the Institute of Medicine (IOM) of the National Academy of Sciences. This draft was reviewed by telemedicine experts and the content of the guideline was approved by 100% group consensus in 5 meetings held between 1997 and 2000 by a panel of members of the Subproject 4 Group of the Global Health Care Application Project of the G8 countries. CONCLUSIONS: The guideline gives recommendations on all aspects of teleconsultation in any field of medicine and will be updated regularly implementing new evidence.

Computer Security↗

PubMed2003

NOAH--a mobile emergency care system.

The German emergency care system is a very sophisticated one. However, negative headlines like "Emergency Patient Tourism" appearing from time to time, have provoked a thorough deficit analysis which revealed two weak points: communication and documentation. The communication system presently used is a rather outdated one employing analogue voice radio between the ambulance cars/helicopters and the dispatch center and telephone communication between the dispatch center and the emergency rooms. To document the emergency case the on-scene physician is required to fill out a form. A survey showed that many of these forms are filled out incompletely and/or inconsistently or are even missing completely. NOAH, which means "Emergency Organization and Administration Aid" ("Notfall Organisations- und Arbeits-Hilfe" in German) intends to address both of these communication and documentation deficits. The on-scene physician is equipped with a mobile ruggedised PC with an internal digital radio-modern. It provides a direct, digital communication channel from the on-scene physician to the emergency physician starting from the first minutes of the treatment of the emergency patient. It also provides an easy-to-fill-out variant of the paper form mentioned above with an on-line help function and visual aids. A typical course of events with the communication part of NOAH is as follows. The on-scene physician is alarmed via NOAH and can obtain details of the emergency during the approach. He can enter the status codes ("on the move","arrived at the emergency scene","arrived at the patient", etc.) with NOAH. During the first minutes of the treatment of the patient the physician enters a so called "First Message", which requires only 10 to 15 seconds. This message contains basic information like sex, age and the injuries of the patient. It helps the dispatch center (if the on-scene physician desires so) to make an informed recommendation where to bring the patient. This message is also forwarded to the emergency room of the destination hospital, where it can help to start appropriate preparations for the patient. When the on-scene physician has enough time, he can already bring up the documentation masks and give further information to the emergency room.

Documentation↗

PubMed2002

Teleconsultation practice guidelines: report from G8 Global Health Applications Subproject 4.

This report presents a series of recommendations derived from deliberations of the G8 countries Subproject 4 Group (SP4 Group) of the Global Health Care Applications Project entitled, A Teleconsultation Practice Guideline. The recommendations provide an initial step toward developing a general guideline platform for the practice of telemedicine/teleconsultation.

Computer Security↗

PubMedDate not supplied

Effect of 7.0 Tesla MRI on upper eyelid implants.

To ensure the MRI compatibility of various eyelid implants in high-field MRI, 3 eyelid weights made of pure gold (99.99%), pure platinum (99.95%), and a platinum (97%)/iridium (3%) alloy were examined in vitro. Temperature changes, position changes, and imaging artifacts of the different implants were determined in a small-bore 7.0 Tesla MRI system. The 7.0 Tesla MRI system demonstrated that none of the eyelid implants carried a risk of heating or dislocation; therefore, these implants are MRI compatible up to a magnetic field strength of 7.0 Tesla.

Alloys↗