Uncertainty in computational RF dosimetry

Radio-frequency (RF) electromagnetic field dosimetry studies the absorption of electromagnetic energy inside the human body. The absorbed energy is measured in terms of the specific absorption rate (SAR), which is linked to the possible adverse thermal effects of the exposure to RF electromagnetic fields. With advances in computational power and accurate numerical models of the human anatomy, computational methods have gained an increasingly significant role in RF dosimetry in recent years. Nowadays, the finite-difference time-domain (FDTD) method is the most widely used numerical technique in computational RF dosimetry. Computational analysis of the SAR features many modelling and approximation phases that may introduce error and uncertainty. The emphasis of this thesis is to study how reliably the SAR can be assessed by the FDTD method, and how various modelling choices affect the accuracy of the simulated results. In addition to the SAR, also the temperature rise due to the electromagnetic power absorption and its modelling by the bioheat equation is studied. The results of the thesis help to evaluate and identify the possible uncertainty factors and sources of error in computational RF dosimetry, which will produce new information on the reliability and repeatability of computational exposure assessment. Studying the uncertainty and accuracy of the methods also allows, for example, lessening the computational requirements and improving the accuracy of the simulations

SHARM: Segmented Head Anatomical Reference Models

Reliable segmentation of anatomical tissues of human head is a major step in several clinical applications such as brain mapping, surgery planning and associated computational simulation studies. Segmentation is based on identifying different anatomical structures through labeling different tissues through medical imaging modalities. The segmentation of brain structures is commonly feasible with several remarkable contributions mainly for medical perspective; however, non-brain tissues are of less interest due to anatomical complexity and difficulties to be observed using standard medical imaging protocols. The lack of whole head segmentation methods and unavailability of large human head segmented datasets limiting the variability studies, especially in the computational evaluation of electrical brain stimulation (neuromodulation), human protection from electromagnetic field, and electroencephalography where non-brain tissues are of great importance. To fill this gap, this study provides an open-access Segmented Head Anatomical Reference Models (SHARM) that consists of 196 subjects. These models are segmented into 15 different tissues; skin, fat, muscle, skull cancellous bone, skull cortical bone, brain white matter, brain gray matter, cerebellum white matter, cerebellum gray matter, cerebrospinal fluid, dura, vitreous humor, lens, mucous tissue and blood vessels. The segmented head models are generated using open-access IXI MRI dataset through convolutional neural network structure named ForkNet+. Results indicate a high consistency in statistical characteristics of different tissue distribution in age scale with real measurements. SHARM is expected to be a useful benchmark not only for electromagnetic dosimetry studies but also for different human head segmentation applications

Is activation of the vestibular system by electromagnetic induction a possibility in an MRI context?

In recent years, an increasing number of studies have discussed the mechanisms of vestibular activation in strong magnetic field settings such as occur in a magnetic resonance imaging scanner environment. Amid the different hypotheses, the Lorentz force explanation currently stands out as the most plausible mechanism, as evidenced by activation of the vestibulo‐ocular reflex. Other hypotheses have largely been discarded. Nonetheless, both human data and computational modeling suggest that electromagnetic induction could be a valid mechanism which may coexist alongside the Lorentz force. To further investigate the induction hypothesis, we provide, herein, a first of its kind dosimetric analysis to estimate the induced electric fields at the vestibular system and compare them with what galvanic vestibular stimulation would generate. We found that electric fields strengths from induction match galvanic vestibular stimulation strengths generating vestibular responses. This review examines the evidence in support of electromagnetic induction of vestibular responses, and whether movement‐induced time‐varying magnetic fields should be further considered and investigated

16-17-vuotiaiden suomalaisnuorten puheäänen korkeus

Fundamental frequency (F0) in speech is mainly defined by anatomical and biological factors, but it is also affected by different socio-cultural and behavioral models of voice usage. Unoptimal voice usage models can lead to voice disorders. This research examined the F0 of 16−17-year-old Finnish native speakers in reading and in spontaneous speech. In addition, the F0 in a sustained vowel as well as the reading speed was measured, and the students were asked to evaluate their own F0 on a VAS scale. The results were comparedwith Aino Sallinen-Kuparinen’s (1985) study, which stated that the speakers’ educational background and sex influence their F0.The speaking behaviour of Finnish students seems to have changed during the past 30 years: in the original study, girls attending a vocational school used a higher F0 than girls attending a high school. In addition, the speakers’ sex contributed to some differences in the students’ speaking behaviour. In the present study, neither the educational background nor the speaker’s sex had an effect on the pitch level. The girls’ F0 was 216 Hz in reading and 213 Hz in spontaneous speech. The boys had a low F0 compared to internationalstudies: 101 Hz in reading and 97 Hz in spontaneous speech. Possibly the boys in this age are affected by a social norm, which values a low speaking fundamental frequency. Low F0 was preferred also in the self-evaluation: the majority of the test persons estimated their own F0 to be lower than average.Puheäänen korkeuteen (F0) vaikuttavat anatomisten ja biologisten tekijöiden lisäksi erilaiset sosiokulttuuriset ja behavioraaliset käyttäytymismallit. Äänenkäytön kannalta epäoptimaaliset mallit voivat johtaa jopa äänihäiriöihin. Tutkimus selvitti, mikä on suomea äidinkielenään puhuvien 16–17-vuotiaiden nuorten puheäänen korkeus ääneen luettaessa ja spontaanipuheessa. Lisäksi tutkittavilta mitattiin lukunopeus, F0 vokaalifonaatiossa, ja heiltä kerättiin äänenkorkeuden itsearvio. Tuloksia verrattiin Aino Sallinen-Kuparisen (1985) tutkimukseen, jossa havaittiin puhujien sukupuolen ja koulutustaustan vaikuttavan F0:an. Suomalaisnuorten puhekäyttäytyminen näyttäisi muuttuneen 30 vuodessa: Sallinen-Kuparisen (1985) tutkimuksessa ammattikoulutytöt puhuivat lukiotyttöjä korkeammalta ja sukupuolten välillä esiintyi eri puhetehtävissä eri strategioita, mutta tässä tutkimuksessa koulutustausta tai sukupuoli ei ollut yhteydessä äänenkorkeuden säätelyyn puheessa. Tyttöjen F0 oli luennassa 216 Hz ja spontaanipuheessa 213 Hz. Poikien F0 oli kansainvälisesti verrattuna matala: lukunäytteissä 101 Hz ja spontaanipuheessa 97 Hz. Mahdollisesti poikiin vaikuttaa täysi-ikäisyyden kynnyksellä sosiaalinen normi, joka arvostaa matalan puheäänen käyttöä. Matalaa puheääntä suosittiin myös itsearvioissa: valtaosa tutkittavista arvioi puhekorkeutensa keskivertoa matalammaksi

16-17-vuotiaiden suomalaisnuorten puheäänen korkeus

Puheäänen korkeuteen (F0) vaikuttavat anatomisten ja biologisten tekijöiden lisäksi erilaiset sosiokulttuuriset ja behavioraaliset käyttäytymismallit. Äänenkäytön kannalta epäoptimaaliset mallit voivat johtaa jopa äänihäiriöihin. Tutkimus selvitti, mikä on suomea äidinkielenään puhuvien 16–17-vuotiaiden nuorten puheäänen korkeus ääneen luettaessa ja spontaanipuheessa. Lisäksi tutkittavilta mitattiin lukunopeus, F0 vokaalifonaatiossa, ja heiltä kerättiin äänenkorkeuden itsearvio. Tuloksia verrattiin Aino Sallinen-Kuparisen (1985) tutkimukseen, jossa havaittiin puhujien sukupuolen ja koulutustaustan vaikuttavan F0:an.Suomalaisnuorten puhekäyttäytyminen näyttäisi muuttuneen 30 vuodessa: Sallinen-Kuparisen (1985) tutkimuksessa ammattikoulutytöt puhuivat lukiotyttöjä korkeammalta ja sukupuolten välillä esiintyi eri puhetehtävissä eri strategioita, mutta tässä tutkimuksessa koulutustausta tai sukupuoli ei ollut yhteydessä äänenkorkeuden säätelyyn puheessa. Tyttöjen F0 oli luennassa 216 Hz ja spontaanipuheessa 213 Hz. Poikien F0 oli kansainvälisesti verrattuna matala: lukunäytteissä 101 Hz ja spontaanipuheessa 97 Hz. Mahdollisesti poikiin vaikuttaa täysi-ikäisyyden kynnyksellä sosiaalinen normi, joka arvostaa matalan puheäänen käyttöä. Matalaa puheääntä suosittiin myös itsearvioissa: valtaosa tutkittavista arvioi puhekorkeutensa keskivertoa matalammaksi.</p

A Review of Indocyanine Green Fluorescent Imaging in Surgery

The purpose of this paper is to give an overview of the recent surgical intraoperational applications of indocyanine green fluorescence imaging methods, the basics of the technology, and instrumentation used. Well over 200 papers describing this technique in clinical setting are reviewed. In addition to the surgical applications, other recent medical applications of ICG are briefly examined

Human Exposure to Radiofrequency Energy above 6 GHz: Review of Computational Dosimetry Studies

International guidelines/standards for human protection from electromagnetic fields have been revised recently, especially for frequencies above 6 GHz where new wireless communication systems have been deployed. Above this frequency a new physical quantity "absorbed/epithelia power density" has been adopted as a dose metric. Then, the permissible level of external field strength/power density is derived for practical assessment. In addition, a new physical quantity, fluence or absorbed energy density, is introduced for protection from brief pulses (especially for shorter than 10 sec). These limits were explicitly designed to avoid excessive increases in tissue temperature, based on electromagnetic and thermal modeling studies but supported by experimental data where available. This paper reviews the studies on the computational modeling/dosimetry which are related to the revision of the guidelines/standards. The comparisons with experimental data as well as an analytic solution are also been presented. Future research needs and additional comments on the revision will also be mentioned.Comment: 38 pages, 3 figure

Efficiently searching through large tACS parameter spaces using closed-loop Bayesian optimization.

BACKGROUND: Selecting optimal stimulation parameters from numerous possibilities is a major obstacle for assessing the efficacy of non-invasive brain stimulation. OBJECTIVE: We demonstrate that Bayesian optimization can rapidly search through large parameter spaces and identify subject-level stimulation parameters in real-time. METHODS: To validate the method, Bayesian optimization was employed using participants' binary judgements about the intensity of phosphenes elicited through tACS. RESULTS: We demonstrate the efficiency of Bayesian optimization in identifying parameters that maximize phosphene intensity in a short timeframe (5 min for >190 possibilities). Our results replicate frequency-dependent effects across three montages and show phase-dependent effects of phosphene perception. Computational modelling explains that these phase effects result from constructive/destructive interference of the current reaching the retinas. Simulation analyses demonstrate the method's versatility for complex response functions, even when accounting for noisy observations. CONCLUSION: Alongside subjective ratings, this method can be used to optimize tACS parameters based on behavioral and neural measures and has the potential to be used for tailoring stimulation protocols to individuals

Method for the Intraoperative Detection of IDH Mutation in Gliomas with Differential Mobility Spectrometry

Isocitrate dehydrogenase (IDH) mutation status is an important factor for surgical decision-making: patients with IDH-mutated tumors are more likely to have a good long-term prognosis, and thus favor aggressive resection with more survival benefit to gain. Patients with IDH wild-type tumors have generally poorer prognosis and, therefore, conservative resection to avoid neurological deficit is favored. Current histopathological analysis with frozen sections is unable to identify IDH mutation status intraoperatively, and more advanced methods are therefore needed. We examined a novel method suitable for intraoperative IDH mutation identification that is based on the differential mobility spectrometry (DMS) analysis of the tumor. We prospectively obtained tumor samples from 22 patients, including 11 IDH-mutated and 11 IDH wild-type tumors. The tumors were cut in 88 smaller specimens that were analyzed with DMS. With a linear discriminant analysis (LDA) algorithm, the DMS was able to classify tumor samples with 86% classification accuracy, 86% sensitivity, and 85% specificity. Our results show that DMS is able to differentiate IDH-mutated and IDH wild-type tumors with good accuracy in a setting suitable for intraoperative use, which makes it a promising novel solution for neurosurgical practice.Peer reviewe