Biomedical subjects

E R Ritenour

Publications and source records attributed to E R Ritenour.

At least 19 recordsLinked to original sources

PubMed1999

MRI compatibility and visibility assessment of implantable medical devices.

We have developed a protocol to evaluate the magnetic resonance (MR) compatibility of implantable medical devices. The testing protocol consists of the evaluation of magnetic field-induced movement, electric current, heating, image distortion, and device operation. In addition, current induction is evaluated with a finite element analysis simulation technique that models the effect of radiofrequency fields on each device. The protocol has been applied to several implantable infusion pumps and neurostimulators with associated attachments. Experiments were performed using a 1.5-T whole-body MR system with parameters selected to approximate the intended clinical and worst case configuration. The devices exhibited moderate magnetic field-induced deflection and torque but had significant image artifacts. No heating was detected for any of the devices. Pump operation was halted in the magnetic field, but resumed after removed. Exposure to the magnetic field activated some of the neurostimulators.

Artifacts↗

PubMed1999

The potential for radiation-induced skin damage in interventional neuroradiological procedures: a review of 522 cases using automated dosimetry.

The Food and Drug Administration (FDA) has recommended the monitoring of radiation skin dose to patients during procedures having the potential for radiation damage. Radiologists need information about typical radiation doses during interventional procedures. The skin doses to patients during 522 interventional neuroradiological procedures have been monitored using an automated dosimetry system. Estimated entrance skin doses (ESD) were binned into 0.5 Gy increments and compared to FDA recommended thresholds for inclusion in the patient record. Percentages of procedures exceeding the above mentioned thresholds are presented. In addition, the percentage of dose in each view and the percentage of dose in fluoroscopic and digital angiographic modes are shown. Six percent of embolization procedures and one percent of cerebral angiograms are estimated to have potential for main erythema (ESD>6 Gy). All types of procedures have potential for temporary erythema and exceed the threshold for inclusion in the patient record (ESD> 1 Gy) at the 95% percentile. The types of procedures with most potential for skin damage also have significant percentages of dose in the digital angiographic mode. Thus, monitoring fluoroscopic time alone underestimates the potential for skin injury. On the other hand, combining the doses in the posterior-anterior and lateral views, tends to overestimate the potential for radiation injury.

Biophysical Phenomena↗

PubMed1999

Lossy compression should not be used in certain imaging applications such as chest radiography. For the proposition.

Computational techniques are frequently used to compress image data so that transmission and storage requirements are reduced. If the computational techniques result in no loss in image resolution, the technique is referred to as lossless compression. Greater compression of data may yield some loss in spatial or temporal resolution, and is referred to as lossy compression. In some radiologic examinations [e.g., gastrointestinal (GI) studies], some resolution loss may be tolerable, whereas in others (chest examinations and mammography) it conceivably could result in missed pathology. Without lossy compression, however, data requirements can be overwhelming for transmission, storage and retrieval of images such as chest films. The unanswered question, addressed in this Point/Counterpoint issue, is whether some degree of lossy compression can be tolerated in chest radiography.

Humans↗

PubMed1996

Gray-scale sonographic characterization of aminoglycoside-induced nephrotoxicosis in a canine model.

RATIONALE AND OBJECTIVES: The diagnostic usefulness of gray-scale sonography was evaluated in a canine model of aminoglycoside-induced nephrotoxicosis. METHODS: Sonography was performed before and during the onset and progression of nephrotoxicosis induced by administration of a toxic dosage of gentamicin. Subjective visualization of increased renal cortex echogenicity (IRCE) was objectified with digital image analysis methods. Results of both subjective and objective evaluation were correlated with clinicopathologic tests and renal cortex biopsy obtained concurrently. RESULTS: Subjective visualization of IRCE was associated with significant nephrotoxicosis and was superior to serum creatinine elevation in nephrotoxicity detection. Objective detection of IRCE improved nephrotoxicity detection sensitivity to that of increased urine enzymuria. CONCLUSIONS: Based on the above results, subjective visualization of IRCE in patients with aminoglycoside-induced nephrotoxicity may occur before azotemia and is suggestive of significant renal dysfunction; application of digital image analysis methods may lead to earlier sonographic recognition of nephrotoxicity.

Animals↗

PubMed1996

Physics overview of screen-film radiography.

The main components of the imaging system are the x-ray source, patient, image receptor (here, a screen-film system), processor, view box, and observer. The x-ray tube produces a beam of x rays, characterized by its spatial and energy distributions. The characteristics of the patient being radiographed--that is, the differential in attenuation of the x-ray beam among various structures within the patient (or subject contrast)--should exert the greatest influence on the final image. After passing through the patient, the x-ray beam bears the imprint of the attenuation processes (ie, absorption and scatter of photons) that took place within the patient. Subject contrast may be defined in terms of the ratio of the energy carried to the image receptor in two different locations. The number of x rays needed at the image receptor to produce the image and the radiation dose to the patient can be reduced by using an intensifying screen. The response of a screen-film system to x-ray exposure may be predicted in advance by observing the characteristic curve of the system. Radiographic image descriptors include contrast, resolution, and the detectability of subtle features. Detectability is heavily influenced by the characteristics of the observer.

Humans↗

PubMed1996

Estimation of arcuate artery resistive index as a diagnostic tool for aminoglycoside-induced acute renal failure in dogs.

OBJECTIVE: To determine the potential clinical usefulness of duplex Doppler estimation of arcuate artery resistive index (a measure of intrarenal blood flow impedance) for diagnosis of aminoglycoside-induced nephrotoxicosis. ANIMALS: 30 adult, female, mixed-breed dogs, allotted to 3 groups of 10 dogs each as: toxic dosage of gentamicin, therapeutic dosage of gentamicin, and saline solution sham equivalent in volume to that of the toxic dosage of gentamicin. PROCEDURE: After baseline screening to establish normalcy (serum biochemical analysis, endogenous creatinine clearance determination, urinalysis, urine protein-to-creatinine ratio, urine culture, gray-scale sonography, and percutaneous ultrasound-guided renal biopsy), results of arcuate artery resistive index determination were compared with serum creatinine and urine specific gravity values on a Monday-Wednesday-Friday data collection schedule for 10 days. Endogenous creatinine clearance determination, ultrasound-guided renal biopsy, and urine culture were repeated at the end of data collection in all 3 groups. RESULTS: Significant differences in resistive index measurements were not observed, despite clinicopathologic and renal biopsy results compatible with severe acute tubular necrosis in dogs of the toxic dosage group. CONCLUSIONS: Duplex Doppler sonography of arcuate artery blood flow impedance, expressed as the resistive index, appears to have poor clinical usefulness as a diagnostic tool in this disorder. CLINICAL RELEVANCE: Normal arcuate artery resistive index values obtained in dogs for which aminoglycoside-induced nephrotoxicosis is suspected do not exclude the disorder. If abnormal arcuate artery resistive index values are obtained for such dogs, further evaluation for nephropathies other than aminoglycoside-induced nephrotoxicosis may be considered.

Acute Kidney Injury↗

PubMed1995

A survey of films for use as dosimeters in interventional radiology.

Analysis of radiation doses in interventional radiological procedures that can lead to deterministic radiation effects such as erythema and epilation would assist physicians in planning patients care after exposure and in reducing doses. Photographic films used to measure skin exposure in the past are too sensitive for the high doses involved in interventional procedures. Seventeen different types of films, many of which are generally available in hospitals, were surveyed to see if any would meet the demands of interventional radiology. Sensitometric curves obtained demonstrate that most films are inappropriate for high dose procedures. Using Kodak Fine Grain Positive and Dupont duplicating films and automatic processing, doses as high as 2.8 Gy could be measured with reasonable accuracy. Similar results can be obtained by manually processing Kodak XV-2 verification film at room temperature.

Automation↗

PubMed1994

Medical physics.

Explore the source record for details and available documents.

Diagnosis, Computer-Assisted↗

PubMed1994

Volumetric high-resolution CT in the diagnosis of interstitial lung disease and bronchiectasis: diagnostic accuracy and radiation dose.

OBJECTIVE: The purpose of this study was to evaluate the diagnostic accuracy and radiation dose of volumetric high-resolution CT in the diagnosis of interstitial lung disease and bronchiectasis when four contiguous sections were acquired at each of three levels. The potential benefits were weighed against the increased radiation dose of multiple scans. SUBJECTS AND METHODS: High-resolution CT scans of four contiguous sections were obtained at each of three locations (the aortic arch, the carina, and 2 cm above the diaphragm) in 50 consecutive patients (mean age, 44 years old) with known or suspected interstitial lung disease or bronchiectasis who were referred for evaluation with high-resolution CT. Each individual scan was analyzed for the presence of motion-induced streaking, blurring, or doubling. The diagnostic information contained in each set of four scans was compared with that contained in the first of the four scans in the set. RESULTS: Motion degraded at least one of the four images in each set in 69 (46%) of 150 volumetric acquisitions. When the full set of four images was considered instead of just the first scan from the set, the number of motion-free studies in patients with suboptimal respiratory suspension was increased by 40% (from 99 to 139). Diagnostic accuracy was improved as more features were identified on contiguous scans: the sensitivity of the first scan compared with that of the complete set of four scans was 84% for the detection of bronchiectasis, 97% for ground-glass opacity, 88% for honeycombing, 88% for septal thickening, and 86% for nodular opacities. Although the integral radiation exposure for a set of four CT scans was 2.8 times that of a single scan obtained with standard technique, peak skin exposure was unchanged. Slightly increased image noise with the reduced technique compromised diagnostic ability in 6% of studies. CONCLUSION: The use of volumetric high-resolution CT increased diagnostic accuracy, particularly for bronchiectasis at the lung bases, without increasing peak skin radiation exposure. With the availability of four contiguous scans per anatomic level, the subjective confidence in interpretation and number of motion-free studies also increased.

Adult↗

PubMed1993

A survey of radiation oncologists regarding their radiation physics instruction.

The American Association of Physicists in Medicine, Committee on Training of Radiologists conducted a survey of radiation oncologists requesting information regarding their radiation oncology physics training. General questions were asked of the oncologist regarding their radiation oncology practice such as number of oncologists, number of new patients treated, and the size and type of facility in which the practice is located. The oncologist also responded to questions regarding their educational background. The survey requested the radiation oncologists to answer questions regarding the adequacy and importance of their training in specific areas of radiation physics. The responders indicated that the importance of most physics topics in their clinical practice corresponded to the level of their understanding. The survey indicated that for most radiation oncologists their physics instruction was an important and interesting part of their residency program.

Health Physics↗

PubMed1993

A teleconferencing system.

Training of health professionals commonly involves multiple sites in order to best utilize the available clinical material. However, this makes it difficult to achieve continuity in the presentation of didactic material. We have installed a teleconferencing system using high speed switching Asynchronous Transfer Mode (ATM) for transmission of audio, video and digital images. We aimed to emulate the ambience of a classroom at three sites in the training program. We are now in the first of a four phase evaluation trial with US West. Experience with implementing a new teleconferencing system using ATM switching is described.

Computer Communication Networks↗

PubMed1991

Absence of mutagenic effects of continuous and pulsed ultrasound in cultured (AL) human-hamster hybrid cells.

Mutagenic effects of continuous and pulsed ultrasound were looked for using an in vitro assay system, the AL hybrid, that is up to 100 times more sensitive for mutagens such as x-rays and neutrons than the assays used previously to evaluate ultrasound. Cells in suspension in rotated plastic test tubes were insonated with continuous wave ultrasound at 1 MHz, ISPTP = 0.62-40 W/cm2 for 0-40 min. Cells attached in the central region of culture flasks received pulsed exposures at fc = 2.5 MHz, PRF = 1 kHz, 2 and 8 cycles per pulse, with p- = 1.2 MPa (ISPTA = 31-180 mW/cm2) for 0-30 min. Although these exposures were cytotoxic (the plating efficiency was decreased to approximately 65% by the highest doses), induction of mutation, if any occurred, was less than would be expected in this test system from 10-30 cGy of x-ray.

Animals↗

PubMed1989

Screening mammography. A risk versus risk decision.

The potential risk of a radiologic procedure often is compared with the potential benefit of the procedure. While risk vs. benefit analysis has been useful as a step toward increased communication and understanding among radiologists, referring physicians, and the general public, it has the disadvantage that risk and benefit are fundamentally different quantities. Hence, their juxtaposition for purposes of comparison presents contextual difficulties. In this article, the concept is presented of comparing the risk of doing a procedure with the risk of choosing not to do the procedure. An example of risk vs. risk analysis of screening mammography for women over the age of 50 is given, with the conclusion that the risk of having yearly mammograms is less than 1/10 the risk of early death caused by failure to diagnose breast cancer by x-ray mammography. This approach to risk analysis would yield interesting data for examinations that are part of more complicated diagnostic pathways.

Breast Neoplasms↗

PubMed1986

Health effects of low level radiation: carcinogenesis, teratogenesis, and mutagenesis.

The carcinogenic effects of radiation have been demonstrated at high dose levels. At low dose levels, such as those encountered in medical diagnosis, the magnitude of the effect is more difficult to quantify. Three reasons for this difficulty are (1) the effects in human populations are small compared with the natural incidence of cancer in the populations; (2) it is difficult to transfer results obtained in animal studies to the human experience; and (3) the effects of latency period and plateau increase the complexity of population studies. In spite of these difficulties, epidemiologic studies of human populations exposed to low levels of radiation still play a valuable role in the determination of radiation carcinogenecity. They serve to provide upper estimates of risk and to rule out the appearance of new effects that may be masked by the effects of high doses. While there is evidence for mutagenic effects of radiation in experimental animals, no conclusive human data exist at the present. It is not possible to rule out the presence of genetic effects of radiation in humans, however, because many problems exist with regard to the epidemiologic detection of small effects when the natural incidence is relatively large. In animals, subtle effects (eg, a decrease in the probability of survival from egg to adult) may occur with greater frequency than more dramatic disorders in irradiated populations. However, these types of genetic abnormalities are difficult to quantitate. Current risk estimates are based primarily upon data pertaining to dominant mutations in rodents. Some specific locus studies also permit identification of recessive mutation rates. The embryo and fetus are considered to be at greater risk for adverse effects of radiation than is the adult. This sensitivity was predicted in 1906 by the law of Bergonie and Tribondeau and has been demonstrated in human and animal populations. At high dose levels (above 15 rem), the effects of radiation depend upon the gestational stage at which irradiation occurs. Prior to the second week, the predominant effect is preimplantation death, while during the period of major organogenesis (second to sixth week), growth retardation and CNS abnormalities may be produced. These effects have not been demonstrated with a high degree of statistical significance at low dose levels (below 15 rem) and are not considered to present a serious hazard for patients undergoing radiologic exams.

Abnormalities, Radiation-Induced↗

PubMed1986

Radiation exposure risk to the surgeon during operative angiography.

Intraoperative angiography has become an essential adjunct to reconstructive vascular surgery. Therefore, radiation exposure and its potential risks to the performing surgeon need to be known. To study this, we designed experimental and clinical tests quantifying the radiation exposure to the surgeon during different intraoperative angiograms. Radiation exposure to various parts of the surgeon's body was quantified by thermoluminescence dosimetry. During each exposure a surgeon standing one foot from the x-ray tube received an absorbed dose equivalent to 0.24 to 1.4 millirems, which is about half that of an intraoperative cholangiogram. With 5 000 millirems considered the maximum permissible dose, this would imply that an upper limit of about 3 500 intraoperative angiograms each year (68 each week) could be performed safely. Comparatively, abdominal angiography carried the most significant risk (p = 0.01) and peripheral angiography was the least hazardous. Fluoroscopy increased radiation exposure more than four times that of nonfluoroscopic procedures (p = 0.05). The surgeon's extremities received the greatest dose, followed by the eyes and neck, suggesting the need for individual monitoring devices for those parts to be worn by surgeons who perform operative angiograms more frequently than average. Our study indicates that the radiation dose received by the surgeon during operative angiography, especially that of peripheral vessels, is minimal. Operative arteriography is not only a simple and readily available diagnostic tool, but it is quite a safe procedure if applied correctly.

Angiography↗

PubMed1982

Solid tumor models for the assessment of different treatment modalities. XIX. Tumor cure rates and tumor control following sequential administration of radiation and cyclophosphamide.

Tumor cure rates greater than 50% have been realized by the administration of three and four series of 1500 rads radiation and 150 mg/kg (0.9 g/m2) cyclophosphamide which were separated by 1, 7. or 11 days. Increasing the time between treatment modalities from 1 to 7 and 11 days provided a 2- to 3-week recovery period for each treatment modality without a reduction in cure rates. However, the mean time for complete response increased from 24.8 +/- 17 days for 1 day, 30.7 +/- 3.0 days for 7 days, and 38.3 +/- 4.8 days for 11 days between treatment modalities. Giving the second series of radiation and cyclophosphamide on days 16 and 17 resulted in a cure rate of 50%. Increasing this interval to 21-22 days resulted in no cures. The results of giving each modality alone at 11-day intervals have been compared with results of altering administration of the two modalities at 11-day intervals. Comparing the three regimens where a treatment was given every 11 days, the numbers of animals with cures were 0 of 10 for cyclophosphamide alone, 2 of 10 for radiation alone, and 5 of 9 for alternation of the two treatments every 11 days. Well-defined periods of accelerated growth occur between 10 and 20 days after administration of single doses of either radiation or cyclophosphamide. The increased effectiveness of alternate utilization of the two modalities suggests that prior treatment by one modality increases tumor sensitivity to the second modality.

Animals↗

PubMed1981

Solid tumor models for the assessment of different treatment modalities: XVI. Sequential combined modality (Cyclophosphamide-Radiation) therapy.

A tumor cure rate of 60% was realized when three series of combined radiation (1500 rads) and cyclophosphamide (150 mg/kg) doses were given sequentially to rats with hepatoma 3924A and the time between modalities held constant at 7 days. This sequence was previously shown to enhance tumor sensitivity and diminish host toxicity. The first series was given on days 0 and 7; second, days 14 and 21; and third, days 28 and 35. The cure rate was reduced to 10% when the time of the second series was increased from 14 to 32 days (first series, days 0 and 7; second, days 32 and 39; and third, days 63 and 70). No cures were obtained when the time of the second series of combined cyclophosphamide and radiation was further increased from 14 to 40 days; however, this treatment schedule resulted in at least a threefold increase in life span over controls of 30 +/- 1 days. Two and three single 1500 rad doses of radiation given 14 to 40 days apart produced skin changes within accepted limits of normal tissue tolerance. No major long-term hematological changes in peripheral blood and bone marrow have been demonstrated to date following two and three courses of cyclophosphamide given 14 to 40 days apart. Experimental results indicate that the frequency and dosage of cyclophosphamide and radiation used are within clinically acceptable doses and scheduling.

Animals↗

PubMed1980

Solid tumor models for the assessment of different treatment modalities. XIII. Comparison of response and recovery of host and solid tumor to cyclophosphamide and radiation.

A study of the effects of local tumor radiation alone (1500R) and cyclophosphamide alone (150 mg/kg) on the experimental solid tumor rat hepatoma 3924A has been completed. Cyclophosphamide was more effective in controlling tumor growth than either radiation or 5-fluorouracil (5-FU) (150 mg/kg) previously reported. Parallel recovery of bone marrow with increasing animal survival in "split dose" cyclophosphamide toxicity studies (as with 5-FU) indicates that bone marrow is the critical organ for sequential chemotherapy. Recovery of intestinal mucosa following cyclophosphamide (and 5-FU) occurred much earlier than recovery of bone marrow, substantiating the fact that bone marrow is the critical organ governing the time of administration of a second series of chemotherapeutic agents. The longest period of time (seven days) between delivery of radiation and administration of cyclophosphamide resulted in the most effective use of the two modalities. Tumor growth delay was 1.2 times greater than the additive effects of each agent given alone. Radiation and cyclophosphamide given at other time intervals resulted in either an additive or less than additive effect. One of the greatest difficulties to overcome in the more effective clinical use of combined modality therapy is increased toxicity. In these studies, the least host toxicity occurred when the effects of combined radiation and cyclophosphamide on the tumor were greatest. Results of experimental studies to date suggest that sequential combined modality therapy may be given at a time of maximum tumor growth rate that occurs following the previous treatment series. Since the time of maximum tumor growth rate occurs after recovery of the bone marrow from the previous treatment series, combined chemotherapy-radiotherapy schedules of this type should permit sequential administration of chemotherapeutic agents, such as 5-FU and cyclophosphamide, at the time of enhanced tumor sensitivity and diminished host toxicity.

Animals↗