Effects of extrinsically warmed contrast media on image quality and clinical adverse events in patients undergoing coronary computed tomography angiography: a randomized controlled trial

Introduction

Coronary computed tomography angiography (CCTA) has become a first-line imaging modality for detecting coronary artery disease due to its satisfactory spatial and temporal resolutions of both the lumen and wall of coronary artery vessels (1). The main objective of using CCTA to evaluate the coronary arteries is to select a reliable contrast material (CM) protocol based on CM characteristics to achieve sufficient vascular enhancement without raising beam hardening artifacts (2). CM viscosity is the critical factor, as it can increase with higher concentration and lower injection pressures and is directly influenced by temperature; prewarming CM to basal body temperature (BBT) (37 ℃) instead of room temperature (RT) (23 ℃) leads to lower viscosity (3). Theoretically, prewarming CM may yield higher attenuation levels, better image quality, and fewer clinical adverse events.

Studies on the impact of prewarming CM on image quality and the incidence of clinical adverse events and equivalence evaluation remain debated, and coronary imaging-relevant studies remain limited. Only a few previous studies have focused on low-osmolality contrast media (LOCM) (4). The American College of Radiology (ACR) has not provided a conclusive recommendation on prewarming iodine-based CM, especially for CCTA, but has instead made relatively conservative suggestions claiming that prewarming CM may be beneficial in specific circumstances such as high-rate power injections, injections with viscous CM, arterial injections through small-caliber catheters, or arterial studies as timing and peak enhancement are critical (5). This position has also been cited and endorsed by multiple studies in this field (6,7). As The Joint Commission’s accreditation standards require daily temperature logs and regular maintenance records for medical warming equipment (8), these mandates impose additional device requirements and more complex operational procedures for the extrinsic warming CM protocol. It is precisely these added compliance and resource costs that have led many institutions to reevaluate the overall benefits and drawbacks of injecting prewarmed CM (as discussed in studies focusing on the implementation of warming protocols (6,7).

Therefore, we designed this randomized controlled trial to comprehensively evaluate the benefits of prewarming CM for CCTA. The primary focus of our study was to compare consequences (image quality, allergic or allergic-like reactions, etc.) of iopamidol-370 mgI/mL at different temperatures (prewarmed CM vs. RT) in patients undergoing CCTA. This trial is registered with ClinicalTrials.gov (NCT05489055). We present this article in accordance with the CONSORT reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-121/rc).

Methods

Patient population and ethics

We prospectively recruited symptomatic coronary patients recommended for CCTA examinations by clinical cardiologists from February 2020 to July 2020. The exclusion criteria were as follows: hemodynamic instability, renal insufficiency (estimated glomerular filtration rate <30 mL/min per 1.73 m²), prior adverse reactions to iodinated CM, aged younger than 18 years, and unsuitability for injection with an 18-gauge needle. A total of 224 patients were eligible for this study and assigned to either the BBT-CM group (n=112; 50 males, 62 females; mean age, 62.61±14.57 years, age range: 25–89 years) or the RT-CM group (n=112; 63 males, 49 females; mean age, 64.16±14.7 years, age range, 32–94 years). The BBT-CM group received prewarmed CM [37 ℃ (99 ℉)] and the RT-CM group received CM at RT [~23 ℃ (~73.4 ℉)]. A 1:1 computer-generated randomization was performed using MATLAB software (MathWorks, Natick, MA, USA). Stratification factors were sex (male and female), age (<60 and ≥60 years), and body mass index (BMI; <26 and ≥26 kg/m²). Participants were equally divided into 2 groups by variable block randomization.

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of Chongqing University Central Hospital (Chongqing Emergency Medical Center, No. 2022-IRB-50) and all participating patients gave their informed consent for the present research.

CCTA acquisition parameters and CM protocol

CCTA was performed with a 256-detector row CT system (Revolution CT, GE Healthcare, Milwaukee, WI, USA) according to Society of Cardiovascular Computed Tomography (SCCT) guidelines. The CT scan parameters were as follows: tube voltage: 120 kV for patients with a BMI ≥26 kg/m² and 100 kV for those with a BMI <26 kg/m², Smart-mA, collimator width: 160 mm, rotational speed: 0.28 s/rotation, technique: SnapShot Freeze (SSF), noise index: 22.0, pitch selection: auto, scan field of view: cardiac large, iterative algorithm: Adaptive Statistical Iterative Reconstruction-V (ASiR-V) within the range of 30–40%, scan method: contrast medium tracking, monitoring layer: 1–2 cm below the tracheal bifurcation, vascular threshold at the monitoring layer: 150 Hounsfield units (HU), scan range: from 1–2 cm below the tracheal ridge (adjusted according to the patient’s size) to the diaphragm of the heart and 1–2 cm wider than the left and right heart borders. Iopamidol (370 mg I/mL; manufactured by Nanjing Zhengda Tianqing Pharmaceutical Co., Ltd., Nanjing, China; National Drug Approval Number: H20203293) was injected as contrast medium via an 18–20 G intravenous indwelling needle with a dual-barrel high-pressure syringe (Ulrich, Ulm, Germany) at a flow rate of 3.5–6 mL/s, followed immediately by a flush with isotonic NaCl solution (normal saline) to ensure complete contrast agent delivery and reduce peri-venous artifacts. A free-breathing scan (80 mA, 100 kV, once per second) of the monitoring layer (the lumen of the descending aorta) was started 6 seconds after injection of the contrast medium, and a breath-hold CCTA scan was started 5 seconds after the contrast enhancement threshold (150 HU) was reached. The RT-CM group received room-temperature CM (~23 ℃), while the BBT-CM group received prewarmed CM (37 ℃). The total dose of contrast was 0.9 mL/kg, far below the Food and Drug Administration (FDA)-recommended dose for elderly patients with pre-existing kidney disease.

Data postprocessing

The image with the highest quality after SSF was selected for analysis. Vascular reconstruction was performed with Cardiac Analysis software in GE Advanced Workstation V4.7 (GE HealthCare, Chicago, IL, USA) by two experienced radiologists (* and *, both with more than 20 years of experience), and image reconstruction and quality assessment were accomplished by multiplanar reconstruction, maximum density projection, and volume reconstruction. The enhancement values and noise values of the ascending aorta root, proximal right coronary artery (RCA), proximal left anterior descending artery (LAD), proximal circumflex artery, and perivascular adipose tissue were independently measured by 2 experienced radiographers (Y Liu and P Zeng, both with more than 10 years of experience) with measuring tools in 3D software, and the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of each part were calculated. We selected the maximum possible area of nonvascular walls and intraluminal plaques as the region of interest (ROI) for measurement. An experienced cardiologist (with more than 15 years of experience) first determined whether a patient had indications for CCTA based on the following clinical manifestations and clinical history: (I) People with risk factors for coronary heart disease, such as middle-aged and older men, postmenopausal women, a long history of smoking or chronic diseases such as hypertension, diabetes, hyperlipidemia, or long-term unhealthy lifestyle or heavy workload. (II) People who had clinical symptoms of coronary heart disease, such as chest pain, chest tightness, suffocation, toothache, neck pinching, subxiphoid pain, discomfort in the left upper arm, etc., or were suspected of having such symptoms by clinical examinations, such as electrocardiogram, ultrasound, or 24-hour dynamic electrocardiogram. (III) People who underwent coronary stent implantation or bypass surgery. Then, the patient is subjected to a CCTA examination, and the clinical diagnostic value of this method is evaluated by reviewing the images.

Primary outcome

The noninferiority test for coronary artery CT attenuation was prespecified with a noninferiority margin of −25 HU (Δ=25 HU) for the between-group difference (body-temperature minus room-temperature), based on established reference values and prior study designs (9). Sample size was calculated using Power Analysis Software (PASS; version 15.0.7, https://www.ncss.com/) for a two-sample noninferiority test of means. The margin was selected based on prior research indicating that a vascular attenuation of approximately 375 HU is diagnostically sufficient (1,2); therefore, allowing a reduction of no more than 25 HU (~6.7% of 375 HU) provides a clinically stringent threshold. Noninferiority was concluded if the lower bound of the two-sided 95% confidence interval for the mean difference (body-temperature minus room-temperature) was greater than −25 HU.

Secondary outcome

Objective image quality was rated using the SNR [mean attenuation divided by the mean standard deviation (SD)] and CNR (mean vascular attenuation minus HU of the vessel, divided by the SD of the attenuation of epicardial fat surrounding the left main coronary artery and then divided by image noise) (10). Overall image quality was graded on a four-point Likert scale (11,12): 1= excellent (absence of artifacts related to motion or coronary calcification); 2= good (minor artifacts); 3= moderate (considerable artifacts but maintained visualization of the arterial lumen); and 4= poor (nondiagnostic because of severe motion artifacts or severe coronary calcification). Readers were blinded to the allocated protocol.

The participant completed the written questionnaire evaluating clinical adverse events directly after each CT scan. All adverse events, including contrast extravasation, were examined by the blinded radiographer at the time of the CCTA examination using electronic case report forms and checked by an independent study monitor.

Adverse events were categorized as extravasation, allergic or allergic-like reactions, and physiologic reactions. The radiology staff recorded an estimate of the volume of extravasated CM for extravasations. Allergic, allergic-like, and physiologic reactions were identified by evaluating notes within the electronic medical record (EMR) according to the elements of such reactions specified in nomenclature from the ACR manual. Allergic reactions were recorded according to symptoms of an immune response to the CM, such as cold urticaria or pruritus. Feelings of shivering, goosebumps, or cold were evaluated, and an open field was provided for the patient to record any other uncomfortable experiences. Physiologic reactions were categorized according to other symptoms that would not be considered classic allergic or allergic-like reactions, such as warm sensation, nausea, emesis, headache, and urgency desire. Urgency desire is defined in the questionnaire (13) as the sudden and intense ‘‘urge’’ or need to urinate and is scored as 1= not at all, 2= a little, 3= moderately, 4= a great deal, and 5= a very great deal. The duration of patient monitoring in the observation room after the occurrence of adverse events varied depending on the reaction type and severity, according to the attending physician in charge of the patient’s care.

Statistical analysis

Statistical analyses were performed by using the statistical software SPSS 12.0 (SPSS, Chicago, IL, USA). A repeated measure analysis of variance (RM-ANOVA) with Greenhouse-Geisser correction was used to assess the statistical significance of intergroup differences in the image quality at three coronary bifurcations: RCA, LAD, and left circumflex coronary artery (LCX). Then, the data did not meet the strict normal distribution, but this study did not require any assumptions about the distribution. Intergroup comparisons were performed with independent two-sample Mann-Whitney U tests. Intraobserver variation expressed as the coefficient of variation (CV) was used for image quality intracomparison. Bonferroni correction (n=3) was applied for multiple comparisons of image index at different coronary bifurcations. A Bonferroni-corrected P<0.05 was considered statistically significant.

Results

Patient demographics and CCTA characteristics

Three participants were excluded from the final analysis prior to randomization: two due to hemodynamic instability as evaluated by a cardiologist, and one who did not meet the age inclusion criterion (younger than 18 years), as detailed in the participant flow diagram (Figure 1). Key demographic and clinical characteristics are detailed in Table 1.

Figure 1 Patient enrollment and randomization flowchart. BBT-CM, basal body temperature contrast media; CAD, coronary artery disease; CT, computed tomography; CTA, computed tomography angiography; GFR, glomerular filtration rate; RT-CM, room temperature contrast media.

The CM and radiation dose parameters are shown in Table 2. There were no significant differences between groups. The mean CM volume, which was administered based on the same protocol (0.9 mL/kg), did not differ significantly between the BBT-CM group (57.02±7.21 mL) and the RT-CM group (57.53±7.22 mL) (t=0.24, P=0.81). The mean flow rate was 4.697±0.578 in the BBT-CM group and 4.748±0.595 mL/s in the RT-CM group (t=−6.7, P=0.5038).

Repeat-measure ANOVA reveals CM temperature × coronary vessel interaction for image quality

The results of statistical ANOVA for image quality parameters are shown in Table 3. Comparing image quality at the three coronary bifurcations using repeated-measures ANOVA with Greenhouse-Geisser correction revealed that there were significant main effects and CM temperature × coronary bifurcation interaction effects. For enhancing value comparison, there were significant main effects of bifurcation (F_{(1, 222)}=6.457; P=0.002) and CM temperature (F_{(1, 222)}=61.258, P<0.0001) and a significant interaction effect of CM temperature × coronary bifurcation (F_{(1, 222)}=6.243; P=0.002). We also found that there was a significant main effect of coronary bifurcation (F_{(1, 222)}=5.441; P=0.005), CM temperature (F_{(1, 222)}=7.142; P=0.001), and CM temperature × coronary vessel interaction (F_{(1, 222)}=10.3; P=0.002) for SNR. Additionally, for the comparison of CNR, there were significant differences in CM temperature (F_{(1, 222)} =3.042; P=0.049), and only a trend of coronary bifurcation (F_{(1, 222)}=3.690; P=0.056) but no CM temperature × coronary vessel interaction (F_{(1, 222)} =1.035; P=0.356) was found.

Inter- and intraobserver variation for the image quality parameters

The results of the index value of intercomparison with Bonferroni correction (n=3) are shown in Table 4. The BBT-CM group showed significantly higher enhancing values than the RT-CM group at the LAD (399.86±105.75 vs. 408.23±113.74, P<0.001) and the LCX (397.06±113.64 vs. 458.95±113.18, P<0.0001). Compared with the RT-CM group, the BBT-CM group had a significantly increased SNR at the RCA (11.85±10.55 vs. 14.76±4.92, P<0.001), the LAD (10.50±8.92 vs. 14.85±4.86, P<0.001), and the LCX (11.24±11.12 vs. 13.91±4.45, P<0.001). In addition, the BBT-CM group had a significantly increased CNR at the RCA (15.09±12.09 vs. 17.57±5.32 P<0.001), the LAD (15.26±9.36 vs. 17.62±5.24, P<0.001) and the LCX (14.94±12.50 vs. 16.69±5.02, P<0.001).

The CV was used for image quality intracomparison, and the BBT-CM group achieved a sound performance compared to the RT-CM group. For the enhancing value, CV was on average 34% of the RT-CM and 29.8% of the BBT-CM at the RCA, 41.3% of the RT-CM and 21.4% of the BBT-CM at the LAD, and 39.8% of the RT-CM and 28.3% of the BBT-CM at the LCX. For the SNR, CV was on average 101.1% of the RT-CM and 35.2% of the BBT-CM at the RCA, 105.4% of the RT-CM and 35.2% of the BBT-CM at the LAD, and 115% of the RT-CM and 32.8% of the BBT-CM at the LCX. For the CNR intracomparison, CV was on average 88.6% of the RT-CM and 31.8% of the BBT-CM at the RCA, 68.5% of the RT-CM and 30.8% of the BBT-CM at the LAD, and 90.7% of the RT-CM and 31.5% of the BBT-CM at the LCX.

Noninferiority assessment

The absolute difference in mean attenuation (calculated as the BBT-CM group minus the RT-CM group) was +10.51 HU [95% confidence interval (CI): −123.61 to -65.32] at the RCA, +8.37 HU (95% CI: −37.29 to 20.55) at the LAD, and +61.89 HU (95% CI: 57.92 to 117.20) at the LCX (Figure 2). The predefined noninferiority margin was set at −25 HU (i.e., favoring the RT-CM group). For the LAD, the lower limit of the 95% CI (−37.29 HU) was below the −25 HU margin, indicating that the attenuation with prewarmed CM was not noninferior to that with RT-CM. For the LCX, the entire 95% CI was above zero and far from the noninferiority margin, demonstrating superiority of prewarmed CM. For the RCA, the 95% CI for the between-group difference remained below zero, indicating a statistically significant reduction in attenuation with prewarmed contrast medium. However, the CI straddled the prespecified noninferiority margin (−25 HU), so noninferiority within this margin could not be established, despite the point estimate (10.51 HU) suggesting only a modest numerical decrease. Therefore, the noninferiority of prewarmed CM was not consistently demonstrated across all coronary bifurcations; its effect was vessel-specific, showing potential detriment in the LAD, clear benefit in the LCX, and an inconclusive trend in the RCA.

Figure 2 Absolute difference in mean attenuation of the coronary bifurcation (room temperature CM group minus prewarmed CM group). The dashed line shows the noninferiority margin, set at −25 HU. Error bars indicate the 95% CI of the difference. CI, confidence interval; CM, contrast media; HU, Hounsfield units; LAD, left anterior descending artery; LCX, left circumflex coronary artery; RCA, right coronary artery.

Clinical adverse events

Adverse events are recorded in Table 4. No contrast extravasation was observed in the two groups. In the BBT-GM group, there were two cases of mild allergic-like reactions, including one case of nausea, and one case of erythema, whereas in the RT-CM group, there was only one case of mild allergic-like reactions, which appeared as nausea. The patients in the BBT-CM group had more severe cases of warm sensations than those in the RT-CM group (BBT-CM group vs. RT-CM group: moderate case, 20 vs. 8; severe case, 9 vs. 9). Additionally, the micturition desire increased in the BBT-CM group (BBT-CM vs. RT-CM: mild case, 93 vs. 75; severe case, 3 vs. 0).

Discussion

The main finding of our study is that prewarmed CM was found to have different effects on mean attenuation at the three coronary vessel bifurcations, manifesting as significant inferiority in the RCA, noninferiority in the LAD, and superiority in the LCX. Improvements in objective and subjective image quality in the prewarmed CM group were significant, and improvements in the SNR and the CNR interacted with the coronary artery bifurcations.

This prospective randomized trial provides high-level evidence indicating that image quality (i.e., SNR, CNR) is better with prewarmed CM in patients undergoing cardiothoracic CTA. As shown in two CCTA scans in which different temperature CM protocols were used in the same patient for preoperative evaluation and postoperative follow-up (Figure 2), extrinsic warming of CM achieved better image quality in the three coronary vessels. We performed inter- and intra-comparisons of extrinsically warmed CM and RT CM for image quality. A smaller CV value in the extrinsic warming CM protocol meant that the image quality was insensitive to confounding factors. Interestingly, the improvement in image quality and vessel attenuation is coronary vessel-specific, as revealed by RM-ANOVA. The noninferiority trials for vascular attenuation revealed that contrast media at BBT was noninferior in the LAD and may be superior in the LCX, but was significantly inferior in the RCA. The attenuation in smaller vessels may be sensitive to the increase in CM concentration due to extrinsic warming. The RCA is the largest vessel, comparable to the left coronary artery, which is the root of the LAD and the LCX. The LCX is the smallest vessel of the three coronary bifurcations. In addition, the most common anatomic variation, such as stenosis, is an anomalous LCX, present in approximately 0.7% of patients (14).

For CCTA, delivering a bolus that ensures high attenuation and precisely synchronizing scan acquisition are desirable for optimal arterial enhancement (15). Extrinsic warming serves to alter the bolus kinetics and injection pressure of the contrast media to increase the contrast delivery rate and shorten the injection duration and thereby potentially improve arterial contrast (15,16). The higher viscosity of CM might result in inhomogeneous mixing and therefore an inferior attenuation value for the coronary vessels (17). In addition, the reduced retention of the prewarmed CM will neutralize the impact of coronary CM concentration differences on streak artifacts (18).

In the results of the current study, extrinsic warming achieved a higher vascular attenuation level at these three coronary bifurcations with a lower contrast dose (57.017±7.18 g) than at RT (57.532±7.189 g). This means that a low concentration of prewarmed contrast medium could still maintain contrast enhancement in coronary arteries without impairing image quality and at a significantly lower radiation dose in CCTA. Pazhenkottil et al. demonstrated that a significantly lower amount of CM might help prevent contrast-induced nephropathy and its consequences (19). The peak pressure was significantly higher for CM at RT than it was for prewarmed CM because of the velocity reduction. The mean flow rate in the present study was relatively low (mean flow rate of 4.697±0.578 mL/s) compared to the CM at RT (4.748±0.595 mL/s). Extrinsic warming serves to alter the bolus kinetics and injection pressure of the contrast media to mitigate the erythrocyte shear rate and platelet aggregation and thereby potentially mitigate the extravasation rate (20). Although the sample size included in this study was small and the occurrence rate of Kounis syndrome was difficult to assess, we still found that the prewarmed CM group had no cases of feeling cold, whereas there were 2 cases in the RT CM group. As cold extremities are an important prodrome for anaphylactic shock, coronary spasm, and Kounis syndrome, prewarmed CM for CCTA may be a safer protocol for patients. The degranulation of mast cells leads to the release of allergic inflammatory mediators, including histamine, proteases, leukotrienes, thromboxane, and platelet activating factor (21). Contrast media maintained at RT may be a cold irritant to the body compared to warmed media, in turn increasing heart rate, blood pressure, and the release of mast cell mediators (22).

This study had several limitations. Firstly, it was a single-center randomized controlled trial; generalizability to other centers might be challenging. Secondly, the sample size was based on a noninferiority margin for vessel attenuation based on earlier studies in which a mean attenuation of 300–400 HU was found to be optimal for CCTA (23), and a decrease in attenuation of 10% was pronounced clinically significant. Thirdly, the CM temperature was measured in the bottle, and the injected temperature may have been overestimated. Finally, renal function for iodine metabolism was not directly measured.

Conclusions

Prewarming CM improves overall image quality metrics (SNR and CNR) at coronary bifurcations, with vessel-specific effects on attenuation of coronary bifurcations on CCTA. Although prewarming CM for CCTA did not cause a significantly different impact on the incidence of adverse reactions, it increased the incidence of certain physical reactions, which may be related to renal iodine metabolism. A further multiple-center study must be performed before prewarming CM is considered a prerequisite in state-of-the-art injection protocols for CCTA.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CONSORT reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-121/rc

Trial Protocol: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-121/tp

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-121/dss

Funding: This work was supported by the Fund of Research Program of Chongqing Health Bureau (No. 2008-2-269).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-121/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of Chongqing University Central Hospital (Chongqing Emergency Medical Center, No. 2022-IRB-50) and all participating patients gave their informed consent for the present research.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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