Comparative study of abdominal CT enhancement in overweight and obese patients based on different scanning modes combined with different contrast medium concentrations

Abstract

PURPOSE:

To compare image quality, iodine intake, and radiation dose in overweight and obese patients undergoing abdominal computed tomography (CT) enhancement using different scanning modes and contrast medium.

METHODS:

Ninety overweight and obese patients (25 kg/m²≤body mass index (BMI)< 30 kg/m² and BMI≥30 kg/m²) who underwent abdominal CT-enhanced examinations were randomized into three groups (A, B, and C) of 30 each and scanned using gemstone spectral imaging (GSI) +320 mgI/ml, 100 kVp + 370 mgI/ml, and 120 kVp + 370 mgI/ml, respectively. Reconstruct monochromatic energy images of group A at 50–70 keV (5 keV interval). The iodine intake and radiation dose of each group were recorded and calculated. The CT values, contrast-to-noise ratios (CNRs), and subjective scores of each subgroup image in group A versus images in groups B and C were by using one-way analysis of variance or Kruskal–Wallis H test, and the optimal keV of group A was selected.

RESULTS:

The dual-phase CT values and CNRs of each part in group A were higher than or similar to those in groups B and C at 50–60 keV, and similar to or lower than those in groups B and C at 65 keV and 70 keV. The subjective scores of the dual-phase images in group A were lower than those of groups B and C at 50 keV and 55 keV, whereas no significant difference was seen at 60–70 keV. Compared to groups B and C, the iodine intake in group A decreased by 12.5% and 13.3%, respectively. The effective doses in groups A and B were 24.7% and 25.8% lower than those in group C, respectively.

CONCLUSION:

GSI +320 mgI/ml for abdominal CT-enhanced in overweight patients satisfies image quality while reducing iodine intake and radiation dose, and the optimal keV was 60 keV.

Keywords

Abdominal CT enhancement gemstone spectral imaging radiation dose low tube voltage low-concentration contrast medium

1 Introduction

With the increasing clinical application of computed tomography (CT) enhancement technology, the hazards of ionizing radiation, nephropathy induced by iodine contrast medium, and adverse reactions have attracted increasing attention [1 –4]. Abdominal CT-enhanced is an important auxiliary method for identifying abdominal injuries, inflammation, tumors, and vascular diseases and has significant clinical diagnostic value. Clinically, single or even multiple abdominal CT multiphase enhancement examinations can be performed if necessary during the progression of abdominal diseases from discovery to treatment to review and follow-up [5]. Overweight and obese patients usually require a higher tube voltage, tube current, and total iodine content to achieve adequate image quality; as a result, they are also exposed to higher ionizing radiation and iodine intake [6].

Technologies such as gemstone spectral CT imaging, low tube voltage technology, iterative reconstruction, and deep-learning algorithms are becoming increasingly common for significantly enhancing image quality and dramatically minimizing iodine intake and radiation dose of patients, and have important clinical application value [7 –10]. In this study, based on an 8 cm-wide detector and the adaptive statistical iterative reconstruction-Veo (ASiR-V) algorithm, set up three groups in combination with varying contrast medium concentrations: gemstone spectral imaging (GSI) group, low tube voltage group, and conventional group. For overweight and obese patients undergoing abdominal CT-enhanced, the scanning protocol should be optimized with the lower iodine intake and radiation dose while satisfying the image quality. Meanwhile, discuss the optimal monochromatic value for displaying abdominal CT-enhanced images of the arterial and portal vein phase in the GSI mode.

2 Materials and methods

2.1 Patient information

The ethics committee of our hospital approved this study, and patients or their families have signed an informed consent form. Overweight and obese patients (25 kg/m²≤body mass index (BMI) < 30 kg/m² and BMI≥30 kg/m²) were included in the study. The exclusion criteria for patients were as follows: severe cardiac, hepatic, renal insufficiency and iodine contrast medium allergy; Pregnant, lactating, or unable to cooperate with the study; Have a history of liver or spleen resection; There are metal implants or large masses (> 5 cm) in the scan area.

Collect prospectively the data from 90 overweight and obese patients (51 males and 39 females) who underwent abdominal CT-enhanced examinations at the hospital between September 2022 and April 2023. The patients were split into groups A, B, and C, utilizing the random number table method, with 30 in each group. The age range was 17–85 years, the weight range was 60.0–102.0 kg, and the BMI range was 25.00–33.20 kg/m² with an average of (27.55±2.24) kg/m² (Table 1). There were 13 normal cases, 51 cases of liver, kidney, and spleen cysts, 16 hepatic hemangiomas, ten pancreatitis cases, 13 gallbladder and bile duct diseases, ten hepatic occupying calcifications, three hepatic malignancies, two adrenal adenomas, two renal cancers, one splenic artery aneurysm, two pancreatic cancers, four gastrointestinal diseases, and one retroperitoneal ganglion tumor.

Table 1
Analysis of general data

Group Sex (N) Age (years) Weight (kg) BMI (kg/m²)

Male Female

A (n = 30) 16 14 53.37±13.91 76.53±9.63 27.68±2.37

B (n = 30) 16 14 54.93±12.67 75.65±7.71 27.60±2.32

C (n = 30) 19 11 55.33±13.89 76.38±10.50 27.38±2.07

F/χ² value 0.814^a 0.178 0.077 0.138

P value 0.665 0.837 0.926 0.871

Group	Sex (N)	Age (years)	Weight (kg)	BMI (kg/m²)
A (n = 30)	16	14	53.37±13.91	76.53±9.63	27.68±2.37
B (n = 30)	16	14	54.93±12.67	75.65±7.71	27.60±2.32
C (n = 30)	19	11	55.33±13.89	76.38±10.50	27.38±2.07
F/χ² value	0.814^a	0.178	0.077	0.138
P value	0.665	0.837	0.926	0.871

Note: BMI, body mass index.

2.2 CT technology

2.2.1 Scanning protocol

All patients underwent abdominal CT-enhanced scans from the diaphragm superior to the anterior superior iliac spine using a GE Revolution 256-row gemstone spectral CT scanner (GE Healthcare, a subsidiary of General Electric Company. Waukesha, USA). Group A was scanned in the GSI mode with a low-concentration contrast medium (ioversol, 320 mgI/ml. Jiangsu Hengrui Pharmaceutical Co., LTD. China). Group B received 100 kVp combined with a conventional contrast medium (iopamidol, 370 mgI/ml. Shanghai Bolecke Xinyi Pharmaceutical Co., LTD. China). Group C was scanned using 120 kVp combined with a conventional contrast medium (iopamidol, 370 mgI/ml). The GSI Assist tube current technique was applied in group A, and the 3D smart mA technique was used in groups B and C. All other scanning parameters were identical for three groups (Table 2).

Table 2
Scan parameters of the three groups

Parameters Group A Group B Group C

kV models GSI Manual Manual

Tube voltage 80 kVp·140 kVp 100 kVp 120 kVp

Tube current 445 mA 200–600 mA 200–600 mA

Noise index 8.0 7.0 7.0

Detector width 80 mm 80 mm 40 mm

Pitch 0.992:1 0.992:1 0.984:1

Same scanning parameters Tube speed 0.5 s/rot; SFOV 50 cm, matrix 512×512, scanned layer thickness and spacing are 5 mm; 50% pre-ASiR-V combined with 60% post-ASiR-V technique automatically reconstructs; window width 400 HU, window position 40 HU.

Parameters	Group A	Group B	Group C
kV models	GSI	Manual	Manual
Tube voltage	80 kVp·140 kVp	100 kVp	120 kVp
Tube current	445 mA	200–600 mA	200–600 mA
Noise index	8.0	7.0	7.0
Detector width	80 mm	80 mm	40 mm
Pitch	0.992:1	0.992:1	0.984:1
Same scanning parameters	Tube speed 0.5 s/rot; SFOV 50 cm, matrix 512×512, scanned layer thickness and spacing are 5 mm; 50% pre-ASiR-V combined with 60% post-ASiR-V technique automatically reconstructs; window width 400 HU, window position 40 HU.

Note: GSI, gemstone spectral imaging.

2.2.2 Contrast injection protocol

Puncture the right anterior elbow vein with a 20 g intravenous needle. The total amount of contrast medium injection was 1 ml/kg, and the iodine flow rate was 1.1 g I/s (3.5 and 3.0 ml/s for 320 and 370 mgI/ml, respectively) [11], followed by 30 ml of saline injection at the same speed. Using the contrast Smart Prep technique with a 20 mm² region of interest (ROI) was placed on the abdominal aorta below the diaphragm for scanning. The trigger threshold was set to 150 HU. When the CT value reached the trigger threshold, the arterial phase was scanned after a 5.9 s delay, and the portal vein phase and delayed phase were scanned for 30 s and 150 s after the completion of the arterial phase, respectively.

2.2.3 Image reconstruction

Subgroup images, A1–A5 and V1–V5 with a layer thickness of 0.625 mm, were reconstructed using monochromatic energies of 50 keV, 55 keV, 60 keV, 65 keV, and 70 keV in the arterial and portal vein phase images of group A. All images with a layer thickness and spacing of 0.625 mm in the three groups were transferred to the GE AW 4.7 workstation and PACS system for measurement and analysis.

2.3 Image quality analysis

2.3.1 Objective evaluation of image quality

A total of 16 ROIs were placed on the abdominal aorta (arterial phase), main portal vein (portal vein phase), liver and spleen at the hepatic hilum layer, pancreas at the pancreatic body layer, kidneys at the renal hilum layer (renal cortex in the arterial phase and renal medulla in the portal vein phase), and erector spinae muscle of the same layer [12]. The liver and spleen ROI area was (50±2) mm², and that of the abdominal aorta, main portal vein, pancreas, and kidneys was (20±2) mm². Calcification, plaque formation, and stenosis should be avoided when measuring blood vessels. Large vessels, artifacts, and significant lesions should be avoided when measuring organs. The CT values and noise values (standard deviation [SD]) for the aforementioned parts were measured and recorded, and the contrast-to-noise ratio (CNR) was calculated according to the following formula: CNR = (CT organ or vessel –CT erector spinae muscle)/SD erector spinae muscle.

2.3.2 Subjective evaluation of image quality

Two radiologists with > 10 years of experience in abdominal diagnosis used a five-point evaluation standard (Table 3) to score the images using a double-blind method [13, 14], and the final score was averaged from the subjective scores of the two physicians. Subjective score≥3 was considered as meeting the clinical diagnosis requirements.

Table 3
Subjective evaluation criteria for image quality on a five-point scale

Score Image quality Noise and artifacts Anatomical detail Organs and lesions

5 Excellent Good noise suppression, almost no artifacts Sharp edge, visible small blood vessels, small lymph nodes Clear display for better diagnosis

4 Good Less noise and artifacts Good, Continuous blood vessels Visible lesions for easy diagnosis

3 Intermediate There are parts, acceptable Not bad, acceptable Indistinct, does not affect the diagnosis

2 Poor More noise and artifacts Poor, interrupted blood vessels Suspected lesion, affects diagnosis

1 Unacceptable Severe noise or artifact Unable to display Seriously affects the diagnosis

Score	Image quality	Noise and artifacts	Anatomical detail	Organs and lesions
5	Excellent	Good noise suppression, almost no artifacts	Sharp edge, visible small blood vessels, small lymph nodes	Clear display for better diagnosis
4	Good	Less noise and artifacts	Good, Continuous blood vessels	Visible lesions for easy diagnosis
3	Intermediate	There are parts, acceptable	Not bad, acceptable	Indistinct, does not affect the diagnosis
2	Poor	More noise and artifacts	Poor, interrupted blood vessels	Suspected lesion, affects diagnosis
1	Unacceptable	Severe noise or artifact	Unable to display	Seriously affects the diagnosis

2.4 Iodine intake and radiation dose

Iodine intake was calculated using the following formula: iodine intake (g) = [patient weight (kg) ×1 ml/kg×contrast medium concentration (mgI/ml)]/1000. The CT dose index of the volume (CTDIvol) and dose-length products (DLP) were recorded from the dose reports of the patients in the three groups, and the effective dose (ED) was computed as follows: ED = DLP×k, k = 0.015 mSv/(mGy·cm) [15].

2.5 Statistical analysis

Data were statistically analyzed using SPSS version 26.0 (IBM Corp. Armonk, NY). Continuous variables were expressed as mean±standard deviation ( $\bar{x}$ ± s). The Chi-square test was used to compare sex differences. For comparison of the above other data, one-way analysis of variance (ANOVA) was employed for those consistent with the normal distribution, whereas the Kruskal–Wallis H test was adopted for those disobeying. When ANOVA was used for pairwise comparisons, the Bonferroni test was used when the variances were equal. Tamhane’s method was used when the variances were not uniform. The kappa test was used to evaluate the subjective score consistency of the two radiologists. Kappa values≥0.75 indicated good consistency, 0.40–0.75 indicated medium consistency, and < 0.40 was indicated bad consistency. Statistical significance was set at P < 0.05.

3 Results

3.1 Analysis of general data

There was no significant distinctions among the three groups of patients in terms of sex, age, weight, or BMI (χ² = 0.814, F = 0.178, 0.077, and 0.138, P > 0.05), as shown in Table 1.

3.2 Analysis of objective evaluation of image quality

At 50 keV and 55 keV levels: The CT values of the dual-phase images in all parts of group A were higher than those in groups B and C (P < 0.05), except that the CT value of the liver in the arterial phase did not differ from those in groups B and C (P > 0.05). The CNRs of the dual-phase images in all parts of group A were similar to those of groups B and C (P > 0.05), except for a higher CNR of the pancreas and kidneys in the dual-phase images compared to groups B and C (P < 0.05).

At 60 keV level: The CT values of the dual-phase images in all parts of group A were higher than those in groups B and C (P < 0.05), except for the CT values of the liver and spleen in the dual-phase images, and the pancreas in the portal vein phase, which were similar to those in groups B and C (P > 0.05). The CNRs of the pancreas in the arterial phase and liver in the dual-phase images in group A were higher than those in groups B and C (P < 0.05); however, the CNRs of the rest were similar to those in groups B and C (P > 0.05).

At 65 keV level: The CT values of the dual-phase images in all parts of group A were similar to those in groups B and C (P > 0.05), except for the renal cortex in the arterial phase, which had a higher CT value than those in groups B and C (P < 0.001), the liver in the arterial phase, and the spleen and pancreas in the portal vein phase, which had a lower CT value than those in groups B and C (P < 0.05). The CNR of the renal cortex in the arterial phase and that of the spleen in the portal vein phase were respectively higher and lower in group A than those in groups B and C (P < 0.001, P < 0.05); the rest were similar to those in groups B and C (P > 0.05).

At 70 keV level: Except the CT values of the abdominal aorta, spleen, pancreas, and renal cortex in the arterial phase of group, which were similar to those in groups B and C (P > 0.05), the rest were lower than those in groups B and C (P < 0.05). The CNR of the spleen in the portal vein phase in group A was lower than that in groups B and C (P < 0.05); however, the remaining values were not significantly different from groups B and C (P > 0.05).

The differences between the mean CT values and mean CNRs of the dual-phase images at each part in groups B and C were not statistically significant (P > 0.05). Shown in Table 4, Fig. 1 and 2.

Table 4
Comparison of objective and subjective evaluation of image quality in group A, B and C

Group A B C F/H value P value

50 keV 55 keV 60 keV 65 keV 70 keV

Arterial Phase (AP)

AA CT 557.48±56.04^bc 475.67±43.96^bc 396.13±41.81^bc 339.15±35.69 294.33±33.12 317.82±47.80 309.65±36.89 130.017^a < 0.001

Liver CT 75.28±9.96 70.03±9.31 67.02±7.92 63.22±7.90^bc 60.32±6.17^bc 71.14±8.18 72.31±8.30 120.033 < 0.001

Spleen CT 166.77±35.41^bc 146.17±26.92^bc 128.84±26.22 114.31±18.50 104.16±17.42 110.62±19.97 114.76±14.20 19.392^a < 0.001

Pancreas CT 155.19±17.49^bc 133.60±17.65^bc 119.80±12.77^bc 104.81±10.29 96.70±8.05 98.91±11.82 97.99±7.46 69.346^a < 0.001

Kidney CT 299.49±38.23^bc 251.01±34.38^bc 214.77±27.45^bc 185.68±24.86^bc 158.70±16.68 157.86±15.88 153.25±18.40 102.377^a < 0.001

SD 25.18±2.16^bc 21.90±1.68^bc 19.35±1.79^bc 17.04±1.14 16.05±1.57 16.51±1.62 14.71±1.85 160.978^a < 0.001

AA CNR 18.68±3.00 17.82±2.25 16.85±2.76 15.98±2.52 14.70±2.22 15.85±3.89 16.96±3.48 7.840^a < 0.001

Liver CNR 0.61±0.43 0.62±0.46 0.64±0.36 0.66±0.34 0.68±0.46 0.69±0.47 0.81±0.66 0.392^a 0.883

Spleen CNR 4.02±1.43 3.84±1.22 3.69±1.46 3.49±1.05 3.33±1.22 3.08±1.06 3.65±1.16 1.974 0.071

Pancreas CNR 4.02±1.09^bc 3.83±1.21^bc 3.60±0.90^bc 3.28±0.80 3.03±0.90 2.54±0.82 2.56±0.73 11.927 < 0.001

Kidney CNR 10.20±1.61^bc 9.73±1.95^bc 8.87±1.57^bc 8.41±1.63^bc 7.15±1.42 6.19±1.37 6.43±1.59 29.469 < 0.001

Subjective score 3.72±0.46^bc 3.80±0.52^bc 4.28±0.72 4.42±0.57 4.32±0.68 4.30±0.62 4.35±0.67 34.471^a < 0.001

Portal Vein Phase (PVP)

MPV CT 251.64±35.82^bc 215.73±31.88^bc 184.29±26.23^bc 162.56±23.40 143.77±19.10^bc 167.29±9.74 158.31±12.55 49.827^a < 0.001

Liver CT 143.22±17.36^bc 126.61±15.22^bc 112.20±12.32 103.17±10.32 94.36±9.60^bc 111.72±11.87 106.38±8.52 38.950^a < 0.001

Spleen CT 161.19±18.49^bc 140.22±15.50^bc 122.64±13.12 109.33±11.99^bc 101.48±13.33^bc 125.91±7.69 120.11±7.39 46.646^a < 0.001

Pancreas CT 131.01±10.01^bc 115.09±10.93^bc 99.94±9.00 90.27±7.48^bc 83.17±8.19^bc 100.82±5.20 96.71±8.13 84.895^a < 0.001

Kidney CT 186.87±29.57^bc 161.96±23.84^bc 139.72±17.70^bc 125.69±19.12 108.20±12.97^bc 126.74±12.87 119.34±13.27 44.370^a < 0.001

SD 24.66±2.94^bc 22.18±2.64^bc 19.30±1.84^bc 17.53±1.83 16.04±1.85 16.61±1.56 14.61±1.63 151.689^a < 0.001

MPV CNR 7.19±1.81 6.77±2.04 6.21±1.56 5.83±1.39 5.42±1.21 6.08±0.92 6.28±1.33 4.106^a < 0.001

Liver CNR 3.00±0.72 2.86±0.84 2.67±0.69 2.56±0.71 2.44±0.65 2.70±0.86 2.69±0.80 6.169 0.102

Spleen CNR 3.72±0.96 3.43±0.81 3.18±0.70 2.89±0.57^bc 2.86±0.62^bc 3.55±0.69 3.63±0.74 22.070 < 0.001

Pancreas CNR 2.95±0.74^bc 2.61±0.74^bc 2.32±0.66 2.04±0.59 1.88±0.54 2.00±0.54 1.95±0.75 28.774 < 0.001

Kidney CNR 5.51±1.54^bc 4.98±1.40^bc 4.60±1.20^bc 4.24±1.30 3.58±0.94 3.56±0.83 3.50±1.03 11.795^a < 0.001

Subjective score 3.48±0.51^bc 3.57±0.54^bc 4.27±0.76 4.18±0.99 4.05±0.63 4.22±0.67 4.07±0.55 41.268^a < 0.001

Group	A	B	C	F/H value	P value
Arterial Phase (AP)
AA CT	557.48±56.04^bc	475.67±43.96^bc	396.13±41.81^bc	339.15±35.69	294.33±33.12	317.82±47.80	309.65±36.89	130.017^a	< 0.001
Liver CT	75.28±9.96	70.03±9.31	67.02±7.92	63.22±7.90^bc	60.32±6.17^bc	71.14±8.18	72.31±8.30	120.033	< 0.001
Spleen CT	166.77±35.41^bc	146.17±26.92^bc	128.84±26.22	114.31±18.50	104.16±17.42	110.62±19.97	114.76±14.20	19.392^a	< 0.001
Pancreas CT	155.19±17.49^bc	133.60±17.65^bc	119.80±12.77^bc	104.81±10.29	96.70±8.05	98.91±11.82	97.99±7.46	69.346^a	< 0.001
Kidney CT	299.49±38.23^bc	251.01±34.38^bc	214.77±27.45^bc	185.68±24.86^bc	158.70±16.68	157.86±15.88	153.25±18.40	102.377^a	< 0.001
SD	25.18±2.16^bc	21.90±1.68^bc	19.35±1.79^bc	17.04±1.14	16.05±1.57	16.51±1.62	14.71±1.85	160.978^a	< 0.001
AA CNR	18.68±3.00	17.82±2.25	16.85±2.76	15.98±2.52	14.70±2.22	15.85±3.89	16.96±3.48	7.840^a	< 0.001
Liver CNR	0.61±0.43	0.62±0.46	0.64±0.36	0.66±0.34	0.68±0.46	0.69±0.47	0.81±0.66	0.392^a	0.883
Spleen CNR	4.02±1.43	3.84±1.22	3.69±1.46	3.49±1.05	3.33±1.22	3.08±1.06	3.65±1.16	1.974	0.071
Pancreas CNR	4.02±1.09^bc	3.83±1.21^bc	3.60±0.90^bc	3.28±0.80	3.03±0.90	2.54±0.82	2.56±0.73	11.927	< 0.001
Kidney CNR	10.20±1.61^bc	9.73±1.95^bc	8.87±1.57^bc	8.41±1.63^bc	7.15±1.42	6.19±1.37	6.43±1.59	29.469	< 0.001
Subjective score	3.72±0.46^bc	3.80±0.52^bc	4.28±0.72	4.42±0.57	4.32±0.68	4.30±0.62	4.35±0.67	34.471^a	< 0.001
Portal Vein Phase (PVP)
MPV CT	251.64±35.82^bc	215.73±31.88^bc	184.29±26.23^bc	162.56±23.40	143.77±19.10^bc	167.29±9.74	158.31±12.55	49.827^a	< 0.001
Liver CT	143.22±17.36^bc	126.61±15.22^bc	112.20±12.32	103.17±10.32	94.36±9.60^bc	111.72±11.87	106.38±8.52	38.950^a	< 0.001
Spleen CT	161.19±18.49^bc	140.22±15.50^bc	122.64±13.12	109.33±11.99^bc	101.48±13.33^bc	125.91±7.69	120.11±7.39	46.646^a	< 0.001
Pancreas CT	131.01±10.01^bc	115.09±10.93^bc	99.94±9.00	90.27±7.48^bc	83.17±8.19^bc	100.82±5.20	96.71±8.13	84.895^a	< 0.001
Kidney CT	186.87±29.57^bc	161.96±23.84^bc	139.72±17.70^bc	125.69±19.12	108.20±12.97^bc	126.74±12.87	119.34±13.27	44.370^a	< 0.001
SD	24.66±2.94^bc	22.18±2.64^bc	19.30±1.84^bc	17.53±1.83	16.04±1.85	16.61±1.56	14.61±1.63	151.689^a	< 0.001
MPV CNR	7.19±1.81	6.77±2.04	6.21±1.56	5.83±1.39	5.42±1.21	6.08±0.92	6.28±1.33	4.106^a	< 0.001
Liver CNR	3.00±0.72	2.86±0.84	2.67±0.69	2.56±0.71	2.44±0.65	2.70±0.86	2.69±0.80	6.169	0.102
Spleen CNR	3.72±0.96	3.43±0.81	3.18±0.70	2.89±0.57^bc	2.86±0.62^bc	3.55±0.69	3.63±0.74	22.070	< 0.001
Pancreas CNR	2.95±0.74^bc	2.61±0.74^bc	2.32±0.66	2.04±0.59	1.88±0.54	2.00±0.54	1.95±0.75	28.774	< 0.001
Kidney CNR	5.51±1.54^bc	4.98±1.40^bc	4.60±1.20^bc	4.24±1.30	3.58±0.94	3.56±0.83	3.50±1.03	11.795^a	< 0.001
Subjective score	3.48±0.51^bc	3.57±0.54^bc	4.27±0.76	4.18±0.99	4.05±0.63	4.22±0.67	4.07±0.55	41.268^a	< 0.001

Note: ^a: variance not equal, using Welch’s result or H test. ^b: Statistically significant (P < 0.05) compared with group B. ^c: Statistically significant (P < 0.05) compared with group C. AP: arterial phase, PVP: portal vein phase, AA: abdominal aorta, MPV: main portal vein.

Fig. 1

Computed tomography (CT) images of cases in groups A, B, and C. Note: Case A, female, mild dilation of pancreatic duct; case B, male, abscess of right lobe of liver; case C, male, right kidney cyst and pancreatitis. BMI were 25.61 kg/m², 26.06 kg/m², and 26.12 kg/m², respectively. Figures A11–A53 and V14–V56 show five subgroups of images (50–70 keV, 5 keV interval) of the arterial and portal vein phases in case A. The image noise is greater at 50 keV and 55 keV, and a diagnostic effect can be achieved at 60–70 keV, which is similar to that of groups B and C. Figures B1–B6 and C1–C6 represent the dual-phase images of the low-tube voltage and conventional groups at the levels of hepatic hilum, pancreatic body, and renal hilum, respectively. The image quality of group A at the 60 keV was no significant difference from that of groups B and C.

Fig. 2

Comparison of CT values and CNRs for dual-phase images of various organ and blood vessel in different scanning modes. (**P < 0.001, *P < 0.05) Note: The CT values of each part in group A were higher than or similar to those in groups B and C at 50–60 keV, and similar to or lower than those in groups B and C at 65 keV and 70 keV, except for the renal cortex at 65 keV. The CNRs of the abdominal aorta and spleen in the arterial phase, the main portal vein, and the liver dual-phase images in group A were not statistically significant compared with those in groups B and C at 50–70 keV (P > 0.05). AP: arterial phase, PVP: portal vein phase.

3.3 Analysis of subjective evaluation of image quality

The two radiologists had consistent subjective scores of image quality for each subgroup of group A and for both groups B and C (all Kappa value > 0.75), and all images had a subjective score of > 3, which met the clinical diagnostic requirements. The subjective scores of the dual-phase images in group A were lower than those in groups B and C at the 50 keV and 55 keV levels (AP: 3.72±0.46, 3.80±0.52; PVP: 3.48±0.51, 3.57±0.54. P < 0.05), and the differences compared with those in groups B and C at the 60–70 keV levels were not significant (AP: 4.28±0.72, 4.42±0.57, 4.32±0.68; PVP: 4.27±0.76, 4.18±0.99, 4.05±0.63. P > 0.05). There was no statistically significant difference between the subjective score of group B and group C (AP: 4.30±0.62, 4.35±0.67; PVP: 4.22±0.67, 4.07±0.55. P > 0.05). As illustrated in Table 4, Fig. 3.

Fig. 3

Comparison of subjective scores of dual-phase images in different scanning modes. Note: The subjective scores of the dual-phase images in group A were lower than those of groups B and C at 50 keV and 55 keV (P < 0.05) and similar to those in groups B and C at 60–70 keV (P > 0.05). There was no significant distinction between the subjective scores of the dual-phase images in groups B and C (P > 0.05). AP: arterial phase, PVP: portal vein phase.

Considering the objective and subjective evaluations of the dual-phase images of each subgroup in group A, 60 keV was found to be the optimal monochromatic energy value for abdominal CT-enhanced in overweight and obese patients using GSI combined with a low-concentration contrast medium.

3.4 Analysis of iodine intake and radiation dose

The iodine intake of group A was reduced by 12.5% and 13.3%, compared with those in groups B and C, respectively (24.49±3.08, 27.99±2.85, 28.26±3.89. P < 0.001), and the difference between groups B and C was not statistically significant (P > 0.05). The effective doses of groups A and B decreased by 24.7% and 25.8%, respectively, compared with that in group C (12.85±1.22, 12.67±1.21, 17.07±2.93. P < 0.001), and the difference between groups A and B was not statistically significant (P > 0.05). As seen Table 5.

Table 5
Iodine intake and radiation dose

Group Iodine intake (g) CTDIvol (mGy) DLP (mGy·cm) ED (mSv)

A 24.49±3.08^c 24.04±0.87^c 856.35±81.51^c 12.85±1.22^c

B 27.99±2.85 24.60±0.94^c 844.37±80.68^c 12.67±1.21^c

C 28.26±3.89 35.29±4.44 1138.12±195.51 17.07±2.93

F/H value 12.166 64.487^a 29.731^a 29.731^a

P value < 0.001 < 0.001 < 0.001 < 0.001

Group	Iodine intake (g)	CTDIvol (mGy)	DLP (mGy·cm)	ED (mSv)
A	24.49±3.08^c	24.04±0.87^c	856.35±81.51^c	12.85±1.22^c
B	27.99±2.85	24.60±0.94^c	844.37±80.68^c	12.67±1.21^c
C	28.26±3.89	35.29±4.44	1138.12±195.51	17.07±2.93
F/H value	12.166	64.487^a	29.731^a	29.731^a
P value	< 0.001	< 0.001	< 0.001	< 0.001

Note: ^a: variance not equal, using Welch’s result or H test. ^c: Statistically significant (P < 0.05) compared with group C. CTDIvol: The CT dose index of the volume, DLP: dose-length products, ED: effective dose.

4 Discussion

CT-enhanced examination has the advantages of being noninvasive, convenient, and cost-effective and is increasingly used in clinical applications. However, the high ionizing radiation generated by CT examinations is concerning [16, 17]. Overweight and obese patients are usually exposed to higher doses of ionizing radiation because of their larger body sizes. Presently, the reduction in CT radiation dose is mainly achieved by reducing the magnitude of the tube voltage and current, using an iterative reconstruction algorithm, increasing the pitch, and adopting a wide-detector [8 , 19]. Increased renal metabolic burden, persistent renal failure risk, and incidence of cardiovascular and cerebrovascular diseases caused by iodine contrast media in CT enhancement are also concerns [20]. Although there is still a lack of strong evidence for acute kidney injury from iodine contrast media, patients can still benefit from reducing iodine intake. Changing the iodine contrast concentration, total volume injected, injection flow rate, and physicochemical properties can affect patient safety and tolerability [3 , 22].

GSI imaging utilizes single-source dual-energy technology to switch between 80 kVp and 140 kVp instantaneously within 0.25 ms, which makes two different energy X-rays, homologous and isotropic, to produce different X-ray attenuation of substance, and can reconstruct 101 monochromatic energy images with different CT values and noise values within the scope of 40–140 keV. Low-keV images have high noise levels and relatively low subjective evaluations. In high-keV images, hardening artifacts are reduced, the image gradually becomes smooth, and the image noise is reduced; however, the CNR is also reduced [23, 24]. When keV increases to a certain level, the image is like a “skin buffing” beauty effect, which leads to distortion and affects the detection rate of diseases and may even the situation of “missed and misdiagnosed.” Therefore, the optimal keV value for image display should be selected according to the different scanning sites and examination items in the GSI scanning mode. In this study, group A used the GSI mode combined with a low-concentration contrast medium to perform an abdominal CT-enhanced scan in overweight and obese patients, which not only reduced iodine intake by approximately 12.5% –13.3% compared with group B (low tube voltage scanning protocol) and group C (conventional scanning protocol) using a conventional concentration contrast medium. Moreover, the image quality at 60 keV was higher than or similar to that of groups B and C, achieving a good clinical diagnostic effect. This is because the κ-edge value of the iodine atom is 33.2 keV, and if the effective energy is greater than this value, the iodide contrast in organs and tissues will be amplified with the decrease of keV, especially in the portal vein phase. Abdominal CT-enhanced imaging can not only help diagnose various vascular diseases but also diseases of the abdominal parenchymal organs, some cavity organs, and lymph nodes. We found that the CT values and CNRs of each monochromatic energy dual-phase image in group A were the best at 50–60 keV, and the subjective scores were the best at 60–70 keV; however, the noise values were larger at 50 keV and 55 keV. Therefore, 60 keV was the optimal monochromatic value for observing the abdominal arterial and portal vein phases in overweight and obese patients. In clinical practice, we found that in patients with a large body weight or poor circulation and contrast medium injection, image quality degradation caused by poor arteriovenous display can be compensated by low-keV images, avoiding the risk of increasing iodine intake and radiation dose due to increasing the dosage of contrast medium and re-scanning.

Reducing the tube voltage is one of the most efficient strategies for lowering the X-ray radiation dose because the X-ray volume output increases in proportion to the square of the tube voltage. When using the same value of milliampere-seconds, a low tube voltage produces much fewer X-ray photons than a high tube voltage; however, the fewer the X-ray photons, the greater the image noise, which also affects image quality. The findings of this study demonstrated that the radiation doses received by groups A and B were noticeably lower than those received by group C (P < 0.001); however, the difference between groups A and B was not statistically significant (P > 0.05). This is because the noise index of group A was set to 8 HU at 2.5 mm, the tube current was set to 445 mA, and the GSI Assist technique was adopted. Group B used the low tube voltage technology; it also benefits from the fact that groups A and B both used an 8 cm-wide detector, while group C used a 4 cm detector. In this study, although the effective dose was reduced by 24.7% and 25.8% in groups A and B, respectively, compared with group C, the image quality was not affected by the noise caused by the reduction in the number of X-ray photons, which was attributed to the ASiR-V, the latest generation of iterative reconstruction algorithms. It combines Veo technology and multi-model (noise, object, physics) reconstruction with the advantages of high resolution with low contrast, fast reconstruction speed, and stronger noise reduction ability. Therefore, ASiR-V is able to correct and lessen the image noise in existing spatial models, improve image contrast, and ensure image quality.

The findings of this study also indicated that the CNR of the abdominal aorta differed at 50 keV and 55 keV versus 65 keV and 75 keV; the CNR of the renal cortex differed at 50 keV versus 65 keV and 70 keV, and at 55 keV versus 70 keV. This may be due to the higher concentration of iodine aggregation in the abdominal aorta and renal cortex, the high absorption of X-ray energy in the measured ROI, and the fact that the difference in CT value varies greatly with the change in monochromatic energy value. Therefore, there is a large difference in the CNRs between the two ends of the subgroup. The hepatic CNR during the arterial phase increased with increasing keV, whereas the CT values and CNRs of the remaining organs and vascular dual-phase images gradually decreased with increasing monochromatic energy. This is probably because the liver is the largest parenchymal organ in the body, and the average iodine concentration absorbed by the liver parenchyma is low before the contrast medium is distributed to the left, middle, and right arteries of the liver through the common hepatic artery in the arterial phase. The attenuation coefficient of X-rays does not change much at different keV energy levels, while the noise value changes significantly, resulting in a higher CNR of the liver in the arterial phase instead of decreasing.

Our study has some limitations: (1) The image quality evaluation did not involve the detection rate of lesions at each site. (2) A more detailed study of ASiR-V at different pre- and post-weight levels has not been performed.

In conclusion, the 8 cm-wide detector based GSI scanning mode combined with 320 mgI/ml iodine contrast medium, while setting 60 keV, is the optimal scanning protocol for abdominal CT-enhanced scanning in overweight and obese patients.

Funding

This study was funded by Key R & D projects of Baoding City (grant number:2141ZF307), Hebei Province medical science research project (grant numbers:20200572), Medical Science Foundation of Hebei University (grant numbers: 2021A10 and 2021X06), Postgraduate’s Innovation Fund Project of Hebei University grant numbers: HBU2023BS001), Hebei Province medical technology tracking project (grant numbers: 2023093), and Affiliated hospital of Hebei university outstanding foundation (grant numbers: 2019Z004 and 2021Q002).

Conflict of interest

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Ethical approval

All procedures performed in our study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study. All patients signed informed consent.

This article does not contain any studies with animals performed by any of the authors.

This prospective study received institutional board approval from the affiliated hospital of Hebei University and each participant provided informed consent.

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