[Influence of body constitution on bone mineral density measured by digital radiogrammetry]. / Einfluss der Körperkonstitution auf die mittels digitaler Radiogrammetrie evaluierte Knochenmineraldichte.

PURPOSE: In addition to many established osteodensitometric techniques, digital radiogrammetry (DXR) is considered to be a reliable method for measuring the cortical bone mineral density (DXR-BMD). This study investigates the influence of body constitution on BMD of healthy adults as calculated by DXR. MATERIALS AND METHODS: In a prospective study, 246 adults without bone affecting diseases in their clinical history underwent DXR for analysis and calculations of bone mineral density and determination of metacarpal index (MCI) and porosity index (PI). Height, weight and body mass index (BMI) were recorded for each patient. RESULTS: For all individuals and for all BMI subgroups, both height (0.55 < R < 0.70, p < 0.01) and body weight (0.56 < R < 0.78, p < 0.01) correlated closely with DXR-BMD. Only in the over-weight group, no significant correlation was found between body weight and DXR-BMD. In addition, a significant reduction of the relative DXR-BMD and MCI values was observed between the over-weight and the under-weight group as well as between normal-weight and under-weight individuals (p < 0.01). Otherwise, cortical porosity decreased with increasing body weight. CONCLUSION: Similar to Dual Energy X-ray Absorptiometry-based studies (DXA), digital radiogrammetry measures an increase in BMD with increasing body weight. Therefore DXR, which provides a precise technique without influence of soft tissue, seems to be a promising technique for quantifying marginal alterations in cortical BMD as well for following the course of osteoporosis.

Gd-enhanced 3D phase-contrast MR angiography and dynamic perfusion imaging in the diagnosis of renal artery stenosis.

The objective of this study was to investigate the role of contrast enhancement using a three-dimensional (3D) phase-contrast (PC) magnetic resonance (MR) sequence (3D PC-MRA) and to assess the value of a dynamic MR perfusion study of the kidneys to determine the hemodynamic relevance of unilateral renal artery stenosis (RAS). Seventeen patients with unilateral RAS were examined on a standard 1.0 T imaging system using a phase shift and magnitude sensitive 3D PC sequence (TR=160 ms, TE=9 ms, venc. 30 cm/s). Following the initial pre-contrast 3D PC-MRA a dynamic first pass perfusion study was performed using a Turbo-FLASH 2D sequence (TR=4.5 ms, TE=2.2 ms, TI=400 ms) after bolus injection of 0.15 mmol gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)/kg body weight. The 3D PC-MRA was then repeated during infusion of 0.15 mmol Gd-DTPA/kg body weight. Evaluation by three independent readers was based on maximum intensity projection images. Source images were rendered on request. Signal intensity (SI) over time curves of the renal cortex were obtained from the dynamic perfusion study and analyzed for maximum signal enhancement as well as temporal relationship to the aortic SI curve. Results from 3D PC-MRA revealed a sensitivity (pre-/post-contrast) of 100%/89%, specificity of 76%/63%, positive predictive value of 80%/69 %, negative predictive value of 90%/78%, and accuracy of 85%/75% (p=0.07). Interobserver agreement was kappa=0.61/kappa=0.47 (pre/post Gd-DTPA), respectively. Increased signal-to-noise was present in all segments of the renal arteries post contrast (p=0.0003). This came along with image degradation due to aliasing and elevated SI of venous flow that partially obscured the renal arteries. Dynamic SI curves showed a significantly decreased maximum SI in RAS (p=0.01-0.001). A temporal delay of cortical signal intensity enhancement could not be confirmed in this setting. Gd-enhanced 3D PC-MRA did not yield a superior diagnostic value in the diagnosis of RAS compared to pre-contrast measurements. Dynamic perfusion imaging of the kidneys, in combination with 3D PC-MRA, can contribute additional information in suspected unilateral RAS.

[In vitro study of morphology of the bladder wall using MR tomography at 1.0 Tesla: correlation with histology]. / In-vitro-Untersuchung der Morphologie der Harnblasenwand in der MR-Tomographie bei 1,0 Tesla: Korrelation mit der Histologie.

PURPOSE: Evaluation of the potential of various MR techniques to differentiate bladder wall layers verified by histological findings. MATERIAL AND METHOD: 6 bladder specimens of pigs were examined in vitro using T1-weighted spin-echo-sequences, T2-weighted Turbo-SE, fat suppressed T2-weighted SE, and inversion recovery sequences. The MR images were obtained before and after fixating the specimens in formalin. Measurements of the thickness of bladder wall layers were performed on both sets of MR images as well as on histological sections, RESULTS: T2-weighted SE images showed three layers of different signal intensities: one innermost band of very high signal, one inner band of low and one outer band of intermediate signal corresponding histologically tunica propria and two different muscle layers. Inversion recovery technique provided similar findings but were able to avoid chemical-shift artifacts. After 24 hours in formalin, the signal intensity relation of the two muscle layers was inverted. The thickness of total bladder wall was not reduced significantly. Concerning the thickness of urinary bladder wall, histological measurements and evaluation of MR images correlated well. CONCLUSION: MR imaging enables the differentiation of three bladder wall layers. Inversion recovery technique achieved the best image quality by avoiding chemical shift artifact.

Phase-contrast MR angiography for detection of arteriosclerotic renal artery stenosis.

PURPOSE: To compare the accuracy of 3-D phase-contrast (PC) MR imaging with a 2-D time-of-flight (TOF) technique in the detection of arteriosclerotic renal artery stenosis. MATERIAL AND METHODS: Twenty-two patients with 28 angiographically proven renal artery stenoses were examined in a prospective blinded fashion by using 2-D TOF MR angiography (MRA) with venous saturation (FLASH) and 3-D PC MRA. The renal arteries were subdivided into 3 segments and graded for the presence of stenoses on a scale of 0-4 by 3 radiologists in blind. RESULTS: The accuracy of TOF and PC imaging in detecting renal artery stenoses was 65% and 77% respectively. Both 2-D TOF and 3-D PC MRA depicted 84% of the stenoses of the proximal renal artery greater than 50% in diameter. Renal artery stenoses greater than 50% and more than 15 mm in distance from the aorta were detected in 40% of cases with the 2-D TOF sequence and in 76% with the 3-D PC technique (p < 0.05). The rate of false-negative results was 32%. CONCLUSION: PC MRA is better at visualizing stenoses in the middle segment of the renal arteries and supplements conventional TOF techniques with additional information. However, even when the two techniques are combined, the false-negative rate in the MR imaging of stenoses of the renal arteries still needs to be reduced.

[Digital hilar tomography. A comparison with the conventional technique]. / Digitale Hilustomographie. Ein Vergleich mit der konventionellen Technik.

The aim of the following study was to compare conventional hilar tomography and digital hilar tomography. 20 patients were examined both with conventional and digital hilar tomography using the same tomographic technique and the identical exposure dose. All patients underwent computed tomography of the chest as a golden standard. The digital technique, especially the edge-enhanced image version, showed superior image quality. ROC-analysis by 4 readers found equal diagnostic performance without any statistical difference. Digital hilar tomography shows a superior and constant image quality and lowers the rate of re-exposure. Therefore, digital hilar tomography is the preferable method.

Staging of urinary bladder neoplasms with MR imaging: is Gd-DTPA helpful?

This study was performed to investigate whether intravenous administration of Gd-DTPA can improve the accuracy of MR imaging in the detection and staging of bladder neoplasms. In 68 patients with suspected urinary bladder neoplasms, MR examinations were performed with T1-weighted SE sequences before and after intravenous administration of Gd-DTPA. The findings were compared with surgical staging using the TNM classification. Overall staging accuracy of contrast enhanced MR was 46%; if stages Ta-T3a were combined into one group, the accuracy was 69%. Accuracy was low (19%) in tumors without muscular bladder wall invasion (Ta). In cases with extravesical spread (greater than or equal to T3b), the accuracy of staging was 87%. Contrast enhanced MR detected extravesical extension of tumor with a sensitivity of 93% and a specificity of 95%. Contrast enhancement increased the sensitivity for detection of urinary bladder neoplasms from 70% on precontrast T1-weighted scans to 79% on postcontrast scans. In comparison with T2-weighted scans, the Gd-DTPA enhanced T1-weighted scans had better image quality and lower acquisition times.

Gadolinium-enhanced magnetic resonance imaging in the staging of urinary bladder neoplasms.

Magnetic resonance imaging (MRI) proved to be an important diagnostic tool in the correct staging of bladder neoplasms. The advantage of multiplane imaging and high soft-tissue contrast may be extended by the use of MRI contrast media such as the gadoliniumdiethylene-triaminepentaacetic acid complex. In 60 patients with suspected or proved bladder tumors, the results of preoperative gadolinium-enhanced MRI were correlated with the histopathologic findings. The staging accuracy of infiltrating tumors was 83% and sensitivity and specificity 86% and 83%, respectively. Three tumors could only be localized after administration of gadolinium. All active tumors demonstrated significant contrast enhancement after intravenously injected gadolinium. Small papillary tumors or carcinoma in situ remain problematic to preoperative staging procedures. The advantages of gadolinium-enhanced MRI will best be employed in the exact pretherapeutic staging of infiltrative bladder neoplasms or in restaging procedures after chemotherapy and radiotherapy.

Urinary bladder neoplasms: evaluation with contrast-enhanced MR imaging.

Forty-eight patients with urinary bladder neoplasms were examined with magnetic resonance imaging before and after intravenous administration of gadolinium diethylene-triaminepentaacetic acid (DTPA). Spin-echo sequences with short repetition and echo times were used in all patients; in 20 a gradient-echo technique was used to perform sequential imaging. In 31 patients ratios of tumor signal intensity to that of fat, muscle, and bone marrow were calculated before and after Gd-DTPA enhancement on T1-weighted spin-echo images. Increases in tumor signal intensity on T1-weighted spin-echo images were statistically significant after contrast enhancement (alpha = 1%, P less than .0001). The average rise in relative signal intensity after contrast enhancement was 120% for the tumor-fat ratio (tumor-marrow ratio, 105%; tumor-muscle ratio, 85%). Tumor signal intensity peaked within 120 seconds and remained on a plateau for up to 45 minutes. Necrotic tissue within the tumor, seen in three cases, was detectable only on contrast-enhanced images.