{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T14:19:14Z","timestamp":1788272354861,"version":"build-2803163510"},"reference-count":31,"publisher":"Wiley","issue":"8","license":[{"start":{"date-parts":[[2026,8,6]],"date-time":"2026-08-06T00:00:00Z","timestamp":1785974400000},"content-version":"vor","delay-in-days":5,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"},{"start":{"date-parts":[[2026,8,1]],"date-time":"2026-08-01T00:00:00Z","timestamp":1785542400000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/doi.wiley.com\/10.1002\/tdm_license_1.1"}],"funder":[{"DOI":"10.13039\/501100002597","name":"Kyung Hee University","doi-asserted-by":"publisher","award":["20242243"],"award-info":[{"award-number":["20242243"]}],"id":[{"id":"10.13039\/501100002597","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001321","name":"National Research Foundation","doi-asserted-by":"publisher","award":["RS\u20102023\u201000264160"],"award-info":[{"award-number":["RS\u20102023\u201000264160"]}],"id":[{"id":"10.13039\/501100001321","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001321","name":"National Research Foundation","doi-asserted-by":"publisher","award":["RS\u20102026\u201025481820"],"award-info":[{"award-number":["RS\u20102026\u201025481820"]}],"id":[{"id":"10.13039\/501100001321","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["aapm.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Medical Physics"],"published-print":{"date-parts":[[2026,8]]},"abstract":"Abstract<\/jats:title>\n \n Background<\/jats:title>\n \n Transcranial magnetic resonance\u2010guided focused ultrasound (tcMRgFUS) allows precise focal heating under magnetic resonance imaging (MRI) guidance for neurological therapies. However, large hemispherical transducers inherently affect the transmit radiofrequency (RF) field (|B\n 1<\/jats:sub>\n +<\/jats:sup>\n |) inhomogeneity, producing dark\/black\u2010band artifacts owing to general electromagnetic (EM) field interactions.\n <\/jats:p>\n <\/jats:sec>\n \n Purpose<\/jats:title>\n \n As the position and orientation of the transducer vary in practice, we assessed the effects of such changes on the |B\n 1<\/jats:sub>\n +<\/jats:sup>\n | field and specific absorption rate (SAR). We compared relative variations across realistic configurations to identify clinically meaningful trends.\n <\/jats:p>\n <\/jats:sec>\n \n Methods<\/jats:title>\n \n Three\u2010dimensional (3D) finite\u2010difference time\u2010domain simulations were performed using Sim4Life (v7.2.1, ZMT, Z\u00fcrich, Switzerland). The simulation model comprised a 16\u2010leg high\u2010pass birdcage RF coil matched to a standard clinical 3T whole\u2010body scanner (bore diameter: 600\u00a0mm), a generic hemispherical tcMRgFUS system (transducer and water bolus), and a Duke human model. A spatial voxel mesh was applied with a maximum size of 2\u00d72\u00d72 mm\n 3<\/jats:sup>\n for the RF coil, tcMRgFUS system, and the head region of the human model, yielding approximately 43 to 48 million mesh cells per configuration. Transducer translations (lateral:\u00a0\u00b1\u00a040\u00a0mm, vertical:\u00a0\u00b1\u00a040\u00a0mm, longitudinal: \u221210 to +20\u00a0mm) and rotations (\u221250\u00b0 to +10\u00b0) were simulated across 85 configurations (78 translations, and 7 rotations). The peak spatial SAR averaged over 10\u00a0g (\n ps<\/jats:sub>\n SAR\n 10g<\/jats:sub>\n ), head\u2010averaged SAR (\n hd<\/jats:sub>\n SAR), and |B\n 1<\/jats:sub>\n +<\/jats:sup>\n |\u2010field distributions were computed and normalized to 1\u00a0W input power to quantitatively assess the impact of the modeled positioning configurations within the investigated parameter space.\n <\/jats:p>\n <\/jats:sec>\n \n Results<\/jats:title>\n \n Lateral and vertical translations (\u00b1\u00a0x and\u00a0\u00b1\u00a0y) that brought the transducer closer to the head intensified EM coupling between the RF coil and the transducer, increasing |B\n 1<\/jats:sub>\n +<\/jats:sup>\n | inhomogeneity, whereas +z translation similarly strengthened this coupling by concentrating its EM influence over a smaller cranial volume. In contrast, \u2010z translation spread dark\u2010band artifacts more uniformly across the head, paradoxically improving homogeneity despite a lower spatially averaged |B\n 1<\/jats:sub>\n +<\/jats:sup>\n |\u2010field. Across all translation configurations, 3D |B\n 1<\/jats:sub>\n +<\/jats:sup>\n | homogeneity and mean intensity decreased by up to 3.26% and 0.004 \u00b5T, respectively, whereas rotational changes produced reductions of up to 8.53% and 0.03 \u00b5T. In terms of RF safety, the presence of the transducer increased\n ps<\/jats:sub>\n SAR\n 10g<\/jats:sub>\n by 15.79% (from 0.0646 to 0.0748\u00a0W\/kg) and\n hd<\/jats:sub>\n SAR by 77.42% (from 0.0186 to 0.033\u00a0W\/kg). Among positional changes,\n ps<\/jats:sub>\n SAR\n 10g<\/jats:sub>\n and\n hd<\/jats:sub>\n SAR increased by up to 0.04\u00a0W\/kg at a lateral translation of (40, 0, 0) mm and 0.009\u00a0W\/kg at a rotation of \u221250\u00b0, respectively. These findings indicate that both the extent of head inclusion within tcMRgFUS and the transducer\u2013head distance should be actively managed to minimize |B\n 1<\/jats:sub>\n +<\/jats:sup>\n | perturbation and associated SAR increases.\n <\/jats:p>\n <\/jats:sec>\n \n Conclusions<\/jats:title>\n \n These results demonstrate that transducer position and angle substantially affect |B\n 1<\/jats:sub>\n +<\/jats:sup>\n | homogeneity and\n ps<\/jats:sub>\n SAR\n 10g<\/jats:sub>\n , with direct implications for system performance and safety. These simulation\u2010based findings highlight that the extent of head inclusion within tcMRgFUS and the transducer\u2013head distance are key factors governing EM field perturbation and RF safety. Therefore, accounting for positional and angular variability is essential for the setup and operation of tcMRgFUS systems, and the relative trends identified provide a basis for informing clinical positioning protocols and evaluation frameworks.\n <\/jats:p>\n <\/jats:sec>","DOI":"10.1002\/mp.70631","type":"journal-article","created":{"date-parts":[[2026,8,7]],"date-time":"2026-08-07T05:22:33Z","timestamp":1786080153000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Impact of transducer position on B\n 1<\/sub>\n +<\/sup>\n homogeneity and RF safety in transcranial MR\u2010guided focused ultrasound: An electromagnetic simulation study"],"prefix":"10.1002","volume":"53","author":[{"given":"Eunwoo","family":"Lee","sequence":"first","affiliation":[{"name":"Department of Health Sciences and Technology, GAIHST Gachon University Incheon South Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Taewoo","family":"Nam","sequence":"additional","affiliation":[{"name":"Department of Health Sciences and Technology, GAIHST Gachon University Incheon South Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Daniel","family":"Hernandez","sequence":"additional","affiliation":[{"name":"Neuroscience Research Institute Gachon University Incheon South Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kisoo","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering Kyung Hee University Yongin South Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kyoung\u2010Nam","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of Health Sciences and Technology, GAIHST Gachon University Incheon South Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2026,8,6]]},"reference":[{"key":"e_1_2_8_2_1","doi-asserted-by":"publisher","DOI":"10.1038\/s41582\u2010020\u201000418\u2010z"},{"key":"e_1_2_8_3_1","doi-asserted-by":"publisher","DOI":"10.3174\/ajnr.a8038"},{"key":"e_1_2_8_4_1","unstructured":"GandhiD Clinical trial for MR guided focused ultrasound (FUS) thalamotomy of central lateral thalamic nucleus for the treatment of medication\u2010refractory trigeminal neuralgia.Clinicaltrials.gov; August 08 2020.https:\/\/clinicaltrials.gov\/ct2\/show\/NCT04579692"},{"key":"e_1_2_8_5_1","unstructured":"InSightec.Blood\u2010brain barrier (BBB)disruption using Exablate focused ultrasound during the standard of CareTreatment of brain metastases of non\u2010small cell lung cancer (NSCLC) origin.Clinicaltrialsgov; August 12 2022.https:\/\/clinicaltrials.gov\/ct2\/show\/NCT05317858"},{"key":"e_1_2_8_6_1","doi-asserted-by":"publisher","DOI":"10.1007\/s11060\u2010021\u201003807\u20106"},{"key":"e_1_2_8_7_1","unstructured":"GoodmanW Baylor College of Medicine \u201cClinicaltrials.gov; May 31 2023. 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