David B. Washburn

Diffraction enhanced x-ray imaging

Diffraction enhanced imaging is a new x-ray radiographic imaging modality using monochromatic x-rays from a synchrotron which produces images of thick absorbing objects that are almost completely free of scatter. They show dramatically improved contrast over standard imaging applied to the same phantom. The contrast is based not only on attenuation but also the refraction and diffraction properties of the sample. This imaging method may improve image quality for medical applications, industrial radiography for non-destructive testing and x-ray computed tomography.

Medical applications of diffraction enhanced imaging.

We have developed a new X-ray imaging technique, diffraction enhanced imaging (DEI), which can be used to independently visualize the refraction and absorption of an object. The images are almost completely scatter-free, allowing enhanced contrast of objects that develop small angle scattering. The combination of these properties has resulted in images of mammography phantoms and tissues that have dramatically improved contrast over standard imaging techniques. This technique potentially is applicable to mammography and other fields of medical X-ray imaging and to radiology in general, as well as possible use in nondestructive testing and X-ray computed tomography. Images of various tissues and materials are presented to demonstrate the wide applicability of this technique to medical and biological imaging.

The effect of rare earth filtration on patient exposure, dose reduction, and image quality in oral panoramic radiology

Rare earth intensifying screen material (Gd2O2S:Tb) was added to the standard Al filtration of an oral panoramic x-ray unit, resulting in a beam capable of achieving reductions in patient dose without a loss of image quality. The added rare earth filtration technique resulted in patient dose reductions of 21-56%, depending on anatomic sites, when compared to the conventional Al filtration technique. Films generated from both techniques were measured densitometrically and evaluated by a panel of practicing clinicians. Diagnostically significant differences were minimal. The results indicate that use of rare earth filters in oral panoramic radiography is an effective means of reducing exposures of dental patients to ionizing radiation.

Parameter optimization and calibration of 19F magnetic resonance imaging at 1.5 tesla

Fluorine-19 magnetic resonance imaging is limited by the fact that acquisition times are long and that high concentrations must be used in order to obtain good signal to noise. A significant improvement in signal to noise ratio may be brought about by the addition of Gd-DTPA, a paramagnetic agent which shortens T1. Images of phantoms containing trifluoroacetic acid (TFA) doped with Gd-DTPA were obtained using a standard spin echo sequence in a 1.5 T field. Interpulse times (TR and TE) and Gd-DTPA concentrations were optimized to yield maximum signal to noise ratios. The use of fast-field-echo scans to image fluorine is also demonstrated. Signal averaging successive FFE scans yields good signal to noise and resolution and may find clinical applicability in imaging areas subject to motion.

Efficacy and Feasibility of Breast Shielding during Abdominal Fluoroscopic Examinations

RATIONALE AND OBJECTIVES The purpose was to measure radiation exposure to the breasts during abdominal fluoroscopic examinations and evaluate the efficacy of breast shielding with a leaded vest. MATERIALS AND METHODS Sixty-six women underwent routine abdominal fluoroscopic examinations. During the examinations one breast was covered with a leaded shield. Radiation doses to both breasts were measured with a thermoluminescent dosimeter. The amount of radiation at the skin of the shielded breast was then compared with that at the skin of the nonshielded breast. RESULTS Radiation exposure to the breasts varied substantially with the type of examination being performed and with the individual patient. The average radiation level at the skin of the unshielded breast was 119 mR (range, 0-6,320 mR), compared with 59.6 mR (range, 0-1,640 mR) at the shielded breast. The average reduction in radiation exposure was 50% with shielding. CONCLUSION Although the average level of radiation exposure to the breast during abdominal fluoroscopic examinations is generally low, use of a leaded vest can further reduce radiation to the breast for different types of examinations.

Preliminary experience with monoenergetic photon mammography

We are using a beam port at the National Synchrotron Light Source Facility at Brookhaven National Laboratory as a source of monoenergetic photons. The photon source is radiation from a bending magnet on the x-ray storage ring and provides a usable x-ray spectrum from 5 keV to over 50 keV. A tunable crystal monochromotor is used for energy selection. The beam is 79 mm wide and 0.5 mm high. We imaged the ACR mammography phantom and a contrast-detail phantom using a phosphor plate as the imaging detector. Phantom images were obtained at 16, 18, 20, and 22 keV. Phantom thickness varied from 15 mm to 82 mm. These images were compared to images obtained with a conventional dedicated mammography unit. Subjective preliminary results show that image contrast of the monoenergetic images is similar to those obtained from the conventional x-ray source with somewhat sharper and cleaner images from the monoenergetic source. Quantitative analysis shows that the monoenergetic images have improved contrast compared to the polyenergetic derived images. Entrance skin dose measurements show a factor of 5 to 10 times less radiation for the monoenergetic images with equivalent or better contrast. Although there remain a number of technical problems to be addressed and much more work to be done, we are encouraged to further explore the use of monoenergetic imaging.

Educational outreach to mammography facility staff to assist with compliance with the mammography quality standards act in rural North Carolina

RATIONALE AND OBJECTIVES The purpose of this project was to develop and evaluate an educational program targeted at mammography facilities in rural areas of North Carolina that were having difficulty complying with the 1992 Mammography Quality Standards Act (MQSA). MATERIALS AND METHODS Fourteen facilities deemed at risk for closure under MQSA were identified by state inspection personnel. Problems at the facilities were evaluated by a radiologist, a physicist-educator, and a radiation physicist through a written survey, review of phantom and clinical images, and a site visit. Individual advice and instruction were provided on-site by the physicist-educator, with written materials provided in follow-up. A repeat site visit was made 4-6 months after the initial visit. RESULTS Of 51 problems identified at the 12 institutions that completed the program, 35 (69%) were corrected. All facilities that had failing phantom scores at the inspection prior to the intervention had passing scores at the inspection after the intervention. There was a statistically significant increase in the sum of the phantom scores for the facilities offered this intervention compared with those not offered it (P = .03). CONCLUSION This educational program improved mammography quality at participating facilities.

Effects of processing conditions on mammographic image quality

RATIONALE AND OBJECTIVES Any given mammographic film will exhibit changes in sensitometric response and image resolution as processing variables are altered. Developer type, immersion time, and temperature have been shown to affect the contrast of the mammographic image and thus lesion visibility. The authors evaluated the effect of altering processing variables, including film type, developer type, and immersion time, on the visibility of masses, fibrils, and speaks in a standard mammographic phantom. MATERIALS AND METHODS Images of a phantom obtained with two screen types (Kodak Min-R and Fuji) and five film types (Kodak Min-R M, Min-R E, Min-R H; Fuji UM-MA HC, and DuPont Microvision-C) were processed with five different developer chemicals (Autex SE, DuPont HSD, Kodak RP, Picker 3-7-90, and White Mountain) at four different immersion times (24, 30, 36, and 46 seconds). Processor chemical activity was monitored with sensitometric strips, and developer temperatures were continuously measured. The film images were reviewed by two board-certified radiologists and two physicists with expertise in mammography quality control and were scored based on the visibility of calcifications, masses, and fibrils. RESULTS Although the differences in the absolute scores were not large, the Kodak Min-R M and Fuji films exhibited the highest scores, and images developed in White Mountain and Autex chemicals exhibited the highest scores. CONCLUSION For any film, several processing chemicals may be used to produce images of similar quality. Extended processing may no longer be necessary.

Monochromatic beam mammography studies using synchrotron radiation (abstract)

Preliminary experiments have been carried out on the X27C R&D beamline at the National Synchrotron Light Source (NSLS) to explore the potential improvement in contrast in breast imaging using monochromatic synchrotron x‐rays [R. E. Johnson et al., SPIE (1995) (to be published)]. In our present study, images have been obtained of ACR, contrast detail and anthropomorphic phantoms at 16 to 24 keV. Phantom thickness varied from 42 to 80 mm. Synchrotron images using a Fuji image plate detector and standard mammographic film have been compared to each other and with conventionally produced images. The preliminary results show an improved contrast over the conventional images with lower absorbed dose in the phantoms. The image plate detector was used for our fist experiments because it was readily available and produces digital data. Experiments using an additional analyzer crystal as a scatter rejection element are also underway at the NSLS [D. Chapman, SRI ‘95 (these proceedings)]. We plan to evaluate a variet...