LED Goggles Research Articles

Eye lens dose assessment in interventional cardiology

Introduction: Medical professionals performing fluoroscopy guided interventional procedures in cardiology are exposed to a risk of radiation induced cataract, especially if the eye lens dose exceeds the annual dose limit of 20 mSv. Aim: The aim of the current study is to measure the eye lens exposure in three interventional cardiology departments, to analyze the relationship between patient dose and eye lens dose and to study the effectiveness of lead goggles without side protection. Material and methods: Measurements were performed in three departments with participation of 4 interventional cardiologists and 6 nurses. The exposure of the eye lens was measured with EYE-DTM (Radcard) passive dosimeters. Results: For nurses the annual eye lens dose varied from 1.6 mSv to 4.3 mSv. For the interventional cardiologists the results were between 3.2 mSv and 31.4 mSv. The dose reduction factor of the studied safety goggles without side protection is 1 and 1.1. Conclusions: There is a risk of exceeding the annual exposure limit of 20 mSv among interventional cardiologists The eye lens exposure depends on the workload and the clinical complexity of the procedures, as well as on the use of radiation protection devices. Due to the specifics of the procedures, the use of goggles with side protection is recommended. The eye lens dose for nurses is lower than the annual limit, which can be explained with the larger distance between the patient and the nurses and partial shielding by the main operator. Lead glasses without side shielding are not recommended because the exposure occurs from the side.

The practice of radiation protection in an interventional neuroradiology service.

Interventional neuroradiology procedures subject professionals who work in this area to high doses of ionizing radiation, and such exposure leads to a higher chance of occupational diseases related to this physical risk. Radiation protection practices aim to reduce the occurrence of such damage to the health of these workers. To identify how the practice of radiation protection occurs in a multidisciplinary team of an interventional neuroradiology service in the state of Santa Catarina, Brazil. A qualitative, exploratory, and descriptive research conducted with nine health professionals from the multidisciplinary team. Non-participant observation and a survey form were used as data collection techniques. For data analysis, descriptive analysis based on absolute and relative frequency and content analysis were used. Although some practices showed the use of radiation protection measures in practice, such as workers taking turns to perform procedures and continuous use of the lead apron as well as the mobile suspended protection, we found that most of the practices violate the principles of radiation protection. Among these inadequate radiological protection practices, the following aspects were observed: not wearing lead goggles, not using collimation to obtain the image, poor knowledge of the principles of radiation protection and biological effects of ionizing radiation, and non-use of an individual dosimeter. There was a lack of know-how of the multidisciplinary team working in interventional neuroradiology regarding the practice of radiation protection.

Awareness about radiation hazards and knowledge about radiation protection among healthcare personnel: A quaternary care academic center-based study.

Background:The use of medical radiation in diagnosis and procedural and surgical treatment is increasing. Therefore, healthcare personnel should be adequately aware and knowledgeable about radiation hazards to protect themselves and their patients from its adverse effects. The objective of this study was to examine awareness about radiation hazards and knowledge about protection methods among the anesthesia personnel and surgical subspecialists of a quaternary care academic center.Methods:A validated questionnaire was completed by anesthetic personnel and surgical subspecialists. It consisted of questions that required demographic information and assessed awareness about radiation hazards. In addition, 15 multiple-choice questions assessed knowledge about radiation across the following domains: the main principle of radiation protection, personal annual radiation dose, personal protection equipment, safe distance from an X-ray machine, and susceptible organs.Results:A total of 270 potential participants were emailed and invited to respond to an online questionnaire, and the response rate was 79.3%. Of the 214 participants, 69.2% were women; the mean age of the sample was 34.8 years. Most of the participants (63.1%) considered radiation exposure that occurs as a part of daily work to be very harmful; 86.4% and 78.5% reported that they always wore a lead apron and a thyroid shield when working in an environment that entails radiation exposure, respectively. The mean score for knowledge about radiation hazards and protection was 6.4 ± 2.0 (maximum possible score = 15) Therefore, there is a need to improve anesthetic personnel and surgical subspecialists’ knowledge about radiation protection, especially with regard to the use of lead goggles and harmful doses of radiation.Conclusion:The present findings suggest that there is a reasonable level of awareness but a relative lack of knowledge about radiation hazards and protection among anesthesia personnel and surgical subspecialists. Therefore, continuing medical education on radiation hazards and protection must be mandated.

Assessment of orthopedist exposure to occupational doses of radiation in foot and ankle surgeries

Objective: To measure the doses of occupational radiation to which a physician who performs orthopedic surgery of the foot and ankle using a fluoroscopy device is exposed during work and to compare those doses with the values provided in the current legislation and propose measures of radioprotection. Methods: Thermoluminescent dosimetry (TLD) was used to measure radiation in critical target areas (whole-body, lens, thyroid, right and left hands) of the surgeon’s body during all the surgical procedures performed by him between 12/19/2017 and 2/5/2018. From the mean dose values obtained for the procedures, the dose of annual radiation exposure was estimated for each of the regions analyzed and compared with the current legislation. Results: The estimate of the annual radiation dose received by the surgeon to the chest region, above the lead apron, was 5 times higher than that established by the national legislation. However, considering the use of the lead apron, the dose was acceptable. Estimates of equivalent doses for the limbs and thyroid had results within the levels required by the current legislation. The equivalent dose for the lens, on the other hand, was 4 times higher than that established by the legislation. Conclusion: During the workday, the foot and ankle orthopedic surgeon is exposed to doses of radiation higher than those considered acceptable. The data corroborate the need to wear radiological protective clothing, especially a lead apron and goggles. Level of Evidence IV; Prognostic Study; Case Series.

S167. Testing reliability of visual evoked potentials for intraoperative monitoring of visual pathways: A multicenter study

Introduction Unfavorable surgical outcome is a major concern when performing surgery around the visual pathway. Previously documented results on the usefulness of visual evoked potentials (VEPs) for intraoperative neuromonitoring (IONM) indicate their limited utility, mainly due to their instability and variability. We conducted this study at two different Hospitals in Spain, to evaluate the reproducibility of VEPs recording after implementing a number of methodological improvements. Methods Intraoperative VEPs were obtained from 36 eyes in 18 surgeries, including: 11 standard transsphenoidal pituitary surgery (STSS); four extended transsphenoidal surgery (ETSS) with supreasellar craniopharyngioma, sphenoid bone’s sellar region and orbital cavity lesions; and three occipito-parietal gliomas. Surgeries were performed altogether at the Ramon y Cajal University Hospital (Madrid) and Lozano Blesa Clinical University Hospital (Zaragoza). Total intravenous anesthesia (TIVA) with propofol was used in all cases. VEPs were elicited by LED goggle stimulation with stimulus duration of 15–20 ms, intensity of 2–3 cd/s.m-2 and repetition rate from 0.7 Hz to 2.1 Hz. In 17 cases, the recording scalp electrodes were placed at O1-Oz and O2-Oz, using lateral O1 (LO1-Oz) and lateral O2 (LO2-Oz) electrodes (5 cm left of O1 and 5 cm right of O2, respectively). In two cases, VEPs were obtained using subdural recording electrodes placed at the occipital cortex. Band pass filter setting was 1–3 Hz for the high pass filter and 300–1000 Hz for the low pass filter. All anesthetic regimens, and stimulation and recording protocols were the same at both centres. Results Baseline VEPs were obtained prior to first incision in all cases. In all cases, all waveforms were reproducible and remained stable throughout surgery, making it feasible for intraoperative neuromonitoring. A transient decrease in amplitude was noted in two cases. The surgeon was warned and the surgical procedure was temporarily halted, with subsequent VEP improvement in both cases. In the cases with subdural recordings, the reproducibility and stability were the same, but the amplitude of the VEPs was higher. None of the patients had worsening of postoperative visual function. Conclusion With the following mentioned modifications: (1) Total intravenous anesthesia; (2) Additional placing of scalp electrodes (LO1 and LO2); and (3) Montage selection with LO1, O1, O2 and LO2 referred to Oz; we have obtained reproducible and stable VEPs. Based on the results of our study, intraoperative VEPs are reproducible and reliable, and thus, suitable for intraoperative neurophysiological monitoring in surgeries where the visual pathway is at risk.

Measurement of dose reduction factors for X-rays and its relevance in eye lens monitoring applications

Lead (Pb) goggles used by radiation workers while performing fluoroscopy-guided diagnostic and interventional procedures reduce the doses to eye lenses substantially. In majority of the cases, the dosimeter intended to measure eye lens doses is worn close to the eyes but outside the lead (Pb) goggles. In such situations, additional reduction factors are required to approximate the actual doses which eye lens might have received. However, the value of the dose reduction factor (DRF) for a given energy may vary due to the dependence on the methodology of measurement, that is, whether the dose is estimated free-in-air or on a phantom. Due to this reason, the DRFs quoted by suppliers or manufactures cannot be implemented directly for dose estimation. Free-in-air as well as on phantom studies for the measurement of DRFs for lead (Pb) goggles having equivalent thickness of 0.75 mm were performed using optically stimulated luminescence (OSL)-based dosimeters. Measurements were carried out for photon energies having relevance in interventional cardiology (IC) and radiology (IR), and other facilities where eye lens monitoring might be important. It has been found that the DRFs differ substantially for irradiations done free-in-air and on the phantom. The results showed that for X-ray energies relevant to IC/IR procedures, the DRF values were found in the range of ~60–90 and 7–15 for free-in-air and on phantom measurements, respectively. Similarly, the DRF values for N-80 as well as 241Am photons were found to be ~15 and ~3.50 for free-in-air and on phantom measurements, respectively. The difference in the DRF values for free-in-air and on phantom measurements would arise due to the presence of backscattering associated with the phantom studies.

Efficacy of Intraoperative Neurosurgical VEP Monitoring

Visual evoked potential (VEP) had not been seemed to be suitable for intraoperative monitoring because of its long latency and needs for addition. Intraoperative visual VEP monitoring under the recent anesthetic and neurophysiological techniques are examined. Since May 2002, VEP monitorings using LED Goggles (1Hz stimulation) by Neuropack MEB2200 (Nihon Koden Co. Ltd.) were performed in 15 neurosurgical operation including 5 transsphenoidal surgery (3 pituitary adenomas and 2 others) and 10 craniotomy (9 brain tumors and an arterio-venous malformation). Propofol anesthesia was performed in 14 operations and an inhalation. Scalp recording with the screw electrodes were monitored in 13 operations, subdural electrodes for direct cortical recording were used in 4, and both 2 methods were used together in 2 operations. Most P100 wave was stably recorded even in intraoperative monitoring. Shorter latency waves in cortical recording than in scalp recording were seemed to be available in intraoperative VEP. In a transsphenoidal surgery for acromegaly, the shortening of the latency after the tumor resection agreed with postoperative improvement of visual symptoms. Intraoperative VEP monitorings were not successful in 5 among 15 operations. LED Goggles was not suitable for intraoperative use and the special light-stimulator for intraoperative monitoring is now prepared.

Determination of individual stimulus--response curves in the visual cortex.

Activation in the visual cortex is typically studied using group average changes in an on-off paradigm for a single flicker frequency. We used functional magnetic resonance imaging (fMRI) to characterize the stimulus-response curve in the visual cortex as a function of flicker frequency in individual subjects, using LED goggles with 17 frequency steps between 0 and 30 Hz. Ten healthy young individuals were studied on two different occasions (mean interval; 22 days). In all but one subject, a third-order polynomial curve could be fitted to the data. From the response curve we calculated the peak response (the frequency where the response amplitude was maximal), the percentage change (relative difference) of the response amplitudes between 8 Hz and the peak frequency, and the average slope of response (towards the peak). On both occasions we could determine a peak response for each subject with small within-subject variability. The average absolute difference in peak response between both sessions was 1.37 Hz (range, 0.2-4.3 Hz), indicating that the peak frequency is rather stable for a given individual. In conclusion, our study illustrates the ability of fMRI to examine the stimulus-response curve in individual subjects in the visual cortex. Based on our findings, the peak response and the slope of response seem highly reproducible within subjects. A similar analysis of the stimulus-response curve may be applicable to other types of stimuli.

Temporal characteristics of cerebral blood flow velocity changes evoked by short-term visual stimulation

The basis of blood flow sensitive imaging techniques is the activation-flow coupling (AFC), the coupling between neuronal activation and regional cerebral blood flow (rCBF). In functional magnetic resonance imaging (fMRI) experiments investigating brain activation the termination of stimulation can a cause drop of the post-activation signal below the preactivation baseline. The nature of this “undershoot” remains controversial. Hedera et al. propose that “undershoot” is caused by a decreased oxygen content in the venous blood compared with the preactivation level and may reflect increased extraction of oxygen as a result of glycolytic metabolism (1). Functional transcranial Doppler ultrasonography (ffCD) allows to measure the cerebral blood flow velocities (CBFVs) within the basal cerebral arteries in real-time. We used fTCD to assess the temporal characteristics of the regional CBFV change evoked by short-term visual stimulation. Methods: Using a 2 MHz TCD device (Multidop T, DWL Sipplingen, Germany) the velocities within the middle cerebral artery (MCA) and the P2-segment of the posterior cerebral artery (PCA) were investigated simultaneously in a 26 year old female subject. As a visual stimulus we used a 0.1 ms light flash of moderate intensity produced by a LED goggle. The stimulus was repeated 80 times using an randomized interval of 10 to 20 s. The goggle shut tightly. For ffCD analysis data were heart cycle integrated, artifact filtered, normalized and baseline corrected using the AVERAGE software package (2). Results: The first significant (pcO.05) CBFV deviation from baseline level occurred t= 1.4 s after stimulation and peaked at t=3.5 s for the PCA. The maximum change was about 8%. Baseline level was reached 7 s after light flash. The full width at half maximum (FWHM) of the bell shaped blood flow velocity increase within the PCA segment was about 3.2 s. A CBFV reduction (“undershoot”) of about 1.5% (pcO.05) occurred from 7 s to 10 s after stimulation. No significant modulations of the CBFV could be observed within the MCA. Discussion: Functional magnetic resonance imaging based on the BOLD contrast is sensitive to blood flow as well as to blood volume modulations. FTCD is only sensitive to blood flow changes. The present study demonstrates a regional postactivation CBFV decrease within the PCA which most likely reflects a regional postactivation CBF decrease within the stimulated visual areas. The CBFV drop can not be caused by global systemic effects because the CBFV within the MCA remained constant during stimulation. The CBFV time course within the PCA was similar to time course of the BOLD signal found in fMR1 studies using a comparable stimulation (3). Conclusion: The postactivation drop in the BOLD signal below the preactivation baseline seems to reflect a regional postactivation CBF decrease.

Vector analysis of visual evoked potentials elicited by pattern reversal and photic stimuli

Objective: The 2D VEPs to pattern reversal (PR) and LED goggle were studied in order to obtain a stable parameter for the functional assessing of posterior visual pathways regardless of the stimulus type used.Design and methods: Apex c latency, bc segment amplitude (V), and bc vector orientation angle (θ) in voltage space were computed from VEPs recorded in 50 normal human beings and two patients with left posterior brain lesions, in an orthogonal Fpz–Oz and T3–T4 montage and displayed as a two channel Lissajous’ trajectory. The effects of stimulus type and stimulated eye were analyzed in the normal group by a two-way ANOVA.Results: The stimulated eye had no effect on any parameter. Apex c latency was slightly longer, and V was greater and more variable in the responses to goggle stimuli, but there was no significant difference in θ, oriented to mid-occipital scalp with very low variability for both stimulus types. The patients showed significant deviations of θ towards the affected hemisphere.Conclusions: The bc vector orientation (θ) is a stable parameter for the evaluation of the posterior visual pathways using both pattern reversal and LED stimuli, specially the latter, useful in unconscious or uncooperative patients.

VEP's in normal full-term and premature neonates: longitudinal versus cross-sectional data

VEPs have been shown to change with CNS maturation in children, yet few studies had documented maturational changes in the premature infant. Using LED goggles, VEPs were studied in 75 neurologically normal infants of 22–42 weeks gestational age (GA) within the first 3 days of life. Twenty of these (22–32 weeks GA) were also followed longitudinally. The 22–23 week GA neonates had no identifiable waves. In all infants >24 weeks a large negative wave is seen with a latency around 300 msec (N300). After 27 weeks GA a late positive wave was present (P400), but with more variable latency and morphology. Between 30 and 35 weeks GA a small positive wave (P200) was seen in over one-third of the neonates; this component was present in all infants > 36 weeks GA. The consistency of the N300 across the ages studied suggests that it might arise from the basilar dendrites in the visual cortex, which are well developed by 24 weeks GA and undergo relatively little further development between 24 weeks and term. The P200 is suggested to arise from the apical dendrites which develop in the last trimester, explaining the emergence of P200 after 30 weeks GA. The infants followed longitudinally showed the same components, emerging in the same order, but with more rapid development (particularly of P200) compared to the cross-sectional studies. These data suggest that there are differences in the maturation of the visual system in the extrauterine versus intrauterine environment.