Biomedical subjects

R M Gagne

Publications and source records attributed to R M Gagne.

7 recordsLinked to original sources

PubMed2001

Regulatory initiatives and framework in the USA: interventional radiology.

Therapeutic procedures using interventional radiology equipment as the imaging tool are often the only available treatment for serious, life-threatening conditions. Many of these procedures require extended periods of radiation exposure often at one location on the patient. As a result, the US Food and Drug Administration (FDA) continues to receive reports of radiation-induced injuries to the skin in patients undergoing some of these therapeutic procedures. The regulatory scheme applicable to interventional radiology equipment in the US is described including federal, state and local aspects, and the impact of professional and non-governmental organisations. Current activities within the FDA and other organisations which have or will affect the use, maintenance and manufacture of interventional radiology equipment are also described.

Equipment Safety↗

PubMed1999

Uncertainties in estimates of lesion detectability in diagnostic ultrasound.

Statistical properties of estimates of focal lesion detectability for medical ultrasonic imaging systems are investigated. Analytic forms for bias and variance of estimates of detectability of a lesion consisting of fully developed speckle embedded within a speckle background are derived. Bias and variance of estimates of detectability are investigated using a computer simulation and experiments on tissue-mimicking phantoms. This work offers a systematic methodology for interpreting measurements on phantoms in order to assess lesion detectability. In addition, it provides useful results which may be used to improve design of phantoms and experiments for imaging-system performance assessment.

Computer Simulation↗

PubMed1996

Alternative methods of obtaining the computed tomography dose index.

The most direct way of getting the value of the multiple scan average dose (MSAD) in computed tomography is to employ a pencil chamber for integration of a single scan dose profile. Because the active length of the pencil chamber is fixed, the measurement can represent the value of the MSAD from a different number of contiguous scans depending on the slice thickness. This characteristic makes it difficult to compare the value of MSAD using the pencil chamber to the information required by Federal regulations on the computed tomography dose index (CTDI). The CTDI, which is the MAD at the center of a set of 14 contiguous scans, is the dose descriptor used in the Federal Performance Standard. Two alternative methods were developed to make the CTDI measurements at the center of a CT dosimetry phantom. These alternative methods were compared to the results of thermoluminescent dosimeter (TLD) measurements from more than 20 different CT scanners. One alternative method involved the use of radio-opaque sleeves with the pencil chamber to limit the length of the single scan dose profile incident on the pencil chamber. In addition, the TLD data were also used to obtain a set of conversion factors for converting the results of a measurement with the pencil chamber without a radio-opaque sleeve to a value of the CTDI. The alternative methods of obtaining the CTDI agree on the average to better than 10% for all values of slice thickness on the different CT scanners.

Government Agencies↗

PubMed1994

Comparison of beam-hardening and K-edge filters for imaging barium and iodine during fluoroscopy.

This study investigated the dose reduction performance of several beam-hardening and K-edge filter materials for the imaging of barium or iodine during fluoroscopy. A computer model was developed to simulate the effect of added filtration on entrance exposure rate (Xp), integral dose rate (Di), contrast (C), signal to noise ratio (SNR), imaging performance per dose (SNR2/Di), and tube load. The model incorporated the response characteristics, in both manual and automatic control modes of operation, of fluoroscopic systems to increasing or decreasing x-ray intensity at the input of the image intensifier. Input parameters to the computer model included choice of filter material and thickness, a barium or iodine test object, tube potential, phantom thickness, a CsI input phosphor, and a set of algorithms for controlling the fluoroscopic system. In all cases, the performance of systems with added filtration was judged with respect to a reference system operating under comparable conditions. In general, either beam-hardening or K-edge filters provided a significant reduction in entrance exposure and integral dose rates, but with an attendant increase in tube load. For a fluoroscopic system constrained to follow a representative automatic brightness control algorithm, added filtration provided a reduction in entrance exposure and integral dose rates for all phantom or uniformly distributed barium thickness. However, the imaging performance per dose, in some cases, decreased rapidly and was less than that of the reference system at large thicknesses. Only as change in the algorithm controlling the kVcp and mA operating points on the fluoroscopic system provided an imaging performance per dose greater than the reference system's at large thicknesses. The practical implementation of adding filtration to fluoroscopic systems is most simply accomplished with beam-hardening filters rather than K-edge filters. However, the systems with K-edge added filtration can provide slightly better performance when used over a limited range of phantom thicknesses such as the range normally associated with pediatric patients.

Algorithms↗

PubMed1987

Average radiation doses in a standard head examination for 250 CT systems.

Approximately 250 computed tomography (CT) systems were surveyed in a nationwide study to determine the average radiation dose resulting from a typical adult head procedure. The multiple scan average dose (MSAD) was selected as the dose descriptor. For the typical adult CT head procedure, the MSAD was generally within 2.2-6.8 rads (22-68 mGy). Variations in dose by a factor of two or more were often seen for a given manufacturer and model. These dose ranges indicate a potential to reduce dose by carefully selecting imaging techniques. Overall, variations in dose can result from differences in the user's choice of technique (desired image quality) or from actual differences in scanner performance (caused by differences in collimation, filtration, or geometry). To use CT appropriately, a facility should consider dose as well as image quality in selecting optimal techniques for typical modes of operation.

Head↗

PubMedDate not supplied

A method for describing the doses delivered by transmission x-ray computed tomography.

A method for describing the absorbed dose delivered by x-ray transmission computed tomography (CT) is proposed which provides a means to characterize the dose resulting from CT procedures consisting of a series of adjacent scans. The dose descriptor chosen is the average dose at several locations in the imaged volume of the central scan of the series. It is shown that this average dose, as defined, for locations in the central scan of the series can be obtained from the integral of the dose profile perpendicular to the scan plane at these same locations for a single scan. This method for estimating the average dose from a CT procedure has been evaluated as a function of the number of scans in the multiple scan procedure and location in the dosimetry phantom using single scan dose profiles obtained from five different types of CT systems. For the higher dose regions in the phantoms, the multiple scan dose descriptor derived from the single scan dose profiles overestimates the multiple scan average dose by no more than 10%, provided the procedure consists of at least eight scans.

Biophysical Phenomena↗

PubMedDate not supplied

Geometrical aspects of computed tomography: sensitivity profile and exposure profile.

A simple model has been developed for the generation of theoretical sensitivity and exposure profiles perpendicular to the tomographic plane in computed x-ray tomography. The model incorporates the functional dependence on scanner geometry, focal spot size and shape, and detector sensitivity. The sensitivity and exposure profiles are best depicted as the convolution of functions, when appropriately scaled, describing the focal spot intensity distribution and the transmittance of the pre- and postpatient collimators. Predictions of the model agree well with experimental results on both sensitivity and exposure profiles for small and large nominal slice thicknesses from five different computed tomography (CT) x-ray systems. The CT x-ray systems selected represent both state of the art and older scanner models. Comparisons are also made on the degree of matching of the sensitivity and exposure profiles for each scanner which can be used as a measure of geometrical efficiency in the direction perpendicular to the tomographic plane.

Humans↗