Optimizing scan timing of hepatic arterial phase by physiologic pharmacokinetic analysis in bolus-tracking technique by multi-detector row computed tomography

Adjustment of scan delay for bolus tracking with cardiothoracic ratio of CT scout image for hepatic artery phase of hepatic dynamic CT

This study aimed to determine the scan delay for bolus tracking in the hepatic artery phase (HAP) of hepatic dynamic computed tomography (CT) using the cardiothoracic ratio (CTR) from CT scout images. We retrospectively studied 188 patients who underwent hepatic dynamic CT, 24 of whom had scan delays adjusted for CTR. The contrast enhancement of the abdominal aorta, portal vein, hepatic vein, and hepatic parenchyma was calculated for HAP. The adequacy of the scan timing for HAP was assessed using three classifications: early, appropriate, or late. The effect of HAP on scan timing adequacy was determined using multivariate logistic regression analysis, and the optimal cutoff value of CTR was evaluated using receiver operating characteristic analysis. The trigger times for bolus tracking (odds ratio: 1.58) and CTR (odds ratio: 1.23) were significantly affected by the appropriate scan timing of the HAP. The optimal cutoff value of CTR was 59.3%. The scan timing of HAP with a scan delay of 15 s was 14% of early and 86% of appropriate, and the proportion of early in CTR ≥ 60% (early, 52%; appropriate, 48%) was higher than that in CTR < 60% (early, 6%; appropriate, 94%). Adjusting the scan delay to 20 s in CTR ≥ 60% increased the proportion of appropriate (early, 4%; appropriate, 96%). The CTR of a CT scout image is an effective index for determining the scan delay for bolus tracking. Adjusting the scan delay by CTR can provide appropriate HAP images in more patients. Trial registration number: R-080; date of registration: 9 March 2023, retrospectively registered.

The evaluation of portal hypertension in cirrhotic patients with spectral computed tomography

BACKGROUND

Iodine concentrations measured using dual-energy spectral CT (DESCT) have been recently proposed as providing good performance for examining tissues hemodynamics.

PURPOSE

To evaluate the diagnostic efficacy of DESCT-derived parameters in evaluating portal venous pressure in patients with liver cirrhosis.

MATERIAL AND METHODS

A total of 71 patients with liver cirrhosis who underwent percutaneous transhepatic portal vein puncture procedures were included in this study. All participants underwent DESCT and gastrointestinal endoscopy within one month before the operation. The direct portal venous pressure of each participant was measured preoperatively.

RESULTS

Stepwise multivariate linear regression analysis showed that the iodine concentrations in the portal vein and hepatic parenchyma during the portal venous phase and the platelet count were independently correlated with the direct portal venous pressure (P < 0.001, P < 0.001, and P = 0.030, respectively). Receiver operating characteristic analysis revealed that the normalized iodine concentration of the hepatic parenchyma had the best performance for identifying clinically significant portal hypertension (≥10 mmHg), esophageal varices, and high-risk esophageal varices (the area under the curve values were 0.951, 0.932, and 0.960, respectively).

CONCLUSION

The normalized iodine concentration of the hepatic parenchyma is a reliable parameter to non-invasively assess portal venous pressure in patients with liver cirrhosis.

Optimized scan delay for late hepatic arterial or pancreatic parenchymal phase in dynamic contrast-enhanced computed tomography with bolus-tracking method

OBJECTIVES

To determine the optimal scan delay corresponding to individual hemodynamic status for pancreatic parenchymal phase in dynamic contrast-enhanced CT of the abdomen.

METHODS

One hundred and fourteen patients were included in this retrospective study (69 males and 45 females; mean age, 67.9 ± 12.1 years; range, 39-87 years). These patients underwent abdominal dynamic contrast-enhanced CT between November 2019 and May 2020. We calculated and recorded the time from contrast material injection to the bolus-tracking trigger of 100 Hounsfield unit (HU) at the abdominal aorta (s) (Time_TRIG) and scan delay from the bolus-tracking trigger to the initiation of pancreatic parenchymal phase scanning (s) (Time_SD). The scan delay ratio (SDR) was defined by dividing the Time_SD by Time_TRIG. Non-linear regression analysis was conducted to assess the association between CT number of the pancreas and SDR and to reveal the optimal SDR, which was ≥120 HU in pancreatic parenchyma.

RESULTS

The non-linear regression analysis showed a significant association between CT number of the pancreas and the SDR (p < 0.001). The mean Time_TRIG and Time_SD were 16.1 s and 16.8 s, respectively. The SDR to peak enhancement of the pancreas (123.5 HU) was 1.00. An SDR between 0.89 and 1.18 shows an appropriate enhancement of the pancreas (≥120 HU).

CONCLUSION

The CT number of the pancreas peaked at an SDR of 1.00, which means Time_SD should be approximately the same as Time_TRIG to obtain appropriate pancreatic parenchymal phase images in dynamic contrast-enhanced CT with bolus-tracking method.

ADVANCES IN KNOWLEDGE

The hemodynamic state is different in each patient; therefore, scan delay from the bolus-tracking trigger should also vary based on the time from contrast material injection to the bolus-tracking trigger. This is necessary to obtain appropriate late hepatic arterial or pancreatic parenchymal phase images in dynamic contrast-enhanced CT of the abdomen.

Noninvasive Assessment of Portal Hypertension Using Spectral Computed Tomography

BACKGROUND

Early diagnosis of portal hypertension is imperative for timely treatment to reduce the mortality rate. However, there is still no adequate method to noninvasively and accurately assess the portal hypertension in routine clinical practice.

PURPOSE

We aimed to evaluate the accuracy of parameters measured using dual energy spectral computed tomography (LightSpeed CT750 HD) in assessing portal venous pressure in patients with liver cirrhosis.

STUDY

Forty-five patients with liver cirrhosis who underwent percutaneous transhepatic portal vein puncture as part of their treatment for liver disease were enrolled in this study. Measurement of direct portal venous pressure was performed preoperatively. All patients underwent dual energy spectral computed tomography within 3 days before their operations.

RESULTS

The iodine concentrations of portal vein and hepatic parenchyma during the portal venous phase and the alanine aminotransferase level were found to be independently correlated with the direct portal venous pressure according to stepwise multivariate linear regression analysis (P<0.001, 0.004, and 0.024, respectively). In a receiver operating characteristic analysis, the area under the receiver operating characteristic of iodine concentrations of the portal vein (ICPV) for identifying clinically significant portal hypertension (≥10 mm Hg) was significantly higher than that of iodine concentrations of hepatic parenchyma (ICliver) and the alanine aminotransferase level (0.944, 0.825, and 0.301, respectively). The threshold ICPV of 58.27 yielded a sensitivity of 93.8%, specificity of 69.2%, positive predictive value of 88.2%, and negative predictive value of 81.8%, respectively.

CONCLUSIONS

ICPV values may be a useful tool in noninvasively assessing the portal venous pressure and identifying clinically significant portal hypertension in liver cirrhosis.

Computed tomography pulmonary angiography and venography with a low dose of contrast medium

The authors developed a method to ensure sufficient opacification of pulmonary vasculature for separate depiction of arteries and veins in three-dimensional form with a small dose of contrast medium utilizing a test injection to determine optimal timing of computed tomography (CT) scanning. The dose was determined by a simulation based on a pharmacokinetic model. The contrast medium was administered at a rate of 5.0 mL/s for 3 s, followed by helical scanning at the timing determined by a dynamic CT scanning following the test injection. Images of 20 consecutive patients acquired with a 64-row CT scanner were evaluated. Quality of vessel depiction was assessed on the basis of the following: HU values at the main pulmonary artery (MPA) and left atrium (LA), distance between the pleural surface and the distal end of the pulmonary vessels on three-dimensional CT pulmonary arteriography and venography (3D-CTPAV), and subjective visual assessment of quality of the 3D-CTPAV images. Time to generate the 3D-CTPAV images was recorded. The mean ± standard deviation (SD) of the HU values at MPA/LA and the distances to the pleural surface for pulmonary arteries/veins were 448.0 ± 123.1/277.3 ± 60.85 HU and 9.21 ± 3.60/10.7 ± 5.45 mm, respectively. The image quality was visually rated as excellent for all of the patients. The mean time ± SD to generate 3D-CTPAV images was 13.6 ± 6.7 min. In conclusion, three-dimensional images of the pulmonary vasculature can be created using 21 mL (including 6 mL for the test injection) of contrast medium.

Spectral CT in evaluating the therapeutic effect of transarterial chemoembolization for hepatocellular carcinoma: A retrospective study

This study aimed to investigate the value of computed tomographic (CT) spectral imaging in evaluating the effect of transarterial chemoembolization (TACE).The records of 67 patients with hepatocellular carcinoma (HCC) who had undergone dynamic spectral CT before treatment were selected for the study. Iodine concentrations pretreatment in liver parenchyma, the HCC lesion(s), portal vein, and aorta were measured from the decomposition images. The normalized iodine concentrations (NIC) were calculated. All of them underwent plain scan or contrast-enhanced CT post-treatment (approximately 4-6 weeks after TACE).The values of arterial phase normalized iodine concentrations (AP NIC) before TACE correlated with the grades of lipiodol deposition in tumors (r = 0.76, P < .001). However, there was no relationship between normalized iodine concentrations in the portal venous phase (PVP NIC) before TACE and the grade of lipiodol deposition (r = 0.17, P = .17). Values of AP NIC in residual tumors pre-TACE were significantly lower than those in partial lesions with deposition of iodized oil. The threshold AP NIC of 0.18 yielded an AUC of 0.895, 83.33% sensitivity, 81.03% specificity, 83.33% positive predictive value (PPV), and 82.76% negative predictive value, respectively. The survival probability in patients with AP NIC values pre-TACE ≥ 0.18 was higher than those whose AP NIC values pre-TACE were < 0.18 (P = .028).Spectral CT with quantitative analysis of AP NIC may help to evaluate the utility and predict the therapeutic effect of TACE. Values of AP NIC had high sensitivity and specificity for differentiating partial tumors with lipiodol deposition from those without lipiodol deposition.

Assessment of Cirrhotic Liver Enhancement With Multiphasic Computed Tomography Using a Faster Injection Rate, Late Arterial Phase, and Weight-Based Contrast Dosing

PURPOSE

This study aimed to update our liver computed tomography (CT) protocol according to published guidelines, and to quantitatively evaluate the effect of these modifications.

METHODS

The modified liver CT protocol employed a faster injection rate (5 vs 3 mL/s), later arterial phase (20-second vs 10-second postbolus trigger), and weight-based dosing of iodinated contrast (1.7 mL/kg vs 100 mL fixed dose). Liver and vascular attenuation values were measured on CTs of patients with cirrhosis from January to September 2015 (old protocol, n = 49) and from October to December 2015 (modified protocol, n = 31). CTs were considered adequate if liver enhancement exceeded 50 Hounsfield units (HU) in portal venous phase, or when the unenhanced phase was unavailable, if a minimum iodine concentration of 500 mg I/kg was achieved. Attenuations and iodine concentrations were compared using the t test and the number of suboptimal studies was compared with Fisher's exact test.

RESULTS

CTs acquired with the modified protocol demonstrated higher aortic (P = .001) and portal vein (P < .0001) attenuations in the arterial phase as well as greater hepatic attenuation on all postcontrast phases (P = .0006, .002, and .003 for arterial, venous, and equilibrium phases, respectively). Hepatic enhancement in the portal venous phase (61 ± 15 HU vs 51 ± 16 HU; P = .0282) and iodine concentrations (595 ± 88 mg I/kg vs 456 ± 112 mg I/kg; P < .0001) were improved, and the number of suboptimal studies was reduced from 57% to 23% (P = .01).

CONCLUSIONS

A liver CT protocol with later arterial phase, faster injection rate, and weight-based dosing of intravenous contrast significantly improves liver enhancement and iodine concentrations in patients with cirrhosis, resulting in significantly fewer suboptimal studies.

Optimization of scan timing for aortic computed tomographic angiography using the test bolus injection technique

BACKGROUND

With fast computed tomography (CT), it is possible for the scanning to outpace the contrast medium bolus during aortic CT angiography (CTA).

PURPOSE

To evaluate the effectiveness of a new method for reducing the risk of outpacing in which the scan start timing (ST) and speed can be estimated from the peak enhancement time measured at the femoral artery using a single test-bolus injection (femoral artery test injection method [FTI method]).

MATERIAL AND METHODS

In 30 cases of aortic CTA, we measured the time to peak enhancement at the femoral artery (TPF) and the ascending aorta (TPA) with test-bolus injection performed twice in each examination. From the resultant linear relationship between TPF and transit time (TT = TPF - TPA), we developed a method for determining the ST and TT from TPF. One hundred patients were assigned to two groups: FTI and bolus tracking (BT), each with 50 patients. CT values were measured in main vessels (ascending aorta, descending aorta, femoral artery). The CT values of the vessels and the rate of cases with more than 300 HU (good cases) were compared between the two groups.

RESULTS

The enhancement in the FTI method was significantly higher than that of the BT method (average CT values: FTI, 388.3 ± 52.4; BT, 281.2 ± 59.1; P < 0.001). The rates of good cases for FTI and BT were 86.0% and 46.0%, respectively.

CONCLUSION

The FTI method was very effective in reducing the risk of outpacing of the contrast medium transit in aortic CTA without the need for an additional contrast medium dose.

Transient washout of hepatic hemangiomas: Potential pitfall mimicking malignancy

Hemangiomas are the most common tumor of the liver and distinguishing them from malignancy is important. This is a report of 3 hemangiomas in 2 patients that exhibit transient washout of gadoxetate disodium (Eovist), relative to blood pool and liver parenchyma, a characteristic that is used to diagnose hepatocellular carcinoma in at-risk patients. It is important to recognize that high-flow hemangiomas can exhibit transient washout when using a small volume of injected contrast agent. This finding is unlikely to be present on CT examinations because of the larger volume of contrast administered.

Imaging Hepatocellular Carcinoma with Dynamic CT Before and After Transarterial Chemoembolization: Optimal Scan Timing of Arterial Phase

RATIONALE AND OBJECTIVES

The aim of this study was to determine the optimal arterial phase delay for computed tomography imaging of hepatocellular carcinoma (HCC) before and after transarterial chemoembolization (TACE) using a low iodine dose protocol.

MATERIALS AND METHODS

A total of 39 patients with known HCC were imaged with dynamic computed tomography of the liver (40-second scan duration, 60 mL of contrast medium), both on the same day before TACE and 1 day after TACE. Time attenuation curves of vessels, nonmalignant liver parenchyma, and 62 HCCs were normalized to a uniform aortic contrast arrival and analyzed.

RESULTS

Maximal arterial phase HCC to liver contrast was reached between 13 and 17 seconds after aortic contrast arrival, both before and after TACE.

CONCLUSIONS

Using our low iodine dose protocol, arterial phase imaging of HCC should be performed between 13 and 17 seconds after aortic contrast arrival, both before and after TACE.

A new method with variable injection parameters in contrast-enhanced CT: a phantom study for evaluating an aortic peak enhancement

Contrast-enhanced CT employs a standard uniphasic single-injection method (SIM), wherein administration is based on two parameters: the iodine administration rate (mgI/s) and the injection duration (s). However, as the SIM uses a fixed iodine administration rate, only a uniform contrast enhancement can be achieved with this method. The iodine administration rate can be increased only by increasing the iodine dose or shortening the injection duration, and no arbitrary adjustments can be made to the peak enhancement characteristics of the time-enhancement curves (TECs) at the fixed injection parameters used in the SIM. To address this problem, we developed a variable injection method (VIM) with a new parameter, the variation factor (VF), to adjust the TECs. A phantom study with the VIM indicated that arbitrary adjustments to the iodine administration rate could be made without changing the injection duration or increasing the iodine load. In our study, VFs of 0.3 and 0.5, which showed earlier achievement of peak enhancements, showed better temporal separation between arterial vasculature and parenchyma or the venous vasculature than that obtained with the SIM. The higher peak enhancement provided by the VF of 0.3 was also considered to improve the contrast in qualitative diagnostic examinations. A VF of 0.5 increased the duration of the enhancement and was considered to produce stable enhancement of contrast in vascular investigations. The VF is now an essential parameter, and the VIM is useful as a reasonable contrast method that may contribute to both improved visualization and improvement in the accuracy of morphologic diagnosis.

[Multicenter trial for optimization of bolus tracking settings and contrast material injection protocol in arterial dominant phase of dynamic computed tomography for diagnosis of hepatocellular carcinoma]

Alongside current improvements in the performance of computer tomography (CT) systems, there has been an increase in the use of bolus tracking (BT) to acquire arterial dominant phase images for dynamic CT at optimal timing for characterization of liver focal lesions. However, optimal BT settings have not been established. In the present study, methods of contrast enhancement and BT setting values were evaluated using a multicenter post-marketing surveillance study on contrast media used in patients with chronic hepatitis and/or cirrhosis who had undergone liver dynamic CT for diagnosis of hepatocellular carcinoma, conducted by Daiichi Sankyo Co., Ltd. The results suggested the contrast injection method to be clinically useful if the amount of iodine per kilogram of body weight is set at 600 mg/kg and the injection duration at 30 s. To achieve a good arterial dominant scan under conditions where the injection duration is fixed at 30 s or the average injection duration is 34 s using the fixed injection rate method, the scan delay time should ideally to be set to longer than 13 s. If using the BT method, we recommend that the BT settings should be revalidated in reference to our results.

The evaluation of haemodynamics in cirrhotic patients with spectral CT

OBJECTIVE

To evaluate haemodynamics in cirrhotic patients with portal hypertension using spectral CT imaging.

METHODS

118 cirrhotic patients with portal hypertension were included in the study group (further divided into Child-Pugh A, B and C subgroups). The control group consisted of 21 subjects with normal liver functionality. All subjects underwent three-phase spectral CT scans. Material decomposition images with water and iodine as basis material pairs were reconstructed. The iodine concentrations for the hepatic parenchyma in both arterial and portal venous phases were measured. The arterial iodine fraction (AIF) was obtained by dividing the iodine concentration in the hepatic arterial phase by that in the portal venous phase. AIF values from the study and control groups were compared using analysis of variance and between subgroups using a post-hoc test with Bonferroni correction, with a statistical significance of p<0.05.

RESULTS

The AIF was 0.25±0.05 in the control group, and 0.29±0.10, 0.37±0.12 and 0.43±0.14 in the study group with Child-Pugh Grades A, B and C, respectively. The difference in AIF between the control and study groups was statistically significant. The differences were statistically significant between the subgroups with multiple comparisons except between the control group and the Child-Pugh A group (p=0.685).

CONCLUSION

AIF measured in spectral CT could be used to evaluate the liver haemodynamics of cirrhotic patients.

ADVANCES IN KNOWLEDGE

The AIF, provided by spectral CT, could be used as a new parameter to observe liver haemodynamics.

Optimum CT reconstruction parameters for vascular and hepatocellular carcinoma models in a liver phantom with multi-level dynamic computed tomography with 64 detector rows: a basic study

We quantified to clarify the optimum factors for CT image reconstruction of an enhanced hepatocellular carcinoma (HCC) model in a liver phantom obtained by multi-level dynamic computed tomography (M-LDCT) with 64 detector rows. After M-LDCT scanning of a water phantom and an enhanced HCC model, we compared the standard deviation (SD, 1 ± SD), noise power spectrum (NPS) values, contrast-noise ratios (CNR), and the M-LDCT image among the reconstruction parameters, including the convolution kernel (FC11, FC13, and FC15), post-processing quantum filters (2D-Q00, 2D-Q01, and 2D-Q02) and slice thicknesses/slice intervals. The SD and NPS values were lowest with FC11 and 2D-Q02. The CNR values were highest with 2D-Q02. The M-LDCT image quality was highest with FC11 and 2D-Q02, and with slice thicknesses/slice intervals of 0.5 mm/0.5 mm and 0.5 mm/0.25 mm. The optimum factors were the FC11 convolution kernel, 2D-Q02 quantum filter, and 0.5 mm slice thickness/0.5 mm slice interval or less.

Challenges to protocol optimization due to unexpected variation of CT contrast dose amount and flow

High-quality computed tomography (CT) exams are critical to maximizing radiologist's interpretive ability. Exam quality in part depends on proper contrast administration. We examined injector data from consecutive abdominal and pelvic CT exams to analyze variation in contrast administration. Discrepancies between intended IV contrast dose and flow rate with the actual administered contrast dose and measured flow rate were common. In particular, delivered contrast dose discrepancies of at least 10% occurred in 13% of exams while discrepancies in flow rate of at least 10% occurred in 42% of exams. Injector logs are useful for assessing and tracking this type of variability which may confound contrast administration optimization and standardization efforts.

C-arm CT during hepatic arteriography tumour-to-liver contrast: intraindividual comparison of three different contrast media application protocols

OBJECTIVE

To compare tumour-to-liver contrast (TLC) of C-arm CT during hepatic arteriography (CACTHA) acquired using three protocols in patients with HCC.

METHODS

This prospective study was IRB approved and informed consent was obtained from each patient. Twenty-nine patients (mean age, 68 ± 7 years; 27 men) with 55 HCCs (mean diameter, 2.6 ± 1.5 cm) underwent three different CACTHA protocols in random order before chemoembolisation. Contrast medium (100 mg iodine/ml) was injected into the common hepatic artery (flow rate 4 ml/s). The imaging delay for the start of the CACTHA examination was 4 s (protocol A), 8 s (protocol B) and 12 s (protocol C) (total amount of injected contrast medium: 48 ml, 64 ml, 80 ml). TLC was measured by placing regions of interest (ROIs) in the HCC and liver parenchyma. Mixed model ANOVAs and Bonferroni corrected post hoc tests were used for statistical analysis.

RESULTS

Mean values for TLC were 132 ± 3.3 HU, 186 ± 5.8 HU and 168 ± 2.8 HU for protocols A, B and C. Protocol B provided significantly higher TLC than protocols A and C (p < 0.001).

CONCLUSION

TLC was significantly higher using an imaging delay of 8 s compared with a delay of 4 or 12 s.