Not All Flat-Panel C-Arms Are Created Equal: A Comparison of Three Major Manufacturers

Introduction

Radiation exposure during fluoroscopy is an ongoing concern and a subject of frequent investigations. ¹ As physicians strive to adhere to the ALARA (as low as reasonably achievable) principle, several techniques are employed to reduce radiation exposure intraoperatively such as increasing the distance between the source of radiation to both patient and provider, utilizing collimation, employing the “last image hold” feature, and encouraging surgeon activation of the foot pedal. ² While automated C-arm settings are commonly used by many practitioners, strong evidence from previous studies supports that adjusting these settings remains one of the most effective approaches to reduce radiation doses. ³ By implementing setting modifications, urologists can further enhance patient and staff safety and optimize fluoroscopy procedures.

In the late 1990s, the flat-panel detector C-arms (FCs) emerged as a compelling alternative to the conventional image intensifier C-arms (CCs). FC manufacturers have advocated several advantages over CCs, such as enhanced patient accessibility, excellent image uniformity, and reduced image distortion, including veiling glare or vignetting. ¹ Nevertheless, FCs were initially hampered by a low signal to electronic noise ratio at low exposure levels commonly used in fluoroscopy, leading to decreased efficiency and performance. Fortunately, later generation FC models have made significant strides in overcoming this limitation, leading to their widespread adoption in various fields utilizing fluoroscopy, including interventional radiology and cardiology.

Several studies have evaluated the radiation exposure and image quality of FCs compared with CCs, revealing varied outcomes. ^{4 –12} Due to the proprietary nature of FC designs, radiation doses and image results may vary significantly between manufacturers. The primary objective of this study was to measure and compare radiation exposure among three commonly utilized FCs. In addition, the study aimed to evaluate and compare image quality across the same set of C-arms, providing valuable insights into their respective performance and safety profiles.

Materials and Methods

Radiation dose measurements

Three nanoDot (Landauer, Glenwood, IL) optically stimulated luminescence dosimeters (OSLDs) were then placed on the cadaver skin. Two OSLDs were positioned dorsally on the skin overlying the upper and lower poles of the kidney. A third OSLD was placed ventrally on the skin in the region of the renal pelvis (Fig. 1). A standard 0.038 guidewire (Cook Medical LLC, Bloomington, IN) was positioned at the height of the renal pelvis to guide image acquisition. The largest C-arm manufacturers worldwide by revenue were invited to provide their most advanced FCs for a head-to-head comparison of image quality and radiation dose. ¹³ The three C-arms provided for testing were the GE OEC Elite (General Electric Company, Boston, MA), the Philips Zenition 70 (Koninklijke Philips N.V., Amsterdam, Netherlands), and the Ziehm Vision RFD (Ziehm Imaging, Nuremberg, Germany). To ensure uniformity, the FCs were positioned to maintain 35.5 cm between the X-ray source and the bottom of the operating table. Technicians and radiation physicists from each manufacturer were invited to be present during testing to ensure device optimization and use according to the manufacturer's specifications.

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FIG. 1.

OSLD positions to measure radiation exposure doses on the cadaver model. A, B, dorsally placed OSLDs; C, ventrally placed OSLD. OSLD = optically stimulated luminescence dosimeter. Color images are available online.

Each FC was tested in five trials at three different conditions: (1) automatic exposure control (AEC), (2) AEC with low dose (LD), and (3) LD with lowest pulse rate (LDLP). In each trial, 300 seconds of fluoroscopy were applied. The AEC and LD settings were implemented using the preset functions on each device. To create the LDLP setting, the machine was converted from continuous fluoroscopy (30 frames per second) to pulsed fluoroscopy, and the pulses were set to the lowest possible setting: 1 pulse per second (pps) for the Philips and Ziehm C-arms and 4 pps for the GE C-arm. The radiation doses detected by each OSLD were measured using a Landauer microStar OSLD reader (Landauer, Glenwood, IL) and recorded. Before fluoroscopy trials, new OSLD chips were acquired, calibrated, and pretest baseline values were recorded.

Image quality assessment

Sample images from all 45 trials were obtained and archived (Fig. 2). Images were distributed to a group of 10 urologists composed of 5 attending physicians and 5 residents in a blinded manner. Participants were instructed to rate the images based on how adequately the position of the guidewire could be determined for the purpose of performing PCNL or other clinical use. Images were graded qualitatively using a visual analog scale from 1 to 10 (10 being the best).

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FIG. 2.

Representative images from each FC in each setting. AEC = automatic exposure control; FC = flat-panel detector C-arm; LD = low dose; LDLP = low dose with lowest pulse rate.

Results

In the AEC setting, the Philips C-arm demonstrated the lowest average radiation dose detected by the ventral OSLDs, measuring 42,446 ± 4635 mrad. Comparatively, the GE C-arm recorded a higher dose of 51,078 ± 4846 mrad, and the Ziehm C-arm had the highest dose at 83,178 ± 5251 mrad (p < 0.001). In the LD setting, once again, the Philips C-arm showed the lowest average radiation dose detected by the ventral OSLDs, measuring 25,926 ± 2639 mrad. The Ziehm C-arm recorded a higher dose of 30,956 ± 1793 mrad, whereas the GE C-arm had the highest dose at 38,209 ± 1493 mrad (p < 0.001). In the LDLP setting, the Ziehm C-arm had the lowest average radiation dose detected by the ventral OSLDs, measuring 4019 ± 154 mrad. The GE C-arm showed a higher dose of 7418 ± 645 mrad, and the Philips C-arm produced 8229 ± 449 mrad (p < 0.001). The dorsally placed OSLDs consistently recorded values that correlated with the values recorded by the ventrally placed OSLDs, but radiation exposure was <1% of the values recorded ventrally across all C-arms and settings (Table 1).

Although the Ziehm C-arm had the highest dose at the AEC setting, depression of the LD button resulted in a 62.8% reduction in radiation exposure to the ventral OSLD, which was a greater reduction than both the Philips (38.9%) and GE (25.2%) C-arms. Similarly, the use of the LDLP setting resulted in different reductions across all three FCs with the highest reduction seen with the Ziehm C-arm at 95.2%, whereas the GE C-arm was reduced by 85.5% and the Philips C-arm by 80.6%.

The average image quality rating in the AEC setting was significantly higher for the Philips C-arm (8.98 ± 0.62) compared with the GE (7.66 ± 1.06) and Ziehm (7.22 ± 1.74) C-arms (p < 0.05). In the LD setting, the quality of the Ziehm C-arm images was rated significantly higher with an average of 8.54 ± 1.27 vs the GE (7.44 ± 0.99) and Philips (6.92 ± 1.87) C-arms (p < 0.05). In the LDLP setting, the GE C-arm images had the highest average quality rating (7.088 ± 1.53), which was significantly higher than the Philips (6.82 ± 1.66) and Ziehm (6.56 ± 1.86) C-arms (p < 0.05). All the images obtained using the Philips and GE C-arms were rated adequate. Of the images from the Ziehm C-arm, 8% were considered inadequate, and all those images were obtained in the LDLP setting.

Variability between the image quality assessments of the attending physicians and residents was generally low. Exceptions to this were the ratings for images produced by the Philips C-arm in the AEC setting and the GE C-arm in the LDLP setting, which were awarded significantly higher scores by the attending physicians than the residents. Image clinical sufficiency ratings for each C-arm in each setting were also largely consistent between the two groups. However, the image generated by the Ziehm C-arm in the LDLP setting did have more discordant ratings and was considered sufficient for clinical use by 54.3% of attending physicians compared with 45.7% of residents.

Discussion

The use of ionizing radiation for diagnostic and therapeutic purposes is crucial in medicine. However, its widespread utilization has also raised concerns, with ∼2% of malignancies believed to be attributed to the increased use of radiologic studies. ¹⁴ Acute skin injuries ranging from erythema to vesicles and erosions have been reported usually after long fluoroscopic procedures with more than 2 Sv. ¹⁵ It has been estimated that patients are exposed to 1 to 1.4 mSv/minute of fluoroscopy. ¹⁶ However, based on our study results, it is clear that the amount of radiation emitted in 1 minute by one machine is not necessarily equivalent to another. Consequently, there is a growing awareness of the importance of radiation safety and the need to limit radiation exposure whenever feasible, especially for patient populations likely to undergo repeat evaluations.

While efforts have been made to increase the use of ultrasound guidance, fluoroscopy remains an integral component of numerous common urologic procedures. In this context, the newer FCs are gaining popularity, but their safety and efficacy have not undergone rigorous evaluation. To ensure radiation safety for both patients and health care providers, it is imperative to comprehensively assess the potential risks and benefits associated with these advanced devices. By conducting rigorous studies to assess the safety profile of FCs, the providers can make informed decisions and implement appropriate protocols, thereby maximizing the advantages of this technology while minimizing radiation exposure.

In this study, we conducted a comprehensive comparison of radiation doses and image quality among three different FC manufacturers. The findings revealed notable variations in radiation doses emitted by each C-arm, even when seemingly similar settings were used. Specifically, the Philips C-arm exhibited the lowest measured dose in the AEC and LD settings, whereas the Ziehm C-arm demonstrated the lowest dose in the LDLP setting. In addition, our analysis of image quality indicated that the GE C-arm performed well, achieving the highest image quality overall. However, it is important to note that the Ziehm C-arm, when set to the LDLP configuration, produced the only images deemed inadequate for clinical use. These results underscore the importance of carefully considering the choice of FC manufacturer and the specific settings employed during fluoroscopic procedures.

There have been several comparisons of FCs to CCs across different settings yielding mixed results. Most recently, Lee et al. examined the performance of these devices during pediatric ureteroscopy, revealing lower radiation doses and higher image quality with FCs than with CCs. ⁴ It is important to note that this study was retrospective in nature, and the dose measurements relied on device-reported data, rather than using an objective measurement device such as OSLD chips, as in the current study. While their findings provide valuable insights into the potential benefits of FCs over CCs in pediatric ureteroscopy, the reliance on device-reported dose measurements and the retrospective design may introduce some limitations.

Comparing the difference between FCs and CCs to that of digital photography and film, FCs represent a fundamentally distinct technology. In lieu of an image intensifier, FCs employ an amorphous silicon thin-film transistor (TFT) arranged in rows and columns of detector elements. These detector elements are separated by “gate” and “drain” lines. When exposed to X-rays, each detector element stores the resulting charge in a capacitor. Upon completing the X-ray exposure, a sequential activation of all TFTs occurs through the gate lines, allowing the charge to flow in parallel through the TFTs and down the drain lines. Subsequently, the output signal undergoes digitization, facilitating the construction of the final image row by row. This intricate process ensures the efficient conversion of X-ray data into digital images, distinguishing FCs as a modern and sophisticated imaging technology, akin to the transformation from analog film photography to digital imagery. ⁴

The literature on comparisons of different FC manufacturers is quite limited. A benchtop study conducted a comparative analysis of the Ziehm and Siemens FCs across four settings, including the “urology” setting. ¹⁷ Their research revealed a statistically significant difference in radiation doses emitted by the two C-arms. Interestingly, except for the cardiology setting, the Ziehm C-arm consistently yielded higher radiation doses and displayed inferior image quality compared with the Siemens model. While acknowledging that their study's scope, C-arm models, and design differ from ours, their findings of substantial variability between two manufacturers despite using seemingly standardized settings align with our own research observations. It is evident from the available literature that further comprehensive investigations comparing various FC manufacturers are warranted. Such studies could provide valuable insights into optimizing radiation safety, image quality, and overall performance in clinical settings.

Although this newer FC technology holds promising advantages, radiation safety continues to be a significant concern. One of the primary issues lies in the proprietary designs adopted by different manufacturers, leading to considerable variations in the amount of radiation produced across different settings. This is further confirmed by our study, where the reduction in radiation exposure was different across the three FCs used when settings were changed from AEC to LD or LDLP. Considering our findings, it becomes evident that urologists play a crucial role in mitigating radiation exposure for both patients and medical staff. While the preprogrammed setting options are undoubtedly convenient, they only offer a fraction of the potential radiation reduction achievable when settings are manually adjusted by the operating physician. ¹⁸ This is consistent with prior studies, which have demonstrated that choosing a LD setting and pulsed fluoroscopy can reduce radiation doses by 60% and 64%, respectively, without compromising clinical safety and efficacy. ^3,19

Clinically, in our institution, we routinely use the LD setting at 1 pps when performing PCNL. We found these LD images to provide adequate information on endoscope and guidewire position, collecting system anatomy, and stent position. The only time AEC is utilized is for one image following completion of stone removal to detect small residual fragments. Hence, there is a clear need to encourage urologists to proactively modify these settings to optimize radiation safety without compromising the diagnostic quality of the produced images. Fortunately, our findings demonstrate that even at the lowest radiation dose, the images generated are generally sufficient for clinical purposes. Moving forward, collaborative efforts between manufacturers, health care professionals, and regulatory bodies could lead to improved standardization of radiation output and safer practices, ultimately enhancing the overall safety profile of this promising technology.

Our study has limitations that should be acknowledged. First, the evaluation was limited to a single cadaveric model and may not fully represent clinical scenarios with live patients. The use of anatomical specimens may not fully reflect the variability in patient anatomy encountered in real-world situations. However, the performance of this study on living patients would be unethical due to radiation exposure concerns. In addition, the use of a cadaver model is the most realistic ethical model available for studying radiation exposure. In this study, we tested only radiation dose and image quality; however, there are many other factors that may be considered when purchasing a C-arm, including ease of use, size, portability, familiarity, and cost.

Finally, we included three specific FC models, potentially limiting generalizability to other manufacturers; however, these three were selected because they are the three largest C-arm manufacturers worldwide by revenue and were willing to participate in the study. Similar to the testing of other devices for use in society including cars, refrigerators, and air conditioners, this study demonstrates that there are differences between C-arm manufacturers and these devices should be tested, regulated, and have their doses reported in a standardized manner.

Despite these limitations, this study yields important information in helping to understand the differences between algorithms utilized by different C-arm manufacturers. Novel information is presented comparing radiation exposure between three different FCs across three different settings used in urologic practice.

Conclusions

At the AEC setting, the Philips C-arm had the best picture quality and the lowest dose of radiation exposure. In contrast at the LDLP, the Ziehm C-arm had the lowest dose of radiation but produced inadequate images in 8% of trials. The GE C-arm had the highest picture quality at the LDLP setting. Understanding these differences in machine output and picture quality could help operating rooms and hospitals when selecting a C-arm for purchase and could help physicians when selecting the C-arm and settings to utilize in unique clinical scenarios.