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Biomedical subjects

K Ewen

Publications and source records attributed to K Ewen.

At least 19 recordsLinked to original sources
PubMed2006

[Reducing radiation exposure for patient and staff during interventional radiology demonstrated for coil embolisation].

PURPOSE: Coil embolization of intracranial aneurysms is a radiographic interventional procedure associated with relatively high radiation exposure for the patient and staff. Modern angiographic fluoroscopy systems have a high potential for reducing radiation exposure of a wide bandwidth (e. g. automatic beam filtering, pulsed fluoroscopy, characteristic curve selection). The purpose of this study was to determine how those features could be implemented in the daily routine. MATERIAL AND METHODS: The radiation exposure for the patient and staff was measured during 60 coiling procedures and compared to the mean values before changing the parameters. RESULTS: Implementation of those dose-reducing features during complex radiographic procedures is limited for various reasons. A 35 % dose reduction during coil embolization was able to be achieved in our trial. CONCLUSIONS: From an economic point of view, some resources implemented by the manufacturer and included in the prime cost of the system are not being fully utilized. With some effort, instruction and further education of the staff could lead to a further reduction in radiation exposure without losing too much image quality.

Embolization, Therapeutic↗
PubMed2004

[Which points deserve special attention in the new guidelines on X-ray use (testing guidelines for experts and quality assurance guidelines)?].

Two important guidelines for the application of X-rays in medicine became effective on 1 October 2003 and 1 December 2003. These are testing guidelines for experts and quality assurance guidelines. Both guidelines are very extensive and not always easy to interpret. In the present paper the authors try to explain in detail some chapters important for radiology and to make the necessary technical background transparent. Both authors took an essential part in forming the guidelines.

Certification↗
PubMed2004

[5 years of "concerted action dose reduction in CT" -- what has been achieved and what remains to be done?].

In May 1998, the German "Concerted Action Dose Reduction in CT" was founded by all parties involved in CT. Its intention was to achieve a significant reduction of the radiation exposure caused by CT, a matter that has increasingly been considered a major challenge since the early nineties. As a result of a number of joint efforts, the essential preconditions have been established by now. The fifth anniversary of the Concerted Action gave rise for both retrospection and outlook on the tasks that have already been accomplished and those that still need to be done. For this purpose, a one-day symposium took place in Berlin on November 4, 2003. The contents of a total of 18 contributions will be outlined here in brief.

Adult↗
PubMed2002

Dose reduction in multi-slice CT of the heart by use of ECG-controlled tube current modulation ("ECG pulsing"): phantom measurements.

PURPOSE: To evaluate the effect of ECG-controlled tube current modulation on radiation exposure in retrospectively-ECG-gated multislice CT (MSCT) of the heart. MATERIAL AND METHODS: Three different cardiac MSCT protocols with different slice collimation (4 x 1, and 4 x 2.5mm), and a pitch-factor of 1.5 and 1.8 were investigated at a multi-slice CT scanner Somatom Volume Zoom, Siemens. An anthropomorphic Alderson-Rando phantom was equipped with LiF-thermoluminescence dosimeters at several organ sites, and effective doses were calculated using ICRP-weighting factors. Scan protocols were performed with ECG-controlled tube current modulation ("ECG pulsing") at two different heart rates (60 and 80 bpm). These data were compared to previous data from MSCT of the heart without use of "ECG pulsing". RESULTS: Radiation exposure with (60 bpm) and without tube current modulation using a 2.5 mm collimation was 1.8 mSv and 2.9 mSv for females, and 1.5 mSv and 2.4 mSv for males, respectively. For protocols using a 1 mm collimation with a pitch-factor of 1.5 (1.8), radiation exposure with and without tube current modulation was 5.6 (6.3) mSv and 9.5 (11.2) mSv for females, and 4.6 (5.2) mSv and 7.7 (9.2) mSv for males, respectively. At higher heart rates (80 bpm) radiation exposure is increased from 1.5 - 1.8 mSv to 1.8 - 2.1 mSv, using the 2.5 mm collimation, and from 4.6 - 5.6 mSv to 5.9 - 7.2 mSv, for protocols using 1 mm collimation. CONCLUSIONS: The ECG-controlled tube current modulation allows a dose reduction of 37 % to 44 % when retrospectively ECG-gated MSCT of the heart is performed. The tube current - as a function over time - and therefore the radiation exposure is dependent on the heart rate.

Coronary Angiography↗
PubMed2001

Radiation exposure in multi-slice CT of the heart.

PURPOSE: To assess radiation exposure of patients undergoing Multi-Row Detector CT (Multi-Slice CT, MSCT) of the heart. MATERIAL AND METHODS: Four different cardiac MSCT protocols with changing slice collimation (4 x 1, and 4 x 2.5 mm), and pitch-factor (1.5, 1.8, and 4) were examined. An anthropomorphic Alderson-Rando phantom was equipped with LiF-thermoluminescent dosimeters at several organ sites, and effective doses were calculated using ICRP-weighting factors. These data were compared to data from standard MSCT of chest and abdomen. RESULTS: Effective dose in different protocols for cardiac MSCT varies from 2.8 to 10.3 mSv (male), and from 3.6 to 12.7 mSv (female). In protocols with thin collimation and low pitch or a combination of several heart examinations, radiation exposure may be comparable to the effective dose of standard MSCT of the chest (male: 11.9 mSv, female: 12.9 mSv) or the abdomen (male: 16.1 mSv, female: 15.7 mSv). Highest organ doses were found for the female breast (up to 46.6 mGy), and the lungs (up to 36.4 mGy) with surface doses as high as 54.3 mGy. CONCLUSIONS: Cardiac MSCT adds significantly to the radiation exposure of patients and can reach the effective dose applied by standard MSCT of chest or abdomen.

Bone Marrow↗
PubMed1999

Maternal uniparental isodisomy for chromosome 14 detected prenatally.

Maternal uniparental disomy (UPD) for chromosome 14 (upd(14)mat) has been associated with a distinct phenotype. We describe the first case of maternal uniparental isodisomy for chromosome 14 detected prenatally, in a pregnancy with mosaicism for trisomy 14 observed in both a chorionic villus sample (CVS) and in amniocytes. Detailed analysis of polymorphic microsatellites showed that the fetus was essentially isodisomic for one of the mother's chromosomes 14 and that recombination had introduced a mid-long arm region of heterodisomy. The fetus, which died in utero at 18 weeks, showed no apparent pathological features. The case demonstrates for the first time a maternal meiosis II non-disjunction of chromosome 14 leading to a trisomic conception which has been incompletely corrected by 'rescue' in the early embryo.

Adult↗
PubMed1999

[Aspects of radiation protection in cardiovascular brachytherapy].

In the scope of cardiovascular brachytherapy beta- as well as gamma-ray emitting radionuclides are used. The handling of radioactive sources is within the range of the radiation protection regulations (Strahlenschutzverordnung [StrlSch V]). According to EU guidelines an amendment of the StrlSch V is required by May 2000. The connected reduction of dose limits now should already be taken into consideration when planning irradiation facilities, likewise in cardiovascular brachytherapy. Temporary regulations for equipment that was already in operation before May 2000 are not planned in the new StrlSch V.

Angioplasty, Balloon↗
PubMed1998

[Radiation exposure of radiation-sensitive risk organs--ocular lens, parotid gland, thyroid gland--in dacryocystography and therapy].

PURPOSE: Evaluation of radiation dose to the radiosensitive head and neck organs and tissues-ocular lens, parotid and thyroid glands--during dacryocystography and fluoroscopy--guided dacryocystoplasty (DCP). METHOD: Radiation dose was determined in an Alderson Rando phantom and in 13 patients. Radiation dose was measured directly using Ca-F2-thermoluminescent dosimetry crystals (TLD) which were placed on each eyelid, parotid gland and thyroid gland. RESULTS: The mean radiation dose to the lens placed next to the path of radiation was 6.58 mGy in the Alderson-Rando phantom and 5.43 mGy in patients during DCP. The mean radiation dose to the contralateral lens was 1.37 mGy and 1.7 mGy to the parotid gland placed next to the x-ray tube. Radiation dose to the thyroid gland was max. 0.4 mGy during DCP. CONCLUSION: Radiation dose to the ocular lens, parotid gland and thyroid gland during fluoroscopy-guided DCP was 25 times higher than during diagnostic dacryocystography. The radiation dose to radiosensitive head and neck organs and tissues during fluoroscopy-guided DCP is much below the threshold dose for ocular lens cataract.

Dacryocystitis↗
PubMed1998

[Dosage measurements in spiral CT examinations of the head and neck region].

PURPOSE: In view of the increasing frequency of computed tomographic examinations the organ doses of the thyroid gland and the eye lenses in spiral CT examinations of the head and neck should be determined. MATERIAL AND METHODS: Standard CT-examinations of the neck, the paranasal sinuses in axial and coronal sections, and the mandibula were simulated by help of an Alderson-Rando phantom. Dose measurements were performed as well in 28 patients. The examinations were carried out in spiral mode ("Somatom AR.SP", "Picker PQ 2000", and "Toshiba Xpress SX") and conventional single slice technique ("Somatom Plus"). Three LiF-TLD were placed on each eyelid and three on the thyroid. RESULTS: With direct exposure to the x-ray-beam the organ doses did not exceed 64 mGy. When exposed by scatter radiation only, doses may be reduced by a factor of up to 10. The measurements in 28 patients showed similar results. CONCLUSIONS: The organ doses in spiral CT correspond with data known from conventional CT.

Head↗
PubMed1998

[Possibilities for dose reduction in coronal spiral CT of the mid-face area].

The radiation dose at the eye lens and the thyroid gland in spiral-CT-examinations is comparable to those known from conventional computed tomography. In view of an increasing artificial radiation exposure, it remains an important aim to achieve dose reduction with persistent adequate imaging quality. We determined the doses of the named organs in four different CT-examination protocols by use of phantom studies and in 45 patients. By reduction of tube current and tube voltage, organ doses can be reduced by half. This is achieved without a relevant loss in diagnostic precision as far as high-contrast structures are concerned. Compared to conventional CT-scanning, the dose reduction reached 75%. Taking into consideration the increasing insensitivity in the z-plane and the worsening of the section-sensitivity profile, a properly chosen increase in pitch may result in a significant dose reduction. CT-scanning of high-contrast structures in the head and neck can and should be performed with the least radiation exposure possible.

Craniofacial Abnormalities↗
PubMed1998

[Calculating the effective dose of occupationally exposed persons in roentgen diagnosis].

The radiation exposure of occupationally exposed staff was measured at tube voltages of 50, 80 and 100 kV. A typical arrangement for fluoroscopic examinations was chosen: the (standing) physician is exposed by the scattered radiation from a (lying) patient. The physician is represented by an Alderson-Rando-Phantom and a spherical phantom similar to an ICRU sphere. Measurements of the partial body dose were performed by film dosimetry in the Alderson-Rando-Phantom in a.p. and in lateral direction of the scattered radiation respectively. From these measurements the effective dose was calculated. The ambient equivalent dose H* (10) in the sphere phantom was determined by the same method. The latter results yield the conversion factor g, which describes the ratio effective dose E to ambient equivalent dose H* (10). A conversion factor of g = 0.3 was established by averaging over the tube voltage and the direction of the scattered radiation. Based on the guidelines 96/29/Euratom and the transition from old to new dose quantities a reduction of the dose limits for occupationally exposed persons by a factor of up to 3.75 will be necessary. Applying the conversion factors can almost compensate that reduction.

Humans↗
PubMed1998

[Effect of collimation and pitch on radiation exposure and image quality in spiral CT of the thorax].

PURPOSE: The aim of the study was to optimize the scan parameters for spiral-CT of the thorax. METHODS: Using a Somatom AR-SP (Siemens AG, Erlangen) CT-unit, four different scanning protocols (collimation/table feed) were compared: A (5/10), B (10/10), C (10/15), D (10/20). High contrast resolution in the xy-plane and in the z-direction were investigated with special phantoms. Noise levels were measured using a water phantom, the radiation exposure of lung parenchyma was investigated using an Alderson-Rande-Phantom. An anthropoid chest phantom was scanned to compare the image quality of the four protocols. RESULTS: Protocol A showed the best resolution in the z-direction; the resolution in the xy-plane was equal for all protocols. Image noise in the center of the water phantom was 58 HU for protocol A and 40 HU for the other three. The following equivalent organ dose were measured for lung parenchyma: A 14 mSv, B 29 mSv, C 20 mSv, D 14 mSv. CONCLUSION: Scanning protocols with small collimation and a pitch of 2 are characterised by low radiation exposure and excellent resolution in the z-direction. These parameters seem to be most suitable for lung scanning.

Diagnostic Imaging↗
PubMed1995

[Radiation exposure of radiologists during angiography: dose measurements outside the lead apron].

The aim of this study was to provide practical information to angiographers concerning radiation exposure to body parts not covered by lead aprons. Individual doses to the neck and hands of radiologists measured in micro-Sieverts were obtained during the course of 80 angiographies of various types. The number of diagnostic and interventional procedures, which might lead to exceeding permissible doses, have been calculated. Possibilities of estimating doses during angiography by means of parameters such as screening times were examined statistically. Especially with regard to the hands, estimations of the doses are insufficient (correlation r = 0.21). Radiologists who undertake much angiographic and particularly interventional work may reach exposure levels requiring protective measures in addition to lead aprons.

Angiography↗
PubMed1995

[Effects of the medical products legislation on roentgen services].

On January 1, 1995 the law concerning medical products (Medizinproduktgesetz-MPG) came into force. It essentially regulates the production, circulation, and the putting into service of medical products as well as equipment. Among other things, the so-called active medical products include medical X-ray equipment whose aspects concerning atomic law remain covered by the radiation protection regulation for X-ray sources (RöV). Parallel to the coming into force of the MPG, the RöV was modified (Section 50, MPG), which in future might result in considerable consequences for the manufacturer, the operator, and the authorities.

Equipment Safety↗