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D J Schaefer

Publications and source records attributed to D J Schaefer.

35 records · Page 2Linked to original sources
PubMed1994

Physiologic responses to an MR imaging procedure performed at a specific absorption rate of 6.0 W/kg.

PURPOSE: To assess the physiologic responses to a magnetic resonance (MR) procedure performed at a whole-body-averaged specific absorption rate (SAR) of 6.0 W/kg. MATERIALS AND METHODS: Tympanic membrane temperature, skin temperature at seven sites, heart rate, blood pressure, oxygen saturation, and cutaneous blood flow in six volunteers were assessed before, for 16 minutes during, and immediately after MR imaging performed at 1.5 T, 64 MHz. RESULTS: Statistically significant (P < .05) increases in temperature of the tympanic membrane and the skin of the chest, abdomen, upper arm, hand, and thigh and in heart rate and cutaneous blood flow were associated with exposure to high SAR. None of these physiologic changes, however, were considered deleterious to the study subjects. CONCLUSION: MR imaging procedures performed at the high SAR studied can be tolerated by persons with normal thermoregulatory function.

Adult↗
PubMed1994

[Epidemiology and treatment of fractures in old age].

The frequency of fractures in the elderly has risen dramatically and will increase further in the future. This is partly a socio-economic problem and is familiar both to surgeons and to the general population. Fractures in such patients have clinical and pathomechanical implications, with unassociated conditions needing treatment. It is necessary to standardize treatment, including operative procedures, which can be performed in every hospital. The therapeutic measures available involve close cooperation between the surgeon, the geriatrician and ancillary workers. For some fractures in the elderly there are already operative procedures that ensure efficient rehabilitation and reintegration into society. Osteoporosis can make osteosynthesis problematic. Radiological measurements of bone density are of diagnostic rather than therapeutic value. Operative procedures and their effectiveness in common fractures in the elderly (hip, distal radius, shoulder) are discussed. It is stated that surgical treatment is very important in mastering this challenge, but other aspects, particularly ethical considerations, are paramount.

Aged↗
PubMed1990

Thermal effects of MR imaging: worst-case studies on sheep.

The objective of this study was to provide a worst-case estimate of thermal effects of MR imaging by subjecting anesthetized unshorn sheep to power deposition at specific absorption rates (SARs) well above approved standards for periods of time in excess of normal clinical imaging protocols. A control period with no RF power was followed by 20-105 min of RF power application. Afterward, there was a 20-min or longer recovery period with no RF power. Eight sheep were given whole-body RF exposure (1.5- to 4-W/kg SAR) while rectal and skin temperatures were monitored. Four sheep were subjected to 4-W/kg head scans for an average of 75 min while temperatures of the cornea, vitreous humor, head skin, jugular vein, and rectum were measured. In head scanning experiments, skin and eye temperatures increased about 1.5 degrees C. Jugular vein temperature rose a maximum of 0.4 degrees C after an average exposure of 75 min. In whole-body exposures, elevation of rectal temperature was correlated with energy input. Deep-body temperature rises in excess of 2.0 degrees C were attained for 4-W/kg whole-body exposure periods greater than 82 min. Animals exposed for 40 min to 4 W/kg in either body coil (three sheep) or head coil (two sheep) were recovered and observed to be in good health for 10 weeks; no cataracts were found. MR power deposition at SAR levels well above typical clinical imaging protocols caused body temperature to increase. For exposure periods in excess of standard clinical imaging protocols the temperature increase was insufficient to cause adverse thermal effects. Studies in healthy humans are needed to determine whether enhanced heat-loss effector mechanisms are likely to cause deep-body temperatures to plateau at an acceptable level, and to elucidate mechanisms that determine subcutaneous temperature.

Animals↗
PubMed1989

Exposure to a 1.5-T static magnetic field does not alter body and skin temperatures in man.

The literature has conflicting reports concerning the effect of static magnetic fields on body and skin temperatures in mammals. Since temperature changes induced by static magnetic fields would have important safety implications for clinical magnetic resonance imaging body (sublingual pocket) and skin (abdomen, forehead, chest, upper arm, forearm, thigh, and calf) temperatures were determined in six normal subjects using a fluoroptic thermometry system during a 20-min exposure to a 1.5-T static magnetic field. Ambient conditions were controlled and held constant. An analysis of variance for repeated measures revealed that there were no statistically significant changes in body or any of the skin temperatures recorded. We conclude that exposure for 20 min to a 1.5-T static magnetic field does not alter body and skin temperatures in man.

Air Movements↗
PubMed1989

Alterations in body and skin temperatures caused by magnetic resonance imaging: is the recommended exposure for radiofrequency radiation too conservative?

Increases in tissue temperature caused by exposure to radiofrequency (RF) radiation are a primary safety concern of magnetic resonance imaging (MRI). Therefore, body and skin temperatures were measured in six subjects before (20 min), during (30 min) and after (20 min) MRI procedures performed at specific absorption rates (SARs) six to 10 times higher than the limit recommended by the UK National Radiological Protection Board. Body temperature was unchanged throughout the experiment. Abdominal skin temperature increased significantly (p less than 0.05) during MRI, decreased significantly post-MRI, but was still significantly (p less than 0.05) higher than baseline. The highest abdominal skin temperature recorded was 36 degrees C. Upper arm, forearm and chest skin temperatures increased significantly (p less than 0.05) during MRI and remained elevated post-MRI. The highest skin temperatures recorded on the upper arm, forearm and chest were 38.1, 36.0 and 34.5 degrees C, respectively. Thigh and calf skin temperatures were not significantly changed during MRI. These alterations in tissue temperatures were physiologically trivial and easily tolerated by the subjects, suggesting that the recommended exposure to RF radiation during MRI of the body for patients with normal thermoregulatory function may be too conservative.

Abdomen↗
PubMed1988

Superficial- and deep-tissue temperature increases in anesthetized dogs during exposure to high specific absorption rates in a 1.5-T MR imager.

Superficial- and deep-tissue heating was measured in five dogs during high-specific-absorption-rate radiofrequency (RF) irradiation to see whether significant temperature changes could be produced by a 1.5-T clinical magnetic resonance imager. The RF power output employed was 6.3 times that required for routine imaging. Temperature probes were placed in both deep and superficial tissues, and temperatures were recorded before, during, and after exposure. In each dog, there was a linear temperature increase of several degrees during RF exposure; the maximal average change was 4.6 degrees C in the urinary bladder. The temperature increase was slightly greater in deep tissues than in superficial tissues. The calculated specific absorption rate, based on the temperature change, averaged 7.9 W/kg for all five dogs. These findings argue for continued caution in the design and operation of imagers capable of high specific absorption rates, particularly when they are used for imaging infants or patients with altered thermoregulatory capability.

Absorption↗
PubMed1986

Effect of a 1.5 T static magnetic field on body temperature of man.

Reports in the literature concerning the effect of static magnetic fields on the body temperature of mammals have been contradictory and confusing. A significant increase in body temperature in human subjects exposed to the static magnetic fields used in magnetic resonance imaging (MRI) would have important safety implications. Therefore, in two separate studies we determined body temperature in 20 subjects exposed to a 1.5 T static magnetic field. One group of subjects (Group I, N = 9) had sublingual pocket temperature measured immediately before and after a 60 min exposure, while another group of subjects (Group II, N = 11) had esophageal temperature determined at 2 min intervals during a 20 min exposure. No statistically significant changes in body temperature were observed in either Group I or II subjects during exposure to the 1.5 T static magnetic field. We conclude that a relatively intense static magnetic field has no effect on body temperature of normal human subjects.

Adult↗
PubMed1986

Thermoregulatory responses to clinical magnetic resonance imaging of the head at 1.5 tesla. Lack of evidence for direct effects on the hypothalamus.

Warming temperature sensitive neurons in the hypothalamus will induce thermoregulatory heat dissipation. Application of radiofrequency (RF) radiation to the head during magnetic resonance imaging (MRI) could, conceivably, heat the brain, causing a generalized peripheral vasodilation and result in a paradoxical and unnecessary decrease in body temperature. To evaluate the thermoregulatory responses to the RF power deposition used during MRI, we measured body (sublingual pocket) and skin temperatures in 15 patients immediately before and after MRI scans of the head. Ear-skin blood flow was determined by laser-Doppler velocimetry to assess local vasomotor tone. A high-field (1.5 tesla/64 MHz) MRI device (General Electric Company) with a coil designed for head/brain imaging was used in this study. Ambient conditions were room temperature 20-24 degrees C and relative humidity 40-50%. The specific absorption rate averaged over the head ranged from 0.83 to 1.20 W/kg. There was a slight but statistically significant elevation in body temperature (36.5 +/- 0.5 to 36.7 +/- 0.4 degrees C). Skin temperatures of the ear (30.0 +/- 1.2 to 32.0 +/- 0.9 degrees C) and forehead (32.4 +/- 0.5 to 32.8 +/- 0.5 degrees C) increased significantly, while hand (29.9 +/- 1.4 to 29.8 +/- 2.1) skin temperature was unchanged. Ear-skin blood flow also increased a statistically significant amount (average change 36%). The data indicate that there was predominantly surface heating associated with MRI of the head which stimulated a local vasodilating response (i.e. significant increase in ear skin blood flow).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

Thermal effects of high-field (1.5 tesla) magnetic resonance imaging of the spine. Clinical experience above a specific absorption rate of 0.4 W/kg.

Current safety guidelines recommend limiting the exposure to radiofrequency (RF) radiation used for clinical magnetic resonance imaging to a whole body average specific absorption rate (SAR) of 0.4 W/kg. Since it may be desirable to image with SARs that exceed this level during MRI of the spine, we evaluated the thermal responses associated with these procedures. Body and skin temperatures were determined in 25 patients immediately before and after MRI. Since the eye is particularly susceptible to thermal injury, corneal temperature was also measured. High-resolution thermography was performed on three subjects to evaluate the surface heating pattern and identify potential thermal 'hot spots'. A 1.5 tesla/64 MHz MRI system with quadrature transmission and reception was used iN this study. The whole body average specific absorption rate ranged from 0.5 to 1.3 W/kg. Ambient conditions were room temperature 20-24 degrees C and relative humidity between 40 and 50 per cent. There was a slight but statistically significant (p less than 0.01) increase in body temperature after MRI (36.5 +/- 0.4 to 36.7 +/- 0.4 degrees C). Temperatures of the hand (30.4 +/- 1.4 to 31.2 +/- 1.0 degrees C), positioning isocenter (32.1 +/- 0.6 to 32.9 +/- 0.5), and cornea (32.5 +/- 0.6 to 32.9 +/- 0.5 degrees C) also increased a statistically significant amount. Thermographic imaging revealed normal heating patterns with no surface 'hot spots'. We conclude that the temperature changes associated with MRI of the spine at the SARs we studied were well below known thresholds for adverse effects and do not appear to be harmful to patients.

Adult↗
PubMed1980

Microwave effects on energy metabolism of rat brain.

Rat brain was exposed to 591-MHz, continuous-wave (CW) microwaves at 13.8 or 5.0 mW/cm2 to determine the effect on nicotinamide adenine dinucleotide, reduced (NADH), adenosine triphosphate (ATP) and creatine phosphate (CP) levels. On initiation of the in vivo microwave exposures, fluorimetrically determined NADH rapidly increased to a maximum of 4.0%-12.5% above pre-exposure control levels at one-half minute, than decreased slowly to 2% above control at three minutes, finally increasing slowly to 5% above control level at five minutes. ATP and CP assays were performed on sham- and microwave-exposed brain at each exposure time. At 13.8 mW/cm2, brain CP level was decreased an average of 39.4%, 41.1%, 18.2%, 13.1%, and 36.4% of control at exposure points one-half, one, two three, and five minutes, respectively, and brain ATP concentration was decreased an average of 25.2%, 15.2%, 17.8%, 7.4%, and 11.2% of control at the corresponding exposure periods. ATP and CP levels of rat brain exposed to 591-MHz cw microwaves at 5mW/cm2 for one-half and one minute were decreased significantly below control levels at these exposure times, but were not significantly different from the 13.8 mW/cm2 exposures. For all exposures, rectal temperature remained constant. Heat loss through the skull aperture caused brain temperature to decrease during the five-minute exposures. This decrease was the same in magnitude for experimental and control subjects. Changes in NADH, ATP, and CP levels during microwave exposure cannot be attributed to general tissue hyperthermia. The data support the hypothesis that microwave exposure inhibits mitochondrial electron transport chain function, which results in decreased ATP and CP levels in brain.

Adenosine Triphosphate↗
PubMed1979

Physical studies on isolated human prothrombin fragment-2. Comparisons with human prothrombin fragment-1.

Variation of pH strongly affects the fluorescence intensity of human prothrombin fragment-1 in a manner suggesting contributions from a number of protropic equilibria including groups with apparent pKa values near 3.0. These results suggest a structural role for pK1a of gamma-carboxyglutamic acid noieties. Added calcium ions (9 mM calcium chloride) quench the fluorescence titration curve uniformly above pH 4. Below pH 4, however, the titration curve in the presence of calcium ions suggests that calcium-ion-dependent processes leading to fluorescence quenching are pH-dependent. Upon back titration of human fragment-1, from pH 9, hysteresis is observed. Human prothrombin fragment-2 fluorescence titration curves are relatively broad at low pH suggesting the titration of normal carboxyl groups. The titration curves of fragment-2 are not affected by the presence of calcium ions, and hysteresis occurs upon back titration from low pH values. Circular dichroism (CD) Cotton effects appear at 232 nm and 280 nm and a trough appears at 203 nm in the CD spectrum of human prothrombin fragment-2. The Cotton effects in the region from 230 nm to 300 nm are sensitive to pH, ellipticity values at 232 nm increasing from approximately 300 at pH 2.5 to 1300 (degree-cm/decimole) at neutral pH and finally become negative at high pH values. In contrast to fragment-1, at neutral pH the fragment-2 Cotton effect at 232 nm is insensitive to the presence of 8 mM calcium chloride.

Calcium↗
PubMedDate not supplied

Accessory equipment considerations with respect to MRI compatibility.

The MR Section of The National Electrical Manufacturers Association (NEMA), in response to a request from the Food & Drug Administration (FDA), recently issued a position paper to address generic issues related to the compatibility of accessory equipment produced by third party equipment manufacturers or MR equipment users and intended to be used in conjunction with MR equipment or within the MR scanning room. The recommendations concern scanning accessories, such as radiofrequency (RF) coils, patient monitoring equipment and injectors, as well as patient comfort accessories and positioning devices. The following issues related to safety performance are discussed: (a) the interaction of the equipment with the MR scanner, (b) interactions of the MR scanner with the equipment, and (c) potential safety hazards for patients and staff that can be posed by accessory equipment in the MR scan environment. The recommendations are based on combined input from NEMA member companies who manufacture MR systems and MR accessories and are presented for consideration in the design of MR accessory products and incorporation of these concepts into testing plans to ensure MR compatibility of third party devices.

Equipment Design↗
PubMedDate not supplied

Tissue engineering of bone: the reconstructive surgeon's point of view.

Bone defects represent a medical and socioeconomic challenge. Different types of biomaterials are applied for reconstructive indications and receive rising interest. However, autologous bone grafts are still considered as the gold standard for reconstruction of extended bone defects. The generation of bioartificial bone tissues may help to overcome the problems related to donor site morbidity and size limitations. Tissue engineering is, according to its historic definition, an "interdisciplinary field that applies the principles of engineering and the life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function". It is based on the understanding of tissue formation and regeneration and aims to rather grow new functional tissues than to build new spare parts. While reconstruction of small to moderate sized bone defects using engineered bone tissues is technically feasible, and some of the currently developed concepts may represent alternatives to autologous bone grafts for certain clinical conditions, the reconstruction of large-volume defects remains challenging. Therefore vascularization concepts gain on interest and the combination of tissue engineering approaches with flap prefabrication techniques may eventually allow application of bone-tissue substitutes grown in vivo with the advantage of minimal donor site morbidity as compared to conventional vascularized bone grafts. The scope of this review is the introduction of basic principles and different components of engineered bioartificial bone tissues with a strong focus on clinical applications in reconstructive surgery. Concepts for the induction of axial vascularization in engineered bone tissues as well as potential clinical applications are discussed in detail.

Bioartificial Organs↗
PubMedDate not supplied

Evaluation of processed bovine cancellous bone matrix seeded with syngenic osteoblasts in a critical size calvarial defect rat model.

INTRODUCTION: Biologic bone substitutes may offer alternatives to bone grafting procedures. The aim of this study was to evaluate a preformed bone substitute based on processed bovine cancellous bone (PBCB) with or without osteogenic cells in a critical size calvarial defect rat model. METHODS: Discs of PBCB (Tutobone) were seeded with second passage fibrin gel-immobilized syngenic osteoblasts (group A, n = 40). Cell-free matrices (group B, n = 28) and untreated defects (group C; n=28) served as controls. Specimens were explanted between day 0 and 4 months after implantation and were subjected to histological and morphometric evaluation. RESULTS: At 1 month, bone formation was limited to small peripheral areas. At 2 and 4 months, significant bone formation, matrix resorption as well as integration of the implants was evident in groups A and B. In group C no significant regeneration of the defects was observed. Morphometric analysis did not disclose differences in bone formation in matrices from groups A and B. Carboxyfluorescine-Diacetate-Succinimidylester (CFDA) labeling demonstrated low survival rates of transplanted cells. DISCUSSION: Osteoblasts seeded into PBCB matrix display a differentiated phenotype following a 14 days cell culture period. Lack of initial vascularization may explain the absence of added osteogenicity in constructs from group A in comparison to group B. PBCB is well integrated and represents even without osteogenic cells a promising biomaterial for reconstruction of critical size calvarial bone defects.

Animals↗