Hepatic metastasis detection: comparison of three CT contrast enhancement methods

A prospective, blinded comparison of three methods of hepatic contrast enhancement in computed tomography (CT) was conducted in 15 patients with colorectal carcinoma metastatic to the liver. Arterial portography (AP-CT) was performed with injection of contrast material into the superior mesenteric artery during CT. Delayed scanning (DS-CT) was performed 4 hours after intravascular administration of contrast material (mean dose, 280 mL). CT with an ethiodized oil emulsion (EOE-CT) was performed 1 hour after slow intravenous infusion of the emulsion. All patients underwent laparotomy following imaging studies. A lesion-by-lesion analysis of 56 metastases showed no significant differences in sensitivity (AP-CT, 77%; DS-CT, 83%; EOE-CT, 82%), but the false-positive rate for AP-CT was significantly higher than that for DS-CT (P less than .001) or EOE-CT (P less than .01). False-positive rates for EOE-CT and DS-CT were not significantly different. The predictive value of a positive test was 63% for AP-CT, 90% for DS-CT, and 81% for EOE-CT. AP-CT does not appear to be clinically useful for detection of hepatic metastases because of the high false-positive rate. No difference could be demonstrated between DS-CT and EOE-CT. DS-CT is a valuable method for hepatic contrast enhancement.     

Iohexol for contrast enhancement of bowel in pediatric abdominal CT

Abdominal CT scans from 160 examinations performed on pediatric patients using iohexol 2 percent as contrast medium for bowel enhancement were evaluated retrospectively. When diluted with a beverage of the child's choice, iohexol has a neutral taste and cannot be detected, and 139 out of 142 patients drank the full amount of dilute contrast offered to them. The enhancement of bowel in the area of interest was graded as good (58%), reasonable (23%), or poor (19%). The contrast medium was prepared from leftovers from our angiocardiography studies. We conclude that the use of water-soluble contrast medium in a low concentration is a safe and cost-effective way of facilitating ingestion of sufficient amounts of the medium in oncologic pediatric patients undergoing cytotoxic and/or radiation treatment.     

Improved uniformity of aortic enhancement with customized contrast medium injection protocols at CT angiography

PURPOSE: To compare the uniformity of aortoiliac opacification obtained from uniphasic contrast medium injections versus individualized biphasic injections at computed tomographic (CT) angiography. MATERIALS AND METHODS: Thirty-two patients with an abdominal aortic aneurysm underwent CT angiography. In 16 patients (group 1), 120 mL of contrast material was administered at a flow rate of 4 mL/sec. In the other 16 patients (group 2), biphasic injection protocols were computed by using mathematic deconvolution of each patient's time-attenuation response to a standardized test injection. Attenuation uniformity was quantified as the "plateau deviation" of enhancement values, which were calculated as the SD of the time-contiguous attenuation values observed during the 30-second scanning period. RESULTS: Group 2 patients received between 77 and 165 mL (mean, 115 mL) of contrast medium. Initial flow rates ranged from 4.1 to 10.0 mL/sec (mean, 6.8 mL/sec) for the first 4-6 seconds; continuing flow rates ranged from 2.0 to 4.8 mL/sec (mean, 3.1 mL/sec) for the remaining 24-26 seconds. The plateau deviation was significantly smaller in group 2 patients (19 HU) versus group 1 patients (38 HU, P <.001). CONCLUSION: At CT angiography, tailored biphasic injections led to more uniform aortoiliac enhancement, compared with standard uniphasic injections of contrast medium.     

Hepatic haemodynamics: interrelationships between contrast enhancement and perfusion on CT and Doppler perfusion indices.

This study compares three techniques that evaluate hepatic haemodynamics for the detection of metastatic liver disease to determine the interrelationships between the techniques and to assess their equivalence. The three techniques studied were dedicated CT measurements of hepatic enhancement, CT measurements of perfusion and Doppler perfusion indices. 53 patients with proven malignancies of either breast or colon underwent a single location dynamic CT for measurement of hepatic perfusion and enhancement, whilst a subset of 12 patients underwent both CT perfusion and Doppler perfusion studies. Statistically significant correlations were found between CT arterial phase enhancement and CT arterial perfusion (r=0.612, p<0.001), and between both of these parameters and Doppler arterial flow (r=0.867, p<0.001 and r=0.842, p<0.001, respectively). Significant correlations were also found between both the ratio of CT arterial enhancement to peak enhancement and the CT arterial perfusion with the Doppler perfusion index (r=0.797, p=0.002 and r=0.725, p=0.008, respectively). Combined CT arterial and portal perfusion correlated with peak liver enhancement (r=0.614, p< 0.001), but Doppler measurements of portal flow did not correlate with any CT parameter. Increased arterial enhancement, perfusion or flow are valuable additional radiological signs for the presence of hepatic metastases that can be elicited by incorporating any one of these methods into existing imaging protocols.     

Hepatic dynamic sequential CT: section enhancement profiles with a bolus of ionic and nonionic contrast agents

The enhancement characteristics in different portions of the liver during dynamic sequential bolus computed tomography (CT) with iodinated contrast material (DSBCT) were prospectively evaluated in 75 patients by using iothalamate meglumine, iopamidol, and iohexol (25 patients received each agent). After baseline noncontrast CT was performed, DSBCT was performed with a 180-mL intravenous bolus administered at 2 mL/sec. Scanning was started 25 seconds after the bolus was initiated, by using a 3-second scan time and rapid cephalocaudal table incrementation, yielding contiguous 8-mm-thick sections at a rate of nine sections per minute. On postcontrast images, peak enhancement was 115% for iopamidol and 117% for iohexol, both of which were superior to iothalamate meglumine at 95% (P less than .05). After peaking, enhancement then decreased for all three contrast agents, although the decline was more precipitous for iothalamate meglumine. Enhancement on the more caudal sections with both iopamidol and iohexol was superior to that with iothalamate meglumine (P less than .05). The data suggest that the enhancement characteristics for the two nonionic agents may be more optimal for detection of focal hepatic lesions than the ionic agent.     

Aortoiliac enhancement during computed tomography angiography with reduced contrast material dose and saline solution flush: influence on magnitude and uniformity of the contrast column

RATIONALE AND OBJECTIVES: To compare the magnitude and uniformity of aortoiliac contrast enhancement obtained from uniphasic contrast material injections versus contrast material injections with reduced iodine dose followed by a saline flush in aortoiliac multislice CT angiography (CTA). METHODS: Twenty-nine patients with abdominal aortic aneurysms underwent aortoiliac CTA using protocols A and B. With protocol A, 120 mL contrast material (300 mgI/mL), and with protocol B, 100 mL contrast material followed by a 40-mL saline solution flush were administered at a flow rate of 4 mL/s. Quantitative analysis was performed by calculating mean aortoiliac attenuation, mean plateau deviation, and mean difference between maximum and minimum attenuation value for both groups. Qualitative analysis was performed by visual assessment of vascular enhancement using 2-dimensional and 3-dimensional postprocessing techniques. RESULTS: The mean aortoiliac attenuation with protocol A was 291 +/- 62 HU, and with protocol B it was 285 +/- 61 HU. The difference of 6 HU was not statistically significant (P = 0.27). Mean plateau deviation was significantly smaller using protocol A than protocol B (16 +/- 9 HU vs. 20 +/- 10 HU, P = 0.03). In addition, the mean difference between maximum and minimum attenuation value was significantly smaller with protocol A than with protocol B (59 +/- 29 HU vs. 72 +/- 32 HU, P = 0.01). Visual analysis showed no difference in contrast material magnitude and homogeneity between the protocols. CONCLUSIONS: In aortoiliac CTA, a saline solution flush after contrast material bolus allows an iodine dose reduction of approximately 20 mL without impairing the magnitude of contrast enhancement but degrades the uniformity of the contrast column. However, the degradation does not affect visual analysis.     

肺动脉CT成像增强技术的优化研究

目的 推导CT肺动脉成像(CTPA)中精确计算对比剂用量公式,并评价其应用于小剂量对比剂预注射法CTPA影像的质量与临床应用的意义.方法 搜集经CTPA检查的连续27例患者小剂量对比剂实验注射形成的TDC数据,分析从注射对比剂开始至上腔静脉下端增强峰值所用时间占注射开始至肺动脉增强峰值时间的比值,测算上腔静脉下端在扫描范围中的水平,推导出计算对比剂使用总量预计算公式( DTs/3+ STs/2).将临床怀疑但CTPA未发现为肺动脉栓塞(PE)的68例患者纳入研究,按检查奇、偶周数分为2组:A组26例,传统增强跟踪自动触发扫描组;B组42例,小剂量对比剂预注射组.在CTPA影像中,2组分别测量右肺动脉主干(RMPA)和右上肺静脉(RUPV)、右肺下叶后基底段动脉(RLPA)和伴行右下肺静脉(RLPV)、RMPA与升主动脉(AA)的CT值,计算每对血管CT值差值,对影像进行评分,并计算对比剂用量、上腔静脉内对比剂硬化伪影分级.采用f检验、x2检验与秩和U检验,分析2组间各值差异的统计学意义.结果 对比剂开始至注射到上腔静脉增强时间与至肺动脉增强时间比为0.65±0.09.A、B2组间RMPA、RLPA的CT值分别为(301±117)、(329±122)与(283±95)、(277±98)HU,差异无统计学意义(t值分别为1.060、2.056,P值均＞0.05),但肺动静脉血管对之间的CT值差(中位数分别为22.5、58.0与170.5、166.5 HU),2组间差异有统计学意义(U=292,P=0.001与U=325,P=0.005);影像评分为5分与4分者B组为85.7％( 36/42)优于A组(46.1％,12/26),差异有统计学意义(x2=14.175,P＜0.01);上腔静脉内对比剂伪影分级(1～3级)B组(分别为34、7、1例)明显好于A组(分别为11、10、5例),差异有统计学意义(x2=10.714,P=0.002);对比剂实际注射总量A组为(87.6±7.3)ml,B组为(40.0±5.4) ml,差异有统计学意义(t=-2.152,P＜0.01).结论 采用小剂量对比剂预注射法与传统方法比较,CTPA影像质量与强化程度一致,但可明显降低肺静脉内对比剂的浓度,对肺动脉的辨识更容易,而且可明显减少上腔静脉内对比剂的硬化伪影对右肺动脉观察的干扰,降低对比剂的用量,有利于减轻患者对比剂肾病的危险.     

Whole-body CT screening: scan delay and contrast injection duration for optimal enhancement of abdominal organs and deep vessels

PurposeTo assess the optimal scan delays and contrast injection durations for contrast-enhanced whole-body computed tomography (CT).Materials and MethodsOne hundred forty-two patients were randomized into three groups: protocol A—scan delay of 65 s after starting contrast injection over 30 s; protocol B—105 and 70 s; and protocol C—145 and 110 s, respectively. Contrast enhancement and diagnostic acceptability were assessed.ResultsQualitative assessment was subtle among the three protocols. Homogenous enhancement of deep veins was more assuredly achieved with protocol C.ConclusionWith protocol C, qualitatively acceptable enhancement can be obtained in whole-body CT.     

Intense contrast enhancement of the adrenal glands: another abdominal CT finding associated with hypoperfusion complex in children.

OBJECTIVE: A constellation of CT findings has been associated with posttraumatic shock in children. Findings include fluid-filled, dilated bowel; intense enhancement of bowel wall, mesentery, pancreas, kidneys, aorta, and inferior vena cava; and small caliber of aorta and inferior vena cava. The objective of this study is to describe an additional CT finding in the hypoperfusion complex: symmetric, intense contrast enhancement of the adrenal glands. CONCLUSION: Intense enhancement (as great as that of adjacent vascular structures) of normal-shaped adrenal glands occurs in association with hemodynamic instability in children. The presence of intense adrenal enhancement may provide additional evidence of hemodynamic instability and help differentiate it from direct bowel injury.     

Periportal contrast enhancement on CT scans of the liver

Periportal contrast enhancement relative to adjacent liver and portal blood has been reported on CT scans in cases of schistosomiasis and hepatic Kaposi sarcoma in AIDS patients. We observed this phenomenon in 10 (8%) of 130 consecutive, contrast-enhanced, nondynamic CT examinations of the abdomen. Thus, the occurrence is more common and less specific than previously reported. Seven of the 10 patients in our series were receiving chemotherapy for malignant disease, and three had abdominal pain with no definitive diagnosis. In four of the 10 patients, corresponding areas of periportal low attenuation or radiolucency were observed on initial dynamically enhanced scans. Periportal enhancement may be related to late diffusion of contrast material into periportal areas that were initially radiolucent. Such diffusion may occur because of endothelial insult. Periportal contrast enhancement appears to be a nonspecific finding on nondynamic contrast-enhanced CT scans of the abdomen. Periportal enhancement is important to recognize because it can mimic the appearance of portal vein thrombosis and may also be used to differentiate intrahepatic biliary dilatation from periportal radiolucency.     

Hepatic cavernous hemangiomas: patterns of contrast enhancement on MR fluoroscopy imaging

PURPOSE: The purpose of this study was to assess the patterns of contrast enhancement of hepatic hemangiomas on gadolinium-enhanced MR fluoroscopy imaging prospectively. METHOD: Investigation was performed on a 0.3-T open MR unit. Gadolinium-enhanced MR fluoroscopy images were obtained in 24 patients with 28 hepatic hemangiomas. Each MR fluoroscopy image was obtained in 2 s and MR fluoroscopy lasted for 10-25 min for each investigation. RESULTS: Three patterns of contrast enhancement were observed in 24 patients on MR fluoroscopy images. Four small lesions were not detected on MR fluoroscopy images. Uniform enhancement was seen in nine lesions (29%), peripheral nodular enhancement progressing centripetally to uniform enhancement was seen in nine lesions (29%), and peripheral nodular enhancement with persistent central hypointensity was seen in six lesions (22%). CONCLUSION: Enhanced MR fluoroscopy technique could obtain dynamic images of hepatic hemangiomas. It can be suggested as a useful technique for the showing of enhancement of hepatic hemangiomas, keeping in mind its low sensitivity in the diagnosis of small hemangiomas.