Optimization of high-concentration (400 mgI/mL) contrast media volume for abdominal computed tomography: a comparison between fixed-dose and total body weight-based protocols

Introduction

Contrast-enhanced computed tomography (CT) is routinely employed for diagnosing abdominal diseases, and the quality of imaging enhancement primarily depends on the contrast media (CM). With the ongoing advances in clinical practice, CM dosing protocols are continually evolving in order to provide optimal enhancement and patient safety. However, standardized recommendations or universally accepted guidelines for CM administration remain lacking, and fixed-dose CM dosing protocols continue to be widely adopted in clinical practice (1-3). Using a fixed-volume protocol with a sufficiently large dose can provide adequate enhancement for most patients, but it may result in CM overuse in underweight patients and poor image quality in overweight patients, leading to inconsistent enhancement effects. Therefore, individualized CM dosing protocols are increasingly being considered necessary to ensure patient safety, optimize image quality, and achieve consistent enhancement across a diversity of patient populations (4-6).

Recently, various weight-based dosing protocols have been proposed that employ body metrics, such as total body weight (TBW), body mass index (BMI), lean body weight, and body surface area (7-9). However, a consensus on the most effective method among these remains lacking. Notably, of these metrics, TBW has emerged as a key determinant of contrast enhancement and is particularly practical for clinical implementation due to its simplicity and ease of use. Previous studies (10-12) on weight-based personalized dosing protocols for abdominal multiphasic CT have predominantly used moderate-concentration CMs, such as iopamidol at 370 mgI/mL or iohexol at 350 mgI/mL.

Iomeprol, a nonionic, water-soluble iodinated contrast medium, has a maximum iodine concentration of 400 mgI/mL and is characterized by its low osmolality and viscosity. Iomeprol with a high iodine concentration (400 mgI/mL) offers unique advantages in multiphasic abdominal contrast-enhanced CT and CT angiography examinations. High-concentration CM not only enhances vascular and parenchymal image quality but also improves lesion detectability (13). Compared with CM with lower concentrations, those with high-concentrations allow for a lower injection volume and a slower injection flow rate, thereby enhancing patient comfort and tolerance (14). Despite these benefits, few studies have been conducted on the application of 400 mgI/mL of CM in abdominal CT, particularly regarding the use of individualized dosing strategies.

Therefore, this study aimed to compare fixed-dose and TBW-adapted dosing protocols for high-concentration (400 mgI/mL) CM in abdominal multiphasic contrast-enhanced CT, with a focus on the differences in overall image quality and vascular and parenchymal enhancement. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1171/rc).

Methods

Patients

This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments and was approved by the Institutional Review Board of The First Affiliated Hospital of Chongqing Medical University (approval No. KX2024-KYC0328-01), which waived the requirement for specific written consent, as general informed consent for CM administration was obtained from all patients prior to examination. The administered CM volumes complied strictly with established clinical and legal guidelines.

From November 2021 to March 2023, consecutive patients clinically indicated for abdominal multiphasic contrast-enhanced CT were retrospectively enrolled. The exclusion criteria were as follows: (I) age <18 years; (II) history of allergy to iodine CM; (III) severe cardiac or renal dysfunction (estimated glomerular filtration rate <30 mL/min/1.73 m²); (IV) partial hepatectomy, splenectomy, and other factors affecting liver blood flow; (V) diffuse liver disease or multiple intrahepatic lesions affecting CT value measurement; and (VI) poor image artifacts deemed to impair quantitative measurement. Data on patients’ age, sex, height, TBW, BMI and primary cancer were recorded for all participants.

General indications for CT imaging included the following: cancer (n=72), pancreatitis (n=3), abdominal abscess (n=3), diverticulitis (n=1), abdominal pain (n=10), hiccups (n=1), hematuria (n=2), cirrhosis (n=1), suspected abdominal mass (n=4), liver abnormality (n=1), nausea and vomiting (n=1), prostatitis (n=1), and hypertension (n=1).

Clinical characteristics

Data on patient demographics (age and sex), TBW, height, and BMI were collected. Before the examination, patients’ TBW was measured in the preparation room with a standard digital weighing scale. Height was also measured, and the BMI was subsequently calculated with the following formula:

BMI=Weight(kg)Height2(m2)[1]

Scanning protocol

All patients underwent an abdominal multiphasic contrast-enhanced CT scan with a 64-row multidetector CT scanner (Discovery 750, GE HealthCare, Chicago, IL, USA). Scanning parameters for 64-row CT were set as follows: a tube voltage of 120 or 100 kVp, a tube current ranging from 200 to 600 mAs based on automatic tube current modulation (Smart mA, GE HealthCare, Waukesha, WI, USA) according to the noise index (NI; NI =13–15), a gantry rotation time of 0.5 s, a pitch of 1, and a section thickness and interval of 1.25 and 1.25 mm, respectively. The scan delay was determined via a bolus-tracking software program (SmartPrep, GE HealthCare), with the region of interest (ROI) set at a threshold of 100 Hounsfield units (HU) within the abdominal aorta. All patients underwent a multiphasic scan, including the unenhanced phase, early arterial phase, late arterial phase, and portal venous phase. When the threshold was reached, diagnostic scans were acquired after an additional average delay of 6 seconds for the early arterial phase, 20–25 seconds for the late arterial phase, and 40–45 seconds for the portal venous phase.

CM injection protocol

Patients were categorized into two main groups based on the date of their examination and the CM protocol in effect at the time. Patients scanned between November 2021 and May 2022 received a fixed-dose protocol (80 mL at 120 kVp). Beginning in June 2022, TBW-based dosing protocols were administered for all patients. This TBW group was further subdivided into five subgroups according to the specific combinations of iodine dose (based on TBW) and tube voltage applied as follows: a TBW-based subgroup of 400 mgI/TBW (kg) at 100 kVp, TBW-based subgroup of 400 mgI/TBW (kg) at 120 kVp, a TBW-based subgroup of 450 mgI/TBW (kg) at 100 kVp, a TBW-based subgroup of 450 mgI/TBW (kg) at 120 kVp, and a TBW-based subgroup of 500 mgI/TBW (kg) at 120 kVp.

The formula for the CM volume was as follows:

CMvolume(mL)=Iodinedose(mgI/kg)TBW(kg)/400(mgI/mL)[2]

Additionally, the CM was warmed to 37 ℃ prior to injection to reduce viscosity and improve patient comfort. The injection flow rate ranged from 3.5 to 4.5 mL/s, and after the CM injection, 40–60 mL of saline was administered as a chaser to enhance the CM delivery and optimize imaging.

Objective image quality analysis

The quantitative image analysis of reconstructed 1.25-mm transverse images was performed by a radiologist with 5 years of experience in abdominal CT. CT attenuation values and standard deviation (SD) values of the liver, pancreas, and subcutaneous fat were measured with a circular ROI approximately 1 cm² in area in the early arterial, late arterial, and portal venous phases. CT attenuation values and SD values were also measured for the abdominal aorta and renal cortex in the early arterial phase, portal vein and renal medulla in the late arterial phase, and hepatic vein in the portal venous phase. Visible blood vessels, bile ducts, the pancreatic duct, lesions, and artifacts were excluded from ROI measurements of the hepatic parenchyma and pancreas. All measurements were performed three times at the same anatomical levels and then averaged to ensure consistency. The SD measured in a circular ROI placed in subcutaneous fat tissue was defined as the image noise.

The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the liver, pancreas, kidney, aorta, hepatic vein, and portal vein were calculated as follows (2):

SNR=CT SD[3]

CNR= CT−CTfatSDfat[4]

Liver, abdominal aorta, hepatic vein, and portal vein contrast enhancement was quantified according to the contrast enhancement index (CEI), which was calculated as follows (8):

CEI=CTenhanced−CTunenhanced[5]

Based on previous experience in abdominal imaging diagnosis (15,16), we considered a liver parenchyma CEI greater than 50 HU as satisfying the diagnostic requirements and an abdominal aorta CEI exceeding 250 HU as conducive to aortic CTA image reconstruction and observation of hypervascular liver lesions (17).

Radiation exposure

The CT dose index volume (CTDI_vol) and dose-length product (DLP) from the dose reports were recorded from the late arterial phase, as only the upper abdomen was scanned during this phase. The effective dose (ED) was calculated by multiplying the DLP by a conversion factor of 0.015 mSv·mGy⁻¹·cm⁻¹ (18).

Statistical analysis

Statistical analysis was performed with SPSS version 20 software (IBM Corp., Armonk, NY, USA). Continuous variables are presented as the mean ± SD, and categorical variables are presented as frequencies and percentages. The Chi-squared test was used to compare the distribution of sex and subjective image quality scores across the six subgroups. One-way analysis of variance was used to compare image noise, CEI, SNR, CNR, CTDI_vol, DLP, and ED across the six subgroups. When significant differences were identified by one-way analysis of variance, the Tukey post hoc test was applied to assess pairwise differences between individual groups. A P value <0.05 indicated a statistically significant difference.

Results

Patient demographics

This study retrospectively enrolled 368 consecutive patients, who were placed in one of six subgroups according to the iodine dose [400, 450, and 500 mgI/TBW (kg); 80 mL] and tube voltage (100 and 120 kVp). No significant differences were observed between the fixed-dose group and TBW-based subgroups in terms of age, sex, body weight, height, or BMI (P>0.05; Table 1).

Objective image analysis

The objective image analysis for the six groups is shown in Table 2. Compared with the other TBW-based subgroups, the 400 mgI/TBW (kg) at 100 kVp, 450 mgI/TBW (kg) at 100 kVp, 500 mgI/TBW (kg) at 120 kVp, and the fixed-dose groups had significantly higher CEI values in the aorta, portal vein, hepatic vein, and liver. No significant differences in CEI were observed for the portal vein, hepatic vein, or liver between the fixed-dose, 400 mgI/TBW (kg) at 100 kVp, 450 mgI/TBW (kg) at 100 kVp, and 500 mgI/TBW (kg) at 120 kVp groups; however, the aorta CEI of the 450 mgI/TBW (kg) at 100 kVp group was significantly higher than that of the 400 mgI/TBW (kg) at 100 kVp, 500 mgI/TBW (kg) at 120 kVp, and fixed-dose groups. For hepatic parenchymal enhancement, the 500 mgI/TBW (kg) at 120 kVp group achieved the highest proportion of patients meeting diagnostic criteria, followed by the 450 mgI/TBW (kg) at 100 kVp group and fixed-dose group (P<0.001). The representative CT images of different CM dosing protocols and tube voltages are shown in Figure 1.

Figure 1 Different scan phase images of abdominal contrast-enhanced CT obtained with different CM dosing protocols and tube voltages. (A1-A4) A 65-year-old man, weighing 50 kg (BMI, 24.8 kg/m²), received a CM injection of 50 mL [400 mgI/TBW (kg)] and was scanned at 100 kVp, with a liver CEI of 51 HU, an aortic CEI of 356 HU, and an aortic SNR of 54.9. (B1-B4) A 56-year-old woman, weighing 66 kg (BMI, 25.1 kg/m²), received a CM injection of 66 mL [400 mgI/TBW (kg)] and was scanned at 120 kVp, with a liver CEI of 45 HU, an aortic CEI of 303 HU, and an aortic SNR of 35.3. (C1-C4) A 48-year-old woman with hepatic nodule, weighing 57.5 kg (BMI, 23.9 kg/m²), received a CM injection of 64 mL [450 mgI/TBW (kg)] and was scanned at 100 kVp, with a liver CEI of 58 HU, an aortic CEI of 388 HU, and an aortic SNR of 37.2. (D1-D4) A 75-year-old man, weighing 60 kg (BMI, 24.3 kg/m²), received a CM injection of 66 mL [450 mgI/TBW (kg)] and was scanned at 120 kVp, with a liver CEI of 46 HU, an aortic CEI of 309 HU, and an aortic SNR of 34.2. (E1-E4) A 54-year-old man, weighing 61 kg (BMI, 25.7 kg/m²), received a CM injection of 76 mL [500 mgI/TBW (kg)] and was scanned at 100 kVp, with a liver CEI of 54 HU, an aortic CEI of 343 HU, and an aortic SNR of 36.7. (F1-F4) A 60-year-old man, weighing 59 kg (BMI, 25.2 kg/m²), received a CM injection of 80 mL [542 mgI/TBW (kg)] and was scanned at 120 kVp, with a liver CEI of 56 HU, an aortic CEI of 347 HU, and an aortic SNR of 39.8. BMI, body mass index; CEI, contrast enhancement index; CM, contrast medium; CT, computed tomography; SNR, signal-to-noise ratio; TBW, total body weight.

The SNRs of the portal vein, hepatic vein, kidney, pancreas, and liver of the 500 mgI/kg at 120 kVp group and fixed-dose groups were significantly higher than those of the 400 mgI/kg at 100 kVp and 450 mgI/kg at 100 kVp groups; these latter values, in turn, were significantly higher than those of the 400 mgI/kg at 120 kVp and 450 mgI/kg at 120 kVp groups. The SNRs of the aorta in the 400 mgI/kg at 100 kVp, 450 mgI/kg at 100 kVp, 500 mgI/kg at 120 kVp, and fixed-dose groups were significantly higher than those of the other groups, and there was no statistically significant difference between these four groups.

The CNRs of aorta and liver in the 400 mgI/kg at 100 kVp, 450 mgI/kg at 100 kVp, 500 mgI/kg at 120 kVp, and fixed-dose groups were significantly higher than those of other TBW groups, and there was no statistical difference between these four groups. The CNRs of the kidney, pancreas, portal vein, and hepatic vein of the fixed-dose group were the highest, followed by the 500 mgI/kg at 120 kVp and 450 mgI/kg at 100 kVp groups, with lower values observed in other TBW groups.

Subjective image analysis

The subjective scores of the six groups were significantly different in the early arterial phase, late arterial phase, and portal venous phase. The subjective score in the 400 mgI/kg at 120 kVp group was the lowest compared with other subgroups in all phases, followed by the 400 mgI/kg at 100 kVp subgroup. No significant difference was found between the 450 mgI/kg 100 kVp, 500 mgI/kg 120 kVp, and fixed-dose groups in terms of the subjective scores. The subjective image quality is summarized in Table 3.

CM dose

The TBW-based subgroups were compared with the fixed-dose group in terms of both dose and corresponding volume, as shown in Table 4. The fixed-dose group was administered the highest dosage of CM, followed by the 500 mgI/kg subgroup and then the 450 mgI/kg subgroups, with the 400 mgI/kg subgroups being administered the least amount.

Radiation exposure

Table 5 summarizes the CTDIvol, DLP, and ED values for each group. There were significant differences in the CTDIvol, DLP, and ED values between the six groups (P<0.001).

Discussion

In recent years, weightbased CM dosing protocols have demonstrated promising value in abdominal CT. Previous studies have compared enhancement effects of CM protocols using various body-size metrics, including TBW, lean body weight, and body surface area. Although some studies have reported no significant differences between these parameters (19,20), others indicate that TBW-based protocols can lower the CM dose without compromising enhancement (21,22), whereas dosing by lean body weight may yield more consistent enhancement (23-25). Our study systematically evaluated and compared the enhancement effect and image quality between fixed-dose and individualized TBW‑based protocols using a high‑concentration CM (400 mgI/mL) at routine tube voltages (100–120 kVp) in abdominal multiphasic CT. The results demonstrated that TBW‑based protocols can achieve comparable enhancement to that of the fixed‑dose protocol while minimizing CM volume and contrast-related adverse effects without compromising diagnostic efficacy. Our work thus provides novel evidence for optimizing TBW‑based personalized dosing in this common clinical setting.

The 450 mgI/kg at 100 kVp protocol provided excellent vascular enhancement across all phases and was superior to its 120 kVp counterpart and comparable to both the fixed-dose and the 500 mgI/kg at 120 kVp protocols. This can be attributed to the mean photon energy at 100 kVp being closer to the k-edge energy of iodine (33.2 keV) than that at 120 kVp, resulting in more efficient photoelectric absorption and greater vascular contrast. Additionally, the use of 100 kVp inherently reduces patients' radiation dose (26-28). Although lower tube voltage increases image noise, which can degrade soft-tissue contrast, its impact on vascular assessment is limited due to the high intrinsic attenuation of contrast-filled vessels. Minor variations in radiation dose among protocols result from the automatic tube current modulation that adapts to the individual patient’s size and are within conventional clinical limits. Therefore, the 450 mgI/kg at 100 kVp protocol represents an effective strategy that synergistically improves vascular enhancement while reducing both CM volume and radiation exposure.

Regarding the enhancement effect of parenchymal organs and blood vessels, the SNR and CNR in the 500 mgI/kg at 120 kVp subgroup were higher than those in other TBW groups, but no significant differences were found compared with the fixed-dose group. A previous study reported that hepatic parenchymal enhancement greater than 50 HU is desirable during the portal venous phase (27). In our study, the proportion of patients achieving liver CEI ≥50 HU in the 500 mgI/kg at 120 kVp subgroup was the highest, enabling 84.7% of patients to meet diagnostic requirements. However, a proportion of patients still exhibited insufficient liver parenchymal enhancement. This can be attributed to differences in body fat content, muscle mass, and blood volume within the TBW, all of which influence the enhancement values of both blood vessels and the liver (29,30).

In terms of subjective image quality, the fixed-dose group and the TBW-based subgroups of 450 mgI/kg at 100 kVp or 500 mgI/kg at 120 kVp received significantly higher scores than did the other TBW-based subgroups. The fixed-dose group received the highest scores overall due to its administration of a higher total contrast volume, which results in superior SNR and CNR for multiple abdominal organs and enhanced visual contrast. Crucially, however, the subjective image quality scores for the TBW subgroups of 450 mgI/kg at 100 kVp and 500 mgI/kg at 120 kVp were not statistically different from those of the fixed-dose group. This indicates that in the assessment of the reviewing radiologists, the image quality achieved by these individualized protocols was diagnostically equivalent to that of the fixed-dose protocol. Importantly, the TBW-based protocol achieved comparable image quality while requiring significantly lower volumes of CM, highlighting the potential of TBW-based dosing protocols to serve as a personalized, efficient, and clinically effective contrast enhancement strategy.

There were several limitations to this study which should be acknowledged. First, the paucity of data from overweight and underweight patients limits the generalizability of our findings. Future studies with larger, more diverse cohorts are needed to validate and refine the TBW-based protocols across the full spectrum of body weights. Second, although this study offers valuable insights into general enhancement patterns, it did not specifically assess protocol performance for specific disease entities, such as hepatocellular carcinoma or pancreatitis. Future studies should evaluate the diagnostic utility of the contrast protocol in relation to its effectiveness in diagnosing specific types of lesions. Third, we did not use conventional iterative reconstruction, and the potential benefit of advanced techniques such as deep learning reconstruction algorithms for image quality under reduced-contrast conditions was not evaluated (31). Future studies incorporating such algorithms are needed to examine their synergy with personalized dosing strategies. Fourth, the lack of a fixed-dose control group scanned at 100 kVp limited our ability to analyze the individual effects of CM dose and tube voltage on image quality. Future studies including such a control group would help clarify their respective contributions.

Conclusions

TBW-based protocols can achieve diagnostic performance comparable to that of fixed-dose ones while significantly reducing the CM volume. Specifically, the 450 mgI/kg at 100 kVp protocol is recommended for vascular imaging, while the 500 mgI/kg at 120 kVp protocol is recommended for imaging parenchymal organs and tumor lesions. These findings support the clinical implementation of TBW-based protocols as a personalized, dose-optimized approach for abdominal CT imaging.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1171/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1171/dss

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1171/coif). W.R. is affiliated with the CT Imaging Research Center, GE Healthcare China. The other 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 The First Affiliated Hospital of Chongqing Medical University (No. KX2024-KYC0328-01) which waived the requirement for specific written consent, as general informed consent for CM administration was obtained from all patients prior to examination.

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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