Detection of hepatocellular carcinoma and liver metastases with BR14: a multicenter phase IIA study.

The study was designed primarily to find the optimal dosage range of BR14 contrast-enhanced ultrasonography (CEUS) to detect malignant focal liver lesions. Secondary objectives were the evaluation of the safety profile and comparison with contrast-enhanced MRI (CE MRI). We studied 25 patients (9 females, 16 males, mean age, 66 years) with known hepatocellular carcinoma or liver metastases at 3 centers over a 3-month period. Each patient underwent a baseline examination and at least 3 CEUS examinations with ascending dose levels (0.25 mL; 1.0 mL; 4.0 mL) of BR14. CE MRI was performed 4 weeks before or after the CEUS examination. Dedicated liver maps were used to record the location, size, and type of detected lesions. Examination quality was documented and safety parameters were assessed. The number of lesions detected by BR14 CEUS increased with dosage, whereas the number of missed lesions and the lesion sizes decreased. Despite the increasing contrast enhancement, substantial differences among dosages were not seen for other image quality parameters. No significant changes were noted in safety parameters and no serious adverse events were reported. We conclude that the recommended dose level of BR14 is between 1 mL and 4 mL; at this dosage, lesion detection is comparable to that of CE MRI.

Characterisation of focal liver lesions with unenhanced and contrast enhanced low MI real time ultrasound: on-site unblinded versus off-site blinded reading.

OBJECTIVE: To compare on-site and blinded off-site reading of baseline ultrasound (US) and contrast enhanced ultrasound (CEUS) for classification and characterisation of focal liver lesions. MATERIALS AND METHODS: 99 patients (57 women and 42 men, age range 18-89 years, mean age: 59 years) with 53 malignant and 46 benign liver lesions were studied with unenhanced US followed by contrast enhanced US after injection of 2.4 ml SonoVue® (Bracco, Milano, Italy). Image interpretation was performed on-site with clinical information available by consensus of two readers and off-site by two independent blinded readers at two different centers. Comparison of pre and post contrast scans and of the different readers was performed. Reference examinations were histology, intraoperative US, MRI or CT. RESULTS: Sensitivity for malignancy improved from 81/89/66% (on-site/off-site reader 1/2) before to 100/96/96% post contrast administration (p<0.05, except for reader 1). Specificity improved from 48/48/54% on baseline US to 89/80/76% on CEUS (p<0.05). Accuracy for specific lesion diagnosis was 62/59/50% pre and 90/77/72% post contrast (p<0.05). Classification and characterisation post contrast were mildly inferior for off-site reading. Agreement between on-site and off-site readers of unenhanced scans was fair (κ=0.29-0.39) while it was good for CEUS (κ=0.63-0.79). CONCLUSIONS: CEUS improves classification and characterisation of focal liver lesions and interobserver agreement compared to conventional US. Classification and characterisation post contrast were mildly but statistically significantly better for on-site than for off-site reading.

Qualitative and quantitative evaluation of hepatocellular carcinoma and cirrhotic liver enhancement using Gd-EOB-DTPA.

OBJECTIVE: The objective of our study was to prospectively evaluate quantitatively and qualitatively the enhancement patterns of cirrhotic liver tissue and hepatocellular carcinoma (HCC) after administration of the hepatocyte-specific contrast agent gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) on dynamic MRI and to determine the time point of maximum liver-to-lesion contrast. SUBJECTS AND METHODS: Twenty-five patients with HCC in liver cirrhosis underwent 1.5-T MRI. T2-weighted turbo spin-echo and T1-weighted 3D gradient-echo sequences before and between 15 seconds and 20 minutes after the injection of 10 mL of Gd-EOB-DTPA were performed. Signal-to-noise ratios (SNRs) of liver parenchyma and liver-to-lesion contrast-to-noise ratios (CNRs) were calculated and plotted over time. Enhancement patterns of HCC were characterized qualitatively by two radiologists. RESULTS: The SNR of liver parenchyma increased significantly at 15 seconds and 60 seconds after contrast injection and remained stable thereafter. HCC showed positive CNR during the arterial phase and increasingly negative CNR during the further time course (p < 0.05). The maximum absolute CNR was found at 20 minutes after contrast injection. There was no correlation between the degree of enhancement at any time point and tumor grade. On qualitative evaluation, 16 HCCs showed arterial enhancement with early washout, and five showed arterial enhancement with late washout. In the remaining four HCCs, enhancement persisted until 20 minutes. Lesion conspicuity at 20 minutes after contrast injection was at least equal to or higher than it was on the remaining sequences in 19 of the 25 patients. CONCLUSION: After Gd-EOB-DTPA injection, most HCCs showed typical arterial enhancement with early washout. Liver-to-lesion contrast was best at 20 minutes.

Hepatic transit time analysis using contrast-enhanced ultrasound with BR1: A prospective study comparing patients with liver metastases from colorectal cancer with healthy volunteers.

We prospectively compared hepatic transit time (HTT) measurements in subjects with liver metastases from colorectal cancer (group a) and healthy volunteers (group b) using contrast-enhanced ultrasound with BR1. The purpose of this study was to verify our hypothesis that the hemodynamic changes of the liver, which occur during metastasis seeding, would shorten the HTT, and we expect that such changes could be used for the detection of occult liver metastases from colorectal cancer in the future. The study had institutional review board approval and all subjects gave informed written consent. Group a and group b consisted of 22 subjects each. Baseline and post contrast images were acquired starting 10 s before and ending 40 s after administration of BR1, using nonlinear imaging at a frame rate of 5/s. The baseline images were used to determine the signal intensity without contrast enhancement as the reference signal. Arrival times (AT) of the contrast agent for the hepatic artery, the portal vein and one hepatic vein were determined using (i) quantitative analysis and (ii) subjective analysis by two blinded readers. HTT was calculated based on arrival time measurements. Quantitative and subjective analysis showed significantly shorter arterial to venous and portal to venous HTT in group a compared with group b (p < 0.001). Arterial to venous HTT (quantitative analysis) was < or = 9 s in 19 of 22 subjects of group a and >9 s in 18 of 22 subjects of group b (sensitivity 86%, specificity 82%, positive predictive value 83%, negative predictive value 86%, area under the curve [AUC] 0.87). Portal to venous HTT (quantitative analysis) was < 7 s in 21 of 22 subjects of group a and > 7s in 15 of 22 subjects of group b (sensitivity 95%, specificity 68%, PPV 75%, NPV 94%, AUC 0.85). There was an inverse relation with number of liver segments involved for arterial to venous and portal to venous HTT in group a (p < 0.05), but no correlation between HTT and overall volume of metastases (group a) or subject age (group b). From the results of our study, we conclude that HTT measurements using contrast-enhanced ultrasound with BR1 can detect hemodynamic changes caused by metastatic liver disease from colorectal cancer. However, comparison with the literature suggests that the use of other contrast agents might provide better results. Comparison of different contrast agents for the purpose of transit time analysis would therefore be useful before embarking on a prospective trial looking at the detection of occult liver metastases in patients with colorectal cancer. (E-mail: jhohmann@uhbs.ch).

Magnetic resonance imaging of experimental inflammatory bowel disease: quantitative and qualitative analyses with histopathologic correlation in a rat model using the ultrasmall iron oxide SHU 555 C.

OBJECTIVES: To quantitatively and qualitatively characterize the MR findings of inflammatory bowel disease in a rat model after i.v. injection of the reticuloendothelial system cell specific ultrasmall iron oxide SHU 555 C. MATERIALS AND METHODS: Colitis was induced in 15 rats using dinitrobenzene sulfonic acid instillation. Five rats served as controls. T1- and T2-weighted spin-echo- and T2*-weighted gradient-echo-sequences were acquired at 2.4 Tesla before and immediately, 15, 45, 60, and 90 minutes, and 24 hours after i.v.-injection of SHU 555 C (0.1 mmol Fe/kg). MR images were evaluated quantitatively regarding thickness and signal-to-noise ratio (SNR) of the bowel wall and qualitatively regarding overall bowel wall signal intensity and the occurrence of bowel wall ulcerations. MR findings were correlated to histology. RESULTS: The inflamed bowel wall was significantly thicker than the noninflamed bowel wall and 90 minutes after contrast injection it showed a significant reduction of SNR in T1- (94 +/- 27 vs. 61 +/- 29; P < 0.01), T2- (67 +/- 26 vs. 28 +/- 17; P < 0.05), and T2*- (92 +/- 57 vs. 10 +/- 7; P < 0.05) weighted images as compared with unenhanced images. At 24 hours, the respective SNR values remained significantly reduced. The signal loss was homogeneous in 12 and focal in 3 of the 15 rats with colitis. Nine rats showed colonic wall ulcerations. In all but one animal (missed focal ulceration) MR findings correlated to the histologic findings. CONCLUSIONS: SHU 555 C leads to a significant signal intensity loss of the inflamed bowel wall in T1-, T2- and T2*-weighted images. SHU 555 C enhanced MRI findings correlate well with histologic findings.

Electromagnetic field-based navigation for percutaneous punctures on C-arm CT: experimental evaluation and clinical application.

The aim of this study was to prospectively evaluate the needle visualization and placement error and use of an electromagnetic field-based tracking navigation device for puncture procedures based on C-arm CT (CACT) images. A commercially available navigation device was mounted on an angiographic X-ray system setup for CACT. After the target was defined, needle placement was performed under real-time visualization of the virtual needle in CACT images. The final, real needle position was assessed by CACT. Punctures were performed in phantoms (n = 76) and in twelve patients (eight biopsies, three drainages, one injection). Procedure times, system error, user error and total error were assessed. In phantoms, mean total error was 2.3 +/- 0.9 mm, user error was 1.4 +/- 0.8 mm and system error was 1.7 +/- 0.8 mm. In the patient study, the targeted puncture was successful in all twelve cases. The mean total error was 5.4 mm +/- 1.9 mm (maximum 8.1 mm), user error was 3.7 +/- 1.7 mm, system error was 3.2 +/- 1.4 mm and mean skin-to-target time was less than 1 min. The navigation device relying on CACT was accurate in terms of needle visualization and useful for needle placement under both experimental and clinical conditions. For more complex procedures, electromagnetic field-based tracking guidance might be of help in facilitating the puncture and reducing both the puncture risk and procedure time.

Influence of intrahepatic vessels on volume and shape of percutaneous thermal ablation zones: in vivo evaluation in a porcine model.

OBJECTIVES: Aim of the study was to evaluate the precise influence of different intrahepatic vessels, vessel sizes, and distances from the applicator on volume and shape of hepatic laser ablation zones in an in vivo porcine model. MATERIALS AND METHODS: The study was approved by the institutional animal care and use committee. Eighteen computed tomography-guided Nd:YAG laser ablations were performed in the livers of 10 pigs at varying distances from hepatic veins and portal fields. After hepatectomy the livers were cut into 2-mm slices perpendicular to the laser applicator axes. For each ablation zone the maximum achievable (ideal) volume, the segmented (real) volume, the maximum radius, and the radius at the position of adjacent hepatic vessels were determined. The shapes of the ablation zones were evaluated qualitatively. Comparative statistics using the unpaired t test and a multiple linear regression analysis were performed. RESULTS: Ideal and real ablation zone volumes differed by 27.3% (8.6 +/- 1.5 mL vs. 6.4 +/- 1.1 mL; P < 0.0001). Thirty-eight of 60 (63%) hepatic veins versus 28 of 31 (90%) portal veins within the central slices of the 18 ablation zones led to a reduction of the ablation zone's radius, depending on the distance between the vessel and the applicator and the vessel type. Portal fields revealed stronger effects than hepatic veins. The vessel diameter showed no independent effect (P > 0.05). When influencing, all hepatic veins showed a focal indentation whereas portal fields always showed broad flattening of the ablation zone. CONCLUSIONS: Portal fields lead to more heat sink than hepatic veins. The effects decreased with the distance between vessel and applicator tip, but less so for portal fields. The 2 vessel types induced considerably different shape alterations of the ablation zones. These results were not dependent on vessel size. This should be considered in the planning of thermal tumor ablations.

MRI of the thorax during whole-body MRI: evaluation of different MR sequences and comparison to thoracic multidetector computed tomography (MDCT).

PURPOSE: To evaluate the accuracy of four MR sequences used as part of a whole-body MRI protocol to detect pulmonary lesions in cancer patients. MATERIALS AND METHODS: A total of 31 oncology patients were imaged in a 1.5T MR scanner (Magnetom Avanto; Siemens Medical Solutions, Germany) for whole-body staging. MR chest imaging included: axial and coronal T2-weighted (T2w)-short-tau inversion-recovery (STIR), axial T2w turbo spin-echo (TSE), and contrast-enhanced (CE) three-dimensional (3D) volumetric interpolated breathhold examination (VIBE). Multidetector computed tomography (MDCT) of the thorax served as the reference standard. The MDCT and MR images were evaluated independently by two radiologists. Comparative analysis was performed per lesion, per lobe, and per patient. Sensitivity, specificity, and predictive values were determined. RESULTS: Compared to MDCT that detected 268 pulmonary lesions ranging from 2 to 75 mm in diameter, the MR sensitivities were 91.1%, 92.5%, 90.8%, and 87.3% for the coronal STIR, the axial STIR, the axial T2w-TSE, and the axial CE 3D-VIBE, respectively. Undetected pulmonary lesions were either calcified or smaller than 10 mm in the axial diameter. With coronal STIR, six false-positive findings were detected; with axial STIR, 14 were detected; with axial T2w-TSE, 10 were detected; and with 3D-VIBE, seven were detected. CONCLUSION: Pulmonary MRI is feasible as part of a whole-body MRI protocol. In our study, STIR images achieved high accuracy compared to chest MDCT for pulmonary lesions of 3 mm in size or larger.

Computed tomography-bronchoscopic simulation for guiding transbronchial fine needle aspiration of extramural targets: a phantom study.

OBJECTIVES: Extramural paratracheal/-bronchial tumors of the mediastinum and the hilum that cannot be seen in bronchoscopy constitute a particular challenge for transbronchial fine needle aspiration cytology. A software prototype was developed as a guidance tool to visualize extramural targets on computed tomography (CT)-bronchoscopy. A phantom study was conducted to evaluate this guidance tool. MATERIAL AND METHODS: For CT-bronchoscopic simulation extramural targets are visualized behind the semitransparent wall in the endoluminal view. An airway phantom with 16 targets was examined by 3 bronchoscopists. In a first pass the targets were bronchoscopically punctured in the conventional way only with knowledge of axial CT-sections. In a second pass guidance by CT-bronchoscopic simulation was used. A postinterventional CT scan of the phantom was conducted to analyze the spatial relationship between the marked puncture sites and the targets. The punctures were classified in hits and failed punctures due to deviation in distance and angle. RESULTS: The total hit rate of the 3 operators was significantly higher with CT-bronchoscopic simulation (32 of 48) than with the conventional method (14 of 48; P < 0.01). Concerning the failed punctures the deviation in distance and angle was significantly smaller with CT-bronchoscopic simulation (P < 0.01, P < 0.05, respectively). CONCLUSION: CT-bronchoscopic simulation significantly increased hit rate of bronchoscopic punctures of extramural lesions compared with conventional orientation using axial CT-sections in this phantom study. These results suggest that CT-bronchoscopic simulation might be a valuable tool for increasing yield and accuracy of bronchoscopic transbronchial fine needle aspiration in patients with mediastinal and hilar masses that are invisible for conventional bronchoscopy.

Reduction of stenosis due to intimal hyperplasia after stent supported angioplasty of peripheral arteries by local administration of paclitaxel in swine.

PURPOSE: To assess if local intra-arterial administration of paclitaxel using drug-coated balloons or an admixture of paclitaxel to contrast medium inhibits stenosis after percutanous transluminal angioplasty (PTA) of peripheral arteries in a porcine overstretch model. METHODS: Neointimal proliferation and stenosis were induced by overstretch and stenting of 40 peripheral arteries in 20 pigs. Paclitaxel was administered locally during PTA using coated balloons (n = 20) or dissolved in contrast medium (n = 10). Conventional balloons and contrast medium were used in a control group (n = 10). Reangiography with quantitative analysis was performed after 5 weeks. RESULTS: On reangiography diameter stenosis and late lumen loss were significantly reduced by both methods of local drug delivery compared with control group; minimal luminal diameter was significantly larger in the treatment groups. CONCLUSIONS: Local short-term administration of paclitaxel during PTA of peripheral arteries using balloons or contrast medium as drug carriers reduced stenosis due to intimal hyperplasia.

Contrast-enhanced abdominal angiographic CT for intra-abdominal tumor embolization: a new tool for vessel and soft tissue visualization.

C-Arm cone-beam computed tomography (CACT), is a relatively new technique that uses data acquired with a flat-panel detector C-arm angiography system during an interventional procedure to reconstruct CT-like images. The purpose of this Technical Note is to present the technique, feasibility, and added value of CACT in five patients who underwent abdominal transarterial chemoembolization procedures. Target organs for the chemoembolizations were kidney, liver, and pancreas and a liposarcoma infiltrating the duodenum. The time for patient positioning, C-arm and system preparation, CACT raw data acquisition, and data reconstruction for a single CACT study ranged from 6 to 12 min. The volume data set produced by the workstation was interactively reformatted using maximum intensity projections and multiplanar reconstructions. As part of an angiography system CACT provided essential information on vascular anatomy, therapy endpoints, and immediate follow-up during and immediately after the abdominal interventions without patient transfer. The quality of CACT images was sufficient to influence the course of treatment. This technology has the potential to expedite any interventional procedure that requires three-dimensional information and navigation.

MRI tumor characterization using Gd-GlyMe-DOTA-perfluorooctyl-mannose-conjugate (Gadofluorine M), a protein-avid contrast agent.

The rationale and objectives were to define the MRI tumor-characterizing potential of a new protein-avid contrast agent, Gd-GlyMe-DOTA-perfluorooctyl-mannose-conjugate (Gadofluorine M; Schering AG, Berlin, Germany) in a chemically induced tumor model of varying malignancy. Because of the tendency for this agent to form large micelles in water and to bind strongly to hydrophobic sites on proteins, it was hypothesized that patterns of dynamic tumor enhancement could be used to differentiate benign from malignant lesions, to grade the severity of malignancies and to define areas of tumor necrosis. Gadofluorine M, 0.05 mmol Gd kg(-1), was administered intravenously to 28 anesthetized rats that had developed over 10 months mammary tumors of varying degrees of malignancy as a consequence of intraperitoneal administration of N-ethyl-N-nitrosourea (ENU), 45-250 mg kg(-1). These tumors ranged histologically from benign fibroadenomas to highly undifferentiated adenocarcinomas. Dynamic enhancement data were analyzed kinetically using a two-compartment tumor model to generate estimates of fractional plasma volume (fPV), apparent fractional extracellular volume (fEV*) and an endothelial transfer coefficient (K(PS)) for this contrast agent. Tumors were examined microscopically for tumor type, degree of malignancy (Scarff-Bloom-Richardson score) and location of necrosis. Eighteen tumor-bearing rats were successfully imaged. MRI data showed an immediate strong and gradually increasing tumor enhancement. K(PS) and fEV*, but not fPV obtained from tumors correlated significantly (p < 0.05) with the SBR tumor grade, r = 0.65 and 0.56, respectively. Estimates for K(PS) and fEV* but not fPV were significantly lower in a group consisting of benign and low-grade malignant tumors compared with the group of less-differentiated high-grade tumors (1.61 +/- 0.64 vs 3.37 +/- 1.49, p < 0.01; 0.45 +/- 0.17 vs 0.78 +/- 0.24, p < 0.01; and 0.076 +/- 0.048 vs 0.121 +/- 0.088, p = 0.24, respectively). It is concluded that the protein-avid MRI contrast agent Gadofluorine M enhances tumors of varying malignancy depending on the tumor grade, higher contrast agent accumulation for more malignant lesions. The results show potential utility for differentiating benign and low-grade malignant lesions from high-grade cancers.

Multipolar radiofrequency ablation of hepatic tumors: initial experience.

Institutional review board approval and patient informed consent were obtained. Use of a multipolar radiofrequency (RF) ablation device in patients with hepatic malignancy was prospectively evaluated with regard to feasibility, achieved ablation zone size and shape, technical effectiveness, and complications. Nineteen malignant liver tumors were treated with the multipolar resistance-controlled RF ablation system, with which up to three internally cooled bipolar coagulation electrodes can be operated simultaneously. Postinterventional imaging was performed with dynamic contrast material-enhanced magnetic resonance (MR) imaging and MR imaging-based three-dimensional planimetry. Complete tumor destruction was achieved in 18 of 19 tumors. Mean ablation zone volume was 52 mL +/- 45 (standard deviation). Thirteen patients were treated with a percutaneous approach; six, with an intraoperative approach. Maximum ablation size was 91 x 62 x 79 mm with the percutaneous and 73 x 98 x 74 mm with the intraoperative approach. Of the 18 completely evaluable ablation zones, 13 were concentric, two were moderately eccentric, two were eccentric, and one was wedge-shaped. The multipolar RF ablation device achieves large ablation zones and has high technical effectiveness in treating hepatic tumors.

Evaluation of MR imaging compatibility of a new intracranial pressure monitoring device.

We report our observations on MR imaging quality and functionality of a recently introduced intracranial pressure monitoring device. The device was tested at two different field strengths in a pig brain specimen to investigate MR imaging artifacts, probe function during and after MR data acquisition, and device-related temperature changes in the brain tissue. Image reading was not impaired, and probe function, although reduced, was not fully interrupted during data acquisition.

Low contrast dose voiding urosonography in children with phase inversion imaging.

Voiding urosonography (VUS) using a microbubble contrast agent has been introduced as an alternative technique in the diagnosis of vesicoureteral reflux (VUR). This study was undertaken to assess if phase inversion ultrasound (PIUS), a recent microbubble specific imaging technique, has advantages over fundamental in VUS and if it allows a reduction of contrast agent dose. Forty-three children with suspected VUR (aged 3 days-12 years, average of 3.9 years) with 92 kidney-ureter units (KUU) were included. Everyone obtained a baseline US scan that was followed by VUS using Levovist as the contrast agent. Constant switching between fundamental and PIUS performed the enhanced part for comparison. Every child underwent VCUG immediately afterwards. Contrast enhancement was stronger and longer lasting on PIUS than on fundamental US in all 43 cases. Reflux was detected in a total of 21 KUU, out of 92 KUU (23%). PIUS revealed VUR in 18; fundamental in 14 KUU and VCUG depicted 16 cases of reflux (p> or =0.29). The mean volume of Levovist dose administered to the bladder was 7.4+/-3.4% of the bladder volume. VUS using PI mode provided considerably stronger and longer enhancement and slightly improved the detection of VUR. It allowed a reduction of contrast dose and cost by approximately 35% over current dose recommendations for fundamental US.

Multiple cerebral aneurysms in factor VII deficiency.

A rare case of multiple cerebral aneurysms and factor VII deficiency is presented. The authors hypothesize a possible combined genetic defect similar to that of other conditions with clotting disorders. Different treatment options are discussed for factor VII deficiency in particular and multiple cerebral aneurysms in general. The authors advise treatment of all detected aneurysms in case of a subarachnoid hemorrhage rather than only treatment of the ruptured aneurysms in order to immediately start the so-called triple-H therapy.

[Risk management from the perspective of the radiation protection officer. Consequences of new radiation protection laws in hospitals]. / Risikomanagement aus der Sicht des Strahlenschutzverantwortlichen. Konsequenzen des neuen Strahlenschutzrechtes im Krankenhausbetrieb.

The implications of the new radiation protection law for hospitals. The novel German radiation control regulation ("Roentgenverordnung") came into effect on July 1, 2002. It contains a number of new rules the majority of which clearly take a more restrictive approach towards the application of ionising radiation. New dose thresholds have been set for control and monitoring areas and written working instructions are now required for all areas of radiology departments. The new regulations also require the indication for a radiological examination to be checked by a radiologist who has completed a formalised training in radiation protection. This particular aspect will have serious implications for every day practice. The necessity of having a trained radiologist on site for 24 hours a day will cause problems in many hospitals. The power of the responsible external independent control body ("ärztliche Stelle") has been increased as have the duties of medical physicists. The performance of x-ray examinations that are not medically indicated is punishable by law as bodily harm. This as well as many other regulations are currently being checked for applicability in terms of guidelines, the majority of which are not yet available.

Use of a blood-pool contrast agent for MR-guided vascular procedures: feasibility of ultrasmall superparamagnetic iron oxide particles.

RATIONALE AND OBJECTIVES: The purpose of this study was to examine the dose dependency of the intravascular signal intensity after injection of ultrasmall superparamagnetic iron oxide (USPIO) particles (SH U 555 C) in a rabbit model studied with a low-field-strength magnetic resonance (MR) imaging system. The results were used to facilitate MR-guided vascular procedures in a pig. MATERIALS AND METHODS: All experiments were performed at 0.2 T. To determine the optimum USPIO (or SH U 555 C) dose for intravascular interventions, the authors acquired coronal three-dimensional MR angiographic images in 12 rabbits after injection of four dose levels (10, 20, 30, and 40 micromol of iron per kilogram body weight). The intraaortic signal intensities were measured in user-defined regions of interest. For numerical analysis, signal intensity enhancement was computed. Subsequently MR image-guided procedures were performed in USPIO-enhanced vessels in one pig. RESULTS: The signal intensity evaluation shows a clear-cut dose dependence in both early and late phases after administration of SH U 555 C. A high-spatial-resolution MR angiogram acquired 20 minutes after injection yielded the best results with the highest dose (40 micromol of iron per kilogram); at that dose, intravascular enhancement was sufficient for vascular procedures for 60 minutes after injection. CONCLUSION: SH U 555 C is a promising contrast agent for MR angiography and MR-guided vascular procedures in an open low-field-strength MR imager.

Heterogeneous delayed enhancement of the liver after ultrasound contrast agent injection--a normal variant.

We report a characteristic heterogeneous delayed liver enhancement pattern that we have encountered in a total of 6 of approximately 1500 subjects who underwent contrast-enhanced liver ultrasonography. The heterogeneous enhancement occurred several min after contrast injection and persisted for up to 1 h. It was seen in diseased as well as healthy livers and appears to represent a "normal variant" of liver enhancement. It was observed with two different contrast agents. The cause of the described effect is unknown; it may be related to the formation of large bubbles and vascular entrapment of these bubbles in the liver.