Noninvasive Assessment of In-Stent Restenosis of the Coronary Artery with Using 16-Slice Computed Tomography

PURPOSE: We strove to evaluate in-stent restenosis of the coronary artery by measuring the in-stent CT attenuation with using 16-multislice CT. MATERIALS AND METHODS: We analyzed the coronary CT angiography, with using 16-slice CT, in 45 stents of 30 patients. The CT attenuation was measured in the lumen of the stented segments and in the lumen of the segment proximal to the stents, and this attenuation was compared with each other. The CT attenuation difference between them was analyzed in relation to the presence of significant in-stent restenosis. Conventional coronary angiography was used as a standard of reference for in-stent restenosis. RESULTS: 12 stents in 12 patients revealed significant restenosis on the conventional coronary angiography. In 6 (50%) of them, the CT attenuation value of the in-stent lumen was lower than that of the proximal segments (373.8 HU vs. 497.1 HU, respectively, p=0.77). In the other 6 stents, a small stent diameter (n=3) and adjacent severe calcification (n=2) accounted for the higher CT attenuation value of the in-stent lumen. In all the stents without significant restenosis, the CT attenuation values of the in-stent lumens were higher than those of their proximal segments. CONCLUSION: The measurement of CT attenuation with using 16-slice CT at the in-stent lumen as compared to the attenuation of the proximal segment provides an objective, confident method for the diagnosis of in-stent restenosis.

Variation of Attenuation Value of Pancreas at Dual Phase MDCT: Comparison of the Bolus-tracking Technique vs. the Fixed Scan Delay Protocol

PURPOSE: To clarify the difference between the bolus-tracking technique and a fixed scan delay protocol in the achievement of the optimal pancreatic phase of the pancreas with MDCT. MATERIALS AND METHODS: 526 patients underwent pancreatic and portal venous phase imaging of the pancreas using 16-channel MDCT. All the examinations were randomized into either scanning using a bolus-tracking technique with a scan delay of 20s after the aorta was enhanced > 100 HU (groups 1 and 2) or scanning with a scan delay of 38 s from the beginning of the injection (groups 3 and 4). A contrast material of 300 mgI/mL (groups 1 and 3) or 370 mgI/mL (groups 2 and 4) at an injection speed of 3 mL/sec was injected at 2 mL/kg body weight. The pancreatic CT attenuation values were compared. RESULTS: The scan delay times of the pancreatic phase in groups 1 and 2 were 38+/-3.8s and 37.4+/-3.4s, respectively. At the pancreatic phase, the pancreatic attenuation values of groups 1 and 2 were slightly higher than those of groups 3 and 4 (115.5+/-15.4 vs 111.7+/-15.1HU; p=0.093, 128.3+/-17.1 vs 119+/-17.1HU; p=0.003). There was no significant difference between groups at the portal venous phase. CONCLUSION: The use of a bolus-tracking technique in the optimal pancreatic phase of pancreatic CT does not significantly improve the pancreatic enhancement but does at higher iodine concentrations.

Occlusive Acute Myocardial Infarct on 16 Multidetector-row Helical CT: An Experimental Study in Rabbits

PURPOSE: We wanted to evaluate the findings and diagnostic accuracy of MDCT for diagnosing occlusive acute myocardial infarction in rabbits. MATERIALS AND METHODS: Myocardial infarction was induced in 14 rabbits. MDCT was performed in the early and delay phases at 1 minute and 6 minutes, respectively, after intravenous contrast injection. The rabbits were sacrificed after scanning. The cardiac specimens were sliced and then stained with triphenyltetrazolium chloride (TTC). The agreement in the transmural extent of infarction between the MDCT scans and the TTC-stained specimens were analyzed by using kappa values. RESULTS: Acute myocardial infarction was found in 9 of 14 rabbits on the TTC-stained specimens and MDCT. The infarcted myocardium was demonstrated as a low-attenuation area on the early phase and as a central low-attenuation area with rim-like enhancement along the endocardial and pericardial sides of the myocardial wall on the delay phase. There was excellent agreement in the scores of the transmural extent of myocardial infarction between the TTC-stained specimens and the early phase scan (kappa value = 0.882, p = 0.000), and there was fair to good agreement between the TTC-stained specimens and the delay phase scan (kappa value = 0.439, p = 0.000). Microscopic examination of the cardiac specimens revealed necrosis of myocardial cells in the central portion and granulation tissue along the endocardial and pericardial sides of the necrotic myocardium. CONCLUSION: 16 slice MDCT scan was useful for the diagnosis of acute myocardial infarction. The early phase scan was more accurate than the delay phase scan for evaluating the transmural extent of myocardial infarction. Histopathologic examination suggested that the low-attenuation area on the delay phase might correspond to necrotic myocardium and the enhanced area might correspond to granulation tissue.

Occlusive Acute Myocardial Infarct on 16 Multidetector-row Helical CT: An Experimental Study in Rabbits

PURPOSE: We wanted to evaluate the findings and diagnostic accuracy of MDCT for diagnosing occlusive acute myocardial infarction in rabbits. MATERIALS AND METHODS: Myocardial infarction was induced in 14 rabbits. MDCT was performed in the early and delay phases at 1 minute and 6 minutes, respectively, after intravenous contrast injection. The rabbits were sacrificed after scanning. The cardiac specimens were sliced and then stained with triphenyltetrazolium chloride (TTC). The agreement in the transmural extent of infarction between the MDCT scans and the TTC-stained specimens were analyzed by using kappa values. RESULTS: Acute myocardial infarction was found in 9 of 14 rabbits on the TTC-stained specimens and MDCT. The infarcted myocardium was demonstrated as a low-attenuation area on the early phase and as a central low-attenuation area with rim-like enhancement along the endocardial and pericardial sides of the myocardial wall on the delay phase. There was excellent agreement in the scores of the transmural extent of myocardial infarction between the TTC-stained specimens and the early phase scan (kappa value = 0.882, p = 0.000), and there was fair to good agreement between the TTC-stained specimens and the delay phase scan (kappa value = 0.439, p = 0.000). Microscopic examination of the cardiac specimens revealed necrosis of myocardial cells in the central portion and granulation tissue along the endocardial and pericardial sides of the necrotic myocardium. CONCLUSION: 16 slice MDCT scan was useful for the diagnosis of acute myocardial infarction. The early phase scan was more accurate than the delay phase scan for evaluating the transmural extent of myocardial infarction. Histopathologic examination suggested that the low-attenuation area on the delay phase might correspond to necrotic myocardium and the enhanced area might correspond to granulation tissue.

Usefulness of Helical CT for the Preoperative Evaluation of Small Advanced Gastric Cancer Mimicking as Early Gastric Cancer at Endoscopy

PURPOSE: We wanted to evaluate the usefulness of helical CT, along with histopathologic correlation, for the preoperative evaluation of small advanced gastric cancers (AGCs) mimicking as early gastric cancer (EGCs) at endoscopy. MATERIALS AND METHODS: From February 2001 to September 2004, we retrospectively reviewed 17 patients with pathologically proven small AGCs that were misinterpreted as EGCs at endoscopy. The preoperative helical CT findings were prospectively analyzed and the CT staging was compared with the pathologic staging that was based on the depth of tumor invasion and status of lymph node metastasis, according to the TNM classification. RESULTS: The endoscopic findings of the 17 AGCs misinterpreted as EGCs were type IIc (n=7), IIb+IIc (n=3), IIa+IIc (n=3), IIa+IIb (n=1), and III (n=3). The mean size of the AGCs on the gross specimen was 2.8 cm (range: 1.2 cm-5 cm). Helical CT clearly depicted the depth of tumor invasion by the marked transmural enhancement or the reticular strands in the exraserosal fat. Preoperative helical CT detected all 17 AGCs (100%) and it correctly diagnosed then as AGCs in 15 (88%) of 17 cases. CT staging for the T category correctly staged 12 cases (71%), it understaged four cases and it overstaged one case. Regional lymph node metastasis was positive in 11 (64%) of 17 cases on the pathologic examination. The CT staging for the N category correctly staged 10 (59%) of 17 cases, it understaged four cases, and it overstaged three cases. CONCLUSION: Preoperative helical CT correctly diagnosed small AGCs mimicking as EGCs at endoscopy. Our results show that helical CT can be useful for the decision-making during the treatment planning for those patients with gastric cancer in which the endoscopic distinction between EGC and AGC is difficult.

Usefulness of Multidetector-row CT in the Evaluation of Reperfused Myocardial Infarction in a Rabbit Model

OBJECTIVE: To evaluate the usefulness of multidetector-row computed tomography (CT) in the evaluation of reperfused myocardial infarction. MATERIALS AND METHODS: Eleven rabbits were subjected to 90-min occlusion of the left anterior descending coronary artery followed by reperfusion. Multidetector-row CT was performed 31 hours+/-21 after the procedure and preand post-contrast multiphase helical CT images were obtained up to 10 min after contrast injection. The animals were sacrificed after 30 days and histochemical staining of the resected specimens was perfomed with 2'3'5-triphenyl tetrazolium chloride (TTC). RESULTS: In all 11 cases, the areas of myocardial infarction demonstrated with TTC-staining were identified on the CT images and the lesions showed hypoenhancement on the early phases up to 62 sec and hyperenhancement on the delayed phases of 5 min and 10 min compared with normal myocardial enhancement. The percentage area of the lesion with respect to the left ventricle wall on CT was significantly correlated with that of the TTC-staining results (p < 0.001 for both early and delayed phase CT) according to the generalized linear model analysis. The areas showing hypoenhancement on early CT were significantly smaller than those with hyperenhancement on delayed CT (p < 0.0001). CONCLUSION: Multidetector-row CT may be useful in the detection and sizing of reperfused myocardial infarction.

Measurement error of spiral CT Volumetry: Influence of Low Dose CT Technique

PURPOSE: To examine the possible measurement errors of lung nodule volumetry at the various scan parameters by using a small nodule phantom. MATERIALS AND METHODS: We obtained images of a nodule phantom using a spiral CT scanner. The nodule phantom was made of paraffin and urethane and its real volume was known. For the CT scanning experiments, we used three different values for both the pitch of the table feed, i.e. 1:1, 1:15 and 1:2, and the tube current, i.e. 40 mA, 80 mA and 120 mA. All of the images acquired through CT scanning were reconstructed three dimensionally and measured with volumetry software. We tested the correlation between the true volume and the measured volume for each set of parameters using linear regression analysis. RESULTS:For the pitches of table feed of 1:1, 1:1.5 and 1:2, the mean relative errors were 23.3%, 22.8% and 22.6%, respectively. There were perfect correlations among the three sets of measurements (Pearson's coefficient = 1.000, p<0.001). For the tube currents of 40 mA, 80 mA and 120 mA, the mean relative errors were 22.6%, 22.6% and 22.9%, respectively. There were perfect correlations among them (Pearson's coefficient = 1.000, p<0.001). CONCLUSION: In the measurement of the volume of the lung nodule using spiral CT, the measurement error was not increased in spite of the tube current being decreased or the pitch of table feed being increased.

The Utility of First-Pass Perfusion CT in Hyperacute Ischemic Stroke: Early Experience

PURPOSE: To evaluate the findings of first-pass perfusion CT in hyperacute stroke patients and to determine the relationship between a perfusion map and final infarct outcome. MATERIALS AND METHODS: Thirty-five patients admitted with ischemic stroke within six hours of the onset of symptoms underwent conventional cerebral CT immediately followed by first-pass perfusion CT. Nineteen underwent follow-up CT or MRI, and three types of dynamic perfusion map - cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) - were evaluated by two radiologists. In these 19 patients, initial perfusion maps correlated with final infarct size, determined during follow-up studies. RESULTS: In all 35 patients, major large vessel perfusion abnormalities [middle cerebral artery - MCA MCA and anterior cerebral artery - ACA (n=2); posterior cerebral artery - PCA (n=8)] were detected. On first-pass perfusion maps depicting CBF and MTT, all lesions were detected, and CBF and delayed MTT values were recorded. CBV maps showed variable findings. In all 19 patients who were followed up, the final infarct size of perfusion abnormalities was less than that depicted on CBF and MTT maps, and similar to or much greater than that seen on CBV maps. CONCLUSION: First-pass perfusion CT scanning is a practical, rapid and advanced imaging technique. In hyperacute stroke patients, it provides important and reliable hemodynamic information as to which brain tissue is salvageable by thrombolytic therapy, and predicts outcome of such treatment.

Mediastinal and Hilar Lymphadenopathy: Cross-Referenced Anatomy on Axial and Coronal Images Displayed by Using Multi-detector row CT

The accurate evaluation of mediastinal and pulmonary hilar lymphadenopathy, especially in patients with lung cancer, is important for determining treatment options and evaluating the response to therapy. To indicate nodal location in detail, mediastinal and hilar lymph nodes have been assigned to one of 14 nodal stations. Mediastinal nodes of greater than 10 mm short-axis diameter are regarded as abnormal, irrespective of their nodal station, while hilar nodes are considered abnormal if their diameter is greater than 10 mm in any axis or they are convex compared to surrounding lung. By providing multiplanar images, multi-detector row CT allows detailed evaluation of thoracic anatomic structures more easily than in the past, when axial images only were available. At cross-referenced imaging, a lymph node depicted at axial imaging in one anatomical location can be visualized simultaneously and automatically at coronal imaging at the exactly corresponding anatomical location. Cross-referenced coincidental axial and coronal images help assess both the size and morphology of mediastinal and hilar lymph nodes.

Epithelioid Hemangioendothelioma of the Liver: Helical CT Findings

PURPOSE: To describe the morphologic features and enhancement patterns of the helical computed tomography (CT) observed in patients with epithelioid hemangioendothelioma (EH) of the liver. MATERIALS AND METHODS: Seven patients (four men and three women; mean age, 41 years) with pathologically proven EHs underwent monophasic (n=2), biphasic (n=2) or triphasic (n=3) helical CT, and the findings were retrospectively analysed. The morphologic features to which attention was directed were tumor number, size, location, shape, margin, surface, the presence of adjacent capsular retraction, vascular encasement and confluent mass formation, while the enhancement pattern was examined in terms of the appearance and degree of enhancement during the arterial or portal phase, and enhancement change during the portal and equilibrium phases. RESULTS: Six patients had multiple tumors, and one had a single lesion. The maximon diameter of these tumors ranged from 0.5 to 12.0 (mean, 3.2) cm, and almost all occurred in the peripheral portion of the liver. The shape, margin and surface features of the tumors varied: in four patients, the margin was poorly defined and the surface was smooth, while in five, adjacent capsular retraction was observed. Vascular encasement was noted in five of six patients with hepatic vessels abutting the tumors, and in all three who were follow up, the growth pattern involved confluent mass formation. In all patients, many tumors showed either nodular (n=3) or irregular (n=4) peripheral enhancement. In all five patients who underwent multiphasic CT, centripetal enhancement was demoustrated. CONCLUSION: Our results disclosed that most patients with EH had multiple tumors, and that almost all were located in the peripheral portion of the liver and involved capsular retraction. The other common CT findings were vascular encasement and a centripetal enhancement pattern. When these CT findings are observed in patients with hepatic tumors, EH should be included in the differential diagnosis.

Focal Nodular Hyperplasia of the Liver: Triphasic Helical CT Findings

PURPOSE: To analyze the morphologic and enhancement patterns of focal nodular hyperplasia (FNH) of the liver observed at triphasic helical CT. MATERIALS AND METHODS: The triphasic helical CT findings of 15 pathologically-proven FNHs in 15 patients (male: female = 7:8; mean age, 40 years) were retrospectively analyzed. Triphasic helical CT images were obtained at 30 secs (arterial phase), 70 secs (portal phase), and 3 mins (equilibrium phase) after the initiation of contrast injection of a total of 120 mL nonionic contrast material at a rate of 3 mL/sec. Image analysis focused on the morphologic and enhancement patterns of the FNHs. Morphologically, their size and margin conspicuity were determined, as well as the presence or absence of a capsule, central scar, malformed arterial vessel, calcification, and mosaic pattern. As for the enhancement pattern, the degree of tumor enhancement (hyper-, iso-, or hypoattenuation) was compared with the surrounding hepatic parenchyma at each phase. All hyperattenuating FNHs were further analyzed after dividing them into two groups, strongly and weakly enhanced. RESULTS: Ten of the 15 tumors were less than 3 cm in diameter. With regard to the other morphologic parameters, a central scar, malformed arterial vessel, and capsule were found in four, four, and five FNHs, respectively. Eleven FNHs showed hyperattenuation, with strong enhancement at the arterial phase. During the portal and equilibrium phases, the enhancement pattern changed to iso- or hypoattenuation in nine and 13 FNHs, respectively. Of six hyperattenuating FNHs at the portal phase, five were weakly enhanced. CONCLUSION: Though our sample was small, we found that FNHs were hyperattenuating lesions, strongly enhanced at the arterial phase but iso- or hypoattenuating during the portal and equilibrium phases. A central scar, malformed arterial vessel, and capsule were observed fairly frequently. Thus, for the differentiation of FNH from other hypervascular hepatic tumors, precise recognition of their CT findings is important.

Acute Appendicitis: Sensitivity, Specificity and Diagnostic Accuracy of Thin-Section Contrast-Enhanced CT Findings

PURPOSE: To assess the sensitivity, specificity, and diagnostic accuracy of individual contrast-enhanced helical CT findings of acute appendicitis. MATERIALS AND METHODS: We retrospectively reviewed the appendiceal helical CT scans, obtained after intravenous contrast administration (abdomen; 7-mm collimation, abdominopelvic junction; 5-mm collimation), of 50 patients with surgically proven acute appendicitis and 112 with alternative diagnoses. The following parameters were analysed by three radiologists: enlarged appendix (> 6 mm in diameter), appendiceal wall thickening, appendiceal wall enhancement, no identification of the appendix, appendicolith(s), (appendiceal) intraluminal air, (appendiceal) intraluminal air extraluminal air, periappendiceal fat stranding, extraluminal fluid, phlegmon, abscess, lymphadenopathy, terminal ileal wall thickening, focal cecal apical thickening, focal colonic wall thickening, and segmental colonic wall thickening. RESULTS: The CT findings of acute appendicitis that statistically distinguished it from alternative diagnoses were an enlarged appendix (sensitivity; 92%, specificity; 93%, diagnostic accuracy; 93%), appendiceal wall thickening (for these three parameters: 68%, 96% and 88%, respectively), periappendiceal fat stranding (90%, 79%, 82%), appendiceal wall enhancement (72%, 86%, 82%), appendicolith (16%, 100%, 74%), and focal cecal apical thickening (14%, 100%, 74%) (for each, p < 0.05). CONCLUSION: On thin-section contrast-enhanced helical CT, an enlarged appendix and periappendiceal fat stranding were found in 90% or more patients with acute appendicitis. Appendiceal wall thickening and enhancement were clearly demonstrated and significant findings for diagnosis. Less common but specific findings include appendicolith, focal cecal apical thickening and intramural air, can also help us establish a diagnosis of acute appendicitis.

Hepatic Arterioportal Shunts: Dynamic CT and MR Features

With the increased temporal resolution available in dynamic computed tomography (CT) and magnetic resonance imaging (MRI), hepatic arterioportal shunts are now more frequently encountered than in the past. The condition occurs in various hepatic diseases in which portal or hepatic venous flow is compromised. The underlying mechanism and the degree of shunt affect its appearance at dynamic imaging. The dynamic CT and MRI findings have been summarized as early enhancement of peripheral portal veins, and wedge-shaped transient parenchymal enhancement during the hepatic arterial phase. Recognition of arterioportal shunt can suggest the presence of a previously unsuspected disorder and avoids false-positive diagnosis or overestimation of a hepatic disease. Familiarity with the pathophysiology of arterioportal shunt also allows investigation of the hepatic hemodynamic changes occurring in various hepatic diseases.

The Quality of Reconstructed 3D Images in Multidetector-Row Helical CT: Experimental Study Involving Scan Parameters

OBJECTIVE: To determine which multidetector-row helical CT scanning technique provides the best-quality reconstructed 3D images, and to assess differences in image quality according to the levels of the scanning parameters used. MATERIALS AND METHODS: Four objects with different surfaces and contours were scanned using multidetector-row helical CT at three detector-row collimations (1.25, 2.50, 5.00 mm), two pitches (3.0, 6.0), and three different degrees of overlap between the reconstructed slices (0%, 25%, 50%). Reconstructed 3D images of the resulting 72 sets of data were produced using volumetric rendering. The 72 images were graded on a scale from 1 (worst) to 5 (best) for each of four rating criteria, giving a mean score for each criterion and an overall mean score. Statistical analysis was used to assess differences in image quality according to scanning parameter levels. RESULTS: The mean score for each rating criterion, and the overall mean score, varied significantly according to the scanning parameter levels used. With regard to detector-row collimation and pitch, all levels of scanning parameters gave rise to significant differences, while in the degree of overlap of reconstructed slices, there were significant differences between overlap of 0% and of 50% in all levels of scanning parameters, and between overlap of 25% and of 50% in overall accuracy and overall mean score. Among the 18 scanning sequences, the highest score (4.94) was achieved with 1.25 mm detector-row collimation, 3.0 pitch, and 50% overlap between reconstructed slices. CONCLUSION: Comparison of the quality of reconstructed 3D images obtained using multidetector-row helical CT and various scanning techniques indicated that the 1.25 mm, 3.0, 50% scanning sequence was best. Quality improved as detector-row collimation decreased; as pitch was reduced from 6.0 to 3.0; and as overlap between reconstructed slices increased.

Analysis of Enhancement Pattern of Sellar and Parasellar Tumors Using Two-Phase Helical CT

PURPOSE: To assess the enhancement patterns of sellar and parasellar tumors at two-phase helical CT. MATERIALS AND METHODS: Thirty-two patients with pathologically proven sellar and parasellar tumors [meningioma (n=17), pituitary mocroadenoma (n=6), neurogenic tumor (n=5), cavernous angioma (n=1), chondrosarcoma (n=1), osteosarcoma (n=1), sphenoid carcinoma (n=1)] were included in this study. Two-phase helical CT was performed after the injection of 90 mL of contrast material at a rate of 3 mL/sec. Transverse helical CT scans were obtained during the early and late phases, with scanning delays of 30 and 120 seconds, respectively. Delayed coronal images were obtained after delayed axial images. Attenuation change and the enhancement patterns of the tumors were visually assessed; the former was also assessed quantitatively as the ratio of the CT number at late-phase axial and coronal scanning to that at early-phase scanning. RESULTS: Visual assessment of two-phase helical CT images revealed decreased attenuation in all 17 meningiomas, no change in all six pituitary macroadenomas and increased attenuation in 5 all five neurogenic tumors on late-phase axial scans as compared with early phase scans. Coronal images showed decreased attenuation in all 17 meningiomas, increased attenuation in all five neurogenic tumors and no change in four pituitary macroadenomas (66.7%). The ratio of CT numbers was significantly different between meningiomas, neurogenic tumors and pituitary macroadenomas(p<0.05). CONCLUSION: According to their histopathology, sellar and parasellar tumors showed characteristic enhancement patterns at two-phase helical CT. An analysis of the observed enhancement patterns can be useful in the differential diagnosis of juxtasellar tumors.

Multiphasic Perfusion CT in Acute Middle Cerebral Artery Ischemic Stroke: Prediction of Final Infarct Volume and Correlation with Clinical Outcome

OBJECTIVE: To assess the utility of multiphasic perfusion CT in the prediction of final infarct volume, and the relationship between lesion volume revealed by CT imaging and clinical outcome in acute ischemic stroke patients who have not undergone thrombolytic therapy. MATERIALS AND METHODS: Thirty-five patients underwent multiphasic perfusion CT within six hours of stroke onset. After baseline unenhanced helical CT scanning, contrast-enhanced CT scans were obtained 20, 34, 48, and 62 secs after the injection of 90 mL contrast medium at a rate of 3 mL/sec. CT peak and total perfusion maps were obtained from serial CT images, and the initial lesion volumes revealed by CT were compared with final infarct volumes and clinical scores. RESULTS: Overall, the lesion volumes seen on CT peak perfusion maps correlated most strongly with final infarct volumes (R2=0.819, p<0.001, slope of regression line=1.016), but individual data showed that they were less than final infarct volume in 31.4% of patients. In those who showed early clinical improvement (n=6), final infarct volume tended to be overestimated by CT peak perfusion mapping and only on total perfusion maps was there significant correlation between lesion volume and final infarct volume (R2=0.854, p=0.008). The lesion volumes depicted by CT maps showed moderate correlation with baseline clinical scores and clinical outcomes (R=0.445-0.706, p<=0.007). CONCLUSION: CT peak perfusion maps demonstrate strong correlation between lesion volume and final infarct volume, and accurately predict final infarct volume in about two-thirds of the 35 patients. The lesion volume seen on CT maps shows moderate correlation with clinical outcome.

A study of Parameters in Spiral CT Volumetry Using Balloon Phantoms

PURPOSE: To evaluate the effects of threshold values, reconstruction interval, slice thickness and table speed on the spiral CT volumetry. MATERIALS AND METHODS: Two phantoms made of a balloon and diluted contrast media underwent spiral CT scanning with section thicknesses of 5, 7 and 10 mm and table speeds of 5, 8 and 10 mm with scans of 5 mm section thickness, 7, 10, and 14 mm with scans of 7 mm section thickness, and 10, 15, and 20 mm with scans of 10 mm section thickness. The volumetric values of phantom A and B were obtained at varying threshold values and a reconstruction interval of 5 and 10 mm for all scans. Volumes were also determined with the threshold value fixed and a reconstruction interval of 1, 5, 7 and 10 mm, respectively. Three-dimensional display and volumetric measurements were obtained using reconstructed images. The effects of threshold value, reconstruction interval, slice thickness and table speed on volumetry were analyzed. RESULTS: Volumetric values varied according to threshold values. Where a threshold value was low, value increased as pitch increased, but where a the threshold value was high, value decreased as pitch increased. With varying threshold values, measurement errors in hydrostatic volumetry were between 0.19 and 27.98%; at a fixed threshold value, measurement errors in CT volumetry were 1.6 to 9.0%. Volume decreased as reconstruc-tion interval increased. Where the table speed/ slice thickness ratio was constant, volume was constant though slice thickness differed. At fixed threshold values, variation in the reconstruction interval was statistically more significant than variation in slice thickness or table speed ( p<0.05, Kruskal-Wallis one-way ANOVA). CONCLUSION: Among serveral spiral scanning and image reconstruction parameters including threshold value, reconstruction interval, slice thickness, and table speed, threshold value most affected the result obtained. At fixed threshold values, the reconstruction interval usded had more effect on CT volumetry than other parameters.

Hepatocellular Carcinoma: Comparison Study on Detecting Tumor Vascularity among Various Imaging Techniques

PURPOSE: To compare the detectability of tumor vascularity using triphasic spiral CT, angiography, CT during hepatic arteriography(CTHA) and single-level dynamic CTHA(SLD-CTHA). MATERIALS AND METHODS: Seventy-nine pathologically confirmed nodular hepatocellular carcinomas(HCCs) in 77 patients were included in this study. Sixty patients were male and 17 were female, and their ages ranged from 31 to 77 (average, 57.4) years. HCCs were classified into three groups according to the size: less than 2 cm (n=20), 2 -4 cm (n=32), and more than 4 cm (n=27) in diameter. If a portion of tumor demonstrated greater enhancement than surrounding liver parenchyma, vascularity was deemed to be present. Detectability by each imaging technique was compared according to size and overall. RESULTS: Hypervascularity was frequently detected by SLD-CTHA [90.9%(40/44)], followed by CTHA[88.0%(66/75)], angiography [80.3%(61/76)], triphasic spiral CT [72.4%(42/58)]. In the less than 2 cm group, detectability rates for triphasic spiral CT, angiography, CTHA and SLD-CTHA were 53.3%(8/15), 55.6%(10/18), 76.5%(13/17) and 87.5%(6/7), respectively. while the 2 -4 cm group demonstrated corresponding figures of 71.4%(15/21), 78.1%(25/32), 84.4%(27/32) and 86.4%(19/22). In the more than 4 cm group, the rate for triphasic spiral CT was 86.4%(19/22), while for angiography, CTHA and dynamic CTHA, it was 100%. CONCLUSION: In the detection of hypervascularity of HCC, SLD-CTHA showed the highest rate, followed by CTHA, angiography, and triphasic spiral CT. In HCCs less than 4 cm in diameter, the corresponding ordering was SLD-CTHA, CTHA, angiography and triphasic spiral CT, but in HCCs of more than 4 cm, angiography, CTHA and SLD-CTHA detected hypervascularity equally well. Lesion size most affected the findings of angiography.

Enhancement Pattern of Hepatocellular Carcinoma on Triphasic Helical CT: Quantitative Study

PURPOSE: To assess the enhancement pattern of hepatocellular carcinoma (HCC), as seen on triphasic helical dynamic computed tomography (CT) by measuring the attenuation value. MATERIALS AND METHODS: Triphasic helical dynamic CT scans of the liver in 94 patients (M:F=73:21; aged 33-81 years) with HCC were evaluated. The condition was confirmed on the basis of histologic (n=28) or clinical (n=66) findings. Scans were obtained at 30, 70, and 180 seconds after the start of contrast material injection, the attenuation values of the solid portion of the HCC and adjacent normal liver parenchyma being measured during the three phases. Enhancement patterns of the HCC nodule and adjacent liver parenchyma were analyzed, and the size of HCCs, the presence or absence of portal vein thrombosis, and the Child classification were also determined. RESULTS: The mean attenuation values of HCC were 69 HU during the arterial phase, 80 HU during the portal phase, and 65 HU during the delayed phase, while those of liver parenchyma were 48 HU, 81 HU and 72 HU, respectively. In 71.3% of cases (67/94), maximum enhancement occurred during the portal phase. Decreased tumor attenuation after peak enhancement was seen in 71.3% of lesions (67/94, Group I). while in 28.7% (27/94, Group II) attenuation showed no significant decrease. There were no statistically significant differences in the size of HCCs, portal vein thrombosis or Child classification between the two groups (p>0.05). CONCLUSION: On triphasic helical dynamic CT, the mean attenuation value of HCCs was highest during the portal phase. Over time, the majority of HCCs showed a decreased attenuation value.

Misregistration Artifact due to Respiratory Motion on Spiral CT of the Liver

PURPOSE: To determine the frequency and patterns of respiratory-induced misregistration artifact seen on spiral CT of the liver. MATERIALS AND METHODS: Two hundred patients with hepatic mass underwent spiral CT, and arterial phase images were compared with those of the portal phase in all cases and or of the delayed phase in 138. The patterns of misregistration artifact were divided into two groups: skipping, where at least two slices in the craniocaudal length of the mass were missed, and the partial volume veraging artifact thus excluded; and overlapping, where the same or reversed images were seen in succeeding sequences. We reviewed the location and size of the masses, and the presence or absence, and patterns of the misregistration artifact. RESULTS: Fourteen (7%) of 200 spiral CT scans demonstrated the misregistration artifact; in five of these there was skipping (involving a hepatic mass larger than 2 cm in two cases, and one smaller than 2 cm in three cases), and in nine there was overlapping (six masses larger than 2 cm, and three smaller than this). A lipiodol-laden mass measuring 5 mm was completely missed during the arterial phase. and in one case the spleen sequence was reversed. Thirteen (93%) of fourteen masses were located in the right lobe. CONCLUSION: Two patterns of misregistration artifact, skipping and overlapping, were observed, and their combined frequency was 7%. So as not to miss small hepatic masses or overestimate their size, careful respiratory control is therefore needed.