Ionizing radiation absorption of vascular surgeons during endovascular procedures

Autonomous navigation of catheters and guidewires in mechanical thrombectomy using inverse reinforcement learning

PURPOSE

Autonomous navigation of catheters and guidewires can enhance endovascular surgery safety and efficacy, reducing procedure times and operator radiation exposure. Integrating tele-operated robotics could widen access to time-sensitive emergency procedures like mechanical thrombectomy (MT). Reinforcement learning (RL) shows potential in endovascular navigation, yet its application encounters challenges without a reward signal. This study explores the viability of autonomous guidewire navigation in MT vasculature using inverse reinforcement learning (IRL) to leverage expert demonstrations.

METHODS

Employing the Simulation Open Framework Architecture (SOFA), this study established a simulation-based training and evaluation environment for MT navigation. We used IRL to infer reward functions from expert behaviour when navigating a guidewire and catheter. We utilized the soft actor-critic algorithm to train models with various reward functions and compared their performance in silico.

RESULTS

We demonstrated feasibility of navigation using IRL. When evaluating single- versus dual-device (i.e. guidewire versus catheter and guidewire) tracking, both methods achieved high success rates of 95% and 96%, respectively. Dual tracking, however, utilized both devices mimicking an expert. A success rate of 100% and procedure time of 22.6 s were obtained when training with a reward function obtained through 'reward shaping'. This outperformed a dense reward function (96%, 24.9 s) and an IRL-derived reward function (48%, 59.2 s).

CONCLUSIONS

We have contributed to the advancement of autonomous endovascular intervention navigation, particularly MT, by effectively employing IRL based on demonstrator expertise. The results underscore the potential of using reward shaping to efficiently train models, offering a promising avenue for enhancing the accessibility and precision of MT procedures. We envisage that future research can extend our methodology to diverse anatomical structures to enhance generalizability.

Robotic applications for intracardiac and endovascular procedures

The large incisions and long recovery periods that accompany traditional cardiac surgery procedures along with the constant patient demand for minimally invasive procedures have motivated cardiac surgeons to implement the robotic technologies in their armamentarium. The robotic systems have been utilized successfully in various cardiac procedures including atrial septal defect repair, left atrial myxoma resection, MAZE procedure and left ventricular lead placement, yet coronary artery bypass and mitral valve repair still comprise the vast majority of them. This review analyzes the development of the robot-assisted cardiac surgery in recent years, its outcomes, advantages, disadvantages, its patient selection criteria as well as its economic feasibility. Robotic endovascular surgery, albeit its limited applications, is presently considered an attractive alternative to conventional endovascular approaches. The increased flexibility and precision along with the wider range of accessible anatomy provided by the endovascular robotic systems, have increased the pool of patients that can be offered minimally invasive treatment options and have helped to overcome many limitations of the traditional endovascular procedures. With this review we aimed to summarize the applications of the commercially available endovascular robotic devices, as well as the limitations and the future perspectives in the field of endovascular robotic surgery.

Recurrent neural networks for generalization towards the vessel geometry in autonomous endovascular guidewire navigation in the aortic arch

PURPOSE

Endovascular intervention is the state-of-the-art treatment for common cardiovascular diseases, such as heart attack and stroke. Automation of the procedure may improve the working conditions of physicians and provide high-quality care to patients in remote areas, posing a major impact on overall treatment quality. However, this requires the adaption to individual patient anatomies, which currently poses an unsolved challenge.

METHODS

This work investigates an endovascular guidewire controller architecture based on recurrent neural networks. The controller is evaluated in-silico on its ability to adapt to new vessel geometries when navigating through the aortic arch. The controller's generalization capabilities are examined by reducing the number of variations seen during training. For this purpose, an endovascular simulation environment is introduced, which allows guidewire navigation in a parametrizable aortic arch.

RESULTS

The recurrent controller achieves a higher navigation success rate of 75.0% after 29,200 interventions compared to 71.6% after 156,800 interventions for a feedforward controller. Furthermore, the recurrent controller generalizes to previously unseen aortic arches and is robust towards size changes of the aortic arch. Being trained on 2048 aortic arch geometries gives the same results as being trained with full variation when evaluated on 1000 different geometries. For interpolation a gap of 30% of the scaling range and for extrapolation additional 10% of the scaling range can be navigated successfully.

CONCLUSION

Adaption to new vessel geometries is essential in the navigation of endovascular instruments. Therefore, the intrinsic generalization to new vessel geometries poses an essential step towards autonomous endovascular robotics.

Artificial intelligence in the autonomous navigation of endovascular interventions: a systematic review

Background

Autonomous navigation of catheters and guidewires in endovascular interventional surgery can decrease operation times, improve decision-making during surgery, and reduce operator radiation exposure while increasing access to treatment.

Objective

To determine from recent literature, through a systematic review, the impact, challenges, and opportunities artificial intelligence (AI) has for the autonomous navigation of catheters and guidewires for endovascular interventions.

Methods

PubMed and IEEEXplore databases were searched to identify reports of AI applied to autonomous navigation methods in endovascular interventional surgery. Eligibility criteria included studies investigating the use of AI in enabling the autonomous navigation of catheters/guidewires in endovascular interventions. Following Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA), articles were assessed using Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2). PROSPERO: CRD42023392259.

Results

Four hundred and sixty-two studies fulfilled the search criteria, of which 14 studies were included for analysis. Reinforcement learning (RL) (9/14, 64%) and learning from expert demonstration (7/14, 50%) were used as data-driven models for autonomous navigation. These studies evaluated models on physical phantoms (10/14, 71%) and in-silico (4/14, 29%) models. Experiments within or around the blood vessels of the heart were reported by the majority of studies (10/14, 71%), while non-anatomical vessel platforms "idealized" for simple navigation were used in three studies (3/14, 21%), and the porcine liver venous system in one study. We observed that risk of bias and poor generalizability were present across studies. No procedures were performed on patients in any of the studies reviewed. Moreover, all studies were limited due to the lack of patient selection criteria, reference standards, and reproducibility, which resulted in a low level of evidence for clinical translation.

Conclusion

Despite the potential benefits of AI applied to autonomous navigation of endovascular interventions, the field is in an experimental proof-of-concept stage, with a technology readiness level of 3. We highlight that reference standards with well-identified performance metrics are crucial to allow for comparisons of data-driven algorithms proposed in the years to come.

Systematic review registration

identifier: CRD42023392259.

Use of surgical augmented intelligence maps can reduce radiation and improve safety in the endovascular treatment of complex aortic aneurysms

OBJECTIVE

The introduction of endovascular procedures has revolutionized the management of complex aortic aneurysms. Although repair has traditionally required longer operative times and increased radiation exposure compared with simple endovascular aneurysm repair, the recent introduction of three-dimensional technology has become an invaluable operative adjunct. Surgical augmented intelligence (AI) is a rapidly evolving tool initiated at our institution in June 2019. In our study, we sought to determine whether this technology improved patient and operator safety.

METHODS

A retrospective review of patients who had undergone endovascular repair of complex aortic aneurysms (pararenal, juxtarenal, or thoracoabdominal), type B dissection, or infrarenal (endoleak, coil placement, or renal angiography with or without intervention) at a tertiary care center from August 2015 to November 2021 was performed. Patients were stratified according to the findings from intelligent maps, which are patient-specific AI tools used in the operating room in conjunction with real-time fluoroscopic images. The primary outcomes included operative time, radiation exposure, fluoroscopy time, and contrast use. The secondary outcomes included 30-day postoperative complications and long-term follow-up. Linear regression models were used to evaluate the association between AI use and the main outcomes.

RESULTS

During the 6-year period, 116 patients were included in the present study, with no significant differences in the baseline characteristics. Of the 116 patients, 76 (65.5%) had undergone procedures using AI and 40 (34.5%) had undergone procedures without AI software. The intraoperative outcomes revealed a significant decrease in radiation exposure (AI group, 1955 mGy; vs non-AI group, 3755 mGy; P = .004), a significant decrease in the fluoroscopy time (AI group, 55.6 minutes; vs non-AI group, 86.9 minutes; P = .007), a decrease in the operative time (AI group, 255 minutes; vs non-AI group, 284 minutes; P = .294), and a significant decrease in contrast use (AI group, 123 mL; vs non-AI group, 199 mL; P < .0001). No differences were found in the 30-day and long-term outcomes.

CONCLUSIONS

The results from the present study have demonstrated that the use of AI technology combined with intraoperative imaging can significantly facilitate complex endovascular aneurysm repair by decreasing the operative time, radiation exposure, fluoroscopy time, and contrast use. Overall, evolving technology such as AI has improved radiation safety for both the patient and the entire operating room team.

Learning-based autonomous vascular guidewire navigation without human demonstration in the venous system of a porcine liver

Purpose

The navigation of endovascular guidewires is a dexterous task where physicians and patients can benefit from automation. Machine learning-based controllers are promising to help master this task. However, human-generated training data are scarce and resource-intensive to generate. We investigate if a neural network-based controller trained without human-generated data can learn human-like behaviors.

Methods

We trained and evaluated a neural network-based controller via deep reinforcement learning in a finite element simulation to navigate the venous system of a porcine liver without human-generated data. The behavior is compared to manual expert navigation, and real-world transferability is evaluated.

Results

The controller achieves a success rate of 100% in simulation. The controller applies a wiggling behavior, where the guidewire tip is continuously rotated alternately clockwise and counterclockwise like the human expert applies. In the ex vivo porcine liver, the success rate drops to 30%, because either the wrong branch is probed, or the guidewire becomes entangled.

Conclusion

In this work, we prove that a learning-based controller is capable of learning human-like guidewire navigation behavior without human-generated data, therefore, mitigating the requirement to produce resource-intensive human-generated training data. Limitations are the restriction to one vessel geometry, the neglected safeness of navigation, and the reduced transferability to the real world.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11548-022-02646-8.

An MR-Safe Endovascular Robotic Platform: Design, Control, and Ex-Vivo Evaluation

OBJECTIVE

Cardiovascular diseases are the most common cause of global death. Endovascular interventions, in combination with advanced imaging technologies, are promising approaches for minimally invasive diagnosis and therapy. More recently, teleoperated robotic platforms target improved manipulation accuracy, stabilisation of instruments in the vasculature, and reduction of patient recovery times. However, benefits of recent platforms are undermined by a lack of haptics and residual patient exposure to ionising radiation. The purpose of this research was to design, implement, and evaluate a novel endovascular robotic platform, which accommodates emerging non-ionising magnetic resonance imaging (MRI).

METHODS

We proposed a pneumatically actuated MR-safe teleoperation platform to manipulate endovascular instrumentation remotely and to provide operators with haptic feedback for endovascular tasks. The platform task performance was evaluated in an ex vivo cannulation study with clinical experts ( N = 7) under fluoroscopic guidance and haptic assistance on abdominal and thoracic phantoms.

RESULTS

The study demonstrated that the robotic dexterity involving pneumatic actuation concepts enabled successful remote cannulation of different vascular anatomies with success rates of 90%-100%. Compared to manual cannulation, slightly lower interaction forces between instrumentation and phantoms were measured for specific tasks. The maximum robotic interaction forces did not exceed 3N.

CONCLUSION

This research demonstrates a promising versatile robotic technology for remote manipulation of endovascular instrumentation in MR environments.

SIGNIFICANCE

The results pave the way for clinical translation with device deployment to endovascular interventions using non-ionising real-time 3D MR guidance.

What we know about intra-operative radiation exposure and hazards to operating theatre staff: A systematic review

BACKGROUND

The widespread adoption of minimally invasive surgery and increased use of intra-operative fluoroscopy places surgeons and trainees at risk of cumulative occupational radiation exposure. Unfortunately, there is limited published data specific to surgeons on the potential health implications. This study aims to review current literature regarding the hazards of cumulative radiation exposure among operating theatre staff.

METHODS

A systematic review was conducted of four databases for studies reporting on cumulative intra-operative radiation exposure for operating theatre staff and the hazards associated with prolonged and frequent use. References from relevant studies were screened for additional texts. English language studies, controlled trials and cross-sectional studies were included. Abstracts and full-text studies were assessed for relevance and eligibility independently by two authors using Covidence.

RESULTS

Six studies were included, with cancer being the most commonly reported long-term health hazard possibly associated with cumulative radiation exposure. A 1.85 fold greater prevalence of all cancers and 2.9 fold greater prevalence of breast cancer was reported amongst female orthopaedic surgeons compared to a sex- and age-adjusted population, but the results were not replicated amongst other surgical specialties. Multiple limitations of quantifying health risks of intra-operative radiation exposure were identified, including identifying a dose-effect relationship and confounders such as nulliparity and maternal age.

CONCLUSION

This article highlights the lack of robust evidence regarding the potential hazards of cumulative occupational intra-operative radiation exposure. This study demonstrates the importance of developing standardised national radiation safety protocols for surgical colleges and subspecialties to minimise risks to operating theatre staff.

KERMA-AREA PRODUCT, ENTRANCE SURFACE DOSE AND EFFECTIVE DOSE IN ABDOMINAL ENDOVASCULAR ANEURYSM REPAIR

This study aims to evaluate patient radiation dose during fluoroscopically guided endovascular aneurysm repair (EVAR) procedures. Fluoroscopy time (FT) and kerma-area product (KAP) were recorded from 87 patients that underwent EVAR procedures with a mobile C-arm fluoroscopy system. Effective dose (ED) and organs' doses were calculated utilising appropriate conversion coefficients based on the recorded KAP values. Entrance surface dose (ESD) was calculated based on KAP values and technical parameters. The mean FT was 22.7 min (range 6.4-76.8 min), resulting in a mean KAP of 36.6 Gy cm2 (range 2.0-167.8 Gy cm2), a mean ED of 6.2 mSv (range 0.3-28.5 mSv) and a mean ESD of 458 mGy (range 26-2098 mGy). The corresponding median values were 17.4 min, 25.6 Gy cm2, 4.4 mSv and 320 mGy. The threshold of 2 Gy for skin erythema was exceeded in two procedures for a focus-to-skin distance (FSD) of 40 cm and six procedures when an FSD of 30 cm was considered. The highest doses absorbed by the adrenals, kidneys, spleen and pancreas and ranged between 3.7 and 313.3 mGy (average 66.8 mGy), 3.3 and 285.1 mGy (average 60.8 mGy), 1.3 and 111.1 mGy (average 23.7 mGy), 1.1 and 92.1 mGy (average 19.6 mGy), respectively. A wide range of patient doses was reported in the literature. The radiation dose received by the patients was comparative or lower than most of the previously reported values. However, higher doses can be revealed due to the X-ray system's non-optimum use and extended FTs, mainly affected by complex clinical conditions, patients' body habitus and vascular surgeon experience. The large variation of patient doses highlights the potential to optimise the EVAR procedure by considering the balance between the radiation dose and the required image quality. Additional studies need to be conducted in increasing the vascular surgeons' awareness regarding patient dose and radiation protection issues during EVAR procedures.

Physician impact on use of fluoroscopy during endovascular procedures to improve radiation safety

OBJECTIVE

To determine whether differences exist in fluoroscopy time and radiation exposure during lower extremity endovascular procedures performed by fellowship trained vascular surgeons vs general surgeons, to minimize radiation exposure to operating room staff.

METHODS

A retrospective review of all lower extremity endovascular procedures was performed from August 1, 2014, to January 29, 2016. The procedures were performed by the surgical department's four surgeons with endovascular privileges: two vascular surgeons and two general surgeons. Only procedures involving lower extremity arterial angiograms with balloon angioplasty, stenting, or atherectomy were included. The operative records were reviewed for each case. The total fluoroscopy time and total radiation dose for each procedure were recorded. Procedures were grouped according to the number of endovascular interventions as one to two interventions, three to four interventions, and five or more interventions performed. Statistical analysis was performed with a P value of less than .05 considered significant.

RESULTS

About 271 lower extremity endovascular procedures were performed during the study period by 4 surgeons. The average age of the patient population was 70 years. The total number of procedures performed over the study period were 112, 45, 91, and 25 for surgeons 1 through 4, respectively. On average, 3.24 interventions were performed during each procedure. Vascular surgeons were found to have shorter fluoroscopy time for procedures involving one to two (7.8 vs 30.1; P < .01), three to four (9.3 vs 34.2; P < .01), and five or more (11.5 vs 51.9; P < .01) interventions. Vascular surgeons were also found to have less radiation exposure compared with general surgeons in procedures with one to two (1.69 vs 3.53; P = .001) and five or more (2.3 vs 5.4; P = .003) interventions. There was no significant difference in radiation exposure between vascular and general surgeons for procedures with three to four interventions (5.86 vs 5.59; P = .95).

CONCLUSIONS

In this small series at our institution, lower extremity endovascular procedures performed by specialty trained vascular surgeons were associated with both decreased operative fluoroscopy time and decreased radiation exposure when compared with general surgeons.

Radiation exposure during non-thrombotic iliac vein stenting

Objective

Fluoroscopic-guided interventions have become a major part of the modern vascular surgeon’s practice. Imaging is typically required to safely and effectively perform both simple and complex endovascular interventions. With an ever-increasing volume of fluoroscopic-guided interventions being performed each year, the minimization of harmful radiation exposure has become of paramount concern for both patients and providers. The purpose of this study was to identify the extent of radiation exposure associated with venography and iliac vein stenting, an intervention utilized in the management of chronic venous insufficiency.

Methods

This was a single-center, retrospective analysis of 40 venograms performed on 29 unique patients over a three-month period. Patients with signs and symptoms of chronic venous insufficiency who failed conservative therapy underwent evaluation of the vena cava and iliofemoral veins with venography and intravascular ultrasound. Stent placement was performed if a >50% cross-sectional area or diameter reduction was identified via intravascular ultrasound. All patients were found to have non-thrombotic iliac vein lesions. All patients wore two individual film badge dosimeters – one on their chest and the other on the abdomen. The same mobile C-arm system was used for all interventions.

Results

There were 15 males and 14 females, with an average age of 70.6 years old (SD ± 9.5; range 53–89) and a mean body mass index of 33.9 kg/m2. Sixteen limbs had C6 disease, 10 had C4 disease, and 14 had C3 disease. Thirty-eight of the 40 procedures resulted in stent placement, with an average of 1.13 stents placed per intervention. The average fluoroscopy time was 76.5 s (SD ± 36.9; range 7.8–209.5), and the mean cumulative air kerma was 1.08 mGy (SD ± 0.55; range 0.362–2.24). Average cumulative air kerma was higher in procedures resulting >1 stent placement compared to those with placement of ≤1 stent (1.44 vs. 1.02 mGy; p = 0.04). Fluoroscopy time was also higher in procedures with >1 stent placed (120.1 vs. 68.8 s; p = 0.0004). The mean deep dose equivalent per procedure from the patient-worn abdominal badge was 0.221 mSv.

Conclusion

With the adjunctive use of intravascular ultrasound, iliac vein stenting can be safely and effectively performed with very low utilization of fluoroscopy, and therefore radiation exposure can be minimized for both patients and surgeons. Placement of >1 iliac vein stent resulted in higher cumulative air kerma and fluoroscopy time.

Analysis of intraoperative radiation use in vascular surgery: Catalyst for quality improvement in patient and personnel safety

OBJECTIVES

There is paucity in the literature reporting radiation usage analysis in vascular surgery. In the era of endovascular surgeries, analyzing the surgeons' use of radiation in vascular procedures can help establish quality improvement initiatives.

METHODS

A retrospective review was undertaken of intraoperative fluoroscopic-guided vascular surgery procedures at a single institution from 2010 to 2017. Mobile C-arms were utilized to gather the six radiation usage metrics and cases were categorized into 6 anatomic surgical fields and 10 surgical procedure types.

RESULTS

Three hundred and eighteen vascular surgery cases were analyzed and notable trends in all radiation usage metrics were identified both across the surgical field location and type of surgical procedure. The highest cumulative dose was identified in embolization cases with a mean of 932.5 mGy. The highest fluoroscopic time was seen in atherectomies with a mean of 2629.6 s. In terms of surgical field, the highest cumulative does and fluoroscopic time was identified in abdomen/pelvis procedures with a mean of 352.1 mGy and 1186.8 s, respectively. Analysis of dose reduction techniques also demonstrated notable trends.

CONCLUSIONS

There were notable trends in the analyzed radiation usage variables both across the surgical field location and type of surgical procedure. Specifically, cases that involve the abdomen/pelvis, embolization and atherectomy have the highest radiation use. These types of cases can be targeted for future improved dose reduction techniques or staged procedures. This data can serve as baseline information for future quality improvement initiatives for patient and personnel radiation exposure safety.

Navigation and visualisation with HoloLens in endovascular aortic repair

Introduction

Endovascular aortic repair (EVAR) is a minimal-invasive technique that prevents life-threatening rupture in patients with aortic pathologies by implantation of an endoluminal stent graft. During the endovascular procedure, device navigation is currently performed by fluoroscopy in combination with digital subtraction angiography. This study presents the current iterative process of biomedical engineering within the disruptive interdisciplinary project Nav EVAR, which includes advanced navigation, image techniques and augmented reality with the aim of reducing side effects (namely radiation exposure and contrast agent administration) and optimising visualisation during EVAR procedures. This article describes the current prototype developed in this project and the experiments conducted to evaluate it.

Methods

The current approach of the Nav EVAR project is guiding EVAR interventions in real-time with an electromagnetic tracking system after attaching a sensor on the catheter tip and displaying this information on Microsoft HoloLens glasses. This augmented reality technology enables the visualisation of virtual objects superimposed on the real environment. These virtual objects include three-dimensional (3D) objects (namely 3D models of the skin and vascular structures) and two-dimensional (2D) objects [namely orthogonal views of computed tomography (CT) angiograms, 2D images of 3D vascular models, and 2D images of a new virtual angioscopy whose appearance of the vessel wall follows that shown in ex vivo and in vivo angioscopies]. Specific external markers were designed to be used as landmarks in the registration process to map the tracking data and radiological data into a common space. In addition, the use of real-time 3D ultrasound (US) is also under evaluation in the Nav EVAR project for guiding endovascular tools and updating navigation with intraoperative imaging. US volumes are streamed from the US system to HoloLens and visualised at a certain distance from the probe by tracking augmented reality markers. A human model torso that includes a 3D printed patient-specific aortic model was built to provide a realistic test environment for evaluation of technical components in the Nav EVAR project. The solutions presented in this study were tested by using an US training model and the aortic-aneurysm phantom.

Results

During the navigation of the catheter tip in the US training model, the 3D models of the phantom surface and vessels were visualised on HoloLens. In addition, a virtual angioscopy was also built from a CT scan of the aortic-aneurysm phantom. The external markers designed for this study were visible in the CT scan and the electromagnetically tracked pointer fitted in each marker hole. US volumes of the US training model were sent from the US system to HoloLens in order to display them, showing a latency of 259±86 ms (mean±standard deviation).

Conclusion

The Nav EVAR project tackles the problem of radiation exposure and contrast agent administration during EVAR interventions by using a multidisciplinary approach to guide the endovascular tools. Its current state presents several limitations such as the rigid alignment between preoperative data and the simulated patient. Nevertheless, the techniques shown in this study in combination with fibre Bragg gratings and optical coherence tomography are a promising approach to overcome the problems of EVAR interventions.

Pattern and degree of radiation exposure during endovascular surgery performed using a mobile C-arm or in a hybrid room

Purpose

A prospective study was conducted to compare radiation exposure to different parts of an endovascular surgeon's body when using a mobile C-arm with that in a hybrid room.

Methods

Exposure during individual procedures performed on 39 patients with a mobile C-arm and 42 patients in a hybrid room, from July 2016 to December 2016, was evaluated.

Results

The procedures performed, fluoroscopy time, and dose-area product were not significantly different between groups. The dose-area product per second in the hybrid room group appeared greater than in the C-arm group (4.5 µGym²/sec vs. 3.1 µGym²/sec). In the C-arm group, the peak skin dose on the right neck (1.77 mSv) and shoulder (1.48 mSv) appeared higher than those on their left side (0.32 mSv, 0.53 mSv, respectively) and the counterparts of the hybrid room group (0.88 mSv, 0.20 mSv, respectively).

Conclusion

The peak skin dose in the hybrid room appeared highest for the lower part of the protective apron. The dose-area product per second seemed to be greater in the hybrid room than when using the C-arm. Thus, attention should be focused on protecting the surgeon's upper body when using the C-arm and the lower body when using the hybrid room.

Closed reduction and percutaneous fixation of sacroiliac luxations in cats using 2.4 mm cannulated screws – a cadaveric study

Objectives: To describe fluoroscopically assisted percutaneous placement of 2.4 mm cannulated screws for fixation of artificially induced sacroiliac luxations in cats, and to evaluate the success of this technique in restoration of normal pelvic anatomy.

Methods: Fluoroscopically assisted closed reduction and percutaneous fixation of sacroiliac luxations using 2.4 mm cannulated screws was performed in cadavers of 12 cats. Pre- and postoperative radiographs and postoperative computed tomographic scans were used to evaluate screw placement, screw purchase within the sacral body, reduction of the sacroiliac joint, pelvic canal diameter ratio, and hemipelvic canal width ratio.

Results: Mean total surgical time was 6 minutes and 10 seconds ± 53 seconds and mean total time of fluoroscopic screening for each procedure was 44 seconds ± 6 seconds. Mean percent of reduction was 98.33% and mean screw purchase within the sacral body was 73%. Eleven out of 12 screws were placed in a satisfactory location in the sacral body. Pelvic canal diameter ratio and hemipelvic canal width ratio indicated successful restoration of the pelvic anatomy.

Clinical significance: Our results confirm that fluoroscopically assisted percutaneous placement of 2.4 mm cannulated screws is a feasible technique for fixation of sacroiliac luxations in cats. Mechanical properties of this fixation technique need to be evaluated before the use in clinical patients.

[Is ultrasound guidance contributive to vascular access in endovascular therapy?]

OBJECTIVES

The aim of this study was to evaluate the contribution of ultrasound guidance (UG) to vascular puncture in endovascular therapy. Ultrasound guidance was evaluated by comparison with the rates of failures and complications of the traditional techniques of percutaneous vascular access.

MATERIALS AND METHODS

We reviewed all the consecutive percutaneous revascularizations (percutaneous transluminal angioplasty and/or stenting, treatment of aneurysms and vascular traumatisms) since the standardization of the systems of closing (extra- and endovascular). The UG began in November 2011. The main objectives of the evaluation were the rate of failure of the punctures and the rate of complications (hematoma requiring transfusion or surgery for hemostasis, false aneurysm, dissection, thrombosis, infection). The failures and the complications were compared between two groups UG- and UG+.

RESULTS

Between January 2008 and December 2014, 841 punctures were carried out by femoral route (85%), brachial route (12%), popliteal route (1%), axillary route (0.5%), and posterior tibial route (0.5%) with introducers between 4F and 12F. There were 20 complications (2.3%): six hematomas, four pseudo-aneurysms, three thromboses, one nervous paralysis, one stent infection, and seven percutaneous failures. The complications and the failures were significantly lower with ultrasound guidance (0.9% vs. 3.6%; P=0.02, and 0.2% vs. 1.4%; P=0.01, respectively).

CONCLUSION

Ultrasound guidance makes it possible to significantly decrease the rate of complications and failures of the percutaneous accesses. This tool allowed a clear increase in the realization of the percutaneous angioplasties in outpatient hospitalization.

Physician and Patient Radiation Exposure During Endovascular Procedures

OPINION STATEMENT

Endovascular procedures expose both patients and physicians to fluoroscopic ionizing radiation that carries a dose-dependent risk of acute toxicity and a small, but demonstrable, long-term risk of malignancy due to resultant genetic mutations. Exposure doses vary widely based upon patient-related factors including body size and anatomic complexity, operator technique, procedure type (diagnostic vs. therapeutic), vascular bed imaged, and imaging equipment employed. Effective dosage may vary as much as 200-fold for physicians and 20-fold for patients depending upon the procedure: for example, complex aortic interventions with branched graft devices may convey mean effective doses of more than 0.4 mSv for physicians and 100 mSv for patients, whereas distal, small-vessel angiography may entail mean effective doses of less than 0.002 mSv for physicians and 5 mSv for patients. Particular attention is given to physicians' ocular exposure, which may cause cataract development, and to hand exposure, which is significantly higher than total body exposure when operators work near the x-ray beam. Given the risks of radiation exposure, numerous strategies have been developed to reduce both physician and patient doses. These measures include physician education about dose-reducing imaging techniques, development of low-dose imaging equipment, introduction of new radiation shielding drapes and caps, and real-time dose monitoring. Here, we review physician and patient effective doses of radiation by procedure type as reported in the literature and present recent data regarding dose-reduction strategies.

Radiation hazards to vascular surgeon and scrub nurse in mobile fluoroscopy equipped hybrid vascular room

PURPOSE

The aim of the present study was to identify the radiation hazards to vascular surgeons and scrub nurses working in mobile fluoroscopy equipped hybrid vascular operation rooms; additionally, to estimate cumulative cancer risk due to certain exposure dosages.

METHODS

The study was conducted prospectively in 71 patients (53 men and 18 women) who had undergone vascular intervention at our hybrid vascular theater for 6 months. OEC 9900 fluoroscopy was used as mobile C-arm. Exposure dose (ED) was measured by attaching optically stimulated luminescence at in and outside of the radiation protectors. To measure X-ray scatter with the anthropomorphic phantom model, the dose was measured at 3 distances (20, 50, 100 cm) and 3 angles (horizontal, upward 45°, downward 45°) using a personal gamma radiation dosimeter, Ecotest CARD DKG-21, for 1, 3, 5, 10 minutes.

RESULTS

Lifetime attributable risk of cancer was estimated using the approach of the Biological Effects of Ionizing Radiation report VII. The 6-month ED of vascular surgeons and scrub nurses were 3.85, 1.31 mSv, respectively. The attenuation rate of lead apron, neck protector and goggle were 74.6%, 60.6%, and 70.1%, respectively. All cancer incidences among surgeons and scrub nurses correspond to 2,355 and 795 per 100,000 persons. The 10-minute dose at 100-cm distance was 0.004 mSv at horizontal, 0.009 mSv at downward 45°, 0.003 mSv at upward 45°.

CONCLUSION

Although yearly radiation hazards for vascular surgeons and scrub nurses are still within safety guidelines, protection principles can never be too stringent when aiming to minimize the cumulative harmful effects.

Meta-analysis of Cumulative Radiation Duration and Dose During EVAR Using Mobile, Fixed, or Fixed/3D Fusion C-Arms

Purpose: To investigate the total fluoroscopy time and radiation exposure dose during endovascular aortic repairs using mobile, fixed, or fixed C-arms with 3-dimensional image fusion (3D-IF). Methods: A systematic search was performed to identify original articles reporting fluoroscopy time (FT) and the kerma area product (KAP) during endovascular aortic repairs. Data were grouped by noncomplex or complex (fenestrated, branched, or chimney) repairs and stratified by type of C-arm. The search identified 27 articles containing 51 study groups (35 noncomplex and 16 complex) that included 3444 patients. Random-effects meta-analysis and meta-regression models were used to calculate the pooled mean estimates of KAP and FT, as well as any effect of equipment or type of intervention. Results are presented with the 95% confidence interval and the statistical heterogeneity ( I2). Results: Within the noncomplex procedure studies, a significant (p<0.001) increase was found in the pooled mean KAP estimate in the fixed C-arm group (181 Gy·cm2, 95% CI 129 to 233; I2=99.7) compared with the mobile C-arm (78 Gy·cm2, 95% CI 59.6 to 97.3; I2=99.6). For complex cases, use of 3D-IF showed a significantly (p<0.001) lower mean KAP (139 Gy·cm2, 95% CI 85 to 191; I2=94%) compared to using fixed C-arms without 3D-IF (487 Gy·cm2, 95% CI 331 to 643; I2=94%). Conclusion: For equivalent fluoroscopy times, the use of a fixed C-arm in noncomplex procedures leads to higher patient radiation doses compared to a mobile C-arm. Complex procedures, which are predominantly performed using fixed C-arms, are associated with the highest radiation dose per intervention. Using fixed C-arms combined with 3D-IF techniques during complex cases might seem an adequate method to compensate for the higher radiation doses measured when a fixed C-arm is used.

Fluoroscopic Radiation Exposure in Spinal Surgery: In Vivo Evaluation for Operating Room Personnel

STUDY DESIGN

Prospective in vivo investigation of fluoroscopic radiation exposure during spinal surgery.

OBJECTIVE

To quantify the total amount of radiation dosage and identify techniques to maintain safe levels of fluoroscopic exposure in the operating room.

SUMMARY OF BACKGROUND DATA

No previous study has performed an in vivo examination of fluoroscopic radiation exposure to the spinal surgeon and operating room personnel. Previous similar studies were in vitro, used older versions of fluoroscopy, and increased fluoro times associated with pedicle screw placement.

METHODS

Thirty-five surgeries were evaluated in 18 males and 17 females (mean age 52.4 y; range, 26.0-79.4). Surgeries included 37 lumbar levels fused, 45 lumbar decompressions, 8 anterior cervical fusions, and 19 transforaminal lumbar interbody fusion procedures. Spinal instrumentation was implemented in all fusion procedures (104 lumbar pedicle screws, 14 iliac, 22 anterior cervical). Radiation dosimetry was obtained through unprotected badges placed on surgeon's chest, first assistant chest, cranial and caudal end of operating table.

RESULTS

Total fluoroscopic time was 37.01 minutes. Mean fluoroscopic time with lumbar spine instrumentation was greater than decompression alone (1.74 vs. 0.22 min). Total fluoroscopic radiation exposure was obtained for surgeon (1225 mrem), first assistant (369 mrem), cranial table (92 mrem), and caudal table (150 mrem). Mean dose/min (mrem/min) was calculated for surgeon (33.1), first assistant (9.97), cranial table (2.48), and caudal table (4.05). To remain below the maximum yearly permissible level of radiation, the estimated total number of minutes for the surgeon would be 453.

CONCLUSIONS

The results of this in vivo study indicate fluoroscopic dosage to the spine surgeon remains below the annual maximum limit of radiation exposure. Increasing distance from radiation source led to a significantly diminished in vivo dosimetry reading. Monitoring fluoroscopic time and maintaining a distance from the beam source, radiation exposure to the spine surgeon may be kept within current safety standards.

Endovascular repair of abdominal aortic aneurysms: vascular anatomy, device selection, procedure, and procedure-specific complications

Abdominal aortic aneurysm (AAA) is abnormal dilatation of the aorta, carrying a substantial risk of rupture and thereby marked risk of death. Open repair of AAA involves lengthy surgery time, anesthesia, and substantial recovery time. Endovascular aneurysm repair (EVAR) provides a safer option for patients with advanced age and pulmonary, cardiac, and renal dysfunction. Successful endovascular repair of AAA depends on correct selection of patients (on the basis of their vascular anatomy), choice of the correct endoprosthesis, and familiarity with the technique and procedure-specific complications. The type of aneurysm is defined by its location with respect to the renal arteries, whether it is a true or false aneurysm, and whether the common iliac arteries are involved. Vascular anatomy can be divided more technically into aortic neck, aortic aneurysm, pelvic perfusion, and iliac morphology, with grades of difficulty with respect to EVAR, aortic neck morphology being the most common factor to affect EVAR appropriateness. When choosing among the devices available on the market, one must consider the patient's vascular anatomy and choose between devices that provide suprarenal fixation versus those that provide infrarenal fixation. A successful technique can be divided into preprocedural imaging, ancillary procedures before AAA stent-graft placement, the procedure itself, postprocedural medical therapy, and postprocedural imaging surveillance. Imaging surveillance is important in assessing complications such as limb thrombosis, endoleaks, graft migration, enlargement of the aneurysm sac, and rupture. Last, one must consider the issue of radiation safety with regard to EVAR.

The Essentials of Cardiac Computerized Tomography

Cardiac computerized tomography (CT) has evolved from a research tool to an important diagnostic investigation in cardiology, and is now recommended in European, US, and UK guidelines. This review is designed to give the reader an overview of the current state of cardiac CT. The role of cardiac CT is multifaceted, and includes risk stratification, disease detection, coronary plaque quantification, defining congenital heart disease, planning for structural intervention, and, more recently, assessment of ischemia. This paper addresses basic principles as well as newer evidence.

Comparative occupational radiation exposure between fixed and mobile imaging systems

OBJECTIVE

Endovascular intervention exposes surgical staff to scattered radiation, which varies according to procedure and imaging equipment. The purpose of this study was to determine differences in occupational exposure between procedures performed with fixed imaging (FI) in an endovascular suite compared with conventional mobile imaging (MI) in a standard operating room.

METHODS

A series of 116 endovascular cases were performed over a 4-month interval in a dedicated endovascular suite with FI and conventional operating room with MI. All cases were performed at a single institution and radiation dose was recorded using real-time dosimetry badges from Unfors RaySafe (Hopkinton, Mass). A dosimeter was mounted in each room to establish a radiation baseline. Staff dose was recorded using individual badges worn on the torso lead. Total mean air kerma (Kar; mGy, patient dose) and mean case dose (mSv, scattered radiation) were compared between rooms and across all staff positions for cases of varying complexity. Statistical analyses for all continuous variables were performed using t test and analysis of variance where appropriate.

RESULTS

A total of 43 cases with MI and 73 cases with FI were performed by four vascular surgeons. Total mean Kar, and case dose were significantly higher with FI compared with MI. (mean ± standard error of the mean, 523 ± 49 mGy vs 98 ± 19 mGy; P < .00001; 0.77 ± 0.03 mSv vs 0.16 ± 0.08 mSv, P < .00001). Exposure for the primary surgeon and assistant was significantly higher with FI compared with MI. Mean exposure for all cases using either imaging modality, was significantly higher for the primary surgeon and assistant than for support staff (ie, nurse, radiology technologist) beyond 6 feet from the X-ray source, indicated according to one-way analysis of variance (MI: P < .00001; FI: P < .00001). Support staff exposure was negligible and did not differ between FI and MI. Room dose stratified according to case complexity (Kar) showed statistically significantly higher scattered radiation in FI vs MI across all quartiles.

CONCLUSIONS

The scattered radiation is several-fold higher with FI than MI across all levels of case complexity. Radiation exposure decreases with distance from the radiation source, and is negligible outside of a 6-foot radius. Modern endovascular suites allow high-fidelity imaging, yet additional strategies to minimize exposure and occupational risk are needed.

Anatomic and procedural determinants of fluoroscopy time during elective endovascular aortic aneurysm repair

Objective

To identify both the procedural and anatomic factors which determine duration of fluoroscopy during elective endovascular aortic aneurysm repair (EVAR).

Methods

We retrospectively analyzed our prospectively maintained EVAR database for the relationship between fluoroscopy time and both procedural (type of graft, configuration, number of components, surgeon) and anatomic factors reflective of aneurysm complexity (15 variables).

Results

A total of 128 patients underwent elective EVAR with a mean fluoroscopy time of 5.7 ± 3.4 min. The type of grafts used consisted of 41 (32%) Zenith, 85 (66.4%) Endurant and 2 (1.6%) Anaconda, with 105 (82%) being bifurcated and 23 (18%) being aorto-uni-iliac (AUI) in configuration. Both the surgeon performing the procedure ( p = 0.001) and graft configuration (bifurcated vs. AUI, p = 0.03) were found to be predictive of fluoroscopy time; while procedural and anatomic variables were not.

Conclusions

The surgeon’s efficiency in the use of fluoroscopy during EVAR is the most important determinant of total fluoroscopy time. Anatomic complexity, make of device, and number of components inserted have minimal impact on duration of fluoroscopy. An endovascular surgeon’s ability to curtail fluoroscopy duration is the key component in minimizing radiation exposure to both the surgical team and the patient.

Eye dosimetry in interventional radiology and cardiology: current challenges and practical considerations

Interventional radiology and cardiology are areas with high potential for risk to eye lens. Accurate assessment of eye dose is one of the most important aspects of correlating doses with observed lens opacities among workers in interventional suites and ascertaining compliance with regulatory limits. The purpose of this paper is to review current approaches and opportunities in eye dosimetry and assess challenges in particular in accuracy and practicality. The possible approaches include practical dosimetry using passive dosemeters or active dosemeters with obvious advantage of active dosimetry. When neither of these is available, other approaches are based on either retrospective dose assessment using scatter radiation dose levels or correlations between patient dose indices and eye doses to the operators. In spite of all uncertainties and variations, estimation of eye dose from patient dose can be accepted as a compromise. Future challenges include development of practical methods for regular monitoring of individual eye doses and development of better techniques to estimate eye dose from measurements at some reference points.

Review of the Use of Ionizing Radiation in Endovascular Aneurysm Repair

Endovascular repair for aortic aneurysm (EVAR) is rapidly increasing in popularity. The nature of this intervention requires significant exposure to ionizing radiation both during the procedure and for postoperative surveillance, generally in the form of computed tomography. Here the authors review the literature for radiation exposure during EVAR, both for the patient and the physician.

Radiation dose to the interventionalist is directly affected by the operating position

We aimed to determine the optimal positioning of the interventionalist with regard to radiation exposure during endovascular aneurysm repairs (EVAR). The radiation absorption of two vascular surgeons and one trainee was prospectively monitored during a series of 10 routine EVARs. Position of the two vascular surgeons varied: surgeon A stood adjacent to the trainee and one person down from the image intensifier (II), whereas surgeon B stood directly across from the trainee at the same level as the II. Surgeon A absorbed significantly less mean body (0.004 mSv versus 0.036 mSv; P = 0.001), eye (0.036 versus 0.222 mSv; P < 0.001) and extremity (0.034 versus 0.212 mSv; P < 0.001) radiation doses compared with surgeon B and also had significantly lower doses of absorbed body (0.004 versus 0.04 mSv; P = 0.047), eye (0.036 versus 0.25 mSv; P = 0.043) and extremity (0.034 versus 0.248 mSv; P = 0.05) radiation relative to the trainee. In conclusion, there is considerable variation in radiation absorption due to the position of the interventionalist relative to the II and other operators. Although positioning of the operator next to the trainee may make it more difficult to assist and teach technical maneuvers, it greatly minimizes radiation exposure to the interventionalist.

Laser targeting with C-arm fluoroscopy: effect on image acquisition and radiation exposure

OBJECTIVES

Reducing unnecessary radiation exposure from medical imaging is paramount. This study assessed whether a laser aiming guide for C-arm fluoroscopy reduced the number of exposures needed to obtain an acceptable image, thereby reducing total fluoroscopy time for hip, knee, and ankle fluoroscopy.

METHODS

An obese cadaver was placed supine on a radiolucent surgical table. Images were obtained by licensed radiologic technologists using a calibrated OEC 9900 Elite C-arm with laser targeting (LT) and without LT (NLT). Dosimeters were placed 1, 3, and 6 ft (30.5, 91.5, and 183 cm) away from the center of the C-arm at 90-degree angles at 2 levels, simulating thyroid and gonadal exposure. Posterior-anterior (PA) images of the bilateral lower extremities were obtained with each technician acquiring 24 centered images (hip, knee, and ankle) using both LT and NLT C-arm fluoroscopy.

RESULTS

Total fluoroscopy time was reduced by 19% when using LT with a 39% reduction for the knee and a 29% reduction for the ankle. The addition of LT improved the likelihood of obtaining a centered image for knees and ankles but not for hips. The gonadal dosimetry data were significantly higher than the thyroid dosimetry badges at 1 ft. At the 3-ft zone, only trace amounts of radiation were detected; the 6-ft zone reported no radiation exposure in either group.

CONCLUSIONS

LT helped with imaging knees and ankles with statistically significant reductions in fluoroscopy time and a statistically significant improvement of image quality defined as obtaining a centered PA image faster. The dosimetry badges detected minimal exposure at 3 ft and no detectable exposure at 6 ft at both levels.

ICRP Publication 117. Radiological protection in fluoroscopically guided procedures performed outside the imaging department

An increasing number of medical specialists are using fluoroscopy outside imaging departments, but there has been general neglect of radiological protection coverage of fluoroscopy machines used outside imaging departments. Lack of radiological protection training of those working with fluoroscopy outside imaging departments can increase the radiation risk to workers and patients. Procedures such as endovascular aneurysm repair, renal angioplasty, iliac angioplasty, ureteric stent placement, therapeutic endoscopic retrograde cholangio-pancreatography,and bile duct stenting and drainage have the potential to impart skin doses exceeding Gy. Although tissue reactions among patients and workers from fluoroscopy procedures have, to date, only been reported in interventional radiology and cardiology,the level of fluoroscopy use outside imaging departments creates potential for such injuries.A brief account of the health effects of ionising radiation and protection principles is presented in Section 2. Section 3 deals with general aspects of the protection of workers and patients that are common to all, whereas specific aspects are covered in Section 4 for vascular surgery, urology, orthopaedic surgery, obstetrics and gynaecology,gastroenterology and hepatobiliary system, and anaesthetics and pain management.Although sentinel lymph node biopsy involves the use of radio-isotopic methods rather than fluoroscopy, performance of this procedure in operating theatres is covered in this report as it is unlikely that this topic will be addressed in another ICRP publication in coming years. Information on radiation dose levels to patients and workers, and dose management is presented for each speciality.

Operator-controlled imaging significantly reduces radiation exposure during EVAR

INTRODUCTION

Adoption of endovascular aneurysm repair (EVAR) has led to significant reductions in the short-term morbidity and mortality associated with abdominal aortic aneurysm (AAA) repair. However, EVAR may expose both patient and interventionalist to potentially harmful levels of radiation, particularly as more complex procedures are undertaken. The aim of this study was to assess whether changing from radiographer-controlled imaging to a system of operator-controlled imaging (OCI) would influence radiation exposure, screening time or contrast dose during EVAR.

METHOD

Retrospective analysis identified patients that had undergone elective EVAR for infra-renal AAA before or after the change to operator-controlled imaging. Data were collected for radiation dose (measured as dose area product; DAP), screening time, total delivered contrast volume and operative duration. Data were also collected for maximum aneurysm diameter, patient age, gender and body mass index.

RESULTS

122 patients underwent EVAR for infra-renal AAA at a single centre between January 2011 and December 2011. 57 of these were prior to installation of OCI and 65 after installation. Median DAP was significantly lower after installation of OCI (4.9 mGy m(2); range 1.25-13.3) than it had been before installation (6.9 mGy m(2); range 1.91-95.0) (p = 0.005). Median screening times before and after installation of OCI were 20.0 min and 16.2 min respectively (p = 0.027) and median contrast volumes before and after the change to OCI were 100 ml and 90 ml respectively (p = 0.21).

CONCLUSION

Introduction of operator-controlled imaging can significantly reduce radiation exposure during EVAR, with particular reduction in the number of 'higher-dose' cases.

The impact of radiological equipment on patient radiation exposure during endovascular aortic aneurysm repair

OBJECTIVES

To compare the patient radiation dose during endovascular aortic aneurysm repair (EVAR) using different types of radiological systems: a mobile fluoroscopic C-arm, mobile angiographic and fixed angiographic equipment.

METHODS

Dose-area products (DAP) were obtained from a retrospective study of 147 consecutive patients, subjected to 153 EVAR procedures during a 3.5-year period. On the basis of these data, entrance surface dose (ESD) and effective dose (ED) were calculated. EVARs were performed using a fluoroscopic C-arm, mobile or fixed angiographic equipment in 79, 26 and 48 procedures, respectively.

RESULTS

Fluoroscopy times were essentially equivalent for all the systems, ranging from 15 to 19 min. The clinical outcomes were not significantly different among the systems. Statistically significant differences among radiological equipment grouping were found for DAP (mobile C-arm: 32 ± 20 Gy cm(2); mobile angiography: 362 ± 164 Gy cm(2); fixed angiography: 464 ± 274 Gy cm(2); P < 10(-6)), for ESD (mobile C-arm: 0.18 ± 0.11 Gy; mobile angiography: 2.0 ± 0.8 Gy; fixed angiography: 2.5 ± 1.5 Gy; P < 10(-6)) and ED (mobile C-arm: 6.2 ± 4.5 mSv; mobile angiography: 64 ± 26 mSv; fixed angiography: 129 ± 76 mSv; P < 10(-6)).

CONCLUSIONS

Radiation dose in EVAR is substantially less with a modern portable C-arm than with a fixed or mobile dedicated angiographic system.

KEY POINTS

• Fluoroscopy during endovascular aortic aneurysm repair can impart a substantial radiation dose. • Radiation doses during EVAR are higher when using mobile/fixed angiographic systems. • Mobile C-arm fluoroscopy imparts a lower dose with an equivalent clinical outcome. • Procedures need to be dose-optimised when using mobile/fixed angiographic systems.