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Systemic lupus erythematosus patients are frequently evaluated for chest pain and may have multiple pulmonary embolism (PE) computed tomography (CT) scans. This study was undertaken to determine the incidence of pulmonary embolism in the University of Michigan Lupus Cohort patients who have undergone PE CT scans and to estimate the associated increased risk of breast and lung cancer from radiation exposure. We reviewed records of patients in the University of Michigan Lupus Cohort (n = 854) and determined the number and outcome of PE CT scans. Radimetrics software was used to perform individualized calculations of radiation dose to the lung and breast of each patient. We used this dose information, the patient's age at the time of scan, and risks according to the Biological Effects of Ionizing Radiation, report VII, to estimate the increased incidence risks of breast and lung cancer. A total of 182 of 856 patients (21%) underwent 357 PE CT scans. The overall rate of positivity was 7.5%. For patients undergoing their first through third scans, the rate of positivity for PE was 8.8%, whereas patients undergoing their fourth through tenth scans had 1.6% positivity. The highest increase in incidence risk was 0.87% for breast and 0.62% for lung. Patients with multiple previous PE CT scans had lower likelihood of a positive result on subsequent scans and higher risks of malignancy. The magnitude of risk should not discourage performance of PE CT when clinically indicated.

The objective of the study was to estimate the increased lifetime cancer risk associated with a single computed tomography (CT) examination for calculus detection in pediatric patients and compare it with the lifetime natural cancer risk.

This paper describes work aimed at combining 3D ultrasound with full-field digital mammography via a semi-automatic prototype ultrasound scanning mechanism attached to the digital mammography system gantry. Initial efforts to obtain high x-ray and ultrasound image quality through a compression paddle are proving successful. Registration between the x-ray mammogram and ultrasound image volumes is quite promising when the breast is stably compressed. This prototype system takes advantage of many synergies between the co-registered digital mammography and pulse-echo ultrasound image data used for breast cancer detection and diagnosis. In addition, innovative combinations of advanced US and X-ray applications are being implemented and tested along with the basic modes. The basic and advanced applications are those that should provide relatively independent information about the breast tissues. Advanced applications include x-ray tomosynthesis, for 3D delineation of mammographic structures, and non-linear elasticity and 3D color flow imaging by ultrasound, for mechanical and physiological information unavailable from conventional, non-contrast x-ray and ultrasound imaging.

When modeling or simulating an ultrasonic pulse-echo system it is necessary to know the transducer waveforms that are the input to the system. In general, accurate transducer modeling is complex and waveform calculation is computationally intensive. Because of this, investigators often assume these waveforms to be simple sinusoids, modulated by Gaussian or exponential envelopes. However, these latter type pulses do not properly represent the complex resoponse of modern piezoelectric transducers. In this paper, a simple set of equations is presented which can approximate the behavior of a number of common transducer configurations. In the first step of the procedure, a simple but accurate model is employed to calculate the step responses of quarter-wave-matched and backed piezoelectric transducers, assuming open circuit conditions. Effects of electrical terminations and transmit/receive bandwidth limitations are accounted for, approximately, by cascaded filtering. Emitted pressure waveforms and echo voltage waveforms synthesized by this simple procedure are very similar to measured waveforms from real transducers. Under most conditions, the method is only an approximation because the model erroneously assumes isolation between the electrical and acoustic networks. However, under many conditions the model is sufficiently accurate to predict actual transducer performance.

This paper reports the development of an improved three-dimensional computer simulation model for evaluation of ultrasonic imaging systems. This model was used to successfully evaluate a signal processing method for improving lesion detection in ultrasound imaging. Linear processing of the rf signal amplitudes from a limited region of tissue was compared with the logarithmic compression employed by most commercial scanners. Two lesions were simulated by spherical distributions of scatterers having backscatter coefficients greater than the scatterers in the surrounding medium. Linear processing improved the differential contrast by a factor of about two.The simulation is based on the three-dimensional distribution of acoustic frequency spectra in a transducer beam and integration of scattered pulses from a corresponding three-dimensional array of scatterers. The simulation reported in previous papers depended upon physical measurement of the impulse response of a transducer. An original contribution described briefly herein, and in more detail in a companion article, is the addition of a model of the transducer's pulse waveform generation. Another new addition is the definition of a specific lesion detection task for objective assessment of a change in image quality following perturbation of some system parameter.

A three-dimensional model for production of gray scale texture in ultrasound B-mode images is described. The model computes time-dependent echo signals resulting from scattering of acoustic pulses by particles randomly distributed in an attenuating medium and transforms these signals into a gray scale image. Specific transducer and pulser-receiver characteristics are accounted for, as well as the three-dimensional nature of the problem, without loss of computational efficiency. The model generates texture that closely corresponds to that found experimentally in ultrasound images of tissue-mimicking phantoms. The dependence of the texture upon the depth of the region that was scanned and on the characteristics of the transducer-receiver system were clearly demonstrated. Good agreement between theory and experiment was found for the texture in phantoms containing simulated spherical low-scatter tumors.

Although conventional dual photon absorptiometry (DPA) techniques can be used to estimate fat and soft tissue content, such estimates are not possible where bone is present. We propose a method that can make these estimates in the presence of bone in the extremities of the body. The combination of this method with the conventional method should yield fat and soft tissue composition from most points within the body. The proposed technique simultaneously measures thicknesses of bone, soft tissue, and fat. These thicknesses are determined from a combination of gamma-ray transmission data at two energies and a measurement of total tissue thickness. To test the technique, a feasibility study was performed with known thicknesses of aluminum (simulating bone), lucite (simulating tissue), and polyethylene (simulating fat). A variety of thicknesses of each material were employed (Al 0-1.3cm, lucite 0-5cm, polyethylene 0-5cm). The accuracies (standard errors of the estimates) of the calculated versus true thicknesses of aluminum, lucite, and polyethylene were 0.6, 2.6, and 2.5, respectively. The estimates of “bone” thickness were insensitive to the presence of varying thicknesses of “fat.” (In contrast, application of the conventional DPA method to the same gamma-ray transmission data yielded underestimates in “bone” thickness due to “fat” by as much as 11.) For a 60 minute (whole body) scan time, the reproducibility of the From the Department of Radiology, University of Washington, Seattle, Washington. Reprint requests Mitchell M. Goodsitt, Ph.D., Department of Radiology, SB-05, University of Washington, Seattle, WA 98195. Received January 16, 1989, and accepted for publication, after revision, May 25, 1989. measurements of the thicknesses of aluminum, lucite, and polyethylene were 0.4, 1.0, and 1.3, respectively. All of these values are in a clinically useful range. Precision could be further improved by replacing the DPA system with a high output dual photon x-ray absorptiometry system.

Two dual-energy CT techniques have been developed to analyze the mineral and fat content of trabecular bone. Both are postprocessing techniques that employ calibration standards. Experiments were performed to test these techniques against conventional single-energy techniques and two other dual-energy techniques. As expected, all of the dual-energy methods estimate the mineral content more accurately when fat is present. In contrast to the other dual-energy methods, the new methods described in this article are unique because they make a separate estimate of the fat content of the bone. The results of preliminary tests of these techniques in estimating fat content have been encouraging. Although not exact, the estimates show the correct trend in increasing proportionately as the fat content increases. Possible applications of the techniques in the study of osteoporosis and other bone diseases are described.

An investigation was performed to determine whether the sound-attenuation-in-suspensions theory of Allegra and Hawley can be used to explain the compressional (longitudinal wave) attenuation of ultrasonically tissue-mimicking materials commonly used in phantoms for testing the performance of medical ultrasound systems. These materials are composed of microscopic graphite particles suspended in a gel. The theory was first tested using materials containing spherical glass beads instead of graphite particles because these materials more closely fit the geometric conditions assumed in the theory. For the glass bead type materials as well as the graphite particle type materials, the attenuation coefficients predicted using the Allegra and Hawley model agreed rather well with experimental measurements over the diagnostic frequency range.

Quantitative CT (QCT) has become a popular method for estimating bone mineral content. In addition, QCT can be used to estimate the fat content of trabecular bone. Although the latter has received little attention, it may prove to be clinically significant. Using a set of custom-built, tissue-mimicking plastic inserts in an anthropomorphic phantom, we tested a variety of methods for estimating mineral and fat content. We also investigated the influence of patient size, reconstruction circle size, and reference phantom choice on the accuracy of the results. Best estimates were obtained when there was a match between patient and reconstruction circle size. Single-energy methods yielded the best estimates of mineral content for inserts that did not contain fat, and dualenergy methods yielded the best estimates for inserts that contained fat. A dual-energy method that we developed was best in estimating the mineral and fat content of the latter inserts. We found that an external calibration reference phantom containing aqueous solutions of K2HPO4could be used satisfactorily to estimate the mineral content of trabecular bone mimicking inserts; however, more representative materials must be used for accurate estimates of fat content.

The authors have been developing a dual-energy quantitative computed tomography (DEQCT) technique that requires calibration standards that mimic the x-ray attenuation properties of bone, red marrow, and yellow marrow. To resolve questions regarding the compositions of red and yellow marrow that appear in the literature, the authors performed chemical analyses of bone marrow samples. The newly derived compositions were used in a simulation study to test the accuracy of the DEQCT technique.

Two dual-energy X-ray absorptiometry (DEXA) systems—the Hologic QDR-1000 and the Norland XR-26 bone densitometers—were evaluated in terms of precision, accuracy, linearity of response, X-ray exposure, and correlation of in vivo spinal measurements. In vitro precision and accuracy studies were performed using the Hologic anthropomorphic spine phantom; linearity of response was determined with increasing thicknesses of aluminum slabs and concentrations of Tums E-X in a constant-level water bath. Both systems were comparable in precision, achieving coefficients of variation (CVs) of less than 1% in bone mineral content (BMC, g), bone area (cm2), and bone mineral density (BMD, g/cm2). Both were accurate in their determination of BMC, bone area, and BMD with reference to the Hologic spine phantom. Both systems also showed good BMC and BMD linearity of response. Measured X-ray skin surface exposures for the Hologic and the Norland systems were 3.11 and 3.02 mR, respectively. In vivo spinal measurements (n=65) on the systems were highly correlated (BMC: r=0.993, SEE=1.770 g; area: r=0.984, SEE=1.713 cm2; BMD: r=0.990, SEE=0.028 g/cm2). In conclusion, both systems are comparable in terms of precision, accuracy, linearity of response, and exposure efficiency.

Dual energy CT and quantitative magnetic resonance (MR) imaging were used to evaluate marrow changes due to radiation. The bright signal intensity seen on MR was shown by the two quantitative techniques to be due to a threefold increase in the marrow fat content compared with nonradiated levels and to a normal control. Fat estimates by MR and dual energy CT were in excellent agreement. Single energy CT overestimates the amount of bone loss in the radiation field. Dual energy CT and quantitative MR can be used to correct this error.

A phantom was designed and constructed for in vitro studies of gallstones using a computed tomographic (CT) scanner. A primary objective of the design was to permit studies of multiple gallstones in a single CT slice. This was accomplished by incorporating in the phantom removable compartments that contain vertically oriented, cone-shaped voids for holding the gallstones and surrounding fluid medium. A slice through the center of the phantom passes through the apex of each coneshaped holder, and hence through the center of each gallstone. The main body of the phantom is made of water-mimicking plastic, and each compartment can accommodate gallstones ranging up to 3 cm in diameter. Initial experience with the phantom has shown it to be a successful design.

Digital breast tomosynthesis (DBT) has been shown to increase mass detection. Detection of microcalcifications in DBT is challenging because of the small, subtle signals to be searched in the large breast volume and the noise in the reconstructed volume. We developed an adaptive diffusion (AD) regularization method that can differentially regularize noise and potential signal regions during reconstruction based on local contrast-to-noise ratio (CNR) information. This method adaptively applies different degrees of regularity to signal and noise regions, as guided by a CNR map for each DBT slice within the image volume, such that potential signals will be preserved while noise is suppressed. DBT scans of an American College of Radiology phantom and the breast of a subject with biopsy-proven calcifications were acquired with a GE prototype DBT system at 21 angles in 3° increments over a ±30° range. Simultaneous algebraic reconstruction technique (SART) was used for DBT reconstruction. The AD regularization method was compared to the non-convex total p-variation (TpV) method and SART with no regularization (NR) in terms of the CNR and the full width at half maximum (FWHM) of the central gray-level line profile in the focal plane of a calcification. The results demonstrated that the SART regularized by the AD method enhanced the CNR and preserved the sharpness of microcalcifications compared to reconstruction without regularization. The AD regularization was superior to the TpV method for subtle microcalcifications in terms of the CNR while the FWHM was comparable. The AD regularized reconstruction has the potential to improve the CNR of microcalcifications in DBT for human or machine detection.