Extravascular iodine in contrast enhancement with computed tomography

Summary Using specimens obtained at operation, tissue-blood ratios of iodinated contrast material (iodine), and in some cases also those of red blood cell tracer (⁵¹Cr), were measured in 23 patients with various kinds of intracranial mass lesions. Results provided confirmatory evidence on the major role played by extravascular iodine in the positive enhancement effect with computed tomography.     

Extravascular proton-density changes as a non-BOLD component of contrast in fMRI of the human spinal cord.

The fractional signal intensity change (Delta S/S) observed during activation in T(2)-weighted fMRI of the spinal cord has previously been shown to depend linearly on the echo time (TE) but to have a positive value of roughly 2.5% extrapolated to zero TE. In this study we investigated the origin of this finding by measuring the Delta S/S in spinal fMRI with very short TEs. Our results demonstrate that the Delta S/S does not approach zero, but has a value as high as 3.3% at TE = 11 ms. At TEs > 33 ms we observed the linear relationship between Delta S/S and TE as in previous studies. These data demonstrate that there is a non-BOLD contribution to signal changes observed in spinal fMRI. We hypothesize that this contribution is a local proton density increase due to increased water exudation from capillaries with increased blood flow during neuronal activation, and term this effect "signal enhancement by extravascular protons" (SEEP).     

多层螺旋CT胰腺检查:两种注射条件对增强效果的影响研究

目的　探讨多层螺旋CT(MSCT)胰腺检查方案中 ,2种注射条件对增强效果的影响。方法　 4 0例无胰腺疾病患者 ,用抽签法将其随机分为 2组 ,每组各 2 0例。A组注射条件为 :对比剂总量为 12 0ml,注射流率为 5ml/s;B组注射条件为 :对比剂总量为 90ml,注射流率为 3ml/s。分别行平扫及胰腺三期 (包括动脉期、胰腺期及肝脏期 )增强扫描 ,比较两组间胰腺期胰腺实质强化程度、胰周主要血管的显示率及显示程度 (根据血管显示的清晰程度评为 0～ 3分 )。结果　A组胰腺期胰腺实质强化程度明显高于B组 (t=3 5 9,P <0 0 1) ,胰周大血管 (动脉指腹腔动脉、肝动脉、脾动脉及肠系膜上动脉 ,静脉指门静脉、脾静脉及肠系膜上静脉 )的显示率 ,A组及B组均为 10 0 % ;胰周其他主要血管(动脉包括胃十二指肠动脉及胰十二指肠前上、后上、前下、后下动脉 ,静脉包括胃结肠干及胰十二指肠前上、后上静脉 )的显示率 ,A组为 5 0 %～ 10 0 % ,B组为 10 %～ 95 % ,两组间差异有显著性意义 (χ2=2 6 2 7,P =0 0 0 )。胰周大血管及胰周其他主要血管的显示程度 ,A组各血管平均评分值分别为2 93～ 3 0 0与 0 6 0～ 2 80 ,B组分别为 2 33～ 2 80与 0 0 7～ 1 5 3,两组间差异均有显著性意义(U =0 0 0及 12 5 0 ,P =0 0 0及 0 0 4 )     

Uniform vascular contrast enhancement and reduced contrast medium volume achieved by using exponentially decelerated contrast material injection method

PURPOSE: To investigate in computed tomographic (CT) angiography whether an exponentially decelerated contrast medium injection, as compared with a standard constant-rate injection, can facilitate uniform vascular contrast enhancement with a reduced contrast material volume. MATERIALS AND METHODS: CT angiography of the abdominal aorta was performed in 46 subjects by using an exponentially decelerated injection method: 134 mL of contrast medium was injected for 40 seconds, starting at 4.0 mL/sec and decreasing exponentially to 2.7 mL/sec by the end of the injection. Twenty-one of these subjects also underwent CT angiography with a constant-rate injection: 160 mL of contrast medium was injected for 40 seconds at a constant rate of 4 mL/sec. Time-enhancement curves and the magnitude of peak vascular enhancement were measured. Enhancement uniformity was evaluated by using three indexes: (a) duration of contrast enhancement achieved within 80% of the peak (80% DCE), (b) SD of the normalized contrast enhancement (SDNCE) measured from the beginning of spiral CT scanning to the time when the enhancement decreased to a level lower than the beginning level, and (c) slope of the enhancement curve calculated by using linear regression analysis. RESULTS: Exponentially decelerated injection resulted in more uniform enhancement. Mean values generated by using exponentially decelerated versus constant-rate injection in 21 paired comparisons were, respectively, 30.8 seconds +/- 5.0 versus 22.6 seconds +/- 7.6 for 80% DCE, 0.052 +/- 0.017 versus 0.086 +/- 0.031 for SDNCE, and 0.47 HU/sec +/- 0.70 versus 2.27 HU/sec +/- 0.87 for slope (P <.001 for all indexes). Compared with the peak enhancement resulting from the constant-rate injection, that resulting from the exponentially decelerated injection was reduced by a mean of 17.2% +/- 10.0. CONCLUSION: Uniform vascular contrast enhancement and reduced contrast medium volume, which are desirable in CT angiography, can be achieved with exponentially decelerated injection.     

Assessment of pancreatic CT enhancement using a high concentration of contrast material

OBJECTIVE: To evaluate the usefulness of pancreatic enhancement using a high concentration of contrast material in CT. METHODS: We performed abdominal CT on 125 patients after dividing them at random into five groups with two different concentrations, two different injection rates and three different injection doses: group A: 100 ml, 300 mgI/mL, 3 mL/sec; group B: 2 mL/kg, 300 mgI/mL, 3 mL/sec; group C: 1.5 mL/kg, 370 mgI/mL, 3 mL/sec; group D: 2 mL/kg, 300 mgI/mL, 5 mL/ sec; and group E: 1.5 mL/kg, 370 mgI/mL, 5 mL/sec. Among these five groups, the two groups given a concentration of 370 mgI/mL received a dose of 1.5 mL/body weight. RESULTS: The peak enhancement value of the pancreas was significantly greater in group E than in groups A and B. However, no statistically significant differences were found among the other groups. CONCLUSION: The fast injection rate using the high concentration of contrast medium provided greater enhancement of the pancreas than the slow injection rate using the routine concentration of contrast medium, and pancreatic CT enhancement depended more on the dose of iodine per second than on that of total iodine.     

Pulmonary masses: contrast enhancement

Radiographic studies to discriminate benign from malignant pulmonary masses have previously focused on the morphologic and, more recently, the computed tomographic (CT) attenuation characteristics of the lung mass. Experience with the use of an intravenously administered iodinated contrast medium in examining the enhancement properties of lung masses was reviewed. Distinctive differences in the vascularity, pathophysiologic features, and pharmacodynamics of malignant versus benign pulmonary masses were identified. Forty-five patients with peripheral pulmonary masses were examined. Enhancement was evaluated by means of optical density values measured on trispiral tomograms of the lung masses before and after bolus injection of contrast medium. Results suggest that contrast enhancement of pulmonary masses can be measured on sectional images and that this may become a feasible diagnostic method in the detection of lung cancer. CT offers a simplified technique that is now being explored by the authors.     

Aortic and hepatic enhancement and tumor-to-liver contrast: analysis of the effect of different concentrations of contrast material at multi-detector row helical CT

PURPOSE: To investigate the effect of different iodine concentrations of contrast material on aortic and hepatic enhancement and the detectability of hypervascular hepatocellular carcinoma (HCC) with multi-detector row computed tomography (CT) and a uniphasic contrast material injection technique. MATERIALS AND METHODS: Two hundred one patients with known or who were suspected of having HCC underwent multi-detector row CT; 58 patients with hypervascular HCC were identified. First-, second-, and third-phase scanning was started with the aortic arrival times plus 15 seconds, plus 30 seconds, and plus 105 seconds, respectively. All patients were assigned randomly into two groups. Patients in groups A and B received iopamidol with an iodine concentration of 300 mg/mL and 370 mg/mL, respectively, with the same total iodine load per patient per body weight. The liver and aorta enhancement and tumor-to-liver contrast (TLC) were measured. Depiction of hepatic arteries was evaluated visually by two radiologists. RESULTS: During the first phase, aortic enhancement was significantly (P <.01) higher in group B, with no significant difference in hepatic enhancement between the two groups. During the second phase, aortic enhancement was significantly (P <.01) higher in group A, with no significant difference in hepatic enhancement. The TLC was significantly (P <.01) higher in group B during the first phase, but there was no significant difference between the two groups during the second phase. There was no significant difference in any parameters between the two groups during the third phase. Depiction of the hepatic arteries in group B was significantly (P <.05) superior to that in group A. CONCLUSION: In the arterial phase, administration of a higher concentration of contrast material is effective for a significantly higher TLC.     

Chemical shift imaging with paramagnetic contrast material enhancement for improved lesion depiction

The depiction of contrast material-enhanced lesions with magnetic resonance imaging can be improved by using chemical shift imaging (CSI) for lipid suppression in combination with gadolinium diethylenetriaminepentaacetic acid (DTPA) enhancement. Gd-DTPA enhancement was combined with the hybrid technique for lipid suppression, which provides water-only images without increasing imaging time or postprocessing. Lesions with high signal intensity due to paramagnetic relaxation enhancement are easily distinguished from low-intensity lipid, which would otherwise dominate T1-weighted images. Preliminary studies were performed to compare Gd-DTPA-CSI images with conventional postcontrast T1-weighted images. In patients examined for orbital, pituitary, and musculoskeletal abnormalities, the Gd-DTPA-CSI technique enabled improved detection and finer anatomic staging of lesions. In theory, a similar result can be achieved by using any chemical shift-selective method that results in true lipid suppression together with paramagnetic contrast agents that generate high signal intensity. This general approach should be applicable to clinical studies in other tissues or organ systems dominated by lipid, including the pelvis, mediastinum, and breast.     

Simulation of aortic peak enhancement on MDCT using a contrast material flow phantom: feasibility study

OBJECTIVE: The objective of our study was to develop a flow phantom simulating aortic peak enhancement after the injection of contrast material on CT and to investigate the validity of the flow phantom by comparing the time-enhancement curves obtained for the flow phantom and humans. MATERIALS AND METHODS: We developed a flow phantom simulating the enhancement pattern of the aorta after the injection of contrast material. In protocols 1, 2, and 3 of the phantom study, 90, 102, and 150 mL of iohexol, respectively, was administered over 35 sec. In protocol 4, 102 mL of iohexol was administered over 25 sec. In phantom protocols 1', 2', and 3', the dose and contrast injection duration were the same as in protocols 1, 2, and 3; however, saline (10 mL) was injected during the 20 sec after contrast delivery. In the human study, 20 patients were randomized into four groups: Groups A, B, and C received 1.5, 1.7, and 2.5 mL of iohexol per kilogram of body weight, respectively, over 35 sec; and group D received 1.7 mL/kg over 25 sec. In patient groups A, B, C, and D, phantom protocols 1, 2, 3, and 4 were used, respectively. Single-level serial CT scans were obtained using a 16-MDCT scanner on the simulated and real aortas after the injection of contrast material. Time-enhancement curves of simulated and real aortas were generated, and aortic peak times and aortic peak enhancement values were calculated. RESULTS: Aortic peak enhancement and aortic peak times in protocols 1-4 and 1'-3' of the phantom study were 2-8% larger and 6-18% longer, respectively, than in the corresponding patient study. The shape of the time-enhancement curves before aortic peak time in protocols 1-3 and 1'-3' of the phantom study closely resembled that of the corresponding patient study. After the aortic peak time, the shape of time-enhancement curves in protocols 1, 2, and 3 of the phantom study was different from the corresponding patient study; however, it was similar in phantom protocols 1'-3' and the corresponding patient study. In all four phantom protocols, the difference between maximal and minimal aortic peak enhancement was less than the SD of the corresponding patient study. CONCLUSION: The level of peak aortic enhancement and the time to peak aortic enhancement were similar in the phantom and human studies when we used our different contrast injection protocols for MDCT.     

Multidetector CT of pancreas: effects of contrast material flow rate and individualized scan delay on enhancement of pancreas and tumor contrast

PURPOSE: To prospectively assess whether high contrast material flow rate (8 mL/sec) and individualized scan delay improve enhancement of normal pancreas with multidetector computed tomography (CT) and, as a result, tumor-to-pancreas contrast of pancreatic adenocarcinoma. MATERIALS AND METHODS: Informed consent was obtained in 40 patients (21 women, 19 men; mean age, 67.1 years); the institutional review board approved this protocol. Patients were referred for multidetector CT because they were suspected of having a pancreatic tumor and were randomized to receive 150 mL of nonionic contrast material (300 mg of iodine per milliliter) at a flow rate of 4 mL/sec (n = 21) or 8 mL/sec (n = 19). Patients underwent dynamic scanning at one level every 2 seconds for 66 seconds after intravenous administration of contrast material. Contrast enhancement of pancreas and tumors was measured with circular regions of interest (analysis of variance and Bonferroni-Holm corrected post hoc t tests). RESULTS: Peak contrast enhancement in pancreas was observed significantly earlier (mean +/- standard deviation, 28.7 seconds +/- 3.5 vs 48.2 seconds +/- 5.3; P < .05) and was significantly higher (129.0 HU +/- 25.7 vs 106.2 HU +/- 35.4, P < .05) with a flow rate of 8 mL/sec than with a flow rate of 4 mL/sec. Tumor-to-pancreas contrast greater than 40 HU lasted significantly longer with a flow rate of 8 mL/sec than with a flow rate of 4 mL/sec (26.4 seconds +/- 11.9 vs 8.6 seconds +/- 8.3, P < .05). With a flow rate of 8 mL/sec, an individualized scan delay of 19 seconds after aortic transit time revealed higher tumor-to-pancreas contrast than did a fixed scan delay, and tumor conspicuity was better. CONCLUSION: With 16-section CT, increased contrast material flow rate of 8 mL/sec and individualized scan delay were associated with improved pancreatic enhancement and tumor-to-pancreas contrast compared with flow rate of 4 mL/sec and fixed scan delay.     

Portal radiographs: digital enhancement of contrast

The quality of low-contrast portal radiographs for radiation therapy can be improved with electronic contrast enhancement. After the image is copied digitally with a laser scanner microdensitometer into 4,096 gray-scale levels (12 bits) and 1,686 X 2,048 pixels, a special software package permits linear, logarithmic, exponential, or sigmoid transformations of the optical density. The precise representation of the portal image can then be interactively adjusted to emphasize the desired anatomy. Clinical examples demonstrate the value of the digital enhancement approach.     

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.     

Polyvinylpyrrolidone contrast enhancement: abscess imaging.

Rabbits with thigh abscesses received an intravenous solution of polyvinylpyrrolidone (PVP) and metallic salts, resulting in a dense ring of contrast enhancement as determined by computed tomography (CT). Enhancement increased during the first two weeks, stabilized, then decreased to control levels at eight weeks. After antibiotics the ring of enhancement appeared to mark the abscess perimeter as it regressed. Normal muscle density did not change. The magnitude and duration of enhancement would improve CT detection of small lesions and be useful in evaluating the efficacy of therapy.