Optimal scan timing of hepatic arterial-phase imaging of hypervascular hepatocellular carcinoma determined by multiphasic fast CT imaging technique.

BACKGROUND: A new multiphasic fast imaging technique, known as volume helical shuttle technique, is a breakthrough for liver imaging that offers new clinical opportunities in dynamic blood flow studies. This technique enables virtually real-time hemodynamics assessment by shuttling the patient cradle back and forth during serial scanning. PURPOSE: To determine optimal scan timing of hepatic arterial-phase imaging for detecting hypervascular hepatocellular carcinoma (HCC) with maximum tumor-to-liver contrast by volume helical shuttle technique. MATERIAL AND METHODS: One hundred and one hypervascular HCCs in 50 patients were prospectively studied by 64-channel multidetector-row computed tomography (MDCT) with multiphasic fast imaging technique. Contrast medium containing 600 mg iodine per kg body weight was intravenously injected for 30 s. Six seconds after the contrast arrival in the abdominal aorta detected with bolus tracking, serial 12-phase imaging of the whole liver was performed during 24-s breath-holding with multiphasic fast imaging technique during arterial phase. By placing regions of interest in the abdominal aorta, portal vein, liver parenchyma, and hypervascular HCCs on the multiphase images, time-density curves of anatomical regions and HCCs were composed. Timing of maximum tumor-to-liver contrast after the contrast arrival in the abdominal aorta was determined. RESULTS: For the detection of hypervascular HCC at arterial phase, mean time and value of maximum tumor-to-liver contrast after the contrast arrival were 21 s and 38.0 HU, respectively. CONCLUSION: Optimal delay time for the hepatic arterial-phase imaging maximizing the contrast enhancement of hypervascular HCCs was 21 s after arrival of contrast medium in the abdominal aorta.

Contrast-independent liver-fat quantification from spectral CT exams.

The diagnosis and treatment of fatty liver disease requires accurate quantification of the amount of fat in the liver. Image-based methods for quantification of liver fat are of increasing interest due to the high sampling error and invasiveness associated with liver biopsy, which despite these difficulties remains the gold standard. Current computed tomography (CT) methods for liver-fat quantification are only semi-quantitative and infer the concentration of liver fat heuristically. Furthermore, these techniques are only applicable to images acquired without the use of contrast agent, even though contrast-enhanced CT imaging is more prevalent in clinical practice. In this paper, we introduce a method that allows for direct quantification of liver fat for both contrast-free and contrast- enhanced CT images. Phantom and patient data are used for validation, and we conclude that our algorithm allows for highly accurate and repeatable quantification of liver fat for spectral CT.

Quantitative myocardial perfusion analysis using multi-row detector CT in acute myocardial infarction.

OBJECTIVE: To assess the feasibility of quantitative myocardial perfusion imaging (MPI) in acute myocardial infarction (AMI), using multi-row detector CT (MDCT) with a model-based deconvolution method. DESIGN, SETTING, PATIENTS AND INTERVENTIONS: Fifteen normal subjects with normal coronary arteries and 26 patients with AMI after reperfusion therapy underwent MPI with MDCT. Perfusion parameters: tissue blood flow (TBF), tissue blood volume (TBV) and mean transit time (MTT) were obtained and compared with clinical parameters, angiography and single-photon emission CT (SPECT) data. Furthermore, the MPI data were compared with data from myocardial magnetic resonance (MR) in 10 subjects. RESULTS: The TBF and TBV of infarcted myocardium were significantly lower than those of non-infarcted areas (TBF, 51.96±19.42 vs 108.84±13.29 ml/100 g/min, p<0.01; TBV, 4.47±2.23 vs 9.79±2.58 ml/100 g, p<0.01). The MTT of infarcted areas did not differ from that of non-infarcted areas. The defect areas on TBV colour maps were significantly associated with peak creatine kinase level, QRS score and SPECT defect score. The ratio of TBF or TBV in the epicardial to endocardial side was significantly higher in infarct myocardium with good collateral circulation than in myocardium with poor/no collateral circulation (p<0.01 for both). The TBF measurements with CT- and MR-MPI were in good agreement by linear regression analysis (R=0.55, p<0.01). CONCLUSIONS: This study demonstrated that MDCT perfusion imaging with deconvolution analysis could quantitatively detect myocardial perfusion abnormalities in patients with AMI and may provide the basis for the non-invasive and quantitative assessment of myocardial infarction.

Multidetector CT of the lung: image quality with garnet-based detectors.

PURPOSE: To evaluate the image quality of both standard- and reduced-dose computed tomography (CT) by comparing multidetector CT with garnet-based detectors with multidetector CT with conventional detectors. MATERIALS AND METHODS: The study was approved by the internal ethics review board. Informed consent was obtained. Eleven cadaveric lungs inflated and fixed by using the Heitzman method were scanned by using both CT with garnet-based detectors and CT with conventional detectors. Tube current was 400 mA for standard-dose and 10 mA for reduced-dose CT, and voltage was 120 kVp. Either normal scan mode with 984 views (conventional and garnet-based detectors) or high-resolution mode with 2496 views was used. Image quality at conventional-detector CT and garnet-based-detector CT in all modes was graded by two independent observers with a five-point scale. The evaluation items included normal lung structures, subjective visual noise, and abnormal CT findings. Quantitative image noise measurements were calculated by measuring the standard deviations in a circular region of interest on each selected image. RESULTS: At standard-dose CT, image quality at CT with garnet-based detectors (high-resolution mode) was significantly improved (P < .001, Tukey-Kramer). However, there was no significant difference between quantitative image noise measurements (P > or = .24). At reduced-dose CT, only noise differed significantly, with both subjective visual noise and quantitative image noise measurements significantly greater at CT with garnet-based detectors (high-resolution mode) (P < or = .01). There was no significant difference in image quality except for noise between conventional-detector CT and garnet-based-detector CT (P > or = .06). CONCLUSION: The image quality of standard-dose garnet-based-detector CT (high-resolution) was significantly improved. Although highly reduced-dose garnet-based-detector CT (high-resolution mode) provided more image noise, overall image quality was not different between conventional-detector CT and garnet-based-detector CT.

Quantitative tissue blood flow measurement of the liver parenchyma: comparison between xenon CT and perfusion CT.

The purpose of this study was to compare measurements of hepatic tissue blood flow (TBF) calculated by xenon and perfusion CT. Seven patients with normal liver and eight with chronic liver disease underwent both xenon and perfusion CT. During xenon CT examinations, serial abdominal CT scans were obtained every minute before and during 4 min of nonradioactive 25% (v/v) xenon gas inhalation and 5 min of administration of oxygen-rich air. Hepatic arterial and portal venous TBF were measured separately with a special imaging system using the Kety-Schmidt expression based on the Fick principle (AZ-7000W; Anzai Medical Co.). The hepatic arterial fraction (HAF) was calculated as follows: [hepatic arterial TBF/(hepatic arterial TBF + portal venous TBF)]. During perfusion CT examinations, total hepatic TBF and HAF were also calculated from the enhanced CT cine image data on a workstation using a commercially available software package based on a deconvolution algorithm (CT Perfusion 3 GE Healthcare, USA). Total hepatic TBF measured by xenon and perfusion CT was 82.9+/-15 and 82.8+/-18 ml/min/100 g, respectively. The measured values by the two techniques showed a significant correlation (R (2)= 0.657, P < 0.05). HAF measured by xenon and perfusion CT was 26.6+/-11 and 21.8+/-13%, respectively. The measured values by the two techniques also showed a significant correlation (R (2)= 0.869, P < 0.05). We conclude that there was a good correlation between hepatic TBF quantified by xenon CT and perfusion CT.

New acquisition method to exclusively enhance the left side of the heart by a small amount of contrast material achieved by multislice computed tomography with 64 data acquisition system.

PURPOSE: To exclusively enhance the left side of the heart by a small amount of contrast material (CM) using rapid acquisition of multislice computed tomography (MSCT) with a 64-data acquisition system (DAS). MATERIALS AND METHODS: Forty consecutive subjects underwent MSCT (Light Speed VCT, GE) with 0.625mm slice thickness to evaluate coronary arteries. We first measured transit time, using 8ml of CM followed by 20ml saline. Dependent upon transit time, total volume of CM was determined, ranging from 45 to 63ml. After injection of CM at a rate of 4ml/s, followed by 47ml saline at 3.5ml/s, ECG-gated MSCT scanning was performed. The mean and standard deviation (S.D.) of CT values of the right atrium (RA), right ventricle (RV), left atrium (LA), left ventricle (LV), ascending aorta (Ao) and each coronary artery were measured. RESULTS: The mean of the CT values of the RA, RV, LA, LV, Ao, right coronary artery, left main, left anterior descending branch, and left circumflex branch were 225+/-76, 251+/-72, 353+/-55, 355+/-51, 352+/-34, 312+/-65, 296+/-57, 285+/-55, and 267+/-60HU, respectively. The corresponding S.D.s of the CT values were 39+/-22, 37+/-16, 32+/-7, 31+/-8HU, 25+/-5, 36+/-15, 31+/-13, 36+/-23, and 40+/-18HU, respectively. The mean of CT values of the RA and RV were significantly lower than those of the LA, LV, Ao, and each coronary artery (P<0.01), with excellent S.D.s. We could easily obtain three-dimensional coronary arterial and LV images without artifact of the RA and RV. CONCLUSIONS: Using 64-DAS MSCT, we successfully obtained exclusive enhancement of the left side of the heart using a small amount of CM.

Assessment of the severity of liver disease and fibrotic change: the usefulness of hepatic CT perfusion imaging.

This study assessed the utility of CT perfusion for quantitative assessment of liver function and fibrosis. Tissue blood flow (TBF), tissue blood volume (TBV), mean transit time (MTT) and hepatic arterial fraction (HAF) were measured with CT perfusion using the deconvolution algorithm in 38 patients with chronic liver diseases and 10 patients without liver disease. Using Child-Pugh classification, 21 patients were classified as Child A, 10 as Child B, and 7 as Child C. In 20 patients, the degree of fibrosis was quantitated in surgically-resected specimens and compared with the perfusion parameters. The mean TBF, TBV, MTT and HAF of patients with-out liver disease were 103.9+/-18 ml/min/100 g, 12.5+/-2.0 ml/100 g, 11.1+/-1.6 sec and 18.4+/-5.6%, respectively (+/-SD). The mean TBF of patients with Child A, B and C were 95.1+/-24, 86.7+/-29 and 75.5+/-6.5 ml/min/100 g, respectively. TBF tended to decrease with the severity of chronic liver disease. The mean HAF of patients with Child A, B and C were 18.6+/-8.3, 29.8+/-11.2 and 40.2+/-11.1%, respectively. HAF of patients without liver disease was significantly different from those of Child B and C (p<0.05, each). However, there were no significant differences in TBV and MTT between each groups. HAF correlated significantly with the degree of fibrosis (R2=0.588, p<0.05). Our results showed that parameters of CT perfusion correlated significantly with the severity of liver fibrosis and cirrhosis. Quantitative measurement of hepatic tissue blood flow by CT perfusion is useful for evaluation of the severity of disease and fibrotic change.

Quantitative tissue blood flow evaluation of pancreatic tumor: comparison between xenon CT technique and perfusion CT technique based on deconvolution analysis.

PURPOSE: There has been one report that tissue blood flow (TBF) quantification with xenon CT was effective in predicting the therapeutic response to an anticancer drug in pancreatic cancer. The purpose of this study was to evaluate the correlation between the TBF of pancreatic tumors calculated with xenon CT and those with perfusion CT, in order to evaluate whether perfusion CT could replace xenon CT. MATERIALS AND METHODS: Nine patients with pathologically proved pancreatic tumors who underwent both xenon CT and perfusion CT were included. RESULTS: Quantitative TBF of pancreatic tumors measured by perfusion CT ranged from 22.1 to 196.2 ml/min/100 g (mean+/-SD, 52.6+/-54.8 ml/min/100 g). In contrast, those obtained by xenon CT ranged from 10.3 to 173.6 ml/min/100 g (mean+/-SD, 47.4+/-49.4 ml/min/100 g). There was a good linear correlation between xenon CT and perfusion CT (y=0.8537x+2.48, R2=0.895: p<0.05). CONCLUSION: The TBF of pancreatic tumors measured by xenon CT and perfusion CT techniques showed a close linear correlation. We can expect that perfusion CT based on the deconvolution algorithm may replace xenon CT to predict the effect of pancreatic tumor treatment with anticancer drugs.

Effect of x-ray tube current on the accuracy of cerebral perfusion parameters obtained by CT perfusion studies.

The purpose of this study was to investigate the effect of x-ray tube current on the accuracy of cerebral perfusion parameters obtained by CT perfusion studies using multi-detector row CT (MDCT). Following the standard CT perfusion study protocol, continuous (cine) scans (1 s/rotation x 60 s) consisting of four 5 mm thick contiguous slices were performed using an MDCT scanner with a tube voltage of 80 kVp and a tube current of 200 mA. We generated the simulated images with tube currents of 50 mA, 100 mA and 150 mA by adding the corresponding noise to the raw scan data of the original image acquired above using a noise simulation tool. From the original and simulated images, we generated the functional images of cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) in seven patients with cerebrovascular disease, and compared the correlation coefficients (CCs) between the perfusion parameter values obtained from the original and simulated images. The coefficients of variation (CVs) in the white matter were also compared. The CC values deteriorated with decreasing tube current. There was a significant difference between 50 mA and 100 mA for all perfusion parameters. The CV values increased with decreasing tube current. There were significant differences between 50 mA and 100 mA and between 100 mA and 150 mA for CBF. For CBV and MTT, there was also a significant difference between 150 mA and 200 mA. This study will be useful for understanding the effect of x-ray tube current on the accuracy of cerebral perfusion parameters obtained by CT perfusion studies using MDCT, and for selecting the tube current.

Prospective respiratory-triggered multidetector row CT (MDCT) for abdominal examinations: initial experience with a prototype.

PURPOSE: To develop a prototype for prospective respiratory-triggered multidetector row computed tomography (MDCT) for abdominal examinations and to assess its feasibility. MATERIALS AND METHODS: The prototype consisted of the following components: an MDCT unit, personal computer (PC), and a respiratory motion detector in the form of a wearable belt with sensors to measure differences in pressure caused by breathing excursions. The registered signals were processed by the PC. The abdominal MDCT images of 10 healthy volunteers were obtained with an incremental axial technique in the expiration phase during normal breathing. Multiplanar reformations (MPR) were then performed. On the basis of the precision of these reconstructions, two radiologists then assessed the accuracy and applicability of the system. RESULTS: Coronal and sagittal MPR images from these prospective respiratory-gated examinations were found to be accurate. In particular, the continuity of borders and surfaces of scanned organs proved the exactness of the previously acquired respiration-correlated axial source images. CONCLUSION: This prototype is feasible to perform prospective respiratory-triggered abdominal MDCT examinations during normal respiration without breathhold. This system may be useful for patients with reduced compliance in holding their breath.

New method of measuring coronary diameter by electron-beam computed tomographic angiography using adjusted thresholds determined by calibration with aortic opacity.

BACKGROUND: In a previous study the adjusted thresholds at which the diameters of coronary arteries determined by enhanced electron-beam computed tomography (CT) scans are equal to the corresponding quantitative coronary angiography measurements were analyzed, and their correlation with maximum CT values for the vessel short axes was determined. A rapid accurate method for such measurements was sought by substituting maximum CT values for the descending aorta in the corresponding axial images for those for the short axes. METHODS AND RESULTS: In 8 patients, 179 sites were measured. Means (+/- SD) of adjusted thresholds and the maximum CT values for vessel short axes and the descending aorta in the corresponding axial images for all vessels were 108 +/-66, 227+/-80, and 363+/-75 Hounsfield Unit (HU), respectively. Adjusted thresholds correlated with the maximum CT values for the corresponding vessel short axes and the descending aorta in the corresponding axial images, with R2=0.55, 0.33, p<0.01, respectively. An abbreviated formula for use of maximum CT values for the descending aorta in the corresponding axial images was y=0.5x-75 (HU) (y= adjusted threshold, x= maximum CT value for the descending aorta in the corresponding axial image). CONCLUSIONS: The abbreviated formula provided a rapid, accurate method for measurements independent of arterial enhancement.

Detection of pulmonary metastases with multi-detector row CT scans of 5-mm nominal section thickness: autopsy lung study.

PURPOSE: To determine the effect of changing pitch and collimation on depiction of pulmonary metastases on scans of 5-mm section thickness obtained with multi-detector row computed tomography (CT) compared with those obtained with single-detector row CT. MATERIALS AND METHODS: In five autopsy lungs, 1,013 metastatic 0.5-30.0-mm nodules were detected at helical CT with 1-mm collimation and histopathologically diagnosed as metastases. Each nodule was numbered, and its localization was recorded as the standard for subsequent studies. Four types of scans of 5-mm section thickness were obtained with multi-detector row CT and four sets of helical pitch and table speed, respectively, as follows: set A, 3:1 and 7.5 mm per rotation; set B, 6:1 and 15 mm per rotation; set C, 6:1 and 30 mm per rotation; set D, conventional and 5-mm interval. Conventional helical CT scans (set E) were obtained with 5-mm collimation at single-detector row CT. Two independent observers evaluated the five sets of CT scans. RESULTS: Acquisition times for sets A-D, respectively, were 1.9, 3.8, 7.5, and 1.5 times faster than they were for set E. The mean numbers of detected nodules were 671 (66%) in set A, 661 (65%) in set B, 678 (67%) in set C, 654 (65%) in set D, and 656 (65%) in set E; there was no significant difference in the number of detected nodules among the five sets (P =.997, McNemar test and Bonferroni equation). CONCLUSION: Regardless of varying pitch or detector collimation, multi- and single-detector row CT scans obtained with 5-mm section thickness have almost the same ability to depict pulmonary metastases and are equivalent.

Coronal multiplanar reconstruction view from whole lung thin-section CT by multidetector-row CT: determination of malignant or benign lesions and differential diagnosis in 68 cases of solitary pulmonary nodule.

PURPOSE: The purpose of this study was to evaluate the usefulness of the coronal multiplanar reconstruction (MPR) view in comparison with transverse helical thin-section CT for both the determination of malignant or benign lesions and the differential diagnosis of solitary pulmonary nodules. MATERIALS AND METHODS: Sixty-eight cases of pathologically proved solitary pulmonary nodule less than 3 cm in diameter were enrolled in this study. For the routine study, transverse helical thin-section CT (1.25 mm collimation, FOV 20 cm) covering the areas with solitary pulmonary nodules as well as whole lung helical thin-section CT (2.5 mm collimation, 1.25 mm reconstruction interval, FOV 34.5 cm, pitch 6:1, high-spatial frequency algorithm) were scanned with a multidetector-row CT (MDCT) scanner. From the whole lung thin-section CT data, coronal MPR views (2.5 mm slice thickness) were reconstructed on a workstation. ROC analysis was used for an observer performance study, in which three observers indicated their confidence level for the determination of malignant or benign lesion for the nodules by means of transverse thin-section CT and coronal MPR. In addition, the observers recorded appropriate disease entities as the final diagnosis of each case. Accuracies of the final diagnosis based on the two sets of images were compared with McNemer' s test. RESULTS: In terms of the determination of malignant or benign lesion, there was no significant difference between the two sets of images (coronal MPR and transverse thin-section CT; mean Az=0.853 and 0.854, respectively). In addition, accuracy of the final diagnosis based on coronal MPR views (74%) was almost equal to that based on transverse thin-section CT (71%) (p=0.3). CONCLUSIONS: The diagnostic efficacy of the coronal MPR view is comparable to that of transverse thin-section CT for the evaluation of solitary pulmonary nodules.

Multidetector CT: diagnostic impact of slice thickness on detection of hypervascular hepatocellular carcinoma.

OBJECTIVE: The objective of our study was to evaluate the diagnostic impact of varying slice thickness on multidetector CT to optimize detection of hypervascular hepatocellular carcinoma. MATERIALS AND METHODS: Forty-three patients with 87 hypervascular hepatocellular carcinomas (diameter: range, 3-80 mm; mean, 22 mm) and 19 patients with either chronic hepatitis or liver cirrhosis and without hepatocellular carcinoma who had undergone early arterial and late arterial phase imaging of the entire liver on multidetector CT were retrospectively enrolled in this study. The detector row configuration was 2.5 x 4 mm, the pitch was 6, and the scanning time was 10.5 sec for each phase. All patients received contrast medium (2 mL/kg of body weight) at a rate of 5 mL/sec; the mean scanning delay for the early arterial phase was 19.0 sec, and the mean delay for the late arterial phase was 34.5 sec. Eighty 2.5-mm-thick reconstruction images, forty 5-mm-thick reconstruction images, and twenty-six 7.5-mm-thick reconstruction images were obtained for each phase. Each image set was interpreted separately by three observers to detect hypervascular hepatocellular carcinoma by viewing images on a workstation monitor. Sensitivity, positive predictive value, and area under the receiver operating characteristic curve (A(z)) were calculated. We used retrospectively excellent follow-up and imaging or pathologic proof as the gold standard. RESULTS: The mean sensitivity and positive predictive value for hypervascular hepatocellular carcinoma were 76% and 69% on 2.5-mm images, 73% and 69% on 5-mm images, and 67% and 76% on 7.5-mm images, respectively. No significant difference in sensitivity among the images was detected, except by one observer who reported a significant difference in the sensitivity between 2.5- and 7.5-mm images (p < 0.05) and between 5- and 7.5-mm images (p < 0.05). The mean A(z) values were 0.79, 0.80, and 0.78 for 2.5-, 5-, and 7.5-mm images, respectively. No significant difference in A(z) values among the images obtained with different slice thicknesses was detected. CONCLUSION: For multidetector CT identification of hypervascular hepatocellular carcinoma, we found little or no advantage in reducing slice thickness to less than 5 mm.

Multi-detector row helical CT angiography of hepatic vessels: depiction with dual-arterial phase acquisition during single breath hold.

PURPOSE: To determine by using multi-detector row computed tomography (CT), in a triphasic hepatic dynamic study, which included single breath-hold dual-arterial phase acquisition, the accuracy and frequency of visualization of the small hepatic arterial and portal venous anatomy with angiographic correlation. MATERIALS AND METHODS: In 62 patients, pre- and postcontrast triphasic helical CT were performed by using a multi-detector row CT scanner, with 2.5-mm detector row collimation, at a pitch of 6. The first and second arterial phases were performed during a single breath hold. One reader, blinded to the results of the angiography, reviewed the first arterial phase images on a cine display to assess hepatic arterial anatomy. Visualization of the portal vein and its branches was assessed by using second arterial and portal venous phase images. RESULTS: Major arterial trunks (celiac, hepatic, superior mesenteric, and left gastric) were depicted in all cases. Visualization of small arteries was as follows: right and left hepatic, 62 (100%) of 62; middle hepatic, 52 (87%) of 60; cystic, 47 (90%) of 52; right gastric, 50 (89%) of 56; and right and left inferior phrenic, 57 (92%) and 55 (89%) of 62, respectively. Subsegmental or more peripheral branches of the portal vein were depicted in 83% of cases during the second arterial phase and in 96% during the portal phase. There was no difference in degree of visualization in these two phases. CONCLUSION: Multi-detector row CT angiography was able to depict the hepatic vascular anatomy.