Accuracy of magnetic resonance cholangiopancreatography for locating hepatolithiasis and detecting accompanying biliary strictures

BACKGROUND AND STUDY AIMS

Magnetic resonance cholangiopancreatography (MRCP) is rapidly replacing diagnostic endoscopic retrograde cholangiopancreatography (ERCP) in various pancreaticobiliary diseases. This study was designed to evaluate the accuracy of MRCP in detection of hepatolithiasis and accompanying biliary strictures.

PATIENTS AND METHODS

A prospective study over 2 years was conducted in 66 patients with primary intrahepatic stones. All patients with hepatolithiasis underwent percutaneous transhepatic cholangioscopy (PTC) within 2 weeks of the MRCP examination. The MRCP findings were compared with those of PTC as the reference standard for assessing the location of intrahepatic stones and the presence or absence of accompanying biliary strictures.

RESULTS

The sensitivity, specificity, and accuracy of MRCP for detecting and locating intrahepatic stones were 97 %, 99 %, and 98 %, respectively. The sensitivity, specificity, and accuracy of MRCP for detecting and locating intrahepatic bile duct strictures were 93 %, 97 %, and 97 %, respectively. During PTC, six of the 66 patients (9 %) were found on histology to have intraductal cholangiocarcinoma in stone-bearing ducts, which had not been suspected on MRCP.

CONCLUSIONS

In this study, MRCP allowed intrahepatic stones and accompanying biliary strictures to be located accurately. MRCP may therefore be able to replace diagnostic ERCP in patients with primary intrahepatic stones. However, MRCP had a limited ability to reveal concurrent intraductal cholangiocarcinoma associated with hepatolithiasis.

Persistent recognition of autologous virus by high-avidity CD8 T cells in chronic, progressive human immunodeficiency virus type 1 infection

CD8 T-cell responses are thought to be crucial for control of viremia in human immunodeficiency virus (HIV) infection but ultimately fail to control viremia in most infected persons. Studies in acute infection have demonstrated strong CD8-mediated selection pressure and evolution of mutations conferring escape from recognition, but the ability of CD8 T-cell responses that persist in late-stage infection to recognize viruses present in vivo has not been determined. Therefore, we studied 24 subjects with advanced HIV disease (median viral load = 142,000 copies/ml; median CD4 count = 71/ micro l) and determined HIV-1-specific CD8 T-cell responses to all expressed viral proteins using overlapping peptides by gamma interferon Elispot assay. Chronic-stage virus was sequenced to evaluate autologous sequences within Gag epitopes, and functional avidity of detected responses was determined. In these subjects, the median number of epitopic regions targeted was 13 (range, 2 to 39) and the median cumulative magnitude of CD8 T-cell responses was 5,760 spot-forming cells/10(6) peripheral blood mononuclear cells (range, 185 to 24,700). On average six (range, one to 8) proteins were targeted. For 89% of evaluated CD8 T-cell responses, the autologous viral sequence was predicted to be well recognized by these responses and the majority of analyzed optimal epitopes were recognized with medium to high functional avidity by the contemporary CD8 T cells. Withdrawal of antigen by highly active antiretroviral therapy led to a significant decline both in breadth (P = 0.032) and magnitude (P = 0.0098) of these CD8 T-cell responses, providing further evidence that these responses had been driven by recognition of autologous virus. These results indicate that strong, broadly directed, and high-avidity gamma-interferon-positive CD8 T-cells directed at autologous virus persist in late disease stages, and the absence of mutations within viral epitopes indicates a lack of strong selection pressure mediated by these responses. These data imply functional impairment of CD8 T-cell responses in late-stage infection that may not be reflected by gamma interferon-based screening techniques.

Helical CT of postoperative patients with gastric carcinoma: value in evaluating surgical complications and tumor recurrence

BACKGROUND

We assessed computed tomographic (CT) features of postoperative complications and recurrent tumors in gastric cancer patients who underwent radical surgery.

METHODS

We performed a retrospective study of 397 patients who had undergone radical surgery for the treatment of gastric carcinoma and underwent postoperative CT in our institution over a 2-year period. Patients were assigned to one of two groups: group A consisted of 47 patients who underwent CT for complications in the early postoperative period, and group B consisted of 355 patients who underwent CT for evidence of tumor recurrence during the follow-up period. We classified recurrent tumors into four categories: local recurrence, lymph node metastasis, peritoneal seeding, and remote metastasis.

RESULTS

In group A, localized fluid collections or abscesses in the surgical bed were found in 38 patients (81%) and usually involved the left subphrenic area (74%) or the superior recess of the lesser sac (47%). In group B, recurrent tumors were found in 196 patients (55%). Among these, lymph node metastasis was the most common pattern (52%), followed by peritoneal seeding (44%), local recurrence (40%), and remote metastasis (37%).

CONCLUSION

CT after radical surgery for the treatment of gastric carcinoma frequently shows postoperative complications or tumor recurrence. Familiarity with the common postoperative complications and patterns of the tumor recurrence is a prerequisite to accurate interpretation of CT findings in these patients.

Biliary obstruction in metastatic disease: thin-section helical CT findings

BACKGROUND

We describe the thin-section helical computed tomographic (CT) findings of biliary obstruction caused by metastasis.

METHODS

Thin-section helical CT (5 mm slice thickness, 1:1 pitch, portal phase) and direct cholangiography in 50 consecutive patients with biliary obstruction caused by metastases were reviewed retrospectively by three radiologists. The primary sites were the stomach ( n = 36), colon ( n = 12), jejunum ( n = 1), and uterus ( n = 1). The level of biliary obstruction was analyzed with the Bismuth classification, and the CT findings of biliary obstruction were classified into six types: small (<2 cm) periductal masses, large (>/=2 cm) periductal masses, extrinsic compression by a metastatic liver mass, high-attenuation intraductal mass, intrapancreatic mass, and no demonstrable lesion.

RESULTS

The level of biliary obstruction was the hilum in 18 patients (36%), the proximal common duct in 20 (40%), the distal common duct in five (10%), and the periampullary area in seven (14%). Of 18 hilar obstructions, tumor involvement of the secondary confluence of intrahepatic bile ducts was seen in 10 (right in six, left in one, and bilateral in three). Periductal masses were seen in 68% (small in 18, large in 16). In one patient (2%), a large metastatic mass of the liver resulted in extrinsic compression and biliary obstruction. Lesions mimicking primary biliary or pancreatic tumor were seen in four, respectively. In seven, we found no obstructing lesion on CT.

CONCLUSION

Biliary obstruction in patients with known primary malignancies can show atypical patterns mimicking primary pancreatobiliary malignancies on thin-section helical CT.

Volume of cervical lymph nodes using 3D ultrasonography. Differentiation of metastatic from reactive lymphadenopathy in primary head and neck malignancy

PURPOSE

To assess the usefulness of volume measurement using 3D US for depicting metastatic cervical lymph nodes.

MATERIAL AND METHODS

Thirty-five cervical lymph nodes in 13 patients with primary head and neck malignancy were included in this study. US with volume acquisition was prospectively performed with a 5-10 MHz linear mechanical volume probe. Volume measurement of the node was calculated using a 3D automatic volume calculation program. The excised nodes matched on US were examined histopathologically.

RESULTS

The volume of malignant nodes ranged from 0.444 to 4.442 cm3, the volume of the benign nodes from 0.143 to 1.176 cm3. Combinations of high positive (>80%) and negative (>90%) predictive values were obtained at a cut-off value of 0.7 cm3.

CONCLUSION

Volume measurement of cervical nodes using 3D US can be a useful tool for differentiating metastatic from benign nodes in patients with primary head and neck malignancy.

Volume of cervical lymph nodes using 3D ultrasonography. Differentiation of metastatic from reactive lymphadenopathy in primary head and neck malignancy

PURPOSE

To assess the usefulness of volume measurement using 3D US for depicting metastatic cervical lymph nodes.

MATERIAL AND METHODS

Thirty-five cervical lymph nodes in 13 patients with primary head and neck malignancy were included in this study. US with volume acquisition was prospectively performed with a 5-10 MHz linear mechanical volume probe. Volume measurement of the node was calculated using a 3D automatic volume calculation program. The excised nodes matched on US were examined histopathologically.

RESULTS

The volume of malignant nodes ranged from 0.444 to 4.442 cm3, the volume of the benign nodes from 0.143 to 1.176 cm3. Combinations of high positive (>80%) and negative (>90%) predictive values were obtained at a cut-off value of 0.7 cm3.

CONCLUSION

Volume measurement of cervical nodes using 3D US can be a useful tool for differentiating metastatic from benign nodes in patients with primary head and neck malignancy.

Accuracy of CT in local staging of gallbladder carcinoma

PURPOSE

To evaluate the accuracy of CT for staging gallbladder cancers, especially the T-factor of the TNM staging system.

MATERIAL AND METHODS

CT investigations of 100 patients with surgically proven gallbladder cancers were retrospectively analyzed. Dynamic helical CT was performed in 16 patients and conventional CT in the remaining 84. On CT, three radiologists attempted tumor staging for these patients; the majority opinion was used for final decision. According to CT protocols (dynamic helical CT vs. conventional CT) and each tumor type (thickened wall/intraluminal mass/massive), the accuracy of CT staging was compared. The CT staging was correlated with the surgico-pathologic results.

RESULTS

The overall accuracy of CT for staging gallbladder cancers was 71%; it was 79% for T1 and T2 tumors, 46% for T3 tumors, and 73% for T4 tumors. For all three readers, the poorest accuracy was obtained in T3 tumors. No statistically significant difference was noted in the accuracy between the groups undergoing conventional CT and dynamic helical CT. A statistically significant difference was noted in the accuracy for staging thickened wall and intraluminal mass types of tumors (p<0.05); the highest accuracy was obtained in the intraluminal mass type (89%) and the massive type (83%), while it was 54% in the thickened wall type.

CONCLUSION

The accuracy of tumor staging with CT in patients with gallbladder cancer depends on the morphological type of tumor. The poorest result is obtained in the thickened wall type.

HIV/Hepatitis B and C co-infection: pathogenic interactions, natural history and therapy

Recent advances in antiretroviral therapy for HIV infection have substantially improved overall mortality, as well as morbidity from life-threatening opportunistic infections. In place of the usual HIV-associated opportunistic infections, morbidity and mortality due to the sequelae of hepatitis B (HBV) and C virus (HCV) infections have taken on a leading role in HIV-infected individuals. This review will examine the pathogenesis of these viruses in the setting of co-infection and the effect of immunosuppression with HIV, the natural history of co-infection, with particular attention to the effect on serological and histological markers, and the effect of immune reconstitution on the course of HBV and HCV infection. Consideration will also be given to the effect of HIV infection on HBV and HCV load (especially for HCV) and progression of liver disease. Finally, we will discuss the rapidly evolving area of therapy, with particular attention to many of the newer agents now in clinical trials, as well as combinations of these agents.

Gastric mucosa-associated lymphoid tissue lymphoma: spectrum of findings at double-contrast gastrointestinal examination with pathologic correlation

Mucosa-associated lymphoid tissue (MALT) is found in the surface epithelium of the stomach. MALT lymphoma is extranodal lymphoma originating from MALT. In the stomach, a strong association with Helicobacter pylori infection has been demonstrated. Low-grade gastric MALT lymphoma has been reported to have variable features at upper gastrointestinal (UGI) examination. Twenty-two patients with low-grade MALT lymphoma had ulcers (n = 11), fold thickening (n = 7), mucosal nodularity (n = 7), masses (n = 6), or prominent areae gastricae (n = 4) at UGI examination. Six patients with high-grade MALT lymphoma had masses (n = 4), fold thickening (n = 3), ulcers (n = 1), or mucosal nodularity (n = 1) at UGI examination. These findings were similar to those in gastric carcinoma or gastritis. Differentiation of low-grade MALT lymphoma from gastritis or gastric carcinoma was more difficult than differentiation of high-grade MALT lymphoma. Lesions of MALT lymphoma associated with H pylori gastritis were diffuse or multiple in 65% of cases; however, lesions of MALT lymphoma without proved H pylori gastritis were focal or solitary in 80% of cases. Therefore, multiplicity of lesions in MALT lymphoma was closely associated with H pylori infection.

Comparison of contrast-enhanced fundamental imaging, second-harmonic imaging, and pulse-inversion harmonic imaging

RATIONALE AND OBJECTIVES

To investigate the feasibility of recent contrast-specific ultrasound techniques in depicting vascular flow and the effects of changing the output power of the transducer and insonation mode on contrast enhancement, the authors performed an experimental study with a flow phantom.

METHODS

While changing the mechanical index and the sound insonation mode (continuous and intermittent), images were obtained with three contrast-enhanced ultrasound techniques: fundamental, second-harmonic, and pulse-inversion harmonic imaging (PIHI) after a bolus injection of microbubble contrast agent. The images were compared on a time-intensity curve.

RESULTS

In assessing fixed flow (10 cm/s), PIHI showed the best depiction of flow signal. In intermittent scanning, increases in the mechanical index caused stronger flow signals and longer enhancement duration in all techniques. However, continuous scanning revealed poor depiction of flow signal regardless of the technique or changes in the mechanical index because of significant bubble destruction.

CONCLUSIONS

Microbubble-enhanced PIHI with intermittent scanning at a high mechanical index can depict vascular flow highly effectively without shortening the duration of enhancement.

Urinary calculi on computed radiography: comparison of observer performance with hard-copy versus soft-copy images on different viewer systems

OBJECTIVE

The purpose of this study was to compare observer performance for detecting urinary calculi using abdominal computed radiography with hard-copy versus soft-copy images and with a high-resolution video monitor versus a liquid-crystal-display (LCD) monitor.

MATERIALS AND METHODS

We compared observer performance for detecting urinary calculi using three sets of radiographs-hard-copy images, soft-copy images displayed on a LCD monitor (1280 x 1024 bits), and soft-copy images displayed on a high-resolution video monitor using receiver operating characteristic curve analysis with a continuous rating scale. Computed radiography was archived with a 2140 x 1760 pixel resolution and a 10-bit depth. The selected data set included 62 images: 27 images showing proven urinary calculi smaller than 6 mm and three in number, and 35 images containing no proven abnormalities. Eleven radiologists (three genitourinary radiologists and eight general radiologists) participated in the study. Interpretations of three sets of randomly distributed radiographs were performed individually in three separate sessions at 1-week intervals.

RESULTS

No statistically significant differences were found in the area under the receiver operating characteristic curve for detecting urinary calculi or in the interpreting times between soft-copy and hard-copy images; the mean areas under the receiver operating characteristic curve of hard-copy images, soft-copy images displayed on an LCD monitor, and soft-copy images displayed on a high-resolution video monitor were 0.579, 0.610, and 0.732, respectively. However, soft-copy images showed relatively improved diagnostic accuracy among less experienced radiologists (p < 0.05).

CONCLUSION

For detecting urinary calculi, soft-copy images offered a diagnostic accuracy similar to or slightly more accurate than that of hard-copy images obtained in a laser-printed film-based environment. The diagnostic performance with soft-copy images viewed on an LCD monitor was comparable to that of soft-copy images viewed on a high-resolution video monitor.

Hepatic hemangiomas with arterioportal shunt: findings at two-phase CT

PURPOSE

To determine the prevalence of arterioportal shunt associated with hepatic hemangiomas, describe the two-phase spiral computed tomographic (CT) findings, and correlate the presence of arterioportal shunt with the size and rapidity of enhancement of hemangiomas.

MATERIALS AND METHODS

The study group consisted of 109 hepatic hemangiomas in 69 patients who underwent two-phase spiral CT during 1 year. CT scans were obtained during the hepatic arterial (30-second delay) and portal venous (65-second delay) phases after injection of 120 mL of contrast material (3 mL/sec). Arterioportal shunts were diagnosed when hepatic arterial phase CT scans showed a wedge-shaped or irregularly shaped homogeneous enhancement in the liver parenchyma adjacent to the tumor and when portal venous phase CT scans showed isoattenuation or slight hyperattenuation, compared with normal liver in that area, and when there was no demonstrable cause of these attenuation differences. The presence of arterioportal shunt in hemangioma was correlated with the size of the tumor and the rapidity of intratumoral enhancement.

RESULTS

Arterioportal shunt was found in 28 (25.7%) of 109 hemangiomas. There was no statistically significant relationship between lesion size and presence of the arterioportal shunt (P =.653). Arterioportal shunt was more frequently found in hemangiomas with rapid enhancement (P <.01).

CONCLUSION

Arterioportal shunts are not uncommonly seen in hepatic hemangiomas at two-phase spiral CT. Hemangiomas with arterioportal shunts tend to show rapid enhancement.

Inactivation of protein farnesyltransferase by active-site-targeted dicarbonyl compounds

Upon farnesylation by protein farnesyltransferase (FTase), key proteins become compartmentalized in cells. For example, cell membrane localization is essential for the mitogenic role of mutant Ras protein, which acts as a switch for cancer cell proliferation. We report that alpha-dicarbonyl compounds derived from the isoprenoid skeleton or other hydrophobic groups potently obstruct farnesylation of a Ras model peptide by human recombinant FTase in vitro. A geranyl-derived isoprenoid diketone, 5,9-dimethyl-8-decene-2,3-dione, at 17 microM caused a 62% reduction in FTase activity after 30 minutes. A farnesyl-derived isoprenoid diketone, 5,9,13-trimethyl-8,12-tetradecadiene-2,3-dione, at 93 microM caused a 94% reduction after 30 minutes. Other dicarbonyl compounds found to be effective against FTase in vitro were (+/-)-6-(camphorquinone-10-sulfonamido)-hexanoic acid, 4,4'-biphenyldiglyoxaldehyde, dehydroascorbic acid 6-palmitate, 2-oxododecanal, and phenylglyoxal. Higher concentrations of the alpha-dicarbonyl compound resulted in more rapid and more extensive inactivation. These findings demonstrate that alpha-dicarbonyl compounds targeted to FTase interfere with protein farnesylation in vitro and may lead to derivatives that have utility as chemotherapeutic agents.

Stimulation of NF-E2 DNA binding by CREB-binding protein (CBP)-mediated acetylation

The hematopoietic transcription factor NF-E2 is an important regulator of erythroid and megakaryocytic gene expression. The transcription cofactor cAMP-response element-binding protein (CREB)-binding protein (CBP) has previously been implicated in mediating NF-E2 function. In this report, we examined the role of CBP, a coactivator with intrinsic acetyltransferase activity, in the regulation of NF-E2. We found that both the hematopoietic-specific subunit of NF-E2, p45, and the widely expressed small subunit, MafG, interact with CBP in vitro and in vivo. CBP acetylates MafG, but not p45, predominantly in the basic region of MafG. Immunoprecipitation experiments with anti-acetyl lysine antibodies demonstrate that MafG is acetylated in vivo in erythroid cells. Transfection experiments further show that CBP stimulates MafG acetylation in intact cells in an E1A-sensitive manner. Acetylation of MafG augments DNA binding activity of NF-E2, and mutations at the major acetylation sites markedly reduce DNA binding and transcriptional activation by NF-E2. Together, these results suggest that recruitment of CBP by NF-E2 to specific erythroid/megakaryocytic promoters might regulate transcription by at least two mechanisms involving both modification of chromatin structure and modulation of transcription factor activity.

Quantitative comparison of tumor vascularity of hepatocellular carcinoma after intravenous contrast agent: conventional versus harmonic power Doppler US

BACKGROUND

The purpose of this study was to make a quantitative comparison between conventional and harmonic power Doppler (PD) ultrasound (US) in depicting vascularity of hepatocellular carcinoma (HCC).

METHODS

Ten nodular HCCs in 10 patients were prospectively examined using a 2-4-MHz convex transducer and a standardized examination protocol. Serial US images were obtained before and 20, 30, 40, 50, 60, 90, 120, 150, 180, 240, and 300 s after intravenous injection of 2 g of contrast agent using conventional and harmonic PD US. The percentage of area with Doppler signal within each HCC nodule (%PDA) was calculated in each image with a PC-based image analysis program, and the results with both US techniques were compared.

RESULTS

In the majority of cases, %PDA was greater on conventional PD US than on harmonic PD US. Mean %PDA of 10 HCCs was significantly higher on conventional PD US than on harmonic PD US except at 20 s after injection. The highest values of mean %PDA were 34.9% in conventional PD US and 19.5% in harmonic PD US at 60 s after injection.

CONCLUSION

Area with PD signals within the HCC is smaller and the duration of effective enhancement is shorter in harmonic PD US than in conventional PD US.

Stimulation of CREB binding protein nucleosomal histone acetyltransferase activity by a class of transcriptional activators

The transcriptional coactivator CREB binding protein (CBP) possesses intrinsic histone acetyltransferase (HAT) activity that is important for gene regulation. CBP binds to and cooperates with numerous nuclear factors to stimulate transcription, but it is unclear if these factors modulate CBP HAT activity. Our previous work showed that CBP interacts with the Epstein-Barr virus-encoded basic region zipper (b-zip) protein, Zta, and augments its transcriptional activity. Here we report that Zta strongly enhances CBP-mediated acetylation of nucleosomal histones. Zta stimulated the HAT activity of CBP that had been partially purified or immunoprecipitated from mammalian cells as well as from affinity-purified, baculovirus expressed CBP. Stimulation of nucleosome acetylation required the CBP HAT domain, the Zta DNA binding and transcription activation domain, and nucleosomal DNA. In addition to Zta, we found that two other b-zip proteins, NF-E2 and C/EBPalpha, strongly stimulated nucleosomal HAT activity. In contrast, several CBP-binding proteins, including phospho-CREB, JUN/FOS, GATA-1, Pit-1, and EKLF, failed to stimulate HAT activity. These results demonstrate that a subset of transcriptional activators enhance the nucleosome-directed HAT activity of CBP and suggest that nuclear factors may regulate transcription by altering substrate recognition and/or the enzymatic activity of chromatin modifying coactivators.

Paclitaxel-induced apoptosis and mitotic arrest assessed by serial fine-needle aspiration: implications for early prediction of breast cancer response to neoadjuvant treatment

The extent of tumor reduction from neoadjuvant chemotherapy for breast cancer correlates with outcome. We investigated whether the initial cellular responses to paclitaxel are related to the extent of tumor reduction. Eleven women with breast cancer received paclitaxel (every 2 weeks for 4 cycles) as neoadjuvant treatment. Serial fine-needle aspirations (FNA; 25-gauge, 1 pass) were obtained before treatment and at 24, 48, 72, and 96 h after the first paclitaxel dose. Microscopic counts of apoptotic and mitotic indices were performed. The change in cancer volume from treatment was determined using radiological measurements with allowance for change in the histopathological amount of cancer. Apoptotic and mitotic responses usually subsided within 4 days. The duration of the initial apoptotic response was different for women with different treatment results. Cumulative apoptotic response for the first 4 days inversely correlated with the proportion of residual cancer after neoadjuvant treatment. FNA is a versatile clinical method to obtain breast cancer cells for therapy response studies. Apoptotic response to the first dose of paclitaxel is almost complete within 4 days, implying that more frequent (weekly) paclitaxel dosing might be beneficial. The apoptotic response to the first dose of paclitaxel appeared to predict the amount of cancer reduction from this treatment. This is a promising start toward the development of an early chemopredictive assay for paclitaxel treatment of breast cancer.

CT of patients with right-sided colon cancer and distal ileal thickening

OBJECTIVE

The purpose of this study was to analyze the incidence and primary causes of distal ileal wall thickening in 131 patients with right-sided colon cancer.

SUBJECTS AND METHODS

During a 2-year period, 131 patients underwent surgical resection for right-sided colon cancer. Of these patients, we analyzed 13 who had distal ileal wall thickening on CT before surgery and also had the cause determined at pathology. CT findings were analyzed with regard to the morphologic features of colonic tumors, bowel wall involvement patterns of the distal ileum, and changes in the pericolic space.

RESULTS

Distal ileal wall thickening occurred in 13 (10%) of the 131 patients who had right-sided colon cancer. Three patients had polypoid colon cancer, whereas the other 10 had infiltrative colon cancer. The mean thickness of the involved colonic segments was 1.6 cm (range, 1.0-2.2 cm) with a mean length of 5.2 cm (range, 2.5-10.0 cm). Pericolic infiltration was mild in six patients and moderate in four patients. The mean length and thickness of the affected ileal segments were 3.2 cm (range, 1.5-6.0 cm) and 1.1 cm (range, 0.7-2.0 cm), respectively. On histopathologic examination, neoplastic processes involved the distal ileum in nine (69%) of the 13 patients. This involvement was caused by either direct tumor invasion in seven patients or lymphatic spread in two. In four patients (31%), nonneoplastic processes with edema and congestion involved the distal ileum.

CONCLUSION

The distal ileum may be abnormally thickened in about 10% of patients with right-sided colon cancer; this thickening results from tumor extension (69%) or a nontumorous process (31%).

Fractal Heteroaggregation of Oppositely Charged Colloids

Floc structures resulting from selective heteroaggregation of positively and negatively charged colloids are investigated as a function of number ratio and shear conditions at pH 6. Negatively charged silica and positively charged alumina-coated silica undergo rapid aggregation due to attractive electrostatic interactions. At either extreme in number ratio, growth is terminated at an early stage, presumably because the aggregates acquire the same sign of charge, eliminating the driving force for further aggregation. For intermediate number ratios, extensive growth occurs, since the distribution of positive and negative charges is more uniform. Structure evolution of large heteroaggregates is assessed by static light scattering. Shear strongly influences the packing geometry and the tendency for the aggregates to undergo restructuring. At high shear (N(Re)>2000), heteroaggregates show relatively dense packing and do not restructure. Fractal dimension D(f) decreases from 2.64 to 2.26 as the number of positive particles is increased. At low shear (N(Re)<200), packing of the particles is more open and restructuring occurs. The lowest observed fractal dimension is 1.79. In the absence of applied shear, heteroaggregates with D(f)=1.79 rearrange to more compact structures with D(f)=1.88. Copyright 2000 Academic Press.

Preoperative evaluation of Klatskin tumor: accuracy of spiral CT in determining vascular invasion as a sign of unresectability

BACKGROUND

To assess the accuracy of spiral computed tomography (CT) in predicting the resectability of Klatskin tumor as determined by vascular invasion.

METHODS

Twenty-one consecutive patients with Klatskin tumor who had undergone laparotomy were included in this study. The preoperative thin-section (5-mm-thick) spiral CT scans of these patients were assessed for the surgical resectability of tumor by evaluating the vascular invasion. The criterion for vascular invasion indicating unresectability was the tumoral invasion of the proper hepatic artery or main portal vein or simultaneous invasion of one side of the hepatic artery and the other side of the portal vein.

RESULTS

All nine patients with tumors thought to be unresectable on the basis of CT findings had tumors that were unresectable at surgery (positive predictive value, 100%). Of 12 patients with tumors thought to be resectable, six had resectable tumors (negative predictive value, 50%). Spiral CT failed to detect small hepatic metastasis (n = 1), lymph node metastasis (n = 1), extensive tumor (n = 2) and variation of bile duct (n = 2), which precluded surgical resection.

CONCLUSION

Spiral CT is a reliable method for detecting vascular invasion and unresectable tumors. However, it has limitations in detecting variations of the bile duct or the intraductal extent of tumor.

MRI in staging advanced gastric cancer: is it useful compared with spiral CT?

PURPOSE

During the last decade, rapid progress has been made in MR technology. Our objective was to evaluate the role of MRI in staging advanced gastric cancer (AGC; gastric cancer invading the muscularis propria) and to compare it with that of spiral CT.

METHOD

We prospectively performed both MR and CT examinations on 26 patients with AGC proven by endoscopic biopsy. Contrast-enhanced CT and nonenhanced MRI with a 1.0 T scanner using FLASH, HASTE, and true-FISP sequences were obtained in each patient after injection of antiperistaltic drug and ingestion of 1 L of tap water. Fifty-two sets of CT and MR images were analyzed by two radiologists in consensus without any information from other images. T and N staging of AGC was determined according to the TNM classification. All patients underwent surgery within 1 week after both examinations. Diagnostic accuracy of each staging of AGC on CT or MRI was evaluated by comparison with the pathologic results.

RESULTS

MRI was slightly superior to CT in T staging (81 vs. 73%, respectively; p < 0.05). Although MRI had a tendency to overstage the pathologic T2 cancer, positive predictability of T2 stage and sensitivity of T3 stage were high (100%, respectively). Regarding the N staging, CT was slightly superior to MRI (73 vs. 65%; p > 0.05). However, both CT and MRI demonstrated the tendency of understaging in N staging.

CONCLUSION

Although MRI was superior to spiral CT in T staging, MRI cannot completely replace spiral CT in staging AGC because of its limitation in N staging.

Radiological features of leiomyomatous tumors of the colon and rectum

PURPOSE

The purpose of this study was to evaluate the radiological features of 12 pathologically proven cases of colorectal leiomyomatous tumors.

METHOD

A retrospective analysis of radiologic findings was performed in 12 patients with pathologically proven colorectal leiomyomatous tumors (2 leiomyomas and 10 leiomyosarcomas). Available radiologic studies included abdominal CT scans in 11 patients, double contrast barium studies in 4, and pelvic MRI in 1. On imaging, we evaluated the size, tumor margin (smooth or lobulated), morphologic appearance, growth patterns (endocolic, exocolic, or combined), contrast enhancement patterns, presence or absence of calcification within the tumors, and metastasis.

RESULTS

The involved tumor sites were the colon in 2 patients and the rectum in 10. The mean tumor size was 7.9 cm (range 2-15 cm): It was 3.5 cm in leiomyomas and 8.8 cm in leiomyosarcomas. On imaging studies, the tumor margin was smooth in three patients and lobulated in nine, with endocolic growth in one, exocolic in four, and combined in the remaining seven. Eight of the 12 tumors showed varying degrees of internal necrosis with heterogeneous contrast enhancement. Dystrophic calcification was noted in five patients. Metastasis was seen in the liver in three patients at the time of initial diagnosis, and lymphadenopathy was noted in two patients (paraaortic space in one and perirectal space in two).

CONCLUSION

Although rare, the diagnosis of leiomyomatous tumor may be suggested especially when the tumor occurring in the colorectum shows exocolic growth or calcification with varying degree of internal necrosis.

Factors influencing vascular and hepatic enhancement at CT: experimental study on injection protocol using a canine model

PURPOSE

The purpose of this work was to evaluate the effects of contrast medium injection parameters on aortic, portal vein, and hepatic enhancement at spiral CT and to assess optimal injection protocol for hepatic CT.

METHOD

Ten 15 kg dogs underwent single level dynamic CT through the hepatic hilum at 5 s intervals just after the injection of contrast medium for 3 min. With use of different volumes (1, 2, and 3 ml/kg), injection rates (0.5, 1, and 2 ml/s), and concentrations (150, 200, and 300 mg/ml), a total of 270 spiral CT scans were performed. In each scan, time-attenuation curves of aorta, portal vein, and liver were obtained. The degree of maximum contrast enhancement (Imax), time to maximum enhancement (Tmax), and time to equilibrium phase (Teq) for to each injection protocol were analyzed.

RESULTS

Alterations in contrast material volume, injection rate, and concentration had significant impact on contrast enhancement of the liver. With increasing volume of contrast medium, Imax, Tmax, and Teq of aorta, portal vein, and liver increased (p < 0.005). With increasing rate of injection, on the other hand, Imax of aorta and liver increased (p < 0.05), but Tmax and Teq decreased (p < 0.005). Change of concentration of contrast medium had a significant effect on Imax of vessels (p < 0.05).

CONCLUSION

Maximum contrast enhancement of liver and vessels was influenced mainly by injection volume of contrast medium and the time to peak enhancement by injection rate of contrast medium. Under given amounts of contrast medium, therefore, the strategy of increasing volume by dilution and faster injection might give better Imax values without penalty for the duration of an optimal temporal window (Tmax and Teq).