Determination of blood flow to the transplanted kidney. A novel application of phase-contrast, cine magnetic resonance imaging.

There is at present no noninvasive method that reliably measures blood flow in the poorly functioning renal allograft. The present study was designed to evaluate phase-contrast cine magnetic resonance imaging (PC-cine-MRI) for this purpose. We recruited for study 18 patients who had received kidney transplants 13-66 months earlier from closely related living donors. As judged by the glomerular filtration rate, which was elevated for a single kidney (76 +/- 4 ml/min 1.73 m2), allograft function was excellent, permitting the assumption of unimpaired renal extraction of paminohippuric acid (PAH). Allograft blood flow was determined consecutively on the same day, first by the standard PAH clearance technique and they by the product of the velocity of protons and renal vein cross-sectional area using PC-cine-MRI. MRI determinations could not be completed because of claustrophobia in two patients and failure to image the terminus of the allograft vein another two. Comparison of blood flow in the remaining 14 subjects revealed the two techniques to be strongly related (r = 0.91, P < 0.001). On the average, the renal blood flow rate was similar by each method; 732 +/- 62 by PAH clearance and 703 +/- 69 ml/min by PC-cine-MRI, but the agreement among individuals between the two methods was only modest, with a 95% confidence interval of agreement from -214 to +254 ml/min. We conclude that PC-cine-MRI provides a fairly accurate and noninvasive method for determining the rate of blood flow in the transplanted kidney. With further refinement it should permit the role of depressed blood flow in a variety of acute and chronic forms of human allograft dysfunction to be elucidated in humans for the first time.

Dual-energy scanned projection radiography of osseous metastatic disease.

Dual-energy scanned projection radiography was used to evaluate eight patients with both lytic and blastic metastatic disease in the axial skeleton. The ability to selectively cancel obscuring soft-tissue structures from images resulted in improved conspicuity of involved sites, compared with conventional radiographic studies, despite greater quantum noise and lower inherent spatial resolution. Other desirable features of the technique include a projected format, image enhancement by contrast and brightness optimization, rapid data acquisition, convenient image storage and retrieval, and low radiation dose. Since the majority of osseous metastases involve axial sites, dual-energy scanned projection radiography may be a useful adjunctive modality in the management of oncology patients.

Dual-energy projection radiography in the evaluation of femoral neck strength, density, and mineralization.

Two different dual-energy projection radiography techniques were utilized in an attempt to predict femoral neck strength, bone density, and bone mineral content in 19 pairs of cadaver specimens. Positive simple linear correlation was observed between dual-energy scanned projection measurements and dry density, ash fraction, cross-sectional cortical bone area and, to a lesser degree, force required for fracture, but not trabecular bone volume, failure time, or Singh trabecular grade. Dual-energy film radiography was found to be a less reliable indicator of femoral neck strength, density, and mineral content. Dual-energy scanned projection results related linearly to mineral-equivalent solution (K2HPO4) concentration, and demonstrated long-term reproducibility in repeated specimen studies. Correction factors derived to account for differences in femoral size and rotation were shown to be reliable over a moderate range of neck projections. Although bone mineral measurement at other sites may provide comparable or greater information concerning hip fracture risk, dual-energy scanned projection radiography appears to be a useful technique for assessment of bone density, mineral content, and strength in the femoral neck.

Heavy-ion radiography: density resolution and specimen radiography.

Heavy-ion radiography is performed by the passage of a beam of nuclei accelerated to energies of several hundred MeV/nucleon through an object. The technique of recording transmitted nuclei in a downstream stack of plastic sheets affords excellent resolution of density by recording the nuclei only at their stopping points. Imaging of a phantom--which stimulated tumors of low density contrast in a body part--by conventional radiography, computed tomographic scanning and the heavy-ion technique indicated superior density resolution for heavy-ion imaging at radiation dose. Superior imaging of tumors in pathologic specimens was demonstrated for heavy-ion imaging compared to conventional radiography. Values of stopping power for various tumors and normal tissues were determined by a computer-aided technique. Heavy-ion radiography shows promise for superior imaging of low contrast tumors at relatively low radiation low levels.

Transient cavitation in tissues during ultrasonically induced hyperthermia.

An isospherical array of ultrasonic transducers designed for hyperthermia treatment of malignant tumors in humans was employed in studies of transient cavitation in tissues during ultrasonic heating. Both in vitro and in vivo studies revealed the presence of transient cavitation within tissues during ultrasonic heating, as indicated by the detection of the first half-order subharmonic of insonifying ultrasound with an interrogating transducer. The applied power to the focal region of the array required to exceed cavitation thresholds in tissue was 75 +/- 8 W/cm2, a level considerably higher than that required to heat tissues to the temperature range used for cancer treatment (43-45 degrees C).

Tissue ablation using an acoustic waveguide for high-intensity focused ultrasound.

High-intensity focused ultrasound (HIFU) has been shown capable of selective tissue destruction in humans, with promise as a tool for ablation of tumors, although one practical problem is reflection of sound at gas or bony interfaces within the body. We evaluated a water-filled cylindrical metal tube as a waveguide for HIFU, since such a general technique might be useful for ablation of otherwise inaccessible tumors in the body. Our studies indicate that such a waveguide is capable of propagating HIFU from a piezoelectric source, with resultant heating of tissue specimens to greater than 80 degrees C, causing focal tissue destruction.

Preliminary evaluation of display format effects on perceptibility in a low contrast ultrasound test object.

A phantom consisting of a gel closely resembling human liver on B-mode scanning, and containing a rounded zone of decreased echogenicity, was used to create a series of B-mode ultrasonic images containing simulated "lesions" in random locations on the final recorded image. A homogeneous gel phantom was used to create a series of blank images. Images were recorded in three display formats: conventional white on black background, conventional black on white background, and black on a white background with luminance normalized to that of the conventional white on black image. Six subjects were presented with a randomized series of scans in the 3 display formats, and receiver operating characteristic analysis was used to assess the effect of display format on low-contrast detectability. Detectability of low-contrast "lesions" was lower in a high contrast image with black on white background compared to the medium contrast image in white on black format. Detectability with the black on white format having normalized luminance was generally intermediate between that observed for the two conventional formats.

Envelope amplitude analysis following narrow-band filtering: a technique for ultrasonic tissue characterization.

Ultrasonic waveforms backscattered from tissue simulating phantoms and from normal and cirrhotic human livers in vivo were digitized to a standard dynamic range prior to envelope detection and determination of envelope amplitude distributions. For 11 individual narrow-band Gaussian-shaped filters of -6 dB bandwidth 200 kHz, and of center frequencies from 2 to 4 MHz, envelope amplitude distributions were plotted and mean values of the values distributions computed. Analysis of data was performed for data from a phantom containing only relatively small graphite scatters (less than 170 mu), and a similar phantom to which glass spheres 0.5 mm in diameter had been added homogeneously. For lower center frequency narrow-band filters, significantly more high-amplitude occurrences were observed for data from the phantom to which glass spheres had been added. Higher center frequency narrow-band filters gave significantly more high-amplitude occurrences for the phantom containing only small scatters. Similar data analysis was performed for in vivo human liver data from ten normal subjects and five patients with known cirrhosis of the liver. For the cirrhotic and normal livers, data analysis using narrow-band filters of relatively low center frequency resulted in more high- amplitude occurrences for cirrhotic, compared to normal liver; the converse was true for narrow-band filtration at relatively high center frequencies. Determination of mean amplitude following narrow-band filtration with a filter centered at 3.4 MHz was found to be quite repeatable for the normal and cirrhotic liver data; analysis of variance showed the measurement was 94.1% a function of the subject examined, and 5.9% related to the data acquisition session.(ABSTRACT TRUNCATED AT 250 WORDS)

Lesion contrast enhancement in medical ultrasound imaging.

Methods for improving the contrast-to-noise ratio (CNR) of low-contrast lesions in medical ultrasound imaging are described. Differences in the frequency spectra and amplitude distributions of the lesion and its surroundings can be used to increase the CNR of the lesion relative to the background. Automated graylevel mapping is used in combination with a contrast-weighted form of frequency-diversity speckle reduction. In clinical studies, the techniques have yielded mean CNR improvements of 3.2 dB above ordinary frequency-diversity imaging and 5.6 dB over sharper conventional images, with no post-processing graylevel mapping.

Gadolinium-enhanced MRI of the abnormal prostate.

A prospective study of the use of a low osmolar gadolinium-based intravenous contrast material for MRI of the abnormal prostate was performed. Eight patients scheduled for prostatectomy, six with prostate cancer and two with benign prostatic hyperplasia (BPH), were imaged preoperatively on a 1.5 T system using a pelvic coil array and employing Gadodiamide (0.3 mmol/kg). T2-weighted fast-spin echo (FSE) imaging was also performed in the same axial planes employed for gadolinium-enhanced studies. Detailed pathologic correlation was performed for the six patients with carcinoma. While regions of BPH and cancer enhanced to a similar degree following intravenous contrast agent, BPH enhancement was more heterogeneous than cancer. No advantages in detecting prostate cancer, in differentiating cancer from BPH or normal prostatic tissue, or in assessing extra-prostatic spread of cancer were observed for the contrast-enhanced studies compared to T2-weighted FSE imaging.

Unenhanced CT in the evaluation of urinary calculi: application of advanced computer methods.

Recent advances in computer hardware and software technology enable radiologists to examine tissues and structures using three-dimensional figures constructed from the multiple planar images acquired during a spiral CT examination. Three-dimensional CT techniques permit the linear dimensions of renal calculi to be determined along all three coordinate axes with a high degree of accuracy and enable direct volumetric analysis of calculi, yielding information that is not available from any other diagnostic modality. Additionally, three-dimensional techniques can help to identify and localize calculi in patients with suspected urinary colic.

Evaluation of gynecologic pelvic masses by ultrasound and computed tomography.

In a prospective study, computed tomography (CT) and ultrasound scanning of the pelvis were performed for 50 patients having clinically suspected pelvic masses or recurrence of known pelvic malignancy. On the basis of these scan images, an attempt was made to characterize pelvic masses on the basis of benign or malignant character and organ of origin. The presence of recurrent tumor in patients previously treated for pelvic malignancy was assessed, and the presence of abdominal metastatic disease was evaluated for all patients. CT was successful in a higher proportion of cases in detecting abdominal metastatic disease due to bowel gas's degrading the abdominal ultrasound scan images. In characterizing suspected pelvic masses and evaluating the presence of recurrent tumor, both CT and ultrasound scanning were accurate in approximately two-thirds of cases. The significant proportion of incorrect results indicates that neither technique is sufficiently accurate to preclude pathologic diagnosis of a pelvic mass or to substitute for exploratory surgery to assess recurrence of pelvic malignancy.

MRI of radiation-induced prostate sarcoma.

A patient with a history of pelvic radiation therapy for seminoma presented with a prostatic tumor, which appeared predominantly of high signal intensity on T2-weighted magnetic resonance images; low-signal-intensity tissue also extended to the pelvic sidewall. At surgical pathology, the tumor was determined to be radiation-induced sarcoma of the prostate, and the extraprostatic tissue was postradiation fibrosis.

Stochastic frequency-domain tissue characterization: application to human spleens "in vivo'.

Ultrasonic waveforms backscattered from normal and pathologic human spleens were recorded in vivo using a high-speed digital data acquisition system. A frequency-domain analysis was performed for 50 digitized waveforms from each spleen, in which autocorrelations of frequency spectra were employed to measure the mean spacing among adjacent tissue scatterers. Mean scatterer spacing for normal spleens averaged 1.10 +/- 0.14 mm, whereas abnormal, diffusely of these measurements are in accord with those expected from splenic histology. The techniques described may be valuable in ultrasonic diagnosis of the spleen and other organs.

Some applications for a personal computer data-base system in radiology.

Applications for a personal-computer-based relational data-base system in an academic radiologist's office are described. These include archival and flexible retrieval of desired cases from clinical-case and teaching-file data bases and data-base management of a transparency-slide collection and radiology journal articles. All applications were implemented by using commercially available software that was specially adapted for each purpose. These data-base systems have been effective organizing tools over the past 4 years.

Differentiation of acoustic shadowing due to calculi and gas collections.

In abdominal sonography, acoustic shadowing may be seen distal either to calculi or gas collections. This in vitro study suggests that acoustic shadows distal to calculi contain significantly fewer echoes, and are therefore more sharply defined than those distal to gas collections. Artifactual reverberation echoes within acoustic shadows distal to gas collections result from virtually total sound reflection at tissue-air interfaces, whereas shadows distal to calculi are primarily due to sound absorption. The appearances of shadowing distal to calculi or gas collections may be of value in clinical sonography.

Follow-up sonography in suspected acalculous cholecystitis: preliminary clinical experience.

Fourteen adult patients with clinically suspected AAC and inconclusive initial sonograms underwent follow-up sonography within 24 hours. Eight patients had initial studies demonstrating a normal thickness of the gallbladder wall. Four of these patients demonstrated progressive thickening of the gallbladder wall on follow-up scans and were diagnosed as having AAC. In three of these patients AAC was proved at surgery, and the remaining patient improved clinically after percutaneous cholecystostomy. Four other patients with normal gallbladder wall thickness on both the initial and follow-up sonograms had benign clinical follow-up results without evidence of AAC. The remaining six patients had a thickened gallbladder on the initial sonogram. In one of these patients, the gallbladder wall thickening resolved on follow-up sonography. In the remaining five patients the gallbladder wall thickening did not change. Four of these patients had benign follow-up results but one patient was found to have AAC at surgery. Follow-up sonography may be helpful to confirm AAC if there is progressive edema of the gallbladder wall. A normal gallbladder wall on an initial study does not exclude early AAC. Thickening of the gallbladder wall on initial studies still remains a problem and other ancillary criteria must be used to establish the diagnosis of AAC.

Contrast resolution of line-scanned digital radiography.

Contrast resolution of a prototype system for line-scanned digital radiography was evaluated using a phantom simulating low contrast tumors within the body. Simulated tumors having radiographic contrast as low as 0.5% were detectable in these studies. The results of these digital radiographic studies compare favorably to those of computed tomography in terms of both low contrast detectability and radiation dosage. Dual energy projection radiographic techniques show promise for eliminating obscuring shadows caused by overlying structures from digital radiographs, thus permitting clinical utilization of the excellent contrast resolution of the line scanned projection system.

Image processing to reduce ultrasonic speckle.

The most significant source of noise in contemporary ultrasonic images is ultrasonic speckle, a phenomenon relating to random interference of ultrasonic waveforms in transducer sample volumes. Averaging of a number of ultrasonic images, which are slightly spatially shifted with respect to one another, leads to image improvement via speckle reduction. Such processing may provide a useful improvement of clinical ultrasonic images.