Optimizing contrast enhancement during helical CT of the liver: a comparison of two bolus tracking techniques

Contrast-to-Noise Ratio Optimization in Coronary Computed Tomography Angiography: Validation in a Swine Model

RATIONALE AND OBJECTIVES

The accuracy of coronary computed tomography (CT) angiography depends upon the degree of coronary enhancement as compared to the background noise. Unfortunately, coronary contrast-to-noise ratio (CNR) optimization is difficult on a patient-specific basis. Hence, the objective of this study was to validate a new combined diluted test bolus and CT angiography protocol for improved coronary enhancement and CNR.

MATERIALS AND METHODS

The combined diluted test bolus and CT angiography protocol was validated in six swine (28.9 ± 2.7 kg). Specifically, the aortic and coronary enhancement and CNR of a standard CT angiography protocol, and a new combined diluted test bolus and CT angiography protocol were compared to a reference retrospective CT angiography protocol. Comparisons for all data were made using box plots, t tests, regression, Bland-Altman, root-mean-square error and deviation, as well as Lin's concordance correlation.

RESULTS

The combined diluted test bolus and CT angiography protocol was found to improve aortic and coronary enhancement by 26% and 13%, respectively, as compared to the standard CT angiography protocol. More importantly, the combined protocol was found to improve aortic and coronary CNR by 29% and 20%, respectively, as compared to the standard protocol.

CONCLUSION

A new combined diluted test bolus and CT angiography protocol was shown to improve coronary enhancement and CNR as compared to an existing standard CT angiography protocol.

Comprehensive Assessment of Coronary Artery Disease by Using First-Pass Analysis Dynamic CT Perfusion: Validation in a Swine Model

Purpose To retrospectively validate a first-pass analysis (FPA) technique that combines computed tomographic (CT) angiography and dynamic CT perfusion measurement into one low-dose examination. Materials and Methods The study was approved by the animal care committee. The FPA technique was retrospectively validated in six swine (mean weight, 37.3 kg ± 7.5 [standard deviation]) between April 2015 and October 2016. Four to five intermediate-severity stenoses were generated in the left anterior descending artery (LAD), and 20 contrast material-enhanced volume scans were acquired per stenosis. All volume scans were used for maximum slope model (MSM) perfusion measurement, but only two volume scans were used for FPA perfusion measurement. Perfusion measurements in the LAD, left circumflex artery (LCx), right coronary artery, and all three coronary arteries combined were compared with microsphere perfusion measurements by using regression, root-mean-square error, root-mean-square deviation, Lin concordance correlation, and diagnostic outcomes analysis. The CT dose index and size-specific dose estimate per two-volume FPA perfusion measurement were also determined. Results FPA and MSM perfusion measurements (P_FPA and P_MSM) in all three coronary arteries combined were related to reference standard microsphere perfusion measurements (P_MICRO), as follows: P_{FPA_COMBINED} = 1.02 P_{MICRO_COMBINED} + 0.11 (r = 0.96) and P_{MSM_COMBINED} = 0.28 P_{MICRO_COMBINED} + 0.23 (r = 0.89). The CT dose index and size-specific dose estimate per two-volume FPA perfusion measurement were 10.8 and 17.8 mGy, respectively. Conclusion The FPA technique was retrospectively validated in a swine model and has the potential to be used for accurate, low-dose vessel-specific morphologic and physiologic assessment of coronary artery disease. ^© RSNA, 2017.

Establishment of the intracranial hemodynamic model based on contrast medium and clinical applications

Ischemic cerebrovascular diseases are one of the most common vascular diseases in aged people and CT perfusion (CTP) is a very popular tool to detect the ischemic changes in brain vascular. The present study aims to establish a novel intracranial hemodynamic model to simulate anterior cerebral artery blood flow, and compare the actual and simulated hemodynamic parameters of healthy people and patients with carotid stenosis or occlusion.A mathematical model of the intracranial hemodynamic was generated using MATLAB software, and data from patients with or without infarct disease (57 and 44 cases, respectively) were retrospectively collected to test the new model. The actual time-density curve (TDC) of anterior cerebral artery was obtained from the original intracranial CTP data, and simulated TDC was calculated from our intracranial hemodynamic model. All model parameters were adjusted according to patients' sex, height, and weight. Time to peak enhancement (TTP), maximum enhancement (ME), and mean transit time (MTT) were selected to evaluate the status of hemodynamics.In healthy people, there were no significant differences of TTP and ME between actual and simulated curves. For patients with infarct symptoms, ME was significantly decreased in actual data compared with simulated curve, while there was no obvious difference of TTP between actual and simulated data. Moreover, MTT was delayed in infarct patients compared with healthy people.Our group generated a computer-based, physiologic model to simulate intracranial hemodynamics. The model successfully simulated anterior cerebral artery hemodynamics in normal healthy people and showed noncompliant ME and MTT in infarct patients, reflecting their abnormal cerebral hemodynamic status. The digital model is reliable and may help optimize the protocol of contrast medium enhancement in intracranial CT, and provide a solid tool to study intracranial hemodynamics.

Triple-phase computed tomography during arterial portography with bolus tracking for hepatic tumors

PURPOSE

The purpose of this study was to assess the usefulness of triple-phase computed tomography during arterial portography (CTAP) using a bolus-tracking technique.

MATERIAL AND METHODS

The subjects were 60 patients with hepatic tumors: 20 patients with metastatic liver tumors with a normal liver and 40 with hypervascular hepatocellular carcinoma (HCC) with liver cirrhosis. The region of interest was set in the portal vein, and CTAP was automatically started after the triggering threshold (180 HU) was reached. Three scans were performed: early phase (E), hepatic parenchymal phase (HP), and late phase (L). The scan start time of E-CTAP was measured. The detection rates of the HCC nodules were evaluated during each CTAP phase.

RESULTS

CTAP was performed by bolus tracking without failure in any of the patients. The mean scan start times in the normal liver group and liver cirrhosis group were 14.3 +/- 1.34 s and 18.5 +/- 2.46 s, respectively, which were significantly different from each other. The detection rates of HCC nodules for E-CTAP, HP-CTAP, and L-CTAP were 29.6%, 100%, and 83.3%, respectively.

CONCLUSION

The bolus-tracking technique enabled us to perform CTAP with optimal timing regardless of the portal blood flow dynamics.

Adaptive Bolus-chasing Computed Tomography Angiography in the Cases of Symmetric and Asymmetric Arterial Flows in Peripheral Arteries

Synchronization of the contrast bolus peak and CT imaging aperture is a crucial issue for computed tomography angiography (CTA). It affects the CTA image quality and the amount of contrast dose. A whole-body CTA procedure means to scan from the abdominal aorta to pedal arteries. In this context, the synchronization is much more difficult with the asymmetric arterial flow in lower extremities than in the case of symmetric arterial flow. In this paper, we propose an adaptive optimal controller to chase the contrast bolus peak while it propagates in the aorta and lower extremities with symmetric flow. In the case of asymmetric flow after the contrast bolus splitting into two lower limbs, we propose a dynamic programming approach to cover the lower limbs optimally. Simulation and experimental results show that the proposed methods outperform the current constant-speed method substantially.

Detection of hypervascular hepatocellular carcinoma with multidetector-row CT: single arterial-phase imaging with computer-assisted automatic bolus-tracking technique compared with double arterial-phase imaging

PURPOSE

To compare single arterial-phase (SAP) computed tomography (CT) imaging with bolus tracking (BT) with double arterial-phase (DAP) CT imaging for detecting hypervascular hepatocellular carcinoma.

MATERIALS AND METHODS

The DAP images were obtained at 25 (DAP-early) and 40 seconds (DAP-late) after the start of contrast material injection. All patients underwent SAP-BT imaging where images were obtained 10 seconds after the CT attenuation value of the aorta reached the threshold value of 120 Hounsfield unit (HU) in 29 (group 120-HU), 160 HU in 30 (group 160-HU), and 200 HU in 32 patients (group 200-HU). Attenuation conspicuity with SAP-BT technique was compared with that with DAP technique using repeated-measures analysis of variance. Attenuation conspicuity and mean scan delays with SAP-BT images obtained with different threshold values were compared using analysis of variance. The sensitivities were compared using McNemar and Fisher exact tests.

RESULTS

Within all groups, mean attenuation conspicuity with SAP-BT and DAP-late was significantly higher than that with DAP-early. Regarding SAP-BT, mean attenuation conspicuity in group 200-HU (42 +/- 18 HU) was significantly higher than those in groups 120-HU (23 +/- 11 HU) and 160-HU (25 +/- 11 HU). Mean scan delays for SAP-BT were 24.2 seconds in group-120 HU, 26.8 seconds in group-160 HU, and 31.1 seconds in group-200 HU (P < 0.001). The mean sensitivity with SAP-BT technique in group 200-HU (92.7%) was significantly higher than those in groups 120-HU (72.4%) and 160-HU (71.1%).

CONCLUSIONS

Single arterial-phase CT scanning with bolus tracking can be effectively used to detect hepatocellular carcinoma when a threshold value of 200 HU is used.

Adaptive Bolus Chasing Computed Tomography Angiography: Control Scheme and Experimental Results

In this paper, a new adaptive bolus-chasing control scheme is proposed to synchronize the bolus peak in a patient's vascular system and the imaging aperture of a computed tomography (CT) scanner. The proposed control scheme is theoretically evaluated and experimentally tested on a modified Siemens SOMATOM Volume Zoom CT scanner. The first set of experimental results are reported on bolus-chasing CT angiography using realistic bolus dynamics, real-time CT imaging and adaptive table control with physical vasculature phantoms. The data demonstrate that the proposed control approach tracks the bolus propagation well, and clearly outperforms the constant-speed scheme that is the current clinical standard.

Bolus characteristics based on Magnetic Resonance Angiography

Background

A detailed contrast bolus propagation model is essential for optimizing bolus-chasing Computed Tomography Angiography (CTA). Bolus characteristics were studied using bolus-timing datasets from Magnetic Resonance Angiography (MRA) for adaptive controller design and validation.

Methods

MRA bolus-timing datasets of the aorta in thirty patients were analyzed by a program developed with MATLAB. Bolus characteristics, such as peak position, dispersion and bolus velocity, were studied. The bolus profile was fit to a convolution function, which would serve as a mathematical model of bolus propagation in future controller design.

Results

The maximum speed of the bolus in the aorta ranged from 5–13 cm/s and the dwell time ranged from 7–13 seconds. Bolus characteristics were well described by the proposed propagation model, which included the exact functional relationships between the parameters and aortic location.

Conclusion

The convolution function describes bolus dynamics reasonably well and could be used to implement the adaptive controller design.

Projection-based bolus detection for computed tomographic angiography

Computed tomographic (CT) angiography is important for imaging studies on cardiovascular structures, peripheral vessels, and solid organs. In practice, a CT angiography scan is triggered by the bolus arrival at a prespecified anatomical location, which is determined using CT fluoroscopy. In this article, we propose a projection-based method adapted from the Grangeat formula to detect the bolus arrival. Then, we evaluate our new method in numerical and animal studies. Our results indicate that this method allows significantly better temporal resolution and is computationally more efficient, as compared with the image-based methods.

[Method for determining scan timing based on analysis of formation process of the time-density curve]

A strict determination of scan timing is needed for dynamic multi-phase scanning and 3D-CT angiography (3D-CTA) by multi-detector row CT (MDCT) . In the present study, contrast media arrival time (T(AR)) was measured in the abdominal aorta at the bifurcation of the celiac artery for confirmation of circulatory differences in patients. In addition, we analyzed the process of formation of the time-density curve (TDC) and examined factors that affect the time to peak aortic enhancement (T(PA)). Mean T(AR) was 15.57+/-3.75 s. TDCs were plotted for each duration of injection. The rising portions of TDCs were superimposed on one another. TDCs with longer injection durations were piled up upon one another. Rise angle was approximately constant in response to each flow rate. Rise time (T(R)) showed a good correlation with injection duration (T(ID)). T(R) was 1.01 TID (R(2)=0.994) in the phantom study and 0.94 T(ID)-0.60 (R(2)=0.988) in the clinical study. In conclusion, for the selection of optimal scan timing it is useful to determine T(R) at a given point and to determine the time from T(AR).

Clinical evaluation of a computer simulated prediction model of contrast enhancement of the liver in spiral CT

OBJECTIVE

A software program was developed simulating a compartmental model of blood circulation based on differential equations. The aim of this study was to compare software-simulated levels of hepatic enhancement with the true values in patients and to test how many patients reach the simulated hepatic enhancement level.

METHODS

As software program the CT application software carebolus 2 (Siemens, Forchheim, Germany) was used. Hepatic contrast-enhancement curves were simulated prior to CT examinations to evaluate a patient specific time delay after contrast application. At the time delay, when the simulation curve showed an enhancement threshold of 40 Hounsfield Units (HU), the CT spiral scan was started applying 120 ml contrast media with 2 ml/s. The simulated curves were compared with the empiric curves of each patient.

RESULTS

25 of 28 patients (89%) achieved 40 HU. The mean enhancement of empiric patients curves was 46.32 +/- 11.9 HU, the mean simulated enhancement was 46.62 +/- 4.3 HU S.D. (P= 0.48). 4.4 values per patient liver could be compared with the simulation curve (122 points for 28 patients): 50% of the patient curves were within a range of 5 HU compared with the simulation curve.

CONCLUSION

Software simulation of contrast enhancement curves of the liver is a feasible and valuable method to predict individual liver enhancement curves. Improvements concerning the integration of cardiovascular parameters and preexisting liver parenchymal diseases into the simulation software have to be arranged.

Effect of contrast material injection duration and rate on aortic peak time and peak enhancement at dynamic CT involving injection protocol with dose tailored to patient weight

PURPOSE

To investigate the effect of duration and rate of contrast material injection on aortic peak time and peak enhancement in an injection protocol in which the contrast material dose is adjusted according to patient weight.

MATERIALS AND METHODS

One hundred ninety-nine patients were randomly divided into three groups in which the fixed duration of contrast material injection was 25 seconds (group A) or 35 seconds (group B) or the fixed injection rate was 4.0 mL/sec (group C). Computed tomography (CT) at the L3 vertebral level was performed before and after contrast material injection. Aortic peak time, aortic peak enhancement, and period when aortic enhancement is 200 HU or greater (T200) were calculated. The Pearson product-moment correlation coefficient (r) was used to investigate relationships between patient weight and aortic peak time, aortic peak enhancement, and T200 in each group.

RESULTS

A significant correlation between aortic peak time and patient weight (r = 0.91, P <.001) was observed in group C. No significant correlations between patient weight and aortic peak time were observed in group A (r = 0.16, P =.21) or B (r = -0.05, P =.69). A significant inverse correlation between aortic peak enhancement and patient weight (r = -0.70, P <.001) was observed in group C. No significant correlations between patient weight and aortic peak enhancement were observed in group A (r = 0.09, P =.48) or B (r = 0.10, P =.41). A significant correlation between T200 and patient weight (r = 0.72, P <.001) was observed in group C. No significant correlations between patient weight and T200 were observed in group A (r = 0.12, P =.34) or B (r = 0.001, P =.99).

CONCLUSION

Aortic peak time, aortic peak enhancement, and T200 were closely related to injection duration in the protocol with contrast material dose determined according to patient weight.

Patency of cavopulmonary connection studied by single phase electron beam computed tomography

PURPOSE

The shunt patency and anatomic alteration of central PA after cavopulmonary connection was assessed by one phase electron-beam computed tomography (EBCT) METHODS: Thirteen patients that received a bi-directional cavo-pulmonary shunt (BCPS, n = 7) or total cavo-pulmonary connection (TCPC, n = 6) were included. The patency of the shunt and the anatomy of intra-pericardial PA were evaluated by EBCT, and compared by angiography and echocardiography.

RESULTS

EBCT accurately evaluated shunt patency and the anatomy of the intra-pericardial PA, except for the incorrect diagnosis of SVC-PA shunt patency and peripheral pulmonary stenosis in two TCPC patients. Both of these patients had bilateral SVC and received either bilateral BCPS or ligation of the left SVC respectively. The baffle between the IVC and PA was partly opacified through a fenestration of the baffle, but was not opacified in two patients without fenestration.

CONCLUSION

EBCT accurately evaluated shunt patency and the anatomy of central PA, however, the accuracy was limited in two cases with bilateral SVC. The opacification of the intra-atrial baffle was insufficient in TCPC cases. Multi-phase CT angiography may overcome this limitation in this patient subset.

Helical computed tomographic portography in ten normal dogs and ten dogs with a portosystemic shunt

Contrast enhanced helical computed tomography (CT) of the liver and portal system is routinely performed in human patients. The purpose of this project is to develop a practical protocol for helical CT portography in the dog. Ten clinically normal dogs were initially evaluated to develop a protocol. Using this protocol, ten dogs with confirmed portosystemic shunts (PSS) were then evaluated. Each patient was anesthetized, and a test dose of sodium iothalamate (400 mg I/ml) at 0.55 ml/kg was injected. Serial images were acquired at the level of T12-13 or T13-L1. The time to maximum enhancement of the portal vein was determined. This time period was used as the period between the second injection (2.2 ml/kg) and the start of the helical examination of the cranial abdomen. Delay times for normal dogs ranged from 34.5 s-66.0 s (median: 43.5 s) or 1.41 s/kg-4.12 s/kg (median: 2.09 s/kg). For patients with a PSS, the delay times were 16.5-70.5 s (median: 34.5 s) or 1.47-19.17 s/kg (median: 3.39 s/kg). The aorta, caudal vena cava, portal vein, shunt vessels, and their respective branches were well visualized on the CT images. Clinical case results were surgically confirmed. The surgeons reported that the information gained from the CT portography resulted in a subjective decrease in surgical time and degree of dissection necessary compared with similar surgeries performed without angiographic information. We believe that helical CT portography in the dog will be a useful adjunct in the diagnosis of PSS. The use of helical CT portography may allow clinicians to give clients a more accurate prognosis prior to surgery and will allow patients with lesions that are not surgically correctable to avoid a costly and invasive procedure.

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.

CT angiography of the arterial system

CTA has become an important diagnostic tool in the evaluation of vascular diseases in virtually all parts of the body. Whereas CTA is able to provide images depicting exquisite anatomic detail, careful scanning technique and selection of scan parameters are critical for high quality studies. The choices to be made when prescribing a scan can seem daunting at first, but if one applies the principles outlined previously, CTA can be a relatively easy, fast, and safe diagnostic technique that is effective in the majority of patients with vascular disease.

Gadolinium-enhanced arterial-phase MR imaging of hypervascular liver tumors: comparison between tailored and fixed scanning delays in the same patients

The purpose of this study was to compare in the same patients tailored and fixed scanning delays during gadolinium-enhanced arterial-phase magnetic resonance imaging of hypervascular liver tumors. Tailored scanning delays were obtained with automated region of interest threshold triggering. A delay of 23 seconds between the start of contrast material injection and imaging was used for fixed delay examinations. Quantitative and qualitative evaluation was performed in 21 patients with normal cardiac function referred for MR assessment of hypervascular liver tumors. In the tailored examinations, the median time delay between the start of contrast material injection and the start of magnetic resonance imaging was 21 seconds (range, 18-34 seconds). The median tumor-to-liver contrast during tailored examinations was 19.1 versus 14.7 during fixed delay examinations. This difference, however, was not significant. Similarly, the enhancement in the aorta, the portal vein, the liver, and the tumor did not differ significantly between examinations performed with tailored and fixed delays. It is concluded that in our group of patients with hypervascular liver tumors and normal cardiac function, no significant improvement in tumor-to-liver contrast and enhancement during the arterial phase was found when gadolinium-enhanced magnetic resonance imaging was performed with a tailored scanning delay rather than with a fixed delay.

Computed tomography fluoroscopy: techniques and applications

Computed tomography fluoroscopy (CTF) was first introduced into clinical practice in Japan in 1993 and in the United States in 1995, yet it has been used predominantly at large academic hospitals. Early literature on CTF is composed primarily of abstracts that detail anecdotal experiences and that have been presented at major meetings. Scientific papers evaluating CTF in clinical practice have been introduced in scientific journals only recently. This article reviews the literature for CTF with specific emphasis on clinical techniques, applications, and results. It is the goal of the author to provide the reader with a basic working knowledge of how to perform CTF-guided procedures and how to integrate CTF into clinical practice.