Optimizing the image quality of peripancreatic blood vessels through the clinical application of single-energy spectral computed tomography (CT) imaging
Introduction
Recently, the incidence of pancreas-related tumors has increased year by year, and determining whether or not peripancreatic blood vessels are invaded and the extent of invasion is crucial for the selection of treatment options for patients (1). Multi-slice spiral computed tomography (CT) technology facilitates noninvasive and rapid visualization of peripancreatic blood vessels. However, this imaging technology has the disadvantage that beam hardening artifacts interfere with the images. As energy spectrum technology and dual energy technology have evolved in recent years (2,3), it has become a valuable tool for vascular imaging with CT. As the energy level of the energy spectrum decreases, the photoelectric effect gradually increases, which promotes the attenuation of X-rays by iodine contrast agents, thereby enhancing the image quality of blood vessels (4). Previously, the majority of abdominal macrovascular investigations were conducted using Gemstone or Revolution (5,6). In our study, United Imaging ATLAS (United Imaging, Shanghai, China) at single energy was used to optimize the image quality of large and some small blood vessels in the abdomen. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-23-1734/rc).
Methods
Participants
In this study, we selected 103 patients who underwent abdominal vascular-enhanced CT examinations at Affiliated Hospital of Hebei University between December 2022 and May 2023. The ages of these patients ranged from 29 to 75 years, with a mean age of 53±22 years. There were 60 males and 43 females. This study was approved by the ethics committee of the hospital. The inclusion criteria for patients were: (I) 22 kg/m2 ≤ body mass index (BMI) ≤25 kg/m2; (II) normal cardiac function. The exclusion criteria were as follows: (I) patients allergic to iodine contrast; (II) patients with hyperthyroidism; (III) patients with renal failure; (IV) patients with any significant motion artifact and artifacts of intracorporeal foreign matter. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Ethics Committee of the Affiliated Hospital of Hebei University (No. HDFY-LL-2019-042). Written informed consent was provided by all participants.
Materials
The China-manufactured device United Imaging ATLAS 968 was used, and all patients who underwent enhanced scanning fasted for at least 4 hours prior to the procedure. At 5 minutes before scanning, the patients ingested 500 mL of purified water to ensure the filling of the gastric cavity. The area scanned extended from 3 to 5 cm of the supradiaphragmatic region to the ischial tuberosity. The contrast agent iodixanol (65 mL; 320 mg/mL) was injected intravenously through the right elbow at a rate of 4 mL/s using an automated double-syringe high-pressure injector, DUAL SHOT alpha7, with an 18-G needle, followed by an additional injection of 30 mL of normal saline. At a threshold of 150 Hounsfield unit (HU), abdominal enhancement was performed using the threshold method to detect the level of the abdominal aorta in the plane. An arterial-phase scan was initiated 3 seconds after the threshold was reached, followed by a portal vein-phase scan 30 seconds later and a delayed-phase scan 120 seconds later. The main scanning parameters included: tube voltage, instantaneous switching between high and low energy (140/80 keV); switching time, 0.23 seconds; tube current, automatic tube current technology; collimator, 80 mm; pitch, 0.24; detector width, 16 cm; the rotation time of the tube ball, 0.35 seconds; the layer thickness, 5 mm; matrix, 512×512. Using the 50% adaptive statistical iterative reconstruction (ASIR) technique with a layer thickness of 0.625 mm, reconstruction was performed. After scanning was completed, the data were transmitted to the United Workstation-Computed Tomography (uWS-CT), the post-processing station of United Imaging Healthcare Technology Co., Ltd.
Image processing and analysis
In uWS-CT, the dual-energy calculation mode was used for image post-reconstruction, which could calculate any single energy from 40 to 140 keV and mixed single energy, as well as calculate the optimal single energy automatically. After using maximum intensity projection (MIP) and volume rendering (VR) techniques to reconstruct the images of the abdominal blood vessels, the density values of the superior mesenteric artery (SMA), gastroduodenal artery (GDA), inferior pancreaticoduodenal artery (IPDA), and superior mesenteric vein (SMV) were measured, respectively. The middle and upper third of the target vessel was selected, and the region of interest (ROI) was placed in the center of the cross section of the target vessel with an area of 20 mm2 and greater than 0.5 mm from the vessel edge. The emphasis was on the center of the blood vessel, which needed to be separated from the vessel wall to prevent the influence of the partial volume effect. The contrast-to-noise ratio (CNR) of the above vessels was calculated using the following formula: CT value of the target vessel—CT value of the erector spinae/standard deviation (SD) value of the erector spinae. Using the 5-point vascular evaluation method of Sun et al., 2 physicians with associate titles in the department rated the quality of the abdominal blood vessels at 70 keV, optimal single energy, and mixed energy (7).
Statistical methods
Statistical analysis was performed with SPSS 22.0 (IBM Corp., Armonk, NY, USA), and all measurement data were recorded as the mean ± SD. Using a one-way analysis of variance, the 70 keV, optimal single energy, and mixed energy groups were compared. Pairwise comparisons were analyzed using the least significant difference (LSD) test if variance was homogeneous and the Tamhane test if variance was heterogeneous. The subjective scores of the 2 physicians were compared using the rank-sum test, and their consistency was analyzed using the Kappa test: Kappa value ≥0.75 indicated good consistency, 0.75> Kappa value ≥0.4 indicated fair consistency, and Kappa value <0.4 indicated poor consistency. The Wilcoxon rank sum test was used to compare the subjective evaluation of image quality by the 2 physicians. A P value <0.05 was considered a statistically significant difference.
Results
Inclusion, exclusion, and grouping of patients
In this study, 103 patients were enrolled, 3 of whom were allergic to contrast, 4 had too large respiratory motion artifact during scanning, and 2 experienced renal insufficiency. Eventually, 94 patients were finally included. The differences in age among all enrolled patients were not statistically significant.
Subjective evaluation of image quality at various energy levels
The scores of 2 physicians on the quality of abdominal blood vessel images obtained with the optimal single energy were 4.63±0.50 and 4.65±0.48, respectively, with good consistency (Kappa value =0.889, P<0.05). Both physicians scored the image quality at mixed energy as 3.91±0.57 and 3.94±0.60, and their consistency was good (Kappa value =0.813, P<0.05). The scores of the 2 physicians on the image quality at 70 keV were 4.23±0.83 and 4.19±0.78, with good consistency (Kappa value =0.795, P<0.05). The image quality of the optimal single energy group was superior to that of the mixed energy and 70 keV groups (P<0.05) (Figures 1,2).
Objective evaluation of image quality at different energy levels
The CT values and CNR of each vessel at SMA, GDA, IPDA, and SMV were significantly higher in the optimal single energy group compared to the mixed energy and 70 keV groups (P<0.05). The CT values of each vessel at SMA, GDA, IPDA, and SMV were insignificantly higher (P>0.05) and their CNR was markedly higher (P<0.05) in the 70 keV group than in the mixed energy groups (Tables 1,2).
Table 1
| Items | Group | F | P | ||||
|---|---|---|---|---|---|---|---|
| 70 keV | Mixed energy | Optimal single energy | 70 keV group vs. mixed energy group | 70 keV group vs. optimal single energy group | Mixed energy group vs. optimal single energy group |
||
| SMA | |||||||
| CT (HU) | 260.89±54.27 | 241.66±47.69 | 358.37±70.24 | 108.775 | 0.03 | <0.01 | <0.01 |
| CNR | 15.37±5.56 | 12.19±4.02 | 18.32±6.13 | 31.193 | <0.01 | 0.002 | <0.01 |
| GDA | |||||||
| CT (HU) | 252.41±58.87 | 235.17±53.71 | 323.36±88.23 | 43.588 | 0.11 | <0.01 | <0.01 |
| CNR | 15.32±6.01 | 11.97±4.11 | 18.21±5.16 | 34.71 | <0.01 | 0.002 | <0.01 |
Data are presented as mean ± standard deviation. SMA, superior mesenteric artery; GDA, gastroduodenal artery; CT, computed tomography; HU, Hounsfield unit; CNR, contrast-to-noise ratio.
Table 2
| Items | Group | F | P | ||||
|---|---|---|---|---|---|---|---|
| 70 keV | Mixed energy | Optimal single energy | 70 keV group vs. mixed energy group | 70 keV group vs. optimal single energy group | Mixed energy group vs. optimal single energy group | ||
| IPDA | |||||||
| CT (HU) | 223.17±43.65 | 207.36±45.17 | 300.76±76.27 | 72.2 | 0.04 | <0.01 | <0.01 |
| CNR | 10.31±3.12 | 8.96±2.39 | 13.17±3.76 | 297.449 | <0.01 | <0.01 | <0.01 |
| SMV | |||||||
| CT (HU) | 203.18±18.17 | 187.39±23.21 | 257.74±20.56 | 43.936 | 0.003 | <0.01 | <0.01 |
| CNR | 8.06±2.24 | 6.54±2.18 | 11.21±2.36 | 103.949 | <0.01 | <0.01 | <0.01 |
Data are presented as mean ± standard deviation. IPDA, inferior pancreaticoduodenal artery; SMV, superior mesenteric vein; CT, computed tomography; HU, Hounsfield unit; CNR, contrast-to-noise ratio.
Our research revealed that the image quality of each vessel in the optimal single energy group was superior to that of the mixed energy and 70 keV groups. Specifically, the CT values of SMA in the optimal single energy group were 49% higher than in the mixed energy group and 37% higher than in the 70 keV group. The CT values of GDA in the optimal single energy group were 37% higher than in the mixed energy and 28% higher than in the 70 keV group. The CT values of IPDA in the optimal single energy group were 35% higher than those in the mixed energy group and 45% higher than those in the 70 keV group, whereas the CT values of SMV in the optimal single energy group were 37% higher than those in the mixed energy group and 27% higher than those in the 70 keV group. The CNR of SMA in the optimal single energy group increased by 50% compared to the mixed energy group and by 20% compared to the 70 keV group, and the CNR of GDA in the optimal single energy group increased by 52% compared to the mixed energy group and by 19% when compared to the 70 keV groups. The CNR of IPDA in the optimal single energy group was 47% higher than that in the mixed energy group and 28% higher than that in the 70 keV group, whereas the CNR of SMV in the optimal single energy group was 71% higher than that in the mixed energy group and 39% higher than that in the 70 keV group (Table 3). The optimal single energy group also had higher subjective scores than the other 2 groups. In this study, the optimal single energy range for abdominal image quality was 62±7 keV.
Table 3
| Items | CT (HU) | CNR | |||
|---|---|---|---|---|---|
| Optimal single energy vs. 70 keV |
Optimal single energy vs. mixed energy | Optimal single energy vs. 70 keV |
Optimal single energy vs. mixed energy | ||
| SMA | 37% | 49% | 20% | 50% | |
| GDA | 28% | 37% | 19% | 52% | |
| IPDA | 45% | 35% | 28% | 47% | |
| SMV | 27% | 37% | 39% | 71% | |
“Optimal single energy vs. 70 keV” is the percentage improvement of Optimal single energy over 70 keV. CT, computed tomography; CNR, contrast-to-noise ratio; SMA, superior mesenteric artery; GDA, gastroduodenal artery; IPDA, inferior pancreaticoduodenal artery; SMV, superior mesenteric vein; HU, Hounsfield unit.
Discussion
Pancreatic tumors, especially pancreatic cancer, have a very poor prognosis, with a survival rate of less than 10%. Surgical resection is one of the best treatments for pancreatic tumors (8). The peripancreatic blood vessels must be evaluated before effective surgical intervention, as the incidence of pancreatic malignancy has increased in recent years. However, the peripancreatic blood vessels are complex. As a noninvasive technique for evaluating blood vessels, CTA can clearly depict the anatomy, variation, and invasion of the blood vessels (9,10). In recent years, with the development of energy spectrum technology, the evaluation of blood vessels has been enhanced. The use of CT in the evaluation of blood vessels has unparalleled advantages. Although magnetic resonance imaging (MRI) is more delicate and has a higher image signal-to-noise ratio than CT in the degree of invasion of pancreatic tumors to surrounding tissues, MRI scanning time is long, and repeated breathing training is required, so patients with pancreatic tumors may not be able to sufficiently cooperate. Although positron emission tomography (PET) and positron emission tomography-computed tomography (PET-CT) can evaluate pancreatic tumors and observe whether the tumor has distant metastasis, they are expensive and less applicable. Angiography can also provide effective evaluation of blood vessels, but it is often not adopted because of its invasiveness. CT has the characteristics of high spatial resolution, fast scanning speed, and reasonable price, making it a more practical option.
The BMI of patients in this investigation is limited for 2 reasons. First, the penetration of X-rays increases or decreases with the elevation or reduction in the BMI of patients, which can result in corresponding changes. Second, an increase or decrease in BMI during the application of the contrast agent may result in an insufficient or excessive concentration of the contrast agent in the blood vessel, thereby enhancing the number of factors influencing the image quality of the blood vessels in the absence of a control variable.
In this study, the spectral imaging technique was used to reconstruct the images obtained with the 3 energy forms of 70 keV, mixed energy, and optimal single energy. This indicates that the reconstruction algorithm is an important factor. ASIR is an iterative reconstruction algorithm for data based on denoise models (11). Theoretically, a higher weight value of ASIR is associated with its higher denoise capability. Nevertheless, when the weight value of ASIR is increased to a certain level (for instance, when ASIR is approximately 80%), the contrast of the image decreases significantly (12). Singh et al. reported that the spatial resolution started to decline when the ASIR exceeded 60% (13). Therefore, the weight value of ASIR should not exceed 60% in order to maintain the spatial resolution of the image in the abdominal scan. It has been revealed (14) that the quality of the chest and abdominal scan images decreases with increasing ASIR weight values; therefore, it is recommended to maintain the weight values of ASIR between 40% and 60%. The weight value of ASIR used in this investigation was therefore 50% (15).
In this study, the anterior and posterior inferior pancreaticoduodenal arteries were not selected due to their small lumen diameters, which could lead to large biases in the measurement of the objective parameters due to partial volume effects, which differs slightly from the results obtained by Chen et al. (16). This difference may be attributable to contrast concentration variations and individual differences. However, we believed that the optimal imaging of abdominal blood vessels should be an interval rather than a fixed value with a certain degree of individualization, which is not nearly the same as in the previous study (17) but is consistent with the previous viewpoint. In the meantime, our results showed that the CT values of GDA did not differ statistically between the mixed energy and 70 keV groups. This indicates that the 2 energy levels have a certain degree of equivalence in the imaging of certain blood vessels in the abdomen. In this study, the optimal single energy range for abdominal image quality was 62±7 keV. This result is consistent with the findings of Zhou et al. (18).
To date, the specificity and sensitivity of CT-based imaging examinations for the degree of tumor vascular invasion have been continuously improved by researchers such as Loyer and Teramura et al. (19,20). However, it is undeniable that due to the interference of many factors, the degree of tumor vascular invasion observed by imaging is not consistent with the surgeon’s evaluation, and the future survival rate of patients is also uncertain.
This research has some limitations. First, our study had insufficient samples and lacked was conducted in a single center. Second, although some vessels with small diameters were not selected, partial volume effects may still have impacted the results. Third, the BMI of patients was restricted, limiting the generalizability of this study. This investigation excluded patients with a BMI outside of the acceptable range. Therefore, the BMI range must be expanded for more comprehensive studies.
Conclusions
Spectral CT can enhance the image quality of abdominal blood vessels, and the optimal single energy can further optimize the image quality of abdominal blood vessels. In addition, the optimal single energy should not be a fixed value and must be treated individually. According to the results of our investigation, the optimal single energy of abdominal blood vessels was 62±7 keV. This investigation was conducted using United Imaging ATLAS, which lends credibility to the research of Chinese CT in other fields.
Acknowledgments
We are particularly grateful to all the people who have given us help on our article.
Funding: This work was supported by
Footnote
Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-23-1734/rc
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-23-1734/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 (as revised in 2013). The study was approved by the Ethics Committee of Affiliated Hospital of Hebei University (No. HDFY-LL-2019-042). Written informed consent was provided by all participants.
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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