CT imaging using variable helical pitch scanning for lower extremity arterial disease: reduced contrast medium dose, improved image quality and diagnostic accuracy

doi:10.21203/rs.3.rs-4906092/v1

Objectives

This study aimed to explore the feasibility of reducing contrast medium (CM) volume, improving image quality and diagnostic accuracy using variable helical pitch (VHP) scanning for patients with lower extremity arterial disease (LEAD).

Materials and Methods

Eighty patients who underwent lower extremity CT angiography (CTA) were prospectively enrolled and randomly assigned to either the VHP group (n = 40) or the conventional group (n = 40). Quantitative parameters and qualitative scores were compared between the two groups. Additionally, out of these patients, 72 arteries from 18 patients had DSA as the reference standard, and the diagnostic accuracy for the degree of vessel stenosis was assessed and compared.

Results

In the VHP group, the contrast volume was significantly lower than in the conventional group (79.55 ± 11.87 mL vs. 89.63 ± 10.03 mL, p < 0.001), showing a reduction of 12.7%. For all image quality characteristics, scores in VHP group were significantly superior to those to those in the conventional groups (all p < 0.05). Quantitative analysis revealed that images from the VHP group exhibited superior CT enhancement, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) in the anterior tibial arteries (ATA) and dorsali pedis arteries (DPA) compared to the conventional group (all p < 0.001). Moreover, the VHP group demonstrated significantly higher positive predictive value (PPV) and accuracy than the conventional group (PPV: 100% vs. 76.19%, p = 0.01; accuracy: 100% vs. 84.38%, p = 0.01, respectively).

Conclusions

The implementation of the VHP protocol led to a 12.7% decrease in contrast medium dosage compared to the conventional lower extremity CTA scanning protocol. Furthermore, it improved image quality and diagnostic accuracy, particularly for arteries below the knee.

Peripheral arterial disease

Computed tomography angiography

Contrast media

Image quality

The Lower extremity arterial disease (LEAD) is a prevalent disease in middle-aged and elderly individuals, with an estimated 236 million adults (5.6% of the worldwide population) diagnosed with LEAD^[1]. Patient with LEAD often have coronary artery disease due to their increased risk of atherosclerosis^[2]. This disease significantly impacts patients' quality of life, with high mortality and disability rates, placing a substantial burden on society^[3]. While digital subtraction angiography (DSA) is considered the gold standard for detecting LEAD^[4], it is associated with limitations such as high cost, low patient compliance, invasiveness, and lack of 3D reconstruction after the examination.

With the continuous development of CT technology, CT angiography (CTA) has emerged as a reliable non-invasive diagnostic technology for LEAD, offering fast image acquisition, extended scan range and multi-angle reconstruction capabilities^[5]. The image quality of CTA highly depends on iodinated contrast media (CM), which enhances vessel visualization. For the lower extremity scans with extended scan range, typically more than 80–100 ml of CM is required, a higher dosage compared to other body areas^{[6, 7]}. An elevated dose of CM is associated with a higher risk of contrast-induced kidney injury^[8]. Therefore, a low CM protocol is preferable for clinical use in this context.

Another issue arising from lower extremity CTA is the challenge of examining the arteries below the knee, particularly in scenarios with low CM levels. The blood transit time from the aorta to the lower extremities varies widely among individuals based on their cardiovascular status and underlying vascular disease^{[9, 10]}. Additionally, due to physiological diminishment of contrast media over time and distance traveled, coupled with diameter differences between above-the-knee and peripheral arteries, the bolus transit speed in arteries below the knee is slower^[11]. Therefore, optimal scan speeds for different lower extremity areas are crucial to ensure adequate enhancement and prevent venous overlay.

Variable helical pitch (VHP) is a promising CT technique for optimizing lower extremity CTA scans. It enables a single continuous acquisition with a seamless transition of scanning parameters including helical pitch, noise index, and ECG gating. In the abdominal region, the scan speed can be set as fast or standard; for the lower extremities, it is adjusted to slow based on the individual physiological status. Previous study has demonstrated the feasibility of VHP in chest-abdomen-pelvis scanning with variable target noise levels^{[12, 13]}. This technique also allows for the simultaneous evaluation of the aorta and coronary arteries in patients undergoing transcatheter aortic valve implantation (TAVI) with or without ECG gating^[13]. However, the application of VHP in the lower extremities has not been fully explored yet. The purpose of this study was to evaluate the feasibility of reducing CM volume, improving image quality and diagnostic accuracy using VHP scanning for patients with LEAD.

2.1 Patients

This prospective study was approved by the institutional review board. All Methods were performed in accordance with Declaration of Helsinki principles. Informed consent was obtained from all patients. According to the Declaration of Helsinki principles, this prospective study was approved by the Xi 'an Daxing Hospital Medical Ethics Committee(reference number: LW2023-0008). All experiments conducted adhered to the relevant guidelines and regulations. Informed consent was obtained from all patients.

Patients with suspected LEAD were enrolled between November 2023 and July 2024. The exclusion criteria were as follows: allergy to iodine-containing contrast medium, age below 18 years, thyroid disorder, renal insufficiency with an eGFR less than 30 ml/min/1.73 m², and allergy to contrast medium. A total of 80 patients fulfilled the inclusion and exclusion criteria and were divided evenly into two groups: VHP group (n = 40) and conventional group (n = 40).

2.2 CT image acquisition and reconstruction

CT scans were performed on a 320-row detector CT scanner (Aquilion ONE; Canon Medical Systems, Japan). The identical scan parameters used for the two groups were: tube voltage: 80 kVp, rotation time: 0.75 s/r, collimation: 0.5 × 80mm. Acquisition covered a volume starting from the infrarenal aorta to the toe. The contrast medium (Iodixanol Injection 320 mg/ml; GE Healthcare) was injected through 20G catheter inserted into a right antecubial vein at a rate of 4 mL/s

In the VHP group, a test bolus of 15 mL CM was injected at a rate of 4 mL/s, followed by 20 mL of saline flush. Then two sets of dynamic acquisitions were initiated at low radiation dose (80 kV, 25 mAs) at the level of diaphragm (abdominal aorta) and knee (popliteal arteries), respectively. The monitoring image of the abdominal aorta was started 15 s after the initiation of intravenous injection, and was obtained every 2 s. Once the triggering threshold of 150 HU was reached in the abdominal aorta, the table was moved to the patella level, and the sampling of popliteal arteries began. The time to the maximum attenuation of the diaphragm level (T_A) and knee level (T_B) was calculated from the time-density curve. The time interval from diaphragm level to knee level was then determined as (T_B - T_A), and used to adjust the pitch to ensure the acquisition time closely matched the contrast transit time. The VHP scanning facilitated a continuous acquisition with seamless change of scan pitch and noise index between the area above the knee and below the knee. For the area of above the knee, a relative high pitch (HP₁) and low noise (noise index = 15) were used, covering the structure from the level of the infrarenal aorta to the lower edge of knee. In contrast, for the area of below the knee, a relatively low pitch (HP₂) and high noise (noise index = 20) was utilized, encompassing the structure from the lower edge of patella to the toe. The helical pitch, HP₁ was calculated using the following formula, and the closet value from the three preset values (detailed: 0.637, standard: 0.813, fast: 1.388) was selected as the final value. HP₂ was also chosen from the three preset values, and identified as the value one notch lower than HP₁.

$$\:{\text{H}\text{P}}_{1}=\frac{{\text{S}\text{c}\text{a}\text{n}\:\text{l}\text{e}\text{n}\text{g}\text{t}\text{h}}_{1}\bullet\:\text{g}\text{a}\text{n}\text{t}\text{r}\text{y}\:\text{r}\text{o}\text{t}\text{a}\text{t}\text{i}\text{o}\text{n}\:\text{t}\text{i}\text{m}\text{e}}{{(\text{T}}_{\text{B}}-{\text{T}}_{\text{A}})\bullet\:\text{c}\text{o}\text{l}\text{l}\text{i}\text{m}\text{a}\text{t}\text{i}\text{o}\text{n}\:\text{w}\text{i}\text{d}\text{t}\text{h}}$$

The CM volume for the subsequent lower extremity CTA was calculated as CM_vol = (T_B - T_A) × injection rate (4 mL/s). And the acquisition was started 5 s after CT attenuation reached the threshold of 150 HU.

In the conventional group, the CM volume was determined according to the body weight (≤ 60 kg, 80 mL; 60–90 kg, 100 mL; >90 kg, 120 mL). Bolus tracking with a ROI in the abdominal aortal was used for scan initiation. Data acquisition was started 5 s after CT attenuation reached the threshold of 150 HU. Other scanning parameters were: noise index: 15; helical pitch: standard, 0.828. If the arteries below the knee are not clearly displayed, a rescan will be performed with the same parameters, covering from the toes to the lower edge of the knee.

Images were reconstructed using adaptive iterative dose reduction 3D (AIDR 3D). All reconstructions had a slice thickness of 0.5 mm with 0.3 mm intervals. The reconstructed CTA images were then transferred to a workstation (Vital Images, Canon Medical Systems, Japan) to generate maximum intensity projection (MIP), curved planar reformat (CPR), multiplanar reformation (MPR), and volume rendering (VR) for the analysis.

2.3 DSA

Eighteen patients (10 in the VHP group, and 8 in the conventional group) underwent the DSA procedure within 24 hours after CTA. DSA was conducted by an interventional radiologist using an angiographic system (Optima IGS 330, GE Healthcare). A catheter was inserted into the femoral artery, and an antegrade or retrograde approach was employed to access the target vessel. A total of 20 ml of iodinated CM was manually injected, and images were obtained in a posterior-anterior projection initially. Additional left and right anterior oblique projections were taken if the stenosis could not be adequately assessed from the posteroanterior projection. Lesions were considered significant with computed luminal narrowing exceeded 50%. This degree of luminal narrowing is initially assessed by an interventional vascular surgeon with 10 years of experience, and then reviewed by another equally experienced physician.

2.4 Qualitative image quality evaluation

Two radiologists, with 5 and 8 years of experience in peripheral vascular radiology, independently assessed the image quality of lower extremities. Ratings were assigned using a 5-point Likert scale for overall image quality, diagnostic confidence, and distal vessel visualization, as detailed in Table 2.

Table 1 Patient and scan characteristics in VHP and conventional groups

Parameters	VHP group	Conventional group	p-value
Number of participants	40	40	/
Age (years)	64.35 ± 15.90	66.48 ± 13.36	0.99
Sex (proportion male/female)	30/10	33/7	0.29
Body mass index (kg/m2)	22.97 ± 3.74	22.45 ± 3.94	0.55
Contrast volume (mL)	79.55 ± 11.87^a	89.63 ± 10.03	<0.001
CTDI_vol (mGy)	2.29 ± 0.81	1.91 ± 0.42 /1.31 ± 0.23^b	/
DLP (mGy cm)	297.92 ± 114.96	294.33 ± 70.01	0.56
ED (mSv)	1.43 ± 0.50	1.40 ± 0.32	0.63

Data expressed as mean ± standard deviation.

p < 0.05 was considered statistically significant.

VHP: variable helical pitch; ED: effective dose.

^aRepresents the total contrast volume used in the VHP group, which includes the addition of 15 mL for the test bolus to the final values.

^b Represents two separated scans used in the conventional group: a completed scan from the infrarenal aorta to the toe/a partial scan from the toes to the lower edge of the knee for patients with unclear displayed arteries.

Table 2

Description of the categories of image quality characteristics
Image quality characteristic	Score
Image quality characteristic	1	2	3	4	5
Overall image quality	Non-diagnostic, vessels are not displayed for evaluation	Poor image quality, substantial blurring luminal border	Moderate, moderate sharp delineation of the lumen	Good, average sharp delineation of the lumen	Excellent, sharp delineation of the lumen
Diagnostic confidence	No confidence, vessels are not displayed for evaluation, making it impossible to diagnose vessel narrowing.	Generally confident, vessels are discontinuous, and the degree of narrowing requires other tests for assessment	Confident, vessels are discontinuous, enabling a preliminary assessment of the degree of narrowing	Very confident, vessels are continuously displayed, enabling the assessment of the degree of narrowing, and the details are reliable	Most confident, vessels are continuously displayed, narrowing assessment is indisputable, and details are highly reliable
Distal vessel visualization	Main branches are not completely visualized, and distal branches and dorsalis pedis arteries are also not visualized	Main branches are completely visualized, but distal branches and dorsalis pedis arteries are not visualized	Distal branches and dorsalis pedis arteries are not completely visualized	Several distal branches and dorsalis pedis arteries are visualized	Many distal branches and dorsalis pedis arteries are visualized

2.5 Quantitative image quality evaluation

A radiologist with 5 years of experience in peripheral vascular radiology performed quantitative image analysis. ROI measurements were performed in the aorta, femoral arteries (FA), popliteal artery (PA), anterior tibial arteries (ATA), dorsali pedis arteries (DPA). The area of ROI was set as 3 mm², carefully avoiding calcification, fatty streaks and density artifacts near bones. The mean attenuation (HU) and standard deviation (SD) were recorded. Background attenuation and noise was measured in the closest muscle. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were defined as follows:

$$\:\text{S}\text{N}\text{R}=\frac{{\text{H}\text{U}}_{\text{a}\text{r}\text{t}\text{e}\text{r}\text{y}}}{{\text{S}\text{D}}_{\text{a}\text{r}\text{t}\text{e}\text{r}\text{y}}}$$

$$\:\text{C}\text{N}\text{R}=\frac{{\text{H}\text{U}}_{\text{a}\text{r}\text{t}\text{e}\text{r}\text{y}}-{\text{H}\text{U}}_{\text{m}\text{u}\text{s}\text{c}\text{l}\text{e}}}{\sqrt{\frac{1}{2}({\text{S}\text{D}}_{\text{a}\text{r}\text{t}\text{e}\text{r}\text{y}}^{2}+{\text{S}\text{D}}_{\text{m}\text{u}\text{s}\text{c}\text{l}\text{e}}^{2})}}$$

2.6 Stenosis measurement by using CTA

A radiologist with 10 years of experience, who was blinded to the acquisition technique, assessed CTA images for each patient. The degree of stenosis was determined by identifying the maximum stenosis in the arterial segment and the adjacent proximal non-stenotic lumen using the vascular software package on a workstation (Vital Images, Canon Medical Systems, Japan). A stenosis of 50% or greater was considered clinically significant.

2.7 Radiation dose

The volumetric CT dose index (CTDI_vol) and dose-length product (DLP) values were recorded for each patient. The effective radiation dose was calculated as the product of the DLP and the conversion factor for the lower extremities (K_male = 0.0046; K_female = 0.0057) ^[14]

2.8 Statistical analysis

Statistical analyses were performed using R software (version 3.6.1; http://www.R-project.org). The Shapiro–Wilk test was used to test the normal distribution of the data. For continuous variables with a normal distribution, independent samples t-test was used, whereas non-normally distributed data underwent analysis with the Mann-Whitney U-test. The Fisher test was applied to compare the rates. In the qualitative analysis, inter-reader agreement was assessed by calculating weighted kappa coefficients. The levels of agreement were defined as follows: 0-0.20, poor; 0.21–0.40, fair, 0.41–0.60, moderate; 0.61–0.80, good; and 0.81-1.00, excellent. For the detection of stenosis, the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated using DSA as the reference standard. A p value < 0.05 was considered statistically significant.

3.1 Clinical characteristics

Figure 1 shows the patient inclusion flowchart. As shown in Table 1, there was no significant difference in age, sex, and BMI between the VHP and conventional groups (all p > 0.05). The contrast volume was lower in the VHP group than in the conventional group (79.55 ± 11.87 mL vs. 89.63 ± 10.03 mL, p < 0.001), showing a decrease of 12.7%. There were no significant differences in radiation dose between the two groups (p = 0.87).

3.2 Qualitative image quality

The qualitative evaluation scores are summarized in Table 3. For all image quality characteristics, scores in VHP group were significantly superior to those to those in the conventional groups (all p < 0.05). Both raters exhibited excellent agreement in assessing the overall image quality, diagnostic confidence, and distal vessel visualization, with kappa values of 0.97, 0.77, and 0.86, respectively.

Table 3

Subjective image quality measurements
Parameters	VHP group	Conventional group	p-value
Overall mage quality
Reader 1	4.95 ± 0.22	4.65 ± 0.58	0.003
Reader 2	4.93 ± 0.27	4.65 ± 0.58	0.003
Diagnostic confidence
Reader 1	4.95 ± 0.22	4.23 ± 1.07	< 0.001
Reader 2	4.88 ± 0.40	3.93 ± 0.94	< 0.001
Distal vessel visualization
Reader 1	4.50 ± 0.96	3.95 ± 1.28	0.04
Reader 2	4.78 ± 0.66	4.28 ± 1.13	0.02
Data expressed as mean ± standard deviation.
p < 0.05 was considered statistically significant.
VHP: variable helical pitch.

3.3 Quantitative image quality

The results of the quantitative evaluation of image quality are summarized in Table 4. There were no significant differences in the CT values of the Aorta, FA and PA vessels between the two groups (all p > 0.05). However, the CT values of the VHP group in ATA and DPA were significantly higher than those in the conventional group (all p < 0.001).

Table 4

Quantitative image quality measurements
Parameters	Number	VHP group (N₁)	Conventional group (N₂)	p-value
CT value (HU)
Aorta	N₁ = 40 / N₂ = 40	677.48 ± 170.88	705.01 ± 151.80	0.45
FA	N₁ = 77 / N₂ = 78	616.16 ± 171.75	567.41 ± 215.67	0.34
PA	N₁ = 74 / N₂ = 80	559.97 ± 152.39	582.82 ± 212.51	0.28
ATA	N₁ = 74 / N₂ = 80	460.40 ± 122.50	343.23 ± 190.91	< 0.001
DPA	N₁ = 72 / N₂ = 77	394.85 ± 106.37	282.92 ± 166.05	< 0.001
Image noise (HU)
Aorta	N₁ = 40 / N₂ = 40	23.61 ± 7.75	18.41 ± 8.10	0.002
FA	N₁ = 77 / N₂ = 78	36.60 ± 25.07	35.96 ± 14.17	0.09
PA	N₁ = 74 / N₂ = 80	35.19 ± 36.39	34.34 ± 14.31	0.03
ATA	N₁ = 74 / N₂ = 80	44.35 ± 25.33	41.81 ± 23.18	0.56
DPA	N₁ = 72 / N₂ = 77	40.53 ± 18.75	36.10 ± 10.35	0.54
SNR
Aorta	N₁ = 40 / N₂ = 40	31.95 ± 13.63	44.26 ± 21.36	< 0.001
FA	N₁ = 77 / N₂ = 78	23.97 ± 15.24	18.73 ± 12.37	0.02
PA	N₁ = 74 / N₂ = 80	23.11 ± 12.94	21.89 ± 17.61	0.10
ATA	N₁ = 74 / N₂ = 80	12.55 ± 6.31	10.24 ± 8.95	< 0.001
DPA	N₁ = 72 / N₂ = 77	11.12 ± 6.37	8.19 ± 5.08	0.001
CNR
Aorta	N₁ = 40 / N₂ = 40	35.88 ± 13.14	44.60 ± 21.36	0.02
FA	N₁ = 77 / N₂ = 78	39.09 ± 19.29	45.58 ± 33.63	0.73
PA	N₁ = 74 / N₂ = 80	40.53 ± 20.42	45.93 ± 27.05	0.22
ATA	N₁ = 74 / N₂ = 80	49.95 ± 42.13	41.75 ± 32.78	0.03
DPA	N₁ = 72 / N₂ = 77	40.59 ± 17.05	31.88 ± 32.43	< 0.001
Data expressed as mean ± standard deviation.
p < 0.05 was considered statistically significant.
VHP: variable helical pitch ; FA: femoral artery; PA: popliteal artery; ATA: anterior tibial artery; DPA: dorsali pedis artery; SNR, signal-to-noise ratio; CNR, contrast-to-noise ratio;

In terms of image noise, the Aorta, FA and PA in the VHP group were significantly higher compared to the conventional group (all p < 0.05), while ATA and DPA did not show significant differences compared to the conventional group (all p > 0.05).

The SNR of the aorta of the VHP group was significantly lower than that of that of the conventional group (p < 0.001). The SNRs of the other four arteries of the VHP group were significantly higher than (FA, ATA, and DPA, all p < 0.001) or comparable to (PA, p = 0.10) the conventional group.

The CNR of the aorta of the VHP group was significantly lower than that of the conventional group (p < 0.05). The CNRs of the other four arteries of the VHP group were significantly higher than (ATA and DPA, both p < 0.001) or comparable to (FA and PA, both p > 0.05) the conventional group.

3.4 Diagnostic performance

A total of 72 arteries were analyzed, with 40 arteries in 10 patients in the VHP group, and 32 arteries in 8 patients in the conventional group. Using DSA as the gold standard, the diagnostic efficacy for the detection of stenosis by two groups is analyzed(Table 5,Fig. 2, 3, 4). The PPV and accuracy in the VHP group were significantly higher than those in the conventional group (100% vs. 76.19%, p = 0.01; 100% vs. 84.38%, p = 0.01, respectively). Although the specificity value in the VHP group was higher than that in the conventional group, no statistical difference was observed (100%, vs. 68.75%, p = 0.05). The sensitivity and NPV of the two groups were the same for the two groups (both p = 1.00).

Table 5

Diagnostic performance of VHP and conventional groups
	Sensitivity	Specificity	PPV	NPV	Accuracy
VHP group	100% (28/28)	100% (12/12)	100% (28/28)	100% (12/12)	100% (40/40)
Conventional group	100% (16/16)	68.75% (11/16)	76.19% (16/21)	100% (14/14)	84.38% (27/32)
p-value	1.00	0.05	0.01	1.00	0.01
VHP: variable helical pitch; PPV: positive predictive value; NPV: negative predictive value

This study demonstrated that the implementation of the VHP protocol, as compared with the conventional lower extremity CTA scanning protocol, led to a 12.7% reduction in CM dose. Additionally, it improved image quality and diagnostic accuracy, particularly for arteries below the knee.

Lower extremity CTA has the characteristics of a large scanning range, numerous vascular branches, complex hemodynamic properties, and significant individual variations in blood circulation^{[12, 15]}. Therefore, optimal scanning parameters and contrast agent injection protocols are necessary. Conventional lower extremity CTA adopts a uniform speed for the entire scan range, which fails to provide personalized scanning features, often resulting in suboptimal image quality. This is particularly challenging for diabetic patients who typically exhibit more calcification or acute occlusions in distal vessels^[16], leading to restricted contrast agent flow into these vessels. Although in this study, rescans were performed immediately during conventional CTA for patients with inadequate vessel display below the knee, the improvement in CT enhancement was limited. This challenge in CT enhancement can be overcome by utilizing the VHP technique, which synchronizes the angiographic acquisition to the patient’s circulation status by seamless variations in helical pitches. The CT number was noted to be 30%-40% higher in the ATA and DPA compared to the conventional CTA group. At the same time, a threshold of 200 HU has been suggested for obtaining clinically acceptable images, with 350 HU identified as the optimal vessel attenuation^{[17, 18]}. According to this criterion, 16.3% (58/355) and 0.6% (2/337) of vascular segments were considered non-diagnostic in the conventional and VHP groups, respectively (p < 0.001); and 34.4% (122/355) and 15.1% (51/337) of vascular segments were deemed to have suboptimal vessel attenuation in the conventional and VHP groups, respectively (p < 0.001). Additionally, the subjective scores confirmed that the VHP group had higher distal vessel visualization than conventional group (reader 1: 4.50 ± 0.96 vs. 3.95 ± 1.28, p = 0.04; reader 2: 4.78 ± 0.66 vs. 4.28 ± 1.13, p = 0.02).

The enhanced visualization of distal vessels achieved through the VHP technique also resulted in higher diagnostic confidence and diagnostic efficiency. In the VHP group, diagnostic confidence was shown to be higher compared to the conventional group (reader 1: 4.95 ± 0.22 vs. 4.23 ± 1.07, p < 0.001; reader 2: 4.88 ± 0.40 vs. 3.93 ± 0.94, p < 0.001). Moreover, when utilizing DSA as the gold standard, the overall diagnostic efficiency of VHP group surpassed that of the conventional group, demonstrating significantly higher PPV and accuracy values: PPV: 100% (28/28) vs. 76.19% (16/21), p = 0.01; accuracy: 100% (40/40) vs. 84.38% (27/32), p = 0.01, respectively. The decrease in diagnostic efficiency in the conventional group was primarily attributed to the presence of 5 false positive segments, where the CTA scanning with unchanged pitch failed to capture the arrival of CM in the small distal arteries.

The image quality of lower extremity arterial CTA images is significantly influenced by the contrast agent used, with a wide range of contrast volumes typically ranging from 60 to 140mL^{[6, 19, 20]}. In a study by Rotzinger et al., three image acquisition techniques were compared for lower extremity CTA, highlighting the adaptive anterograde technique (AA) with a test bolus as optimal for vascular enhancement^[21]. However, the total contrast volume of 130 mL used for AA, including 30 mL for the test bolus and 100 mL for the subsequent CTA scan, might not be suitable for patients with kidney failure. In this study, the VHP group used a total contrast volume of 79.55 ± 11.87 mL, falling within the category of studies utilizing relatively lower contrast volumes. Even with the inclusion of a 15 mL CM test bolus, the VHP group achieved a 12.7% reduction in contrast volume compared to the conventional group. Patients with LEAD often experience chronic kidney disease or undergo subsequent intra-arterial procedures. Therefore, reducing the contrast volume assist in lowering the risk of additional renal impairment for these individuals.

In addition to contrast volume, radiation dose is another crucial issue that should be carefully considered, especially as patients with LEAD may undergo repeated scanning on several occasions throughout the course of their disease. Utilizing low tube voltage for patients scanning can effectively reduce the radiation dose. Previous studies employing 70 kV or 80 kV have reported radiation doses ranging from 1.1 to 5.5 mSv^[22–25]. In our study, we conducted CTA scans at 80 kV, the lowest tube voltage available in Canon Medical's CT equipment, resulting in a mean radiation dose of approximately 1.40 mSv for these two protocols. This low dose lower extremity CTA scan can maintain high SNR and CNR, even in the ATA and DPA segments. Dual-energy CT was another commonly used technique to improve vascular attenuation for lower extremity CTA. However, the benefit of dual-energy CTA in reducing CM dosage and enhancing diagnostic accuracy usually come at the expense of increased radiation dose. Kristiansen et al^[26]. halved the CM dosage from 104 mL to 55 mL, with a radiation dose of 9.58 mSv. In a similar study by Ren et al^[27]., the CM dosage was reduced from 90 mL to 45 mL, with a radiation dose of 11.88 mSv. Jia et al^[28]. conducted a dual-energy CTA scan with relatively low radiation dose, improving diagnostic accuracy using 50 keV dual-energy CTA images. Although the radiation dose in his study has been lowered to 3.8 mSv, it remains 2.7 times higher than our 80 kV protocol^[29].

This study has some limitations. First, the sample size of 80 is relatively small, with only 18 patients having DSA as a reference, which may introduce bias in the parameters of diagnostic efficacy obtained. Future studies should include a larger number of samples, as this would not only enhance the reliability of diagnostic efficacy but also allow for subgroup analysis based on the location and severity of narrowing in the segments. Second, VHP is a vendor-specific technique, making it challenging to transfer the user experience described in this study to CT equipment from other manufacturers. Third, the proposed VHP technique requires accurate calculation of the time interval from the diaphragm level to the knee level to determine the helical pitches for different segments. This process may be time-consuming and prone to calculation errors. Future studies should consider introducing simpler, experience-based formulas to calculate the helical pitches.

In conclusion, the use of VHP technique improves the image quality and diagnostic accuracy of lower extremity CTA under conditions of low radiation. In addition, there is a 12.7% reduction in CM volume compared to the conventional protocol.

Data availability statement

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Additional information

No additional information is available for this paper.

Funding statement

This study was funded by the Key R&D Program Projects in Shaanxi Province (No. 2023-YBSF-055).

CRediT authorship contribution statement

Xiao-shi Li: Writing – original draft, Methodology.

Ji-Gang Geng: Investigation, Visualization, Conceptualization.

Yin-Hu Zhu: Visualization.

Li-Yao Liu: Data curation.

Yan-Qiang Qiao: Formal analysis.

Yong-Li Ma: Formal analysis.

Lu Lu: Formal analysis.

Chang-Rui Song: Visualization, Validation.

Yue Qin: Funding acquisition, Supervision.

Guo-Ping Chen: Visualization.

Min Xu: Software, Resources.

Ya-Rong Wang: Project administration.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing in- terests: Min Xu and Xiao Yang are employees of Canon Medical Systems, China. The remaining authors declare no relationships with any companies whose products or services may be related to the subject matter of the article.

Ethics Statement

This study was performed in patients enrolled at our institution, and this study was approved by the Medical Ethics Committee of Xi'an Daxing Hospital (DXYY-YXLL-FJ-074). All participants in this study provided written informed consent.

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No competing interests reported.

CT imaging using variable helical pitch scanning for lower extremity arterial disease: reduced contrast medium dose, improved image quality and diagnostic accuracy

Status:

Version 1

Abstract

Objectives

Materials and Methods

Results

Conclusions

Figures

1. Introduction

2. Materials and methods