Acute Gouty Knee Arthritis: Ultrasound Findings Compared With Dual-Energy CT Findings.

OBJECTIVE: The purpose of this study was to compare findings of ultrasound (US) with dual-energy CT (DECT) findings in patients presenting with suspected gouty knee arthritis. SUBJECTS AND METHODS: This prospective study included 65 patients (52 men and 13 women; median age, 61.7 years [range, 38-87 years]) with an initial clinical diagnosis of acute gouty knee arthritis who underwent DECT performed using a 128-MDCT scanner and US performed using a 5-18-MHz transducer. Both intra- and extraarticular findings obtained using each modality were tabulated. RESULTS: DECT identified gout as the final diagnosis for 52 of 65 patients (80.0%). An alternative diagnosis was confirmed for the remaining 13 patients. US detected gout in 31 of 52 patients (sensitivity, 59.6%) and produced findings negative for gout in seven of 13 patients (specificity, 53.8%). The double contour sign on US was positive for gout in 23 of 52 patients (44.2%) and negative in 12 of 13 patients (92.3%). Extraarticular urate deposition was identified by DECT in 44 of 52 patients, compared with identification by US in 11 of 52 patients (p < 0.001). CONCLUSION: The sensitivity of US for the diagnosis of gouty knee arthritis is limited, particularly with respect to extraarticular urate deposition. The double contour sign is the single most valuable sign for the assessment of gouty knee arthritis by US.

[Ultrasound contrast agents and prostate cancer]. / Ultraschallkontrastmittel und Prostatakarzinom.

Prostatic carcinoma is the most frequent malignant disease in men and associated with very high mortality. The diagnostic work-up of prostatic carcinoma is based on tests to determine the level of prostate-specific antigen (PSA), digital rectal examination, and transrectal sonography. Due to diagnostic limitations, ultrasound-guided prostate biopsy is the method of choice for diagnosis of prostatic carcinoma. New imaging technologies allow detection of prostatic carcinoma, thus facilitating removal of specific biopsy specimens from these regions. Introduction of ultrasound contrast agents ("echo signal enhancers") significantly increased the diagnostic potential of this method, making it possible to visualize tumor vascularization.

Vascular damage induced by type 2 diabetes mellitus as a risk factor for benign prostatic hyperplasia.

AIMS/HYPOTHESIS: The aim of this study was to evaluate the relationship between benign prostatic hyperplasia (BPH) and arteriosclerosis shown in a model of type 2 diabetes in a trans-sectional population study using contrast-enhanced colour Doppler ultrasound for exact assessment of prostatic blood flow. METHODS: Contrast-enhanced transrectal colour Doppler ultrasound was performed using a microbubble-based ultrasound enhancer SonoVue for evaluating prostate vascularity (transitional zone [TZ] and peripheral zone [PZ]) in diabetic BPH patients, non-diabetic BPH patients and healthy subjects. Computer-assisted quantification of colour pixel intensity (CPI) was used to objectively evaluate the prostate vascularity. Resistive index measurements were obtained in the TZ and the PZ. Findings were compared between these three groups. RESULTS: TZ-CPI was significantly lower in diabetic patients than in non-diabetic BPH men (p=0.001), whereas the CPI of the PZ showed no difference between these two groups (p=0.978). TZ-CPI of patients with diabetic and non-diabetic BPH were significantly lower than in controls (p<0.001), but no difference was found between diabetic and healthy patients in the PZ (p=0.022) and borderline significance was seen when comparing patients of the BPH group with the control patients (p=0.019). Resistive index values of the TZ in diabetic patients showed significantly higher values (p<0.001) than the BPH and control groups. CONCLUSIONS/INTERPRETATION: The significantly lower CPI and higher resistive index values of the TZ in diabetic patients compared with patients with non-diabetic BPH and healthy subjects indicate considerable vascular damage in the TZ of these patients. Diabetic vascular damage may cause hypoxia and may contribute to the pathogenesis of BPH.

[The value of ultrasound (US) in the diagnosis of prostate cancer]. / Sonographie des Prostatakarzinoms. Derzeitiger Stand und Zukunftsperspektiven.

The value of ultrasound (US) in the diagnosis of prostate cancer has increased in importance in the past decade, which is mainly related due to the increasing incidence of prostate cancer, the most common malignancy in men. The value of conventional gray-scale US for prostate cancer detection has been extensively investigated. The introduction of US contrast agents has dramatically changed the role of US for prostate cancer detection. Advances in US techniques were introduced to further increase the role of US contrast agents. Although most of these advances in US techniques, which use the interaction of the contrast agent with the transmitted US waves are very sensitive for the detection of microbubbles, are mostly unexplored, in particular for prostate applications. First reports of contrast-enhanced US investigations of blood flow of the prostate have shown that contrast-enhanced US adds important information to the conventional US technique. We present a critical evaluation of the current status of transrectal US imaging for prostate cancer detection. Furthermore, we give background information on US contrast agents and imaging modalities. Early results of contrast-enhanced US suggest the feasibility of the use of US contrast agents to enhance US imaging of the prostate. The application of US contrast agents for the detection and clinical staging of prostate cancer is promising. However, future clinical trials will be needed to determine the promise of contrast-enhanced US of the prostate evolves into clinical application.

Comparison of unenhanced and contrast-enhanced spiral CT for assessing interval change in patients with colorectal liver metastases.

RATIONALE AND OBJECTIVES: The purpose of this study was to determine whether the interval change in hepatic colorectal metastases as assessed with serial computed tomographic (CT) scans without contrast material enhancement differs from that as assessed using serial, portal dominant phase, contrast-enhanced CT scans. MATERIALS AND METHODS: Unenhanced and contrast-enhanced abdominal CT scans were obtained in 28 patients. Three radiologists separately reviewed serial unenhanced and contrast-enhanced studies to assess the interval change in liver metastases. These radiologists recorded total number of lesions, bidimensional measurements of the largest lesions (as many as three), and overall impressions regarding the interval change (none, worse, or better). RESULTS: Among the 84 judgments (28 patients x 3 radiologists), comparisons of unenhanced and contrast-enhanced CT studies were concordant in 60 assessments (71%). Nineteen (23%) showed mild disagreement. Of these, contrast-enhanced CT studies demonstrated disease stability when unenhanced CT studies demonstrated otherwise in 11 judgments, whereas unenhanced CT studies demonstrated stability when contrast-enhanced CT studies demonstrated otherwise in eight assessments. Furthermore, of the five marked disagreements, two resulted from a conclusion of interval improvement on unenhanced CT studies and a conclusion of interval worsening on contrast-enhanced CT studies, whereas three demonstrated the opposite. Neither set of serial CT studies systematically resulted in under- or overestimation of disease progression (McNemar Q test, P < .25). CONCLUSION: The authors found no consistent pattern to demonstrate that serial unenhanced or contrast-enhanced CT studies resulted in over- or underestimation of disease progression.

Sonographically guided renal mass biopsy: indications and efficacy.

PURPOSE: To review the clinical indications, pathologic results, and success rate of all our sonographically guided solid renal mass biopsies over a 5-year period. METHODS: Between 1993 and 1998, 44 consecutive patients underwent sonographically guided percutaneous biopsy of a solid renal mass. Indications included prior history of nonrenal malignancy, metastatic disease of unknown primary origin, previous contralateral nephrectomy for a renal cell neoplasm, a renal transplant mass, suspected renal lymphoma, history of tuberous sclerosis, and poor surgical candidacy. Aspiration biopsies were initially performed with 22- to 18-gauge spinal needles. If the initial cytologic evaluation findings were nondiagnostic, core biopsies were then performed with 20- to 18-gauge core biopsy guns. Dictated sonographic reports of the biopsies were reviewed to determine the following: indication for biopsy, location and size of the renal mass, needle gauge and type, number of needle passes, and complications. Final cytologic and surgical pathologic records were reviewed. RESULTS: Thirty-six (82%) of the 44 biopsy specimens were diagnostic. Aspirated smears were diagnostic in 24 (67%) of these cases, with the diagnosis made on the basis of cell block alone in an additional 2 (6%). A definitive diagnosis came from core biopsy alone in 10 cases (28%). The 18-gauge core needle yielded diagnostic results more reliably than the 20-gauge core needle, and a significant correlation was seen between core biopsy needle size and the rate of diagnostic core samples (P = .017). Pathologic diagnoses included renal cell carcinoma (n = 18), lymphoma (n = 4), oncocytic neoplasm (n = 4), transitional cell carcinoma (n = 2), angiomyolipoma (n = 1), papillary cortical neoplasm (n = 1), and metastatic carcinoma (n = 6). Complications were seen in 4 (9%) of 44 cases; all were treated conservatively. CONCLUSIONS: For specific clinical indications, sonographically guided fine-needle aspiration and core biopsy of a solid renal mass can be performed safely. In many cases, a definitive diagnosis can be made on the basis of fine-needle aspiration alone. However, diagnosis may ultimately require core biopsy, for which 18-gauge core needles would be more reliably diagnostic than 20-gauge needles.

Detection of prostate cancer with a microbubble ultrasound contrast agent.

The diagnosis of prostate cancer is currently limited by the low sensitivity and specificity of systematic conventional grey-scale ultrasonography. We assessed contrast-enhanced colour Doppler ultrasonography by means of a microbubble ultrasound contrast agent to detect tumour vascularity and improve the diagnosis of prostate cancer. The use of a microbubble ultrasound contrast agent for transrectal colour Doppler targeted biopsy significantly improved the detection of prostate cancer compared with systematic biopsy following conventional grey-scale ultrasonography (p<0.001). Contrast-agent enhanced colour Doppler imaging may allow for limited targeted biopsies (five or less), which reduces costs and morbidity.

Imaging prostate cancer: current and future applications.

Various treatment options are available for adenocarcinoma of the prostate--the most common malignant neoplasm among men in the United States. To select an optimum management strategy, we must be able to identify an organ-confined disease (in which local therapy such as surgery or radiation may be beneficial) vs prostate cancer beyond the confines of the gland (for which other treatment approaches may be more appropriate). At present, no standard imaging modality can by itself reliably diagnose and/or stage adenocarcinoma of the prostate. Standard transrectal ultrasound, magnetic resonance imaging (MRI), computed tomography, bone scans, and plain x-ray are not sufficiently reliable when used alone. Fortunately, advances in imaging technology have led to the development of several promising modalities. These modalities include color and power Doppler ultrasonography, ultrasound contrast agents, intermittent and harmonic ultrasound imaging, MR contrast imaging, MRI with fat suppression, MRI spectroscopy, three-dimensional MRI spectroscopy, elastography, and radioimmunoscintigraphy. These newer imaging techniques appear to improve the yield of prostate cancer detection and staging, but are limited in availability and thus require further validation. This article reviews the status of current imaging modalities for prostate cancer and identifies emerging imaging technologies that may improve the diagnosis and staging of this disease.

Prostate cancer: contrast-enhanced us for detection.

PURPOSE: To assess the detection of prostate cancer with contrast material-enhanced transrectal sonography. MATERIALS AND METHODS: Sixty subjects were examined with conventional gray-scale, harmonic gray-scale, and power Doppler sonography. Evaluation was repeated during intravenous infusion of contrast agent. Gray-scale imaging was performed in continuous mode and with intermittent imaging by using interscan delay times of 0.5, 1.0, 2.0, and 5.0 seconds. Sextant biopsy sites were scored prospectively as benign or malignant at baseline imaging and again during enhanced transrectal sonography. RESULTS: Prostate cancer was present in 37 biopsy sites from 20 subjects. Baseline imaging demonstrated prostate cancer in 14 sites in 11 subjects. Enhanced transrectal sonography depicted prostate cancer in 24 sites in 15 subjects. Each of the five subjects in whom prostate cancer was missed had only a single biopsy core with positive findings (Gleason score < or = 6). In three of these five subjects, prostate cancer made up less than 10% of the core. The improvement in sensitivity from 38% (14 of 37 malignant foci) at baseline to 65% (24 of 37 malignant foci) with contrast enhancement was significant (P<.004, McNemar chi(2) test). Specificity was similar at baseline (267 [83%] of 323 malignant foci) and during enhanced transrectal sonography (257 [80%] of 323 malignant foci). Clustered receiver operating characteristic analysis demonstrated significant improvement in diagnostic accuracy during enhanced transrectal sonography (P =.027). CONCLUSION: Enhanced transrectal sonography improves sensitivity for the detection of malignant foci within the prostate without substantial loss of specificity. Low-volume tumors with a Gleason score of 6 or less may not be detected with enhanced transrectal sonography.

The role of preoperative radial artery ultrasound and digital plethysmography prior to coronary artery bypass grafting.

OBJECTIVE: Doppler ultrasound and digital plethysmography are used at our institution to determine the suitability of the radial artery for harvest prior to coronary artery bypass grafting (CABG). The purpose of this study is to determine the value of this preoperative evaluation. METHODS: A retrospective analysis of non-invasive radial artery testing was performed on 187 CABG patients. Criteria used to exclude radial arteries from harvest were anatomic abnormalities (size<2 mm, diffuse calcifications), and perfusion deficits during radial artery occlusion (>40% reduction in digital pressure, non-reversal of radial artery flow, or minimal increase in ulnar velocity). A questionnaire was used to determine the incidence of postoperative hand ischemia or rehabilitation. RESULTS: In 187 patients, 346 arms were evaluated. Ninety-four arms (27.1%) were excluded for harvesting. Anatomical abnormalities included size<2 mm (1.5%), diffuse calcifications (8.7%), congenital anomalies (2.3%), and radial artery occlusion (0.3%). Circulatory abnormalities included non-reversal of flow (7.2%), abnormal digital pressures (5.5%), and inappropriate increase in ulnar velocity (1.7%). A total of 116 radial arteries were harvested. There were no episodes of hand ischemia. No patient required hand rehabilitation. CONCLUSIONS Doppler ultrasound and digital plethysmography identifies both perfusion (14.5%) and anatomical (12.7%) abnormalities that may make the radial artery less suitable as a bypass conduit.

Preoperative evaluation of living renal donors: comparison of CT angiography and MR angiography.

PURPOSE: To compare computed tomographic (CT) angiography and magnetic resonance (MR) angiography for preoperative evaluation of living renal donors. MATERIALS AND METHODS: Thirty-five living renal donors underwent preoperative contrast material-enhanced CT angiography and gadolinium-enhanced MR angiography. Each study was interpreted by two independent radiologists blinded to all other studies and to interpretations provided by other reviewers. Eighteen kidneys had surgical correlation. RESULTS: CT demonstrated 33 supernumerary arteries in 19 patients, bilateral solitary arteries in 16 patients, and 18 proximal arterial branches in 16 patients. MR demonstrated 26 supernumerary arteries in 15 patients, bilateral solitary renal arteries in 20 patients, and 21 proximal arterial branches in 16 patients. Interobserver agreements for MR (kappa = 0. 74) and CT (kappa = 0.73) were similar to the agreement between MR and CT (kappa = 0.74). Among the kidneys chosen for nephrectomy, one small accessory artery and one proximal arterial branch were missed with CT and MR. Two of the accessory arteries suggested at CT were not found at nephrectomy. By averaging data for both modalities, supernumerary arteries were present in 49% of kidney donors and were bilateral in approximately 17%. Proximal arterial branches were present in 46% of kidney donors. CONCLUSION: Preoperative CT and MR angiography of the renal arteries in renal donors demonstrate substantial agreement. Interobserver disagreement in the interpretation of CT and MR angiograms is related to 1-2-mm-diameter vessels.

Initial experience with contrast-enhanced sonography of the prostate.

OBJECTIVE: We investigated the usefulness of contrast-enhanced sonography to depict vascularity in the prostate and improve the detection of prostatic cancer. SUBJECTS AND METHODS: Twenty-six patients with an elevated prostate-specific antigen level (> or = 4 ng/ml) or an abnormal digital rectal examination were enrolled in a phase II study of an i.v. injected sonographic contrast agent. Continuous gray-scale, intermittent gray-scale, phase inversion gray-scale, and power Doppler sonography of the prostate were performed. Sonographic findings were correlated with sextant biopsy results. RESULTS: After the administration of contrast material, gray-scale and Doppler images revealed visible enhancement (p < 0.05). Using intermittent imaging, we found focal enhancement in two isoechoic tumors that were not visible on baseline images. No definite focal area of enhancement was identified in any patient without cancer. Contrast-enhanced images revealed transient hemorrhage in the biopsy tracts of three patients. CONCLUSION: Enhancement of the prostate can be seen on gray-scale and Doppler sonographic images after the administration of an i.v. contrast agent. Contrast-enhanced intermittent sonography of the prostate may be useful for the selective enhancement of malignant prostatic tissue.

Using gray-scale and color and power Doppler sonography to detect prostatic cancer.

OBJECTIVE: We performed a prospective study to assess gray-scale and color and power Doppler sonography for the detection of prostatic cancer and to determine the impact of operator experience. SUBJECTS AND METHODS: Four radiologists with prior experience using gray-scale and Doppler imaging and four urologists with prior experience limited to gray-scale imaging performed sextant biopsies on 251 patients. Each biopsy site was prospectively scored for gray-scale and Doppler abnormality. RESULTS: Cancer was detected in 211 biopsy sites from 85 patients. Overall agreement between sonographic findings and biopsy results as measured with the kappa statistic was minimally superior to chance (kappa = 0.12 for gray-scale, kappa = 0.11 for color Doppler, kappa < or =0.09 for power Doppler). With respect to gray-scale diagnosis of cancer, the performance of radiologists (kappa = 0.12) and urologists (kappa = 0.13) was similar. With respect to power Doppler, the performance of radiologists (kappa = 0.09) was superior to that of urologists (kappa = -0.03, p<0.002). Among patients with at least one positive biopsy for cancer, foci of increased power Doppler flow detected by a radiologist were 4.7 times more likely to contain cancer than adjacent tissues without flow. CONCLUSION: Gray-scale and Doppler imaging did not reveal prostatic cancer with sufficient accuracy to avoid sextant biopsy. Power Doppler may be useful for targeted biopsies when the number of biopsy passes must be limited. There is benefit from increased operator experience with Doppler imaging, but there is no demonstrable benefit of power Doppler over conventional color Doppler sonography.

Size of colorectal liver metastases at abdominal CT: comparison of precontrast and postcontrast studies.

PURPOSE: To investigate whether measurements of hepatic metastases from colorectal carcinoma before contrast material administration are significantly different statistically from measurements after contrast material administration. MATERIALS AND METHODS: Twenty-four patients with hepatic metastases from colorectal carcinoma underwent spiral computed tomography (CT) with 7-mm collimation. The liver was imaged before and in the portal-dominant phase after intravenous contrast material administration. For each scan, one to three discrete liver lesions were selected for measurement (n = 49). Three experienced radiologists performed independent measurements of the selected lesions on both pre- and postcontrast images at a computer workstation. A three-way analysis of variance (ANOVA) was performed: subjects by raters (the three independent radiologists) by pre- or postcontrast status. The dependent variable was the product of bidimensional measurements. RESULTS: Sixty-seven percent (33 of 49) of the lesions were measured as larger on precontrast images; 33% (16 of 49), as smaller. There was high interrater reliability, with an intraclass correlation coefficient greater than 0.9 ANOVA showed significant subject, rater, and contrast material effects (P < .001) for the largest lesions in each liver. Contrast material status was a significant factor for all lesion sizes (P < .003). CONCLUSION: On average, hepatic metastases from colorectal carcinoma are significantly smaller after contrast material administration.

US, CT, and MR evaluation of accessory renal arteries and proximal renal arterial branches.

RATIONALE AND OBJECTIVES: The purpose of this study was to compare color Doppler ultrasound (US), computed tomographic (CT) angiography, and magnetic resonance (MR) angiography for the evaluation of accessory renal arteries and proximal branches of the main renal artery. MATERIALS AND METHODS: Fifty-six subjects who had undergone conventional arteriography of the renal arteries participated in a prospective comparison of Doppler US (45 patients), CT angiography (52 patients), and nonenhanced MR angiography (28 patients). Conventional arteriography depicted 28 accessory renal arteries and 21 proximal branches of the main renal artery within 2 cm of the aorta. RESULTS: US depicted five of 24 accessory renal arteries seen at arteriography but no proximal arterial branches. CT angiography depicted 24 of 26 accessory renal arteries and 13 of 17 proximal arterial branches, as well as 15 additional accessory renal arteries not seen at conventional arteriography. MR demonstrated 11 of 15 accessory arteries, as well as four additional accessory arteries not seen at conventional arteriography. MR did not depict any of nine proximal arterial branches seen at conventional arteriography. CONCLUSION: When compared with US or nonenhanced MR angiography, CT is the preferred method for evaluation of accessory renal arteries and proximal branches of the renal artery.

Renal artery stenosis: CT angiography--comparison of real-time volume-rendering and maximum intensity projection algorithms.

PURPOSE: To compare results of helical computed tomographic (CT) angiography with real-time interactive volume rendering (VR) to CT angiography with maximum intensity projection (MIP) for the detection of renal artery stenosis. MATERIALS AND METHODS: Twenty-five patients underwent both conventional and CT angiography of the renal arteries. Images were blindly reviewed after rendering with MIP and VR algorithms. MIP images were viewed in conjunction with axial CT images; VR models were evaluated in real time at the workstation without CT images. Findings in 50 main and 11 accessory renal arteries were categorized as normal or by degree of stenosis. RESULTS: All arteries depicted on conventional angiograms were visualized on MIP and VR images. Receiver operating characteristic (ROC) analysis for MIP and VIR images demonstrated excellent discrimination for the diagnosis of stenosis of at least 50% (area under the ROC curve, 0.96-0.99). Although sensitivity was not significantly different for VR and MIP (89% vs 94%, P > .1), specificity was greater with VR (99% vs 87%, P = .008 to .08). Stenosis of at least 50% was overestimated with CT angiography in four accessory renal arteries, but three accessory renal arteries not depicted at conventional angiography were depicted at CT angiography. CONCLUSION: In the evaluation of renal artery stenosis, CT angiography with VR is faster and more accurate than CT angiography with MIP. Accessory arteries not depicted with conventional angiography were depicted with both CT angiographic algorithms.

Comparison of Doppler US and CT angiography for evaluation of renal artery stenosis.

RATIONALE AND OBJECTIVES: The authors compared Doppler ultrasound (US) with computed tomographic (CT) angiography in the evaluation of stenosis of the main renal artery. MATERIALS AND METHODS: Fifty-six patients who had undergone conventional angiography of the renal arteries participated in a prospective comparison of Doppler US (45 patients) and CT angiography (52 patients). US evaluation included both the main renal artery and segmental renal arteries. RESULTS: There were 27 main renal arteries with at least 50% stenosis in 20 patients. In 36 patients, there was no significant stenosis. All cases of main renal artery stenosis detected with Doppler US of the segmental arteries were also identified with Doppler US of the main renal artery. The by-artery sensitivity (63%) of US of the main renal artery was greater than that (33%) of US of the segmental arteries. CT angiography was more sensitive (96%) than Doppler US (63%) in the detection of stenosis, but the specificity of CT (88%) was similar to that of US (89%). The difference in the area under the receiver operating characteristic curve (AUC) between CT (AUC = 0.94) and US (AUC = 0.82) was statistically significant (P = .038). CONCLUSION: Doppler US of the main renal artery is more sensitive than Doppler US of segmental arteries in the detection of stenosis. CT angiography is more accurate than Doppler US in the evaluation of renal artery stenosis.

Using phase information in ultrasonic backscatter for in vivo liver analysis.

In recent studies, it has been shown that information about scatterer spacing can be obtained from analyzing the phase of the ultrasound echo from various media. Such information proves to be useful when examining the ultrasonic backscatter from well-organized tissue, such as the liver. By quantifying the deviations in scatterer spacing and/or varying degrees of regularity, conclusions may be drawn about the underlying pathology of the tissue. This paper examines the physical basis of how the scatterer locations affect the phase of the data. Computer simulations were performed that mimic various scattering conditions and that display the effects of differing degrees of regularity, as well as increases in a diffuse random background scattering component. Results of studies on a phantom are also included to investigate and display the phase response under well-controlled scattering conditions. Finally, in vivo data taken from liver scans were analyzed. In this work, it was shown that the phase of the backscattered signal holds valuable information regarding the pathological state of liver tissue. It is suggested that this simple examination of the phase can be refined into a technique to be used as a method to consistently detect the onset of pathological change.

Comparisons of the Rayleigh and K-distribution models using in vivo breast and liver tissue.

There is a strong interest in finding out which statistical model is the most appropriate for describing the envelope of the backscattered ultrasonic echoes from different types of tissues. The Rayleigh model is commonly employed, but this requires conditions, such as the presence of large number of randomly located scatterers with fairly uniform cross-sections, that are not always met. However, our research indicates that a model based on the K-distribution may provide a better fit to empirical data over a range of scattering conditions than the standard Rayleigh model. In this study, we looked at the K-distribution as a descriptor of the backscattered envelope of the breast and liver tissues (in vivo). By examining data from various tissue regions, a goodness-of-fit test (a least squares error method) was used to determine whether a Rayleigh or K-distribution model is more appropriate. From a large group of patients and volunteer scans (a total of 72 subjects), the fit between the K-distribution and the data is shown to have a much smaller error than the Rayleigh model.