Jeffrey B. Guild

Measurement of group delay dispersion of high numerical aperture objective lenses using two-photon excited fluorescence

We determined the group-delay dispersion (GDD) of five microscope objectives by measuring the second-order autocorrelation at the focal points of the objectives with two-photon excited fluorescence as the power square sensor. We found that typical microscope lens systems introduce significant GDD (2000-6500 fs(2)). The third-order dispersion determined for these objectives limits the minimum obtainable pulse width at the focal point of an objective to 20-30 fs if not compensated. No significant chromatic aberration or higher-order dispersion effects were found for any of the optical components measured within the wavelength range of 700-780 nm and for pulse widths greater than 50-60 fs.

Surgeon education decreases radiation dose in complex endovascular procedures and improves patient safety

OBJECTIVE Complex endovascular procedures such as fenestrated endovascular aneurysm repair (FEVAR) are associated with higher radiation doses compared with other fluoroscopically guided interventions (FGIs). The purpose of this study was to determine whether surgeon education on radiation dose control can lead to lower reference air kerma (RAK) and peak skin dose (PSD) levels in high-dose procedures. METHODS Radiation dose and operating factors were recorded for FGI performed in a hybrid room over a 16-month period. Cases exceeding 6 Gy RAK were investigated according to institutional policy. Information obtained from these investigations led to surgeon education focused on reducing patient dose. Points addressed included increasing table height, utilizing collimation and angulation, decreasing magnification modes, and maintaining minimal patient-to-detector distance. Procedural RAK doses and operating factors were compared 8 months pre- (group A) and 8 months post- (group B) educational intervention using analysis of variance with Tukey pairwise comparisons and t-tests. PSD distributions were calculated using custom software employing input data from fluoroscopic machine logs. RESULTS Of 447 procedures performed, 300 FGIs had sufficient data to be included in the analysis (54% lower extremity, 11% thoracic endovascular aneurysm repair, 10% cerebral, 8% FEVAR, 7% endovascular aneurysm repair, 5% visceral, and 5% embolization). Twenty-one cases were investigated for exceeding 6 Gy RAK. FEVAR comprised 70% of the investigated cases and had a significantly higher median RAK dose compared with all other FGIs (P < .0001). There was no difference in body mass index between groups A and B; however, increasing body mass index was an indicator for increased RAK. PSD calculations were performed for the 122 procedures that focused on the thorax and abdomen (group A, 80 patients; group B, 42 patients). Surgeon education most strongly affected table height, with an average table height elevation of 10 cm per case after education (P < .0001). The dose index (PSD/RAK ratio) was used to track changes in operating practices, and it decreased from 1.14 to 0.79 after education (P < .0001). These changes resulted in an estimated 16% reduction in PSD. There was a trend toward a decrease in patient to detector distance, and the use of collimation increased from 25% to 40% (P < .001) for all cases; however, these did not result in a decrease in PSD. The number of cases that exceeded 6 Gy RAK did not change after education; however, the proportion of non-FEVAR cases that exceeded 6 Gy decreased from 40% to 20%. CONCLUSIONS Surgeon education on the appropriate use of technical factors during FGIs improved operating practice, reduced patient radiation dose, and decreased the number of non-FEVAR cases that exceeded 6 Gy. It is essential that vascular surgeons be educated in best operating practices to lower PSD; nonetheless, FEVAR remains a high-dose procedure.

Radiation-induced skin injury after complex endovascular procedures

BACKGROUND Radiation-induced skin injury is a serious potential complication of fluoroscopically guided interventions. Transient erythema occurs at doses of 2 to 5 Gy, whereas permanent epilation, ulceration, and desquamation are expected at doses above this level. Complex endovascular procedures (CEPs), such as fenestrated endovascular aortic aneurysm repair (FEVAR), are associated with high radiation doses, yet the prevalence of radiation-induced skin injury is unknown. We hypothesized that skin injury after these exposures is likely to be underrecognized and underreported. This study examined the frequency and severity of deterministic effects and evaluated patient characteristics that might predispose to radiation injury in CEP. METHODS CEP was defined as a procedure with a radiation dose ≥5 Gy (National Council on Radiation Protection and Measurements threshold for substantial radiation dose level [SRDL]). Radiation dose and operating factors were recorded for all CEPs performed in a hybrid room during a 30-month period. Patient medical records were retrospectively reviewed for evidence of skin injury. Patients were seen in follow-up daily until discharge and then at weeks 2 and 6, months 3 and 6, and 1 year. Phone interviews were conducted to determine the presence of any skin-related complaints. Peak skin dose (PSD) distributions were calculated for FEVARs with custom software employing input data from fluoroscopic machine logs. These calculations were validated against Gafchromic film (Ashland Inc, Covington, Ky) measurements. Dose was summed for the subset of patients with multiple procedures within 6 months of the SRDL event, consistent with Joint Commission recommendations. RESULTS Sixty-one CEPs reached a reference air kerma (RAK) of 5 Gy (50 FEVARs, six embolizations, one thoracic endovascular aortic repair, one endovascular aneurysm repair, one carotid intervention, and two visceral interventions). The patient cohort was 79% male and had a mean body mass index of 31. The average RAK was 8 ± 2 Gy (5.0-15.9 Gy). Sixteen patients had multiple CEPs within 6 months of the SRDL event, with a mean cumulative RAK of 12 ± 3 Gy (7.0-18.4 Gy). The mean FEVAR PSD was 6.6 ± 3.6 Gy (3.7-17.8 Gy), with a mean PSD/RAK ratio of 0.78. Gafchromic film dose measurements were not statistically different from PSD estimations, with a constant of proportionality of 0.99. Three patients were lost to follow-up before their first postoperative visit. No radiation skin injuries were found. CONCLUSIONS This study represents the largest analysis of deterministic skin injury after CEPs, and our results suggest that it is less frequent than expected and not increased in CEPs.

Deterministic effects after fenestrated endovascular aortic aneurysm repair.

BACKGROUND Endovascular aortic aneurysm repairs (EVARs) with fenestrated (FEVAR) stent grafts are high radiation dose cases, yet no skin injuries were found retrospectively in our 61 cases with a mean peak skin dose (PSD) of 6.8 Gy. We hypothesize that skin injury is under-reported. This study examined deterministic effects in FEVARs after procedural changes implemented to detect skin injury. METHODS All FEVARs during a 6-month period with a radiation dose of 5 Gy reference air kerma (RAK; National Council on Radiation Protection and Measurements threshold for substantial radiation dose level [SRDL]) were included. Patients were questioned about skin erythema, epilation, and necrosis, with a physical examination of the back completed daily until discharge and then at 2 and 4 weeks and at 3 and 6 months. PSD distributions were calculated with custom software using input data from fluoroscopic machine logs. These calculations have been validated against Gafchromic (Ashland Inc, Covington, Ky) film measurements. Dose was summed for the subset of patients with multiple procedures ≤6 months of the SRDL event, consistent with the joint commission recommendations. RESULTS Twenty-two patients, 21 FEVARs and one embolization, reached an RAK of 5 Gy. The embolization procedure was excluded from review. The average RAK was 7.6 ± 2.0 Gy (range, 5.1-11.4 Gy), with a mean PSD of 4.8 ± 2.0 Gy (range, 2.3-10.4 Gy). Fifty-two percent of patients had multiple endovascular procedures ≤6 months of the SRDL event. The mean RAK for this subset was 10.0 ± 2.9 Gy (range, 5.5-15.1 Gy), with a mean PSD of 6.6 ± 1.9 Gy (range, 3.4-9.4 Gy). One patient died before the first postoperative visit. No radiation skin injuries were found. Putative risk factors for skin injury were evaluated and included smoking (32%), diabetes (14%), cytotoxic drugs (9%), and fair skin type (91%). No other risk factors were present (hyperthyroidism, collagen vascular disorders). CONCLUSIONS Deterministic skin injuries are uncommon after FEVAR, even at high RAK levels, regardless of cumulative dose effects. This study addresses the concern of missed injuries based on the retrospective clinical examination findings that were published in our previous work. Even with more comprehensive postoperative skin examinations and patient questioning, the fact that no skin injuries were found suggests that radiation-induced skin injuries are multifactorial and not solely dose dependent.

Surgeon radiation dose during complex endovascular procedures

BACKGROUND Surgeon radiation dose during complex fluoroscopically guided interventions (FGIs) has not been well studied. We sought to characterize radiation exposure to surgeons during FGIs based on procedure type, operator position, level of operator training, upper vs lower body exposure, and addition of protective shielding. METHODS Optically stimulable, luminescent nanoDot (Landauer, Inc, Glenwood, Ill) detectors were used to measure radiation dose prospectively to surgeons during FGIs. The nanoDot dosimeters were placed outside the lead apron of the primary and assistant operators at the left upper chest and left lower pelvis positions. For each case, the procedure type, the reference air kerma, the kerma-area product, the relative position of the operator, the level of training of the fellow, and the presence or absence of external additional shielding devices were recorded. Three positions were assigned on the right-hand side of the patient in decreasing relative proximity to the flat panel detector (A, B, and C, respectively). Position A (main operator) was closest to the flat panel detector. Position D was on the left side of the patient at the brachial access site. The nanoDots were read using a microSTARii medical dosimetry system (Landauer, Inc) after every procedure. The nanoDot dosimetry system was calibrated for scattered radiation in an endovascular suite with a National Institute of Standards and Technology traceable solid-state radiation detector (Piranha T20; RTI Electronics, Fairfield, NJ). Comparative statistical analysis of nanoDot dose levels between categories was performed by analysis of variance with Tukey pairwise comparisons. Bonferroni correction was used for multiple comparisons. RESULTS There were 415 nanoDot measurements with the following case distribution: 16 thoracic endovascular aortic repairs/endovascular aneurysm repairs, 18 fenestrated endovascular aneurysm repairs (FEVARs), 13 embolizations, 41 lower extremity interventions, 10 fistulograms, 13 visceral interventions, and 3 cerebrovascular procedures. The mean operator effective dose for FEVARs was higher than for other case types (P < .03), 20 μSv at position A and 9 μSv at position B. For all case types, position A (9.0 μSv) and position D (20 μSv) received statistically higher effective doses than position B (4 μSv) or position C (0.4 μSv) (P < .001). However, the mean operator effective dose for position D was not statistically different from that for position A. The addition of the lead skirt significantly decreased the lower body dose (33 ± 3.4 μSv to 6.3 ± 3.3 μSv) but not the upper body dose (6.5 ± 3.3 μSv to 5.7 ± 2.2 μSv). Neither ceiling-mounted shielding nor level of fellow training affected operator dose. CONCLUSIONS Surgeon radiation dose during FGIs depends on case type, operator position, and table skirt use but not on the level of fellow training. On the basis of these data, the primary operator could perform approximately 12 FEVARs/wk and have an annual dose <10 mSv, which would not exceed lifetime occupational dose limits during a 35-year career. With practical case loads, operator doses are relatively low and unlikely to exceed occupational limits.

The Number of Voiding Radiographs During Cystourethrography in Women With Stress Incontinence or Prolapse Can Be Reduced to Enhance Safety Without Compromising Study Interpretation

Based on a prior study, over 60% of the average radiation dose per cystourethrography (CU) originated from lateral radiograph images (RI). This analysis focuses on the feasibility of decreasing the number of RI without compromising study interpretation.

An iterative deconvolution algorithm for image recovery in clinical CT: A phantom study.

PURPOSE To study the feasibility of using an iterative reconstruction algorithm to improve previously reconstructed CT images which are judged to be non-diagnostic on clinical review. A novel rapidly converging, iterative algorithm (RSEMD) to reduce noise as compared with standard filtered back-projection algorithm has been developed. MATERIALS AND METHODS The RSEMD method was tested on in-silico, Catphan(®)500, and anthropomorphic 4D XCAT phantoms. The method was applied to noisy CT images previously reconstructed with FBP to determine improvements in SNR and CNR. To test the potential improvement in clinically relevant CT images, 4D XCAT phantom images were used to simulate a small, low contrast lesion placed in the liver. RESULTS In all of the phantom studies the images proved to have higher resolution and lower noise as compared with images reconstructed by conventional FBP. In general, the values of SNR and CNR reached a plateau at around 20 iterations with an improvement factor of about 1.5 for in noisy CT images. Improvements in lesion conspicuity after the application of RSEMD have also been demonstrated. The results obtained with the RSEMD method are in agreement with other iterative algorithms employed either in image space or with hybrid reconstruction algorithms. CONCLUSIONS In this proof of concept work, a rapidly converging, iterative deconvolution algorithm with a novel resolution subsets-based approach that operates on DICOM CT images has been demonstrated. The RSEMD method can be applied to sub-optimal routine-dose clinical CT images to improve image quality to potentially diagnostically acceptable levels.

Fluoroscopic Sentinel Events in Neuroendovascular Procedures: How to Screen, Prevent, and Address Occurrence

SUMMARY: Radiation-induced skin injury during fluoroscopic procedures has been recently addressed by The Joint Commission, which defined prolonged fluoroscopy resulting in a cumulative peak skin dose of ≥15 Gy to a single field as a sentinel event (FSE). Neuroendovascular procedures can be associated with a high radiation skin dose and present risks such as potential FSEs. Managing these risks is the responsibility of the interventional neuroradiologist. In this review, we discuss hospital policies needed for screening and preventing FSEs, methods for minimizing radiation-induced skin injury, and actions necessary to address potential FSEs once they have occurred.

Evaluation of fluoroscopic cases qualifying as potential fluoroscopic sentinel events.

RATIONALE AND OBJECTIVES To address the risk of radiation injury during interventional procedures, the Joint Commission has defined prolonged fluoroscopy resulting in a cumulative skin dose of 15 Gy or more to a single field as a reviewable sentinel event. The goal of this work is to present a system for identifying potential fluoroscopic sentinel events (FSE) and describing common case characteristics. MATERIALS AND METHODS Criteria based on fluoroscopic time (FT) > 150 minutes and reference air kerma (RAK) > 6 Gy were used to identify potential sentinel events. Case information including procedure type, number of procedures, and radiation dose parameters was recorded. Peak skin dose (PSD) was calculated by a medical physicist. Values were compared between procedure types and the relationship between FT, RAK, and PSD was evaluated. RESULTS Between 2008 and 2011, 183 events exceeding the investigation criteria were identified in three interventional categories: cardiology (54%), neuroradiology (31%), and vascular (16%). The average number of procedures/patient was 1.7 ± 0.1, with the majority (59.6%) having undergone only one procedure. Most cases could be identified using the RAK criterion alone (96.7%). Based on the PSD/RAK ratio, a threshold RAK of 7.5 Gy would effectively identify all cases that would exceed 15 Gy in PSD. CONCLUSION Radiation delivered during interventional cases can place patients at risk of cutaneous radiation injury and potential sentinel events. Using appropriate thresholds to determine which cases require detailed investigation allows efficient utilization of department resources for identifying sentinel events.

TU‐A‐202‐01: Peak Skin Dose Reconstruction and TJC Sentinel Event

In 2005, the Joint Commission established a new reviewable Sentinel Event tied to radiation exposure. Proper identification and investigation of Sentinel Events are critical issues for maintaining Joint Commission accreditation of a hospital, mandating that the physicist correctly approach this problem. The newly defined sentinel event treats both radiotherapy and fluoroscopy, but we consider only the issues arising from the specific inclusion of prolonged fluoroscopy procedures that result in high (> 1500 rads) cumulative skindoses. The specific details of what constitutes the fluoroscopic Sentinel Event, mechanisms for detecting potential events, how to investigate an event, and what happens in the course of reviewing a Sentinel Event are addressed. The air kerma monitors required by the FDA on fluoroscopic equipment manufactured since 2006 are very useful tools for dose determination in these cases, but they do not provide a direct or complete answer. Case studies are reviewed that illustrate how to estimate doses both with and without cumulative air kerma readings. Learning Objectives: 1. Review the definitions of the new Joint Commission Sentinel Event for fluoroscopic radiation exposure. 2. Identify monitoring policies and procedures to detect potential fluoroscopic Sentinel Events. 3. Discuss practical aspects and pitfalls of using air kerma monitors and technique values to calculate maximum skindoses.