Imaging liver metastases: review and update

Differentiating focal eosinophilic infiltration from metastasis in the liver with gadoxetic acid-enhanced magnetic resonance imaging

Objective

To determine the most useful findings of gadoxetic acid-enhanced 3.0 Tesla (T) MRI for differentiating focal eosinophilic infiltration (FEI) from hepatic metastasis with verification of their usefulness.

Materials and Methods

Pathologically or clinically proven 39 FEIs from 25 patients and 79 hepatic metastases from 51 patients were included in the study. Gadoxetic acid-enhanced 3.0T MRI was performed in all cancer patients. Size differences measured between T2-weighted and hepatobiliary-phase images for lesions > 1 cm and morphologic findings (margin, shape, signal intensity on T1- and T2-weighted images, enhancement pattern on dynamic images, and target appearance on hepatobiliary-phase images) were compared between two groups via Student's t test as well as univariate and multivariate analyses. Diagnostic predictive values of two observers for differentiating two groups were assessed before (session 1) and after (session 2) recognition of results.

Results

Mean size difference (2.1 mm) in FEIs between the two images was significantly greater than for metastases (0.7 mm) (p < 0.05). An ill-defined margin and isointensity on T1-weighted images were independently significant morphologic findings (p < 0.05) for differentiating the two groups. All observers achieved a higher diagnostic accuracy in session 2 (97% and 98%) than session 1 (92% and 89%) with statistical significance in observer 2 (p < 0.05). All observers had significantly higher sensitivities (95%) and negative predictive values (NPVs) (98%) in session 2 than in session 1 (sensitivity, 74% in two observers; NPV, 89% and 88%) (p < 0.05).

Conclusion

With the size change, an ill-defined margin and isointensity on T1-weighted images are the most useful findings for differentiating FEI from hepatic metastasis on gadoxetic acid-enhanced 3.0T MRI.

Diffusion-weighted MRI and liver metastases

Liver metastases are the most frequently encountered malignant liver lesions in the Western countries. Accurate diagnosis of liver metastases is essential for appropriate management of these patients. Multiple imaging modalities, including ultrasound, CT, positron emission tomography, and MRI, are available for the evaluation of patients with suspected or known liver metastases. Contrast-enhanced MRI has a high accuracy for detection and characterization of liver lesions. Additionally, diffusion-weighted MRI (DWI) has been gaining increasing attention. It is a noncontrast technique that is easy to perform, could be incorporated in routine clinical protocols, and has the potential to provide tissue characterization. This article discusses the basic principles of DWI and discusses its emerging role in the detection of liver metastases in patients with extrahepatic malignancies.

Solitary necrotic nodule of the liver: MR findings in 33 pathologically proved lesions

PURPOSE

To determine characteristic magnetic resonance (MR) imaging features of solitary necrotic nodule of the liver.

MATERIALS AND METHODS

MR images features of thirty-two patients (17 men, 15 women; mean age, 43 years; range, 24-76 years) with pathologically proved solitary necrotic nodule of the liver were retrospectively analyzed for number, size, signal intensity features and enhancement patterns.

RESULTS

A total of 33 lesions were identified. The mean diameter was 2.3cm (range 1.0-4.5cm). Thirty lesions (90.9%) were 1.0-3.0cm in diameter and only 3 lesions (9.1%) were larger than 3.0cm. On T1-weighted images, solitary necrotic nodule of the liver appeared hypointense in 31 lesions (93.9%) and isointense in 2 lesions (6.1%). On T2-weighted images, 12 (36.4%) lesions were hyperintense, 15 (45.4%) were isointense or invisible and 6 (18.2%) were hypointense. After injection of gadopentetate dimeglumine, all lesions were hypointense and none of them showed enhancement.

CONCLUSION

Solitary necrotic nodule of the liver is usually small with the size not exceed 3.0cm in diameter. Absence of enhancement on all dynamic phase after gadopentetate dimeglumine administration may be most characteristic feature of solitary necrotic nodule of the liver on MR images, which may help discriminate this entity from metastatic liver tumors and intrahepatic cholangiocarcinoma.

Use of gold nanoshells to constrain and enhance laser thermal therapy of metastatic liver tumours

PURPOSE

To investigate the impact of intravenously injected gold nanoparticles on interstitially delivered laser induced thermal therapy (LITT) in the liver.

METHODS

3D finite element modelling, ex vivo canine liver tissue containing gold nanoparticles absorbing at 800 nm, and agar gel phantoms were used to simulate the presence of nanoparticles in the liver during LITT. Real-time magnetic resonance temperature imaging (MRTI) based on the temperature sensitivity of the proton resonance frequency shift (PRFS) was used to map the spatiotemporal distribution of heating in the experiments and validate the predictions of 3D finite element simulations of heating.

RESULTS

Experimental results show good agreement with both the simulation and the ex vivo experiments. Average discrepancy between simulation and experiment was shown to be 1.6 degrees C or less with the maximum difference being 3.8 degrees C due to a small offset in laser positioning.

CONCLUSION

A high nanoshell concentration in the surrounding liver parenchyma, such as that which would be expected from an intravenous injection of gold nanoshells ( approximately 120 nm) acts as both a beam stop for the laser and secondary heat source for the treatment, helping to better heat the lesions and confine the treatment to the lesion. This indicates a potential to use nanoparticles to enhance both the safety and efficacy of LITT procedures in the liver.

Value of contrast-enhanced ultrasonography in assessing the vascularity of liver metastases: comparison with contrast-enhanced computed tomography

OBJECTIVE

The purpose of this study was to compare the capability of contrast-enhanced ultrasonography (CEUS) and contrast-enhanced computed tomography (CECT) in evaluating the vascularity of liver metastases.

METHODS

Both CEUS and CECT examinations were performed on 70 patients with liver metastases, which were from colon carcinoma in 31, rectal carcinoma in 17, pancreatic carcinoma in 5, and others in 17. In patients with multiple lesions, the most easily observed lesion was selected as the target lesion for evaluation of vascularity.

RESULTS

Peak enhancement of the target lesion during the arterial phase was characterized as hyperenhancement, isoenhancement, hypo-enhancement, and nonenhancement in 61 (87.1%), 6 (8.6%), 3 (4.3%), and 0 (0%) patients on CEUS, respectively, and in 52 (74.3%), 8 (11.4%), 8 (11.4%), and 2 (2.9%) on CECT. Contrast-enhanced ultrasonography showed more lesions with hyperenhancement than CECT (P < .01). The enhancement pattern during the arterial phase was homogeneous, inhomogeneous, and rimlike in 30 (42.9%), 16 (22.9%), and 24 (34.2%) patients on CEUS and in 13 (18.6%), 8 (11.4%), and 49 (70%) on CECT. Contrast-enhanced ultrasonography revealed more lesions with homogeneous enhancement than CECT (P < .01). Contrast-enhanced ultrasonography showed dysmorphic vessels in 33 patients (47.1%) during the arterial phase, whereas CECT showed dysmorphic vessels in 27 (38.6%; P < .01). Contrast-enhanced ultrasonography showed hypervascular lesions in 58.6% of patients, whereas CECT showed hypervascular lesions in 12.9% (P < .01).

CONCLUSIONS

Contrast-enhanced ultrasonography was superior to CECT in assessing the vascularity of liver metastases.

Detection and characterization of liver lesions using gadoxetic acid as a tissue-specific contrast agent

The value of cross-sectional liver imaging is evaluated by the accuracy, sensitivity, and specificity of the specific imaging technique. Magnetic resonance imaging (MRI) has become a key technique for the characterization and detection of focal and diffuse liver disease. More recently, gadoxetic acid, the hepatocyte-specific MR contrast agent, was clinically approved and introduced in many countries. Gadoxetic acid may be considered a "molecular imaging" probe because the compound is actively taken into hepatocytes via the ATP-dependent organic anion transport system in the plasma membrane for the hepatic uptake. The transport of gadoxetic acid from the cytoplasm to the bile is mainly determined by the capacity of the transport protein glutathione-S-transferase. Gadoxetic acid enhances hepatocyte-containing lesions and improves detection of lesions devoid of normal hepatocytes, such as metastases. Innovative rapid MR acquisition techniques with near isotropic 3D pulse sequences with fat saturation parallel the technical progress made by multidetector computed tomography combined with an impressive improvement in tumor-liver contrast when used for gadoxetic acid-enhanced MRI. The purpose of this review is to provide an overview of the development, clinical testing, and applications of this novel MR contrast agent.

Characterisation of small hypoattenuating hepatic lesions in multi-detector CT (MDCT) in patients with underlying extrahepatic malignancy: added value of contrast-enhanced MR images

OBJECTIVE

To retrospectively assess the value of adding gadolinium-enhanced dynamic imaging to standard ununenhanced magnetic resonance imaging (MRI) for characterising hypoattenuating hepatic lesions that are too small to characterise with multi-detector computed tomography (MDCT).

METHODS

Informed consent was waved, and institutional review board approval was obtained. Three hundred and forty-six small (≤ 2 cm) lesions (63 metastatic, 283 benign) in 183 patients with underlying carcinoma who underwent hepatic MRI after CT were retrospectively analysed. Two radiologists independently reviewed images and diagnoses were graded on an ordinal scale from 1 (definitely benign) to 5 (definitely malignant). Receiver operating characteristic analysis was used. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy were also determined.

RESULTS

The areas under the curve of the ununenhanced images alone and with dynamic images were 0.837 and 0.850 for reader 1 (p = 0.616) and 0.771 and 0.783 for reader 2 (p = 0.700). Descriptive statistical values demonstrated sensitivities of 76% and 80%, specificities of 93% and 95%, PPVs of 69% and 79%, NPVs of 95% and 95% and accuracies of 90% and 92%, respectively.

CONCLUSION

The value of adding three-phase contrast-enhanced MRI to unenhanced imaging did not reach statistical significance for characterising small hypoattenuating hepatic lesions on MDCT.

Focal hypoechoic tumors of Fatty liver: characterization of conventional and contrast-enhanced ultrasonography

OBJECTIVE

The purpose of this study was to investigate the characteristics of focal hypoechoic tumors of fatty liver using conventional ultrasonography and contrast-enhanced ultrasonography (CEUS).

METHODS

Sixty-four hypoechoic tumors of fatty liver in 52 patients were examined by both conventional ultrasonography and CEUS. Contrast pulse sequencing and a sulfur hexafluoride contrast agent were used for CEUS. The enhancement patterns were evaluated in real time. Results. Hypoechoic tumors of fatty liver showed posterior echo enhancement, including 71.4% (25 of 35) of hemangiomas, 73.3% (11 of 15) of metastases, and 50.0% (3 of 6) of hepatocellular carcinomas (HCCs) on conventional ultrasonography. During the early arterial phase, 62.5% (5 of 8) of focal nodular hyperplasia lesions showed a central spoked wheel enhancement pattern, whereas the remaining 37.5% (3 of 8) showed eccentric spoked wheel enhancement. During the arterial phase, 97.1% (34 of 35) of hemangiomas showed peripheral enhancement and centripetal fill-in, including ringlike peripheral enhancement (12 of 35), small nodular peripheral enhancement (19 of 35), and massive irregular peripheral enhancement (3 of 35). In total, 76.5% (26 of 34) of hemangiomas were completely filled in. All HCCs showed complete enhancement from 9 to 24 seconds during the arterial phase and began to wash out from 21 to 114 seconds. During the arterial phase, 40.0% (6 of 15) of metastases showed ringlike enhancement; 26.7% (4 of 15) showed slight hyperenhancement; 13.3% (2 of 15) showed hyperenhancement quickly; and the remaining 20.0% (3 of 15) showed heterogeneous hyperenhancement. All metastatic tumors began to wash out from 25 to 40 seconds. In total, 92.2% (59 of 64) of focal hypoechoic tumors of fatty liver were diagnosed as the correct pathologic type with CEUS.

CONCLUSIONS

With CEUS, characterization of hypoechoic tumors of fatty liver is greatly improved.

Does contrast-enhanced ultrasound reveal tumor angiogenesis in pancreatic ductal carcinoma? A prospective study

The purpose of this study is to evaluate tumor vascularity of pancreatic carcinoma noninvasively by contrast-enhanced ultrasound (US) and clarify the diagnostic value of tumor vascularity in subjects with nonresectable advanced pancreatic carcinoma. The study was approved by our institutional review board and written informed consent was obtained from all subjects. Twenty-seven subjects with advanced pancreatic ductal carcinoma were treated by chemoradiotherapy. Contrast-enhanced US, US guided biopsies and dynamic computed tomography (CT) were performed before and after the therapy. We assigned the intratumoral enhancement pattern of US as an enhanced ultrasound (EU) score, from 1 to 4, according to the degree of enhancement area. Intratumoral microvessel density (IMD) and average vessel diameter (AVD) were calculated by means of CD 34 immunostaining. Vascular endothelial growth factor (VEGF) staining was graded on a scale of 1 to 3. EU scores before chemoradiotherapy were compared with IMD, AVD, VEGF, histological grading and hepatic metastasis. After the therapy, local treatment response was evaluated by dynamic CT calculating the maximum area of the tumor, by comparing it with its size in pre- therapy. Subjects who had at least a 50% or more decrease of tumor size lasting more than 4 wk were estimated as partial response (PR), more than a 50% of increase progressive disease (PD) and if neither PR nor PD criteria were met, they were classified as stabled disease (SD). Next, EU scores were compared with IMD, AVD, VEGF and treatment response. Statistically significant differences were evaluated by Pearson's correlation, post-hoc, Spearman's rank correlation, Wilcoxon rank sum and Student's t-test. A p < 0.05 was defined as being statistically significant. Before the therapy, the EU score and IMD were significantly correlated (r = 0.50, p < 0.02), as was VEGF (r = 0.45, p < 0.05). The EU score and AVD were negatively correlated (r = - 0.56, p < 0.02). Significant correlation was found between the EU score and histological grading (p < 0.004). The EU score was higher in subjects who had hepatic metastasis compared with subjects who had no hepatic metastasis (p < 0.05). After chemoradiotherapy, 14 subjects exhibited PR, while 13 showed SD. None of the subjects showed PD. The EU score was smaller in PR than SD (p < 0.05). The EU score significantly decreased after the therapy in PR (p < 0.01) but not in SD. IMD and AVD did not significantly decrease in either PR or SD; however, VEGF decreased significantly in PR (p < 0.01) but not in SD. Contrast-enhanced US could reveal tumor vascularity of pancreatic ductal carcinoma and could be potentially useful to evaluate treatment effect of subjects who receive chemoradiotherapy. Further investigation will be needed to prove the usefulness of contrast-enhanced US.

Three-dimensional contrast-enhanced sonography of vascular patterns of focal liver tumors: pilot study of visualization methods

OBJECTIVE

We investigated visualization methods of 3D sonography with a perflubutane-based contrast agent in the imaging evaluation of vascular patterns of focal liver tumors.

MATERIALS AND METHODS

Eighty-four patients with focal liver tumors underwent automatic scanning with 3D sonography 20-60 seconds after administration of a perflubutane contrast agent. The confirmed final diagnoses were 50 hepatocellular carcinomas, 20 metastatic lesions, nine hemangiomas, and five cases of focal nodular hyperplasia. Tomographic sonographic images reconstructed in 3D parallel slices and rendered sonographic images resembling angiograms were reviewed by two readers.

RESULTS

Sonographic angiograms rendered by maximum intensity of gray values in surface smooth mode showed tumor vessels and early tumor enhancement. The average intensity of gray values with surface texture mode showed unenhanced areas within tumors. Interobserver agreement for classifying enhancement patterns with both tomographic sonography and sonographic angiography was excellent (kappa=0.84). The main pattern, intratumoral vessels with early homogeneous or heterogeneous tumor enhancement, had a sensitivity of 97% (average of both readers), specificity of 94%, and positive predictive value (PPV) of 96% for hepatocellular carcinomas. The presence of tumor vessels with early peripheral ringlike tumor enhancement had a sensitivity of 90%, specificity of 95%, and PPV of 86% for metastatic lesions. Peripheral nodular enhancement had a sensitivity of 84%, specificity of 99%, and PPV of 89% for hemangioma. The presence of spoke-wheel arteries with early tumor enhancement had a sensitivity of 80%, specificity of 100%, and PPV of 100% for focal nodular hyperplasia.

CONCLUSION

Three-dimensional sonography with a perflubutane-based contrast agent is useful in the evaluation of vascular patterns of focal liver tumors.

Critical questions in the imaging of colorectal hepatic metastases

Aggressive treatment of patients with colorectal liver metastases can improve treatment outcome. In this paper, we review current management of patients with colorectal liver metastases and discuss the critical questions that the radiologist should consider when reviewing the imaging of these patients, so as to provide information that is important for formulating treatment strategies by the multidisciplinary management team.

Contrast-enhanced ultrasound assessment of arterial vascularization of small nodules arising in the cirrhotic liver

BACKGROUND AND AIM

Aim of this study was to compare contrast-enhanced ultrasound and multi-detector row computed tomography in detecting arterial hypervascularity in small cirrhotic nodules.

PATIENTS AND METHODS

Sixty-two nodules (41 measuring 1.0-2.0 cm, 21 measuring 2.1-3.0 cm) found in 55 cirrhotic patients were examined with both methods. Lesions displaying arterial hypervascularity with washout in the portal/venous phase on both studies were considered hepatocellular carcinomas and treated; all other nodules were subjected to ultrasound-guided fine-needle biopsy.

RESULTS

The larger nodules (2.1-3.0 cm) included 19 hepatocellular carcinomas (90%), 1 macroregenerative nodule type I and 1 macroregenerative nodule type II; 35 (87%) of the smaller nodules were hepatocellular carcinomas, 2 were macroregenerative nodules type I, 2 macroregenerative nodules type II and 2 hemangiomas. The two studies yielded concordant findings for 54 nodules (87%), including 46 hypervascular on both examinations and 8 that were consistently hypovascular. Two of the latter nodules were hepatocellular carcinomas. The other eight nodules displayed arterial hypervascularity on only one of the studies. Six of these (75%) were hepatocellular carcinomas, including five that were negative in the contrast-enhanced ultrasound study.

CONCLUSION

Computed tomography and contrast-enhanced ultrasound show high agreement in the vascular classification of small nodules detected by ultrasound in cirrhotic livers, although the former technique was slightly more sensitive in the detection of arterial hypervascularization.

Impact of endoscopic ultrasonography and physician specialty on the management of patients with esophagus cancer

While endoscopic ultrasonography (EUS) and EUS-guided fine-needle aspiration (EUS-FNA) are the most accurate techniques for locoregional staging of esophageal cancer, little evidence exists that these innovations impact on clinical care. The objective on this study was to determine the frequency with which EUS and EUS-FNA alter the management of patients with localized esophageal cancer, and assess practice variation among specialists at a tertiary care center. Three gastroenterologists, three medical oncologists, three radiation oncologists and four thoracic surgeons were asked to independently report their management recommendations as the anonymized staging information of 50 prospectively enrolled patients from another study were sequentially disclosed on-line. Compared to initial management recommendations, that were based upon history, physical examination, upper endoscopy and CT scan results, EUS prompted a change in management 24% (95% CI: 12-36%) of the time; usually to a more resource-intensive approach (71%), for example from recommending palliation to recommending neoadjuvant chemoradiation therapy. EUS-FNA plus cytology results altered management an additional 8% (95% CI: 6-15%) of the time. Agreement between specialists ranged from fair (intraclass correlation [ICC=0.32) to substantial (ICC=0.65); improving with additional information. Among specialists, agreement was greatest for patients with stage I disease. EUS and EUS-FNA changed patient management the most for patients with stages IIA, IIB or III disease. EUS, with or without FNA, significantly impacts the management of patients with localized esophageal cancer. With respect to the optimal treatment for each patient, agreement among physicians incrementally increases with endoscopic ultrasound results. Specialty training appears to influence therapeutic decision-making behavior.

Review article: the assessment of liver function using breath tests

BACKGROUND

Hepatologists have long sought to develop a test for assessing liver function, but this aim has been stalled by the complexity of the liver and its diverse functions. Results of metabolic tests, including breath tests, correlate with clinical and histological parameters of patients with liver disorders; however, these tests tend to be cumbersome and impractical for everyday use. The recent development of a real-time, point-of-care liver function breath test has made it straightforward to assess the metabolic function of the liver.

AIM

To review the available data on the use of breath tests for assessing liver reserve in various conditions and their application in various clinical hepatology settings.

RESULTS

The (13)C-methacetin breath test enables accurate follow-up of patients with acute or chronic liver damage, where overall hepatic function is significantly suppressed by known causes of liver disorders, including acute, sub-acute or chronic conditions. The metabolic breath test can detect both gradual and spontaneous improvements in liver function and the effects of treatment.

CONCLUSIONS

Breath testing that provides continuous quantification of methacetin metabolism may be a sensitive tool for the diagnosis and follow-up of patients with liver disorders.

Are metastases really hypovascular in the arterial phase? The perspective based on contrast-enhanced ultrasonography

OBJECTIVE

The purpose of this study was to describe enhancement and vascularity characteristics of liver metastases on real-time low-mechanical index contrast-enhanced ultrasonography.

METHODS

This retrospective study was approved for chart review by our Research Ethics Board. Informed consent was waived. Fifty metastases (colorectal [n = 28], neuroendocrine [n = 6], pancreatic [n = 6], melanoma [n = 3], and other [n = 7]) in 50 patients (38-84 years, 24 male and 26 female) were analyzed. Contrast-enhanced ultrasonography was performed after intravenous injection of a microbubble contrast agent. Two radiologists independently reviewed digital cine clips and static images for the arterial phase intensity and pattern of enhancement and the presence of dysmorphic vessels. Observations on wash-out included its presence and completeness. Disagreement was resolved by consensus. The interval to peak arterial enhancement and beginning of wash-out were determined. Reader agreement was estimated with the kappa statistic.

RESULTS

All but 6 metastases (44/50 [88%]) showed arterial hypervascularity, with dysmorphic vessels in 21 (42%) of 50. The pattern of enhancement was rim in 21 (42%) of 50 and diffuse in 29 (58%) of 50. The time to peak arterial enhancement ranged from 8 to 27 seconds (mean, 15.1 seconds), and the beginning of wash-out ranged from 13 to 50 seconds (mean, 25.2 seconds). Although a thin margin of residual enhancement was seen in 27 (54%) of 50 lesions in the early wash-out phase, all lesions (50/50) showed uniform complete wash-out in the portal phase.

CONCLUSIONS

Contrary to popular belief based on computed tomography and magnetic resonance imaging studies, most hepatic metastases, including those thought to be hypovascular, show transient arterial hypervascularity on contrast-enhanced ultrasonography, followed by rapid and complete wash-out initiated within the conventional arterial phase.

Abdominal MRI advances in the detection of liver tumours and characterisation

With recent technical advances in hardware, software, and intravenous contrast agents, MRI has evolved into a clinically useful procedure to detect and characterise liver tumours. The combination of MRI systems with larger gradients, improved surface coils, and parallel imaging techniques have produced substantial improvements in MRI quality and speed of image acquisition. Images that previously needed several minutes to acquire can now be obtained in several seconds. The notably faster imaging capabilities of new MRI scanners are ideally suited for dynamic contrast-enhanced liver imaging in which early arterial-phase imaging is best for detecting hepatocellular carcinomas and hypervascular liver metastases. The inherent excellent soft-tissue contrast of MRI can be further improved by non-specific extracellular contrast agents and by liver-specific contrast agents. These contrast agents are now routinely used for liver imaging and improve the sensitivity and specificity of hepatobiliary MRI.

Colorectal polyps on portal phase contrast-enhanced CT colonography: lesion attenuation and distinction from tagged feces

OBJECTIVE

The purpose of our study was to determine the attenuation of colorectal polyps on portal phase contrast-enhanced CT colonography (CTC) and evaluate whether enhanced polyps can be clearly distinguished from tagged feces during CTC review.

MATERIALS AND METHODS

Our institutional review board approved this study and waived patient informed consent. Forty-eight colonoscopy-proven polyps (6-20 mm) and 41 polypoid tagged feces (6-19 mm) were selected from contrast-enhanced CTC performed without (n = 37 examinations) and with (n = 10 examinations) fecal tagging, respectively. Scanning was performed 72 seconds after i.v. injection of 150 mL of contrast material at a rate of 2.5 mL/s. Fecal tagging consisted of three doses of 200 mL of 5% weight/volume (w/v) barium sulfate suspension taken at each meal the day before CTC. Attenuation of the polyps and tagged feces was measured. Four independent blinded radiologists reviewed the polyps and tagged feces at both wide (width, 1,500 H; level -400 H) and soft-tissue (width, 400 H; level, 20 H) window settings to distinguish them by using subjective visual assessment.

RESULTS

Polyp attenuation on the portal phase was not correlated with size (R = -0.003; p = 0.99) and was not different between histologic types (p = 0.884). Enhanced polyps (mean +/- SD, 119.9 +/- 25.3 H; range, 50-173 H) showed significantly lower attenuation than did tagged feces (1,521.4 +/- 683.6 H; range, 495-2,683 H) without any overlap (p < 0.0005). An 8-mm sessile adenomatous polyp was misinterpreted as tagged feces by one reviewer. The rest of the lesions were correctly interpreted by all reviewers, resulting in high interobserver agreement (kappa value, 0.988).

CONCLUSION

Polyp attenuation on portal phase contrast-enhanced CTC ranges from 50 to 173 H. Contrast-enhanced polyps are clearly and consistently distinguished from barium-tagged polypoid feces.

The gadolinium complexes with polyoxometalates as potential MRI contrast agents

The two gadolinium (Gd) polyoxometalates, K(15)[Gd(BW(11)O(39))(2)] [Gd(BW(11))(2)] and K(17)[Gd(CuW(11)O(39))(2)] [Gd(CuW(11))(2)] have been evaluated by in vivo and in vitro experiments as the candidates of potential tissue-specific magnetic resonance imaging (MRI) contrast agents. T(1) relaxivities of 17.12 mM(-1) x s(-1) for Gd(BW(11))(2) and 19.95 mM(-1) x s(-1) for Gd(CuW(11))(2) (400 MHz, 25 degrees C) were much higher than that of the commercial MRI contrast agent (GdDTPA). Their relaxivities in bovine serum albumin and human serum transferrin solutions were also reported. After administration of Gd(BW(11))(2) and Gd(CuW(11))(2) to Wistar rats, MRI showed longer and remarkable enhancement in rat liver and favorable renal excretion capability. The signal intensity increased by 37.63+/-3.45% for the liver during the whole imaging period (100 min) and by 61.47+/-10.03% for kidney within 5-40 min after injection at 40+/-1-micromol x kg(-1) dose for Gd(CuW(11))(2), and Gd(BW(11))(2) induced 50.44+/-3.51% enhancement in the liver in 5-50-min range and 61.47+/-10.03% enhancement for kidney within 5-40 min after injection at 39+/-4 micromol x kg(-1) dose. In vitro and in vivo study showed that Gd(BW(11))(2) and Gd(CuW(11))(2) are favorable candidates as tissue-specific contrast agents for MRI.