Efficacy of Barium-Based Fecal Tagging for CT Colonography: a Comparison between the Use of High and Low Density Barium Suspensions in a Korean Population - a Preliminary Study

OBJECTIVE: This preliminarily study was designed to determine and to compare the efficacy of two commercially available barium-based fecal tagging agents for CT colonography (CTC) (high-density [40% w/v] and low-density [4.6% w/v] barium suspensions) in a population in Korea. MATERIALS AND METHODS: In a population with an identified with an average-risk for colorectal cancer, 15 adults were administered three doses of 20 ml 40% w/v barium for fecal tagging (group I) and 15 adults were administered three doses of 200 ml 4.6% w/v barium (group II) for fecal tagging. Excluding five patients in group I and one patient in group II that left the study, ten patients in group I and 14 patients in group II were finally included in the analysis. Two experienced readers evaluated the CTC images in consensus regarding the degree of tagging of stool pieces 6 mm or larger. Stool pieces were confirmed with the use of standardized CTC criteria or the absence of matched lesions as seen on colonoscopy. The rates of complete fecal tagging were analyzed on a per-lesion and a per-segment basis and were compared between the patients in the two groups. RESULTS: Per-lesion rates of complete fecal tagging were 52% (22 of 42; 95% CI, 37.7-66.6%) in group I and 78% (28 of 36; 95% CI, 61.7-88.5%) in group II. The difference between the two groups did not reach statistical significance (p = 0.285). The per-segment rates of complete tagging were 33% (6 of 18; 95% CI, 16.1%-56.4%) in group I and 60% (9 of 15; 95% CI, 35.7%-80.3%) in group II; again, the difference between the two groups did not reach statistical significance (p = 0.171). CONCLUSION: Barium-based fecal tagging using both the 40% w/v and the 4.6% w/v barium suspensions showed moderate tagging efficacy. The preliminary comparison did not demonstrate a statistically significant difference in the tagging efficacy between the use of the two tagging agents, despite the tendency toward better tagging with the use of the 4.6% w/v barium suspension.

Optimization of the Contrast Mixture Ratio for Simultaneous Direct MR and CT Arthrography: an in Vitro Study

OBJECTIVE: This study was designed to determine the optimal mixture ratio of gadolinium and iodinated contrast agent for simultaneous direct MR arthrography and CT arthrography. MATERIALS AND METHODS: An in vitro study was performed utilizing mixtures of gadolinium at six different concentrations (0.625, 1.25, 2.5, 5.0, 10 and 20 mmol/L) and iodinated contrast agent at seven different concentrations (0, 12.5, 25, 37.5, 50, 75 and 92-99.9%). These mixtures were placed in tissue culture plates, and were then imaged with CT and MR (with T1-weighted sequences, proton-density sequences and T2-weighted sequences). CT numbers and signal intensities were measured. Pearson's correlation coefficients were used to assess the correlations between the gadolinium/iodinated contrast agent mixtures and the CT numbers/MR signal intensities. Scatter diagrams were plotted for all gadolinium/iodinated contrast agent combinations and two radiologists in consensus identified the mixtures that yielded the optimal CT numbers and MR signal intensities. RESULTS: The CT numbers showed significant correlation with iodinated contrast concentrations (r = 0.976, p < 0.001), whereas the signal intensities as measured on MR images showed a significant correlation with both gadolinium and iodinated contrast agent concentrations (r = -484 to -0.719, p < 0.001). A review of the CT and MR images, graphs, and scatter diagram of 42 combinations of the contrast agent showed that a concentration of 1.25 mmol/L gadolinium and 25% iodinated contrast agent was the best combination for simultaneous CT and MR imaging. CONCLUSION: A mixture of 1.25 mmol/L gadolinium and 25% iodinated contrast agent was found to be optimal for simultaneous direct MR arthrography and CT arthrography.

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.

Massive Intraventricular Air Embolism after Contrast-enhanced CT: Report of Two Cases

Venous air embolism, although considered as a rare condition, it occurs more frequently than it is recognized. Air embolism has been reported to occur after contrast-enhanced CT examination in up to 23% of patients. Because these emboli are usually small to moderate size and they are venous, the patients are usually asymptomatic. However, a large amount of intravenous air can cause disastrous consequences and it can be fatal. The author reports here on 2 cases of symptomatic massive intraventricular air embolism after contrast enhanced CT with a brief review of the pathophysiology and the recommended treatment of air embolization.

Gadolinium as a CT Contrast Agent: An Experimental Study for the Effects of Injection Parameters in the Rabbit Brain Model

PURPOSE: We wanted to investigate the use of gadolinium based contrast agent (Gd-DTPA) for computed tomography (CT), and we also wanted to assess the effects of valuable injection parameters on enhancement in an experimental rabbit brain model. MATERIALS AND METHODS: In vitro, attenuation measurements of serial dilutions of Gd-DTPA and iopromide were compared. In five rabbits, single level dynamic gadolinium-enhanced brain CT studies were obtained using different injection parameters. A comparison CT scan after iopromide administration was performed. The time-attenuation curves of the brain vessel and parenchyma were obtained and the magnitude of enhancement (Hmax) and the time to peak enhancement (Tmax) were analyzed. RESULTS: In vitro, the attenuation coefficient of undiluted Gd-DTPA (2,578 HU) was higher than that of iopromide (1,761 HU) at equimolar concentrations. In 5 rabbits, the time-attenuation curve demonstrated a distinct pattern with peak enhancement only in the brain vessel, but not in the brain parenchyma. There was increasing linear relationship between the injection rate of Gd-DTPA and Hmax, and a declining linear relationship with Tmax. The higher the concentration of Gd-DTPA, the higher Hmax was, but no significant difference was found for the Tmax. Higher volumes of Gd-DTPA revealed a higher Hmax and a delayed Tmax. CONCLUSION: Enhancement of the brain parenchyma on gadolinium-enhanced CT is minimal, while enhancement of the brain vessels is distinctive. The most important factor affecting Hmax of the vessel is the concentration of the contrast medium and the most important factor affecting Tmax of the vessel is volume of the contrast medium. The gadolinium-based contrast agent may be an reasonable alternative contrast agent for brain CT, and especially in cerebral vessels, and it may also be advantageous for brain parenchyma of those patients with BBB dysfunction.

Hepatic CT Enhancement: Comparison between Dimeric and Monomeric Nonionic Contrast Agents in Rabbits

PURPOSE: To determine the hepatic and vascular enhancement profiles with nonionic dimeric, iodixanol, contrast agent in the rabbit and to compare them with nonionic monomeric, ioversol, contrast agent. MATERIALS AND METHODS: Seven rabbits initially underwent hepatic dynamic CT scan with either iodixanol or ioversol, followed by repeated CT scan with other unused contrast agent with one week interval between scans. Pre and post contrast attenuation values of hepatic parenchyma, aorta and portal vein were measured sequentially. The mean enhancement of the hepatic parenchyma, aorta and portal vein were compared between two agents. The mean peak enhancement and peak enhancement time of the liver, aorta, and portal vein were also compared. RESULTS: The attenuation values of ioversol showed a greater mean hepatic enhancement than iodixanol from 18 seconds to 39 seconds after injection (from late arterial phase to early portal venous phase) with a statistical significance (p<0.05). The mean peak enhancement of hepatic parenchyma, aorta and portal vein was also greater using ioversol than iodixanol, but the mean peak enhancement times of ioversol and iodixanol were nearly identical. CONCLUSION: Ioversol may have the greater effects than iodixanol on hepatic tumor conspicuity, especially from late arterial phase to early portal veneous phase.

Thin Slice Thickness Double-Dose Contrast-Enhanced CT in the Detection of Brain Metastases

PURPOSE: To compare the usefulness of double-dose contrast-enhanced CT (DDCE-CT) and conventional contrast-enhanced CT (CCE-CT) in the detection of metastatic brain lesions. MATERIALS AND METHODS: Sixteen patients with brain metastases were evaluated with both CCE-CT and thinslice DDCE-CT. For CCE-CT, an initial injection of 100 ml contrast medium was given, and DDCE-CT with both 10-mm and 5-mm thickness was performed after the addition of an extra 100 ml of contrast medium. The numbers of metastatic lesions detected by CCE-CT and by DDCE-CT were compared, as were the findings of contrast-enhanced MRI (CE-MRI) and thin-slice DDCE-CT in seven patients who underwent both these procedures. RESULTS: Fourteen metastatic brain lesions were detected by CCE-CT, 22 by 10-mm-thickness DDCE-CT, and 36 by 5-mm thickness DDCE-CT. Thus, almost 2.6 times more lesions were detected by thin-slice DDCE-CT than by CCE-CT. Metastatic lesions were detected by 10-mm-thickness DDCE-CT in 16 patients and by CCECT in seven; in five, edema only was detected, while in four there were no detectable metastases. CCE-CT detected four lesions of less than 5 mm in diameter, while 10-mm-thickness DDCE-CT and 5-mm-thickness DDCE-CT detected seven and 18 lesions, respectively. Eleven lesions were detected by thin-slice DDCE-CT and 17 by CE-MRI in the seven patients who underwent both CE-MRI and DDCE-CT. The lesions detected only by CE-MRI were less than 5 mm in diameter and were discovered in the cerebellum or inferior temporal lobe. CONCLUSION: Thin-slice DDCE-CT was superior to CCE-CT in detecting metastatic brain lesions.

Contrast Media in Abdominal Computed Tomography: Optimization of Delivery Methods

OBJECTIVE: To provide a systematic overview of the effects of various parameters on contrast enhancement within the same population, an animal experiment as well as a computer-aided simulation study was performed. MATERIALS AND METHODS: In an animal experiment, single-level dynamic CT through the liver was performed at 5-second intervals just after the injection of contrast medium for 3 minutes. Combinations of three different amounts (1, 2, 3 mL/kg), concentrations (150, 200, 300 mgI/mL), and injection rates (0.5, 1, 2 mL/sec) were used. The CT number of the aorta (A), portal vein (P) and liver (L) was measured in each image, and time-attenuation curves for A, P and L were thus obtained. The degree of maximum enhancement (Imax) and time to reach peak enhancement (Tmax) of A, P and L were determined, and times to equilibrium (Teq) were analyzed. In the computed-aided simulation model, a program based on the amount, flow, and diffusion coefficient of body fluid in various compartments of the human body was designed. The input variables were the concen-trations, volumes and injection rates of the contrast media used. The program generated the time-attenuation curves of A, P and L, as well as liver-to-hepatocel-lular carcinoma (HCC) contrast curves. On each curve, we calculated and plotted the optimal temporal window (time period above the lower threshold, which in this experiment was 10 Hounsfield units), the total area under the curve above the lower threshold, and the area within the optimal range. RESULTS: A. Animal Experiment: At a given concentration and injection rate, an increased volume of contrast medium led to increases in Imax A, P and L. In addition, Tmax A, P, L and Teq were prolonged in parallel with increases in injection time The time-attenuation curve shifted upward and to the right. For a given volume and injection rate, an increased concentration of contrast medium increased the degree of aortic, portal and hepatic enhancement, though Tmax A, P and L remained the same. The time-attenuation curve shifted upward. For a given volume and concentration of contrast medium, changes in the injection rate had a prominent effect on aortic enhancement, and that of the portal vein and hepatic parenchyma also showed some increase, though the effect was less prominent. A increased in the rate of contrast injection led to shifting of the time enhancement curve to the left and upward. B. Computer Simulation: At a faster injection rate, there was minimal change in the degree of hepatic attenuation, though the duration of the optimal temporal window decreased. The area between 10 and 30 HU was greatest when contrast media was delivered at a rate of 2 -3 mL/sec. Although the total area under the curve increased in proportion to the injection rate, most of this increase was above the upper threshould and thus the temporal window was narrow and the optimal area decreased. CONCLUSION: Increases in volume, concentration and injection rate all resulted in improved arterial enhancement. If cost was disregarded, increasing the injection volume was the most reliable way of obtaining good quality enhancement. The optimal way of delivering a given amount of contrast medium can be calculated using a computer-based mathematical model.

The Usefulness of 0.5 %-Methylcellulous as Oral Contrast Agent: In Subtotal Gastrectomy Patients

PURPOSE: To assess the usefulness of 0.5 %-methylcellulose as oral contrast agent in spiral CT examinationsfor the evaluation of anastomotic site and remnant stomach in patients who have undergone subtotal gastrectomy dueto stomach cancer. MATERIALS AND METHODS: Twenty-seven patients who underwent subtotal gastrectomy for stomachcancer and were referred for the evaluation of anastomosis recurrence and lymph node metastasis wereprosepectively analyzed by spiral CT. They were divided into two groups: before scanning, group A patients drank0.5 %-methylcellulous 500ml as oral contrast agent, while those in group B drank diluted gastrografin 500ml. Threepatients were examined twice. Anatomic delineation of the anastomosis site was graded by two radiologists asexcellent (3), good (2), fair (1), or poor (0). To evaluate the degree of distension, maximal transverse andanterior-posterior diameter of remnant stomach and anastomotic sites were measured. RESULTS: In Group A, anatomicdelineation of the anastomotic site was very much better than in group B (mean score: 2.93 vs 1.80, p<0.05). Inaddition, the maximum diameters of remnant stomach and anastomotic site were significantly larger in group A thanin group B (transverse A-P remnant stomach and anastomosis site: 87.5 +/-14.7mm, 103.3 +/-20.1mm, 17.6 +/-2.9mm vs57.6 +/-20.1mm, 69.9 +/-3 5 . 0 m m , 10.7 +/-7 . 2 m m ) CONCLUSION: In patients who had undergone subtotalgastrectomy, the use of 0.5 %-methylcellulose as oral contrast agent for spiral CT showed excellent anatomicdelineation of the anastomotic site and distension of remnant stomach.

Biliary Stones: Change of CT Attenuation in Water Soluble Contrast Media

PURPOSE: To investigate change of CT attenuation of biliary stones in water soluble contrast media with time as well as the factors contributing to this change. MATERIALS AND METHODS: Thirty biliary stones were placed within cone-shaped plastic tubes, and as a control study, spiral CT scanning was performed 50 minutes after immersion in normal saline. The stones were rescanned at 5, 10, 20, 30, 45, 60, 90 and 120 minutes after immersion in water soluble contrast media. Mean CT attenuation value and volume of the stones were measured after three-dimensional reconstruction of images. Physical factors such as porosity[(wet weight - dry weight) / wetweight]x100, volume, and cholesterol as a chemical factor were measured. RESULTS: The pattern of change of CT attenuation was classified as one of three types. Fifteen stones (50%) were classified as type 1, in which attenuation increased with immersion time; in ten stones, this increase was rapid, particularly within the first 5 minutes. Twelve (40%) were classified as type 2, in which attenuation showed no significant change. Three stones showed no regular pattern, and these were classified as type 3. The mean porosity of type 1 (median; 32.7, mean+/-SD; 52.83+/-34.48) was greater than that of type 2 (median; 6.7, mean+/-SD; 30.58+/-48.25)(p<.05). The volume and cholesterol fraction of stones were not significantly different between type 1 and 2. CONCLUSION: In some biliary stones, CT attenuation value increases in water-soluble contrast media with time, and porosity is the most important factor in attenuation change.

Transient Inhomogeneous Contrast Enhancement of the Spleen on Arterial Phase of Spiral CT

PURPOSE: To assess the relationship between splenic transient inhomogeneous contrast enhancement(CE) on the arterial phase of spiral CT, and splenic volume, and to classify the CE pattern in liver cirrhosis. MATERIALS AND METHODS: We measured the splenic volume of 120 patients, 60 showed inhomogeneous splenic CE on arterial phase,and 60 showed homogeneous splenic CE. CT scans with intrinsic splenic pathology were excluded. Sixteen patients with clinically confirmed liver cirrhosis were included. Splenic volumes of the inhomogeneous and homogeneous CE group were compared. The inhomogeneous group was divided into three grades according to areas of non-enhanced portion (grade I, focal geographic ; grade II, multifocal patchy, grade III, extensive serpentine inhomogeneous CE) , and these were correlated with splenic volume. RESULTS: Among the 60 inhomogeneous CE scans, 23 cases(38.3%) showed splenomegaly (spleen volume>220cm3); in contrast, this applied to only 8 cases (13.3%) of the 60 homogeneous CE scans. Mean splenic volume in the inhomogeneous CE group (226.74+/-129.78cm3) was greater than in the homogeneous CE group (184.56+/-77.44cm3) (p<0.033). A larger splenic volume and extensive inhomogeneous CE(grade III) were noted, and most liver cirrhosis patients(14/16) were grade III. Three such patients who had shown inhomogeneous splenic CE on arterial phase showed inhomogeneous CE even on portal phase. CONCLUSION: Inhomogeneous splenic CE on arterial phase was more common in cases of an enlarged spleen, and more extensive in liver cirrhosis. These findings suggest hemodynamic change of the spleen may be a contributory factor.

Reduced Volume of Contrast Media: Effect on Vascular Opacification and Image Quality in Spiral CT of the Chest

PURPOSE: To evaluate the effect of reduced volume of contrast media on vascular opacification and image quality in spiral CT of the chest. MATERIALS AND METHODS: Sixty patients referred for chest CT were examined withspiral CT with 60ml(n=30) or 90ml(n=30) of 30% ionic contrast media(Rayvist 300 , Schering, Germany) alternately.Injection rate of each group was as follows : 2.0 ml/sec for 20 seconds followed by 1.0 ml/sec for 20 seconds in 60ml group and 2.0ml/sec for 45 seconds in 90ml group. Twenty-five seconds scanning delay was employed. For the objective comparison of vascular opacification, CT numbers were measured at superior vena cava, ascending and descending aorta, right and left pulmonary artery, left atrium, and inferior vena cava. For the subjective comparison three radiologists scored the grade of vascular opacification and image quality blindly and independently. All data were analyzed statistically. RESULTS: The mean values of measured CT numbers in 90ml group were higher than those in 60ml group(p <.05) at the same level. The overall mean score of vascular opacification in 90ml group was 2.86, and 2.31 in 60ml group(p <.0001). In the overall mean score of imagequality, there was no statistically significant difference between 90ml group(2.46) and 60ml group(2.40). CONCLUSION: Althought there is some degradation of vascular opacification in 60ml group, overall image quality is not degraded. Therefore, 60 ml of contrast media can be used in spiral CT of the chest without degradation ofoverall image quality except in spiral CT angiography.

Triple Phase Spiral CT of The Liver: Degree of Liver Parenchymal Enhancement

PURPOSE: To determine the degree and effect of contrast enhancement of the hepatic parenchyma according to different injection rates, amounts and types of contrast materials. MATERIALS AND METHODS: A total of 270 patients were divided into nine groups. Each group received different volumes(120, 130, or 140ml) and was scannedwith different injection rates of 2, 3 or 4 ml/sec. Three kinds of contrast materials(Ultravist 370, Iopamiro 370, Optiray 320) were used. Hepatic enhancement was measured by comparing quantitative regions of interest(ROI) beforeand after bolus injection of contrast material which were evaluated on arterial, portal and delayed phase duringdouble spiral scanning. RESULTS: There was no significant statistical difference in contrast enhancement between the three kinds of contrast materials. In noncirrhotic patients, hepatic enhancement was greatest on portal phase and was greater at a rate of 4ml/sec than 2ml/sec or 3ml/sec on arterial phase. At the same injection rate, thevolume of contrast material was an important factor on portal and delayed phase. In the cirrhotic patients, Child's C showed more delayed peak enhancement than did Child's A. CONCLUSION: The important factors in contrast enhancement were injection rate on arterial phase and volume on portal and delayed phase. The optimal choice mustbe made after considering intrinsic variables ; in addition, our results are helpful for determining enhancement protocol during double spiral CT scanning.

Spiral CT of Hepatocellular Carcinoma: Value of Dynamic Fast Infusion of Contrast Material

PURPOSE: To assess the value of dynamic fast infusion of contrast material in the detection and diagnosis of hepatocellular carcinoma(HCC) with spiral CT. MATERIALS AND METHODS: Two-phase dynamic spiral CT was performed in 59 patients with 104 HCCs. 150ml of nonionic contrast material was injected with an automatic injector at the rateof 5 ml/sec. Two-phase images were obtained at 20-45 sec(arterial dominant phase) and 2-5 min(equilibrium phase)after the initiation of bolus injection of contrast material. The tumors were divided into three groups(5cm) according to the size and the enhancement patterns on two-phase images were compared. RESULTS: Inthe arterial phase, HCCs showed total or partial hyperattenuation in 79% of cases(82/104), isoattenuation in 12%,and hypoattenuation in 9%. In the equilibrium phase, HCCs showed hypoattenuation in 86%(89/104) and isoattenuationin 14%. The most common and characteristic enhancement patterns of HCCs were hyperattenuation in the arterialphase and hypoattenuataion in the equilibrium phase ; in the latter, capsules were demonstrated in 45% of cases. Invasions of the portal and/or hepatic vein were demonstrated in 34% of cases. CONCLUSION: Dynamic fastinfusion(5ml/sec) of contrast material(150ml) is useful in the detection and diagnosis of HCCs with spiral CT.