Low-dose abdominal radiography based on high peak kilovoltage: image quality at standard dose abdominal radiography and potentially 64% dose reduction in a randomized trial

Introduction

Acute abdomen is a clinical condition marked by the sudden appearance of intense abdominal pain, which may be caused by a wide range of associated conditions such as intestinal obstruction, diverticulitis, pancreatitis, or intraabdominal hemorrhage, among others (1). Rapid and accurate diagnosis of patients with acute abdomen is of significant importance for their treatment and prognosis (2,3).

Plain abdominal radiography (AR) has traditionally been the initial imaging investigation for patients presenting with acute abdominal pain. This preference is due to its high specificity for detecting conditions such as gastrointestinal perforation, intestinal obstruction, and other acute abdominal symptoms (4,5). With the advancement of imaging technology, it is now widely recognized that computed tomography (CT) enhances diagnostic accuracy and boosts diagnostic confidence for conditions causing acute abdomen in comparison with AR owing to its excellent spatial resolution (6-8). Nguyen et al. (8) demonstrated that the proportion of patients with acute abdomen requiring further imaging examinations after undergoing low-dose CT (LDCT) scans was significantly lower than that of those who had undergone plain AR, which validated the higher diagnostic efficiency of CT. Meanwhile, some quality improvement studies (9,10) have shown that the frequency of abdominal radiographs can be appropriately increased in clinical practice without increased hospitalization rates or time for patients. However, in clinical scenarios such as under limited-resource settings where CT scans are unavailable, emergency situations requiring rapid examination, and special populations, including children and pregnant women who need to minimize radiation exposure, plain AR still holds advantages over CT scans.

In recent decades, with the marked growth of medical imaging procedures, public concern over ionizing radiation has been increasing (11,12). Despite the relatively low radiation dose of radiography, it still poses a risk of cancer and may inflict damage upon the individuals undergoing examination (13,14). Therefore, reducing the radiation dose of AR while maintaining the image quality is significant for patients’ safety and accurate diagnosis. To the best of our knowledge, no prior studies have prospectively designed scanning protocols to assess the feasibility of low-dose imaging protocols in AR based on a large sample size.

In this study, we aimed to comprehensively assess the efficacy of plain low-dose AR for acute abdomen patients through a comparison of the imaging quality and dose reduction between low-dose abdominal radiography (LDAR) and standard-dose abdominal radiography (SDAR). We present this article in accordance with the CONSORT reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2749/rc).

Methods

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of The First Affiliated Hospital of Harbin Medical University (No. 201504) and informed consent was provided by all individual participants.

Participants

Patients with acute abdominal pain who met the indications for AR examination at The First Affiliated Hospital of Harbin Medical University were included in the study. The inclusion criteria were as follows: (I) patients with suspected intestinal obstruction, gastrointestinal perforation, foreign bodies, constipation, abdominal masses, or those requiring regular AR follow-up; and (II) age ≥18 years. The exclusion criteria were as follows: (I) children, pregnant or breastfeeding women, and women preparing for pregnancy; (II) medication containing heavy metal components within 1 week prior to AR examination; (III) inability to cooperate during the examination; and (IV) patients with severe acute abdominal conditions such as acute pancreatitis or peritonitis. Finally, a total of 354 patients were enrolled. All patients were assigned to the LDAR and SDAR groups using the random table method (Figure 1).

Figure 1 Flow diagram of participant enrollment throughout the study. LADR, low-dose abdominal radiography; SADR, standard-dose abdominal radiography.

This study was registered in the Chinese Clinical Trial Registry (ChiCTR, a World Health Organization Primary Registry), with the identifying number ChiCTR-DCD-15006231. The full URL for the trial record is https://www.chictr.org.cn/showproj.html?proj=10756. The date of registration was 12 April 2015.

AR scanning protocol

All the examinations were performed on a digital radiography system (AXIOM TX, Siemens, Erlangen, Germany) in an erect position. The standard posteroanterior abdominal plain scan was taken with the patients standing 180 cm from the focus to the detector. With automatic exposure control, the LDAR group imaging was carried out at 121 kVp and the SDAR group imaging at 81 kVp. For every acquisition, the exposure values (milliampere-seconds) were recorded (15,16).

Entrance skin dose (ESD) and effective dose (ED) evaluation

The International Commission on Radiological Protection developed the concept of the ESD, which is used to calculate the amount of radiation that is absorbed (mGy) by the skin as it reaches the patient. The manufacturer’s data indicates that the dose administered via abdominal plain scanning was calculated using the following formula:

ESD(mGy)=c(kvpFSD)2(mAsmm.AL)[1]

In the formula, FSD (focus to skin distance) is a measurement of the distance between the patient’s part being exposed to X-rays and the X-ray tube. Moreover, kvp represents the peak tube voltage of the X-ray tube and mAs represents the exposure value, namely, the current of the tube multiplied by the exposure time. In addition, mm.Al provides the minimum inherent filtration equivalent of aluminum, and c is a constant equal to 0.2775 (17). The EDs of all patients were recorded.

Data collection and analysis

All images were quickly interpreted and uploaded onto the Picture Archiving and Communication System (PACS) by two on-duty experienced radiologists, then a written report was sent to the referring physician. If the radiologists confirmed that a plain AR was appropriate for diagnosis, the manual determinations were made by two radiologists in agreement. If not, the plain AR would be imaged again with the standard dose (standard procedure in our institution).

The imaging characteristics and anatomical regions listed below were assessed: overimpression of plain AR, diaphragm, and intestinal gas. The same two radiologists assessed if each plain AR and single criterion was visible using the following five-level confidence rating scale: definitely not present, 1; probably not present, 2; equivocal, 3; probably present, 4; or definitely present, 5. The applied radiation dosage and the patient’s medical history were unknown to the radiologists. In the event of discordant results by the two radiologists, a third senior radiologist made the final decision. All procedures were performed with the same workstation, visualization software (Donghua PACS, Version 4.0; Donghua Software, Beijing, China) and the color monitor (MultiSyncLCD1880SX; NEC, Tokyo, Japan).

Program analysis

All images were processed in a delayed fashion. To process these images, a semi-automated algorithm was suggested and put into practice using Matlab (2014, MathWorks, Natick, MA, USA). The workflow of the program analysis is presented in Figure 2. Firstly, a region of interest (ROI) located at the diaphragm was extracted from the experimental image. A gray intensity histogram was employed to estimate the binarization threshold. On the basis of the binary image, an edge was extracted. To evaluate the sharpness of the edge, a curved line was created to fit the edge. Measurements were made of the separations between the curved line and the actual edge. In order to evaluate the quality of the experimental image, the average of the distances was finally computed to typify the smooth level. In the same manner, the control image was processed. Additionally, a smooth level of the control image was obtained.

Figure 2 The workflow of the program analysis. (A) Matlab analysis area image; (B) segmentation threshold: 49; (C) segmentation results; (D) Matlab analysis image curve fitting results: 0.86252.

Statistical analysis

Statistical analysis was performed using the software SPSS 26.0 (IBM Corp., Armonk, NY, USA). A P value <0.05 was considered statistically significant. For each radiologist and imaging modality, mean values were computed for overimpression, diaphragm, intestinal gas, and ESD between the LDAR and SDAR groups, and compared using Student’s t-test for normally distributed continuous variables or Mann-Whitney test for non-normally distributed continuous variables with 95% confidence interval (CI) calculated.

Results

All images, whether in the LDAR group or the SDAR group, were suitable for a direct diagnosis. In this trial, no patients were exposed to additional doses.

Demographic characteristics

The two patient groups’ demographic information is compiled in Table 1. There were no statistical differences between the two groups in terms of age (P=0.641), gender (P=0.224), height (P=0.955), weight (P=0.118), and body mass index (BMI, P=0.109).

Manual assessment of imaging quality

As shown in Table 2, the mean scores for the overimpression (LDAR with 4.97±0.18, 95% CI: 4.94–4.99 vs. SDAR with 4.68±0.55, 95% CI: 4.60–4.77; P<0.001), diaphragm (LDAR with 4.97±0.18, 95% CI: 4.94–4.99 vs. SDAR with 4.69±0.55, 95% CI: 4.61–4.77; P<0.001), the LDAR were significantly superior to those of the SDAR based on a manual determination. Additionally, there was no statistically significant difference in terms of the mean scores of intestinal gas (LDAR with 4.55±0.71 vs. SDAR with 4.68±0.48; P=0.057) between the two groups.

Program analysis

According to program analysis in Matlab, the diaphragm in the LDAR group was sharper than that in the SDAR group. The mean values of diaphragm sharpness were significantly lower in the LDAR group than they were in the SDAR group (LDAR with 1.27±0.35, 95% CI: 1.19–1.35 vs. SDAR with 1.90±0.48, 95% CI: 1.82–1.98; P<0.001). The lower the value of diaphragm sharpness, the higher the imaging quality.

Comparison of radiation dose parameters

The comparison results of parameters related to radiation dose are shown in Table 3. The milliampere-seconds (mAs; LDAR with 2.25±0.43, 95% CI: 2.19–2.25 vs. SDAR with 13.93±5.77, 95% CI: 13.06–13.93; P<0.001), ESD (LDAR with 1.13±0.22, 95% CI: 1.10–1.13 vs. SDAR with 3.13±1.30, 95% CI: 2.94–3.33; P<0.001) and ED (LDAR with 0.19±0.04, 95% CI: 0.19–0.20 vs. SDAR with 0.53±0.22, 95% CI: 0.50–0.57; P<0.001) were all significantly lower in the LDAR group than they were in the SDAR group. Furthermore, the reductions of ESD and ED in the LDAR group compared to those in the SDAR group were approximately 64%.

Discussion

The manifestations of acute abdominal pain are diverse, and the range of related conditions makes it more difficult to pinpoint the exact cause. The causes of acute abdominal pain can range from mild, self-limiting conditions that resolve on their own to serious, life-threatening conditions that require emergency surgery. In the present study, the LDAR scan using 121 kVp reduced the radiation dose by 64% compared with the SD protocol with 81 kVp and the image quality of the low-dose scan was comparable to that of the SDAR scan and sufficient for clinical diagnosis, which confirms that our LDAR scanning protocol can serve as a useful imaging option for patients with acute abdomen.

CT is currently the initial imaging method for acute abdomen in most cases due to its excellent spatial resolution that enables superior lesion visualization and precise lesion detection, and LDCT technology has performed well in abdominal imaging as it maintains a certain level of image quality while reducing radiation dose (7,18,19). Recent advancements in CT reconstruction algorithms, such as deep learning image reconstruction, have further improved image quality and diagnostic confidence in abdominal LDCT (20). We hold the view that LDCT provides more spatial information about lesions in the diagnosis of abdominal diseases. For populations where LDCT resources are available and not under special protection, LDCT is the preferred option for abdominal imaging. However, there was still a certain radiation risk for patients undergoing LDCT examinations. As for AR, it has long been the preferred imaging modality for acute abdomen (21). Additionally, plain AR holds the strength of low radiation dose, ease of operation, and affordability. The average ED of the LDAR examination in this study was 0.19 mSv, which was significantly lower than the 1.2 mSv of previous literature on LD abdominal CT and therefore enabled further patient safety (22). These benefits make it more suitable than CT for certain groups of patients, such as children, patients with chronic conditions who require multiple scans over a period, and those who are unable to cooperate with the examination and cannot afford CT scans due to financial constraints, thus reducing their risk of radiation exposure, providing greater convenience for examinations, and alleviating their financial burden. Therefore, the plain LDAR in this work still holds value in modern clinical practice and can benefit specific patient populations.

In terms of ED, the ratio of AR to CT was roughly 30%, approximately 1 mSv, which has not yet reached a very low level. The linear no-threshold (LNT) model and as low as reasonably achievable (ALARA) are still employed as the foundation for practical radiological protection purposes (23). Accordingly, this study attempted to explore the diagnostic performance of LDAR for acute abdomen. Confined to the tube and imaging system, the dose of chest radiography had not been optimized until the advent of digital radiography (24-26). The possibility of optimizing the dose of abdominal plain radiography was also made possible by digital radiography, which used high voltage tube and flat panel detectors. Due to the different imaging features of different kilovolts, high-kV imaging offers both low dose and high quality, which was presented in the chest radiography using both digital and conventional imaging. Based on the previous reports in the chest radiography (27), we employed a tube voltage of 121 kVp to achieve low-dose scanning in this study. Our study also made use of the automatic exposure control technique, which automatically modified the tube current to account for variations in patient attenuation within and between individual patients. This approach greatly enhanced imaging quality and laid the groundwork for plain LDAR. The importance of optimizing scanning parameters such as tube voltage and current is equally critical in CT imaging to balance dose and quality, as evidenced by studies in pediatric abdominal protocols (28). Moreover, our results were consistent with the research of Krupinski et al. (29), which was based on digital radiography including AEC. The plain LDAR based on the high peak kilovoltage of 121 kVp in our work achieved a reduced dose reduction of 64% while maintaining the image quality, which further reduces patient radiation exposure and protects their health.

The main strengths of our study were as follows: firstly, it was a large-scale, randomized, controlled experiment that contrasted a plain LDAR with a plain SDAR. Secondly, plain LDAR confidence was enhanced by multimodal evaluation, manual determination, and program analysis. Thirdly, due to the random contrast of the study design, no patients were exposed to additional doses during the study.

The study also had several limitations. Firstly, the study was conducted at a single center and prescribed image quality (Siemens) using quality reference mAs (QRM) (30). Although it has generally been acknowledged that prescribing imaging quality is necessary to optimize dosage, there was still some uncertainty regarding the use of Noise Index to prescribe image quality (GE, Toshiba). Otherwise, it will be of merit to investigate methods of plain LDAR with other AEC models. Secondly, even though the evaluated method was confirmed, the radiation dose of each phantom was assessed. There was not an exact relationship between direct measurement and evaluation. Lastly, confined to a current status in China, there were very few data on plain LDAR for light weight patients.

Conclusions

The LDAR plain with 121 kVp could significantly reduce radiation dose while maintaining comparable image quality of plain SDAR, holding value in specific clinical scenarios.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CONSORT reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2749/rc

Trial Protocol: Available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2749/tp

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2749/dss

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2749/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of The First Affiliated Hospital of Harbin Medical University (No. 201504) and informed consent was obtained from all individual 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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