The aim of this study was to validate a motion-immune (MI) solution to dynamic CT myocardial perfusion measurement, in the presence of motion without image registration. The MI perfusion technique was retrospectively validated in six swine (37.3 ± 7.5 kg) with a motion-susceptible (MS) perfusion technique performed for comparison. In each swine, varying severities of stenoses were generated in the left anterior descending (LAD) coronary artery using a balloon under intracoronary adenosine stress, followed by contrast-enhanced imaging with 20 consecutive volume scans per stenosis. Two volume scans were then systematically selected from each acquisition for both MI and MS perfusion measurement, where the resulting LAD and left circumflex (LCx) measurements were compared to reference microsphere perfusion measurements using regression and diagnostic performance analysis. The MI (P_MI) and microsphere (P_MICRO) perfusion measurements were related through regression by P_MI = 0.98 P_MICRO + 0.03 (r = 0.97), while the MS (P_MS) and microsphere (P_MICRO) perfusion measurements were related by P_MS = 0.62 P_MICRO + 0.15 (r = 0.89). The accuracy of the MI and MS techniques in detecting functionally significant stenosis was 93% and 84%, respectively. The motion-immune (MI) perfusion technique provides accurate myocardial perfusion measurement in the presence of motion without image registration.

BACKGROUND: Computed tomography pulmonary angiography (CTPA) is the primary modality for the detection and diagnosis of pulmonary embolism (PE) while the stratification of PE severity remains challenging using angiography. Hence, an automated minimum-cost path (MCP) technique was validated to quantify the subtended lung tissue distal to emboli using CTPA. METHODS: A Swan-Ganz catheter was placed in the pulmonary artery of seven swine (body weight: 42.6±9.6 kg) to produce different PE severities. A total of 33 embolic conditions were generated, where the PE location was adjusted under fluoroscopic guidance. Each PE was induced by balloon inflation followed by computed tomography (CT) pulmonary angiography and dynamic CT perfusion scans using a 320-slice CT scanner. Following image acquisition, the CTPA and the MCP technique were used to automatically assign the ischemic perfusion territory distal to the balloon. Dynamic CT perfusion was used as the reference standard (REF) where the low perfusion territory was designated as the ischemic territory. The accuracy of the MCP technique was then evaluated by quantitatively comparing the MCP-derived distal territories to the perfusion-derived reference distal territories by mass correspondence using linear regression, Bland-Altman analysis, and paired sample t-test. The spatial correspondence was also assessed. RESULTS: The MCP-derived distal territory masses (MassMCP, g) and the reference standard ischemic territory masses (MassREF, g) were related by MassMCP=1.02MassREF - 0.62 g (r=0.99, paired t-test P=0.51). The mean Dice similarity coefficient was 0.84±0.08. CONCLUSIONS: The MCP technique enables accurate assessment of lung tissue at risk distal to a PE using CTPA. This technique can potentially be used to quantify the fraction of lung tissue at risk distal to PE to further improve the risk stratification of PE.

Background

Computed tomography pulmonary angiography (CTPA) is the primary modality for the detection and diagnosis of pulmonary embolism (PE) while the stratification of PE severity remains challenging using angiography. Hence, an automated minimum-cost path (MCP) technique was validated to quantify the subtended lung tissue distal to emboli using CTPA.

Methods

A Swan-Ganz catheter was placed in the pulmonary artery of seven swine (body weight: 42.6±9.6 kg) to produce different PE severities. A total of 33 embolic conditions were generated, where the PE location was adjusted under fluoroscopic guidance. Each PE was induced by balloon inflation followed by computed tomography (CT) pulmonary angiography and dynamic CT perfusion scans using a 320-slice CT scanner. Following image acquisition, the CTPA and the MCP technique were used to automatically assign the ischemic perfusion territory distal to the balloon. Dynamic CT perfusion was used as the reference standard (REF) where the low perfusion territory was designated as the ischemic territory. The accuracy of the MCP technique was then evaluated by quantitatively comparing the MCP-derived distal territories to the perfusion-derived reference distal territories by mass correspondence using linear regression, Bland-Altman analysis, and paired sample t-test. The spatial correspondence was also assessed.

Results

The MCP-derived distal territory masses (Mass_MCP, g) and the reference standard ischemic territory masses (Mass_REF, g) were related by Mass_MCP=1.02Mass_REF - 0.62 g (r=0.99, paired t-test P=0.51). The mean Dice similarity coefficient was 0.84±0.08.

Conclusions

The MCP technique enables accurate assessment of lung tissue at risk distal to a PE using CTPA. This technique can potentially be used to quantify the fraction of lung tissue at risk distal to PE to further improve the risk stratification of PE.

Objectives

The objective was to retrospectively develop a protocol in swine for optimal contrast media timing in coronary CT angiography (CCTA).

Methods

Several dynamic acquisitions were performed in 28 swine (55 ± 24 kg) with cardiac outputs between 1.5 and 5.5 L/min, for 80 total acquisitions. The contrast was injected (1mL/kg, 5mL/s, Isovue 370), followed by dynamic scanning of the entire aortic enhancement curve, from which the true peak time and aortic and coronary enhancements were recorded as the reference standard. Each dataset was then used to simulate two different CCTA protocols-a new optimal protocol and a standard clinical protocol. For the optimal protocol, the CCTA was acquired after bolus tracking-based trigging using a variable time delay of one-half the contrast injection time interval plus 1.5 s. For the standard protocol, the CCTA was acquired after bolus tracking-based triggering using a fixed time delay of 5 s. For both protocols, the CCTA time, aortic enhancement, coronary enhancement, and coronary contrast-to-noise ratio (CNR) were quantitatively compared to the reference standard measurements.

Results

For the optimal protocol, the angiogram was acquired within -0.15 ± 0.75 s of the true peak time, for a mean coronary CNR within 7% of the peak coronary CNR. Conversely, for the standard CCTA protocol, the angiogram was acquired within -1.82 ± 1.71 s of the true peak time, for a mean coronary CNR that was 23% lower than the peak coronary CNR.

Conclusions

The optimal CCTA protocol improves contrast media timing and coronary CNR by acquiring the angiogram at the true aortic root peak time.

Key points

• This study in swine retrospectively developed the mathematical basis of an improved approach for optimal contrast media timing in CCTA. • By combining dynamic bolus tracking with a simple contrast injection timing relation, CCTA can be acquired at the peak of the aortic root enhancement. • CCTA acquisition at the peak of the aortic root enhancement should maximize the coronary enhancement and CNR, potentially improving the accuracy of CT-based assessment of coronary artery disease.

To investigate the feasibility of quantifying the chemical composition of coronary artery plaque in terms of water, lipid, protein, and calcium contents using dual-energy computed tomography (CT) in a simulation study. A CT simulation package was developed based on physical parameters of a clinical CT scanner. A digital thorax phantom was designed to simulate coronary arterial plaques in the range of 2-5 mm in diameter. Both non-calcified and calcified plaques were studied. The non-calcified plaques were simulated as a mixture of water, lipid, and protein, while the calcified plaques also contained calcium. The water, lipid, protein, and calcium compositions of the plaques were selected to be within the expected clinical range. A total of 95 plaques for each lesion size were simulated using the CT simulation package at 80 and 135 kVp. Half-value layer measurements were made to make sure the simulated dose was within the range of clinical dual energy scanning protocols. Dual-energy material decomposition using a previously developed technique was performed to determine the volumetric fraction of water, lipid, protein, and calcium contents in each plaque. For non-calcified plaque, the total volume conservation provides the third constrain for three-material decomposition with dual energy CT. For calcified plaque, a fourth criterion was introduced from a previous report suggesting a linear correlation between water and protein contents in soft tissue. For non-calcified plaque, the root mean-squared error (RMSE) of the image-based decomposition was estimated to be 0.7%, 1.5%, and 0.3% for water, lipid, and protein contents, respectively. As for the calcified plaques, the RMSE of the 5 mm plaques were estimated to be 5.6%, 5.7%, 0.2%, and 3.1%, for water, lipid, calcium, and protein contents, respectively. The RMSE increases as the plaque size reduces. The simulation results indicate that chemical composition of coronary arterial plaques can be quantified using dual-energy CT. By accurately quantifying the content of a coronary plaque lesion, our decomposition method may provide valuable insight for the assessment and stratification of coronary artery disease.

Background

As combined morphological and physiological assessment of coronary artery disease (CAD) is necessary to reliably resolve CAD severity, the objective of this study was to validate an automated minimum-cost path assignment (MCP) technique which enables accurate, vessel-specific assignment of the left (LCA) and right (RCA) coronary perfusion territories using computed tomography (CT) angiography data for both left and right ventricles.

Methods

Six swine were used to validate the MCP technique. In each swine, a dynamic acquisition comprised of twenty consecutive volume scans was acquired with a 320-slice CT scanner following peripheral injection of contrast material. From this acquisition the MCP technique was used to automatically assign LCA and RCA perfusion territories for the left and right ventricles, independently. Each animal underwent another dynamic CT acquisition following direct injection of contrast material into the LCA or RCA. Using this acquisition, reference standard LCA and RCA perfusion territories were isolated from the myocardial blush. The accuracy of the MCP technique was evaluated by quantitatively comparing the MCP-derived LCA and RCA perfusion territories to these reference standard territories.

Results

All MCP perfusion territory masses (Mass_MCP) and all reference standard perfusion territory masses (Mass_RS) in the left ventricle were related by Mass_MCP = 0.99Mass_RS+0.35 g (r = 1.00). Mass_MCP and Mass_RS in the right ventricle were related by Mass_MCP = 0.94Mass_RS+0.39 g (r = 0.96).

Conclusion

The MCP technique was validated in a swine animal model and has the potential to be used for accurate, vessel-specific assignment of LCA and RCA perfusion territories in both the left and right ventricular myocardium using CT angiography data.

Background

Myocardial perfusion measurement with a low-dose first-pass analysis (FPA) dynamic computed tomography (CT) perfusion technique depends upon acquisition of two whole-heart volume scans at the base and peak of the aortic enhancement. Hence, the objective of this study was to validate an optimal timing protocol for volume scan acquisition at the base and peak of the aortic enhancement.

Methods

Contrast-enhanced CT of 28 Yorkshire swine (weight, 55 ± 24 kg, mean ± standard deviation) was performed under rest and stress conditions over 20-30 s to capture the aortic enhancement curves. From these curves, an optimal timing protocol was simulated, where one volume scan was acquired at the base of the aortic enhancement while a second volume scan was acquired at the peak of the aortic enhancement. Low-dose FPA perfusion measurements (P_FPA) were then derived and quantitatively compared to the previously validated retrospective FPA perfusion measurements as a reference standard (P_REF). The 32-cm diameter volume CT dose index, [Formula: see text] and size-specific dose estimate (SSDE) of the low-dose FPA perfusion protocol were also determined.

Results

P_FPA were related to the reference standard by P_FPA = 0.95 · P_REF + 0.07 (r = 0.94, root-mean-square error = 0.27 mL/min/g, root-mean-square deviation = 0.04 mL/min/g). The [Formula: see text] and SSDE of the low-dose FPA perfusion protocol were 9.2 mGy and 14.6 mGy, respectively.

Conclusions

An optimal timing protocol for volume scan acquisition at the base and peak of the aortic enhancement was retrospectively validated and has the potential to be used to implement an accurate, low-dose, FPA perfusion technique.

Morphological and physiological assessment of coronary artery disease (CAD) is necessary for proper stratification of CAD risk. The objective was to evaluate a low-dose cardiac CT technique that combines morphological and physiological assessment of CAD. The low-dose technique was evaluated in twelve swine, where three of the twelve had coronary balloon stenosis. The technique consisted of rest perfusion measurement combined with angiography followed by stress perfusion measurement, where the ratio of stress to rest was used to derive coronary flow reserve (CFR). The technique only required two volume scans for perfusion measurement in mL/min/g; hence, four volume scans were acquired in total; two for rest with angiography and two for stress. All rest, stress, and CFR measurements were compared to a previously validated reference technique that employed 20 consecutive volume scans for rest perfusion measurement combined with angiography, and stress perfusion measurement, respectively. The 32 cm diameter volumetric CT dose index ([Formula: see text]) and size-specific dose estimate (SSDE) of the low-dose technique were also recorded. All low-dose perfusion measurements (P_LOW) in mL/min/g were related to reference perfusion measurements (P_REF) through regression by P_LOW = 1.04 P_REF - 0.08 (r = 0.94, RMSE = 0.32 mL/min/g). The [Formula: see text] and SSDE of the low-dose cardiac CT technique were 8.05 mGy and 12.80 mGy respectively, corresponding to an estimated effective dose and size-specific effective dose of 1.8 and 2.87 mSv, respectively. Combined morphological and physiological assessment of coronary artery disease is feasible using a low-dose cardiac CT technique.

The purpose of this study is to develop and validate an optimal timing protocol for a low-radiation-dose CT pulmonary perfusion technique using only two volume scans. A total of 24 swine (48.5 ± 14.3 kg) underwent contrast-enhanced dynamic CT. Multiple contrast injections were made under different pulmonary perfusion conditions, resulting in a total of 141 complete pulmonary arterial input functions (AIFs). Using all the AIF curves, an optimal contrast timing protocol was developed for a first-pass, two-volume dynamic CT perfusion technique (one at the base and the other at the peak of AIF curve). A subset of swine was used to validate the prospective two-volume pulmonary perfusion technique. The prospective two-volume perfusion measurements were quantitatively compared to the previously validated retrospective perfusion measurements with t-test, linear regression, and Bland-Altman analysis. As a result, the pulmonary artery time-to-peak ([Formula: see text]) was related to one-half of the contrast injection duration ([Formula: see text]) by [Formula: see text] (r = 0.95). The prospective two-volume perfusion measurements (P_PRO) were related to the retrospective measurements (P_RETRO) by P_PRO = 0.87P_RETRO + 0.56 (r = 0.88). The CT dose index and size-specific dose estimate of the two-volume CT technique were estimated to be 28.4 and 47.0 mGy, respectively. The optimal timing protocol can enable an accurate, low-radiation-dose two-volume dynamic CT perfusion technique.

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.