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1 J. of the Korean Society for Environmental Technology Vol. 19, No. 3, June 18, pp. 218~227 ISSN MRI실의음향성능개선및방음보호구착용을통한 MRI 소음저감대책 장희라 김재수 원광대학교건축공학과 Improvement of Acoustic Performance of MRI Room and Measures to Reduce MRI Noise by Wearing Hearing Protection Device Hee-La Jang Jae-Soo Kim Dept. of Architectural Engineering, Wonkwang University (18 년 2월 7일접수, 4월 2일심사및수정완료, 6월 22일채택 ) Abstract MRI in modern medical science is a technique of imaging by generating a magnetic field to measure and image variation in signals from each tissue and has recently been applied frequently both because of its accuracy and because it does no harm to the human body without radiation exposure. However, MRI causes serious noises while coils move to generate a strong magnetic field and the noises are giving serious physical and psychological distress to the patients. For this reason, various studies are needed to reduce the noises generated from MRI operation; however, South Korea has had very few relevant studies or data. From this perspective, this study analyzed the effectiveness of the methods of increasing the absorption elements within MRI rooms and wearing hearing protection device in reducing noises generated from MRI operation. As a result of the study, the magnetic field strength of.3t was lowered to 6dB(A) only by increasing absorbing power within MRI rooms or wearing hearing protection device. However, good measures should be taken for 1-3T of a magnetic field 6dB(A), which can significantly affect patients. Applying both methods lowered the noise level so that it had no effect on patients with dB(A), with the exception of D Source with 3T for intensity of a magnetic field. Moreover, D Source with dB(A) for 3T is expected to have no significant effect on patients if exposure time is not long. It is expected, therefore, that the efforts to increase absorbing power within MRI rooms and wear hearing protection device will provide a stable examination environment to patients getting an MRI scan. This plan for reducing noises is expected to be useful in developing a measure against noises generated from MRI operation. Keywords : MRI room, MRI operating noise, Noise reduction, Hearing protection device Corresponding author Tel : Fax : soundpro@wku.ac.kr

2 MRI 실의음향성능개선및방음보호구착용을통한 MRI 소음저감대책 219 요지현대의학에쓰이는 MRI(Magnetic Resonance Imaging) 는자기장을발생시켜각조직에서나오는신호의차이를측정하여영상화하는기술로서최근그정확성과방사선에노출되지않아인체에무해하다는장점으로인해많이사용되어지는검사방법이다. 그러나이러한 MRI는강한자기장을발생시키기위해코일이움직이는과정에서매우심각한소음이발생하게되며, 이러한소음으로인해검사를받는환자들에게물리적 심리적고통을주고있다. 따라서 MRI 작동소음저감을위한다양한연구들이필요하나국내의경우아직까지이에대한연구와자료들이매우부족한상황이다. 이러한관점에서본연구에서는 MRI작동소음저감을위해 MRI실내부의흡음요소를증가시키는방법과방음보호구를착용하는방법에따른소음저감효과를분석하였다. 연구결과자기장의세기.3T는내부흡음력증가나방음보호구착용중한가지방법만으로도 6dB(A) 이하로낮아져별다른문제가없었다. 그러나자기장의세기가 1 3T인경우에는대부분 6dB(A) 이상으로나타나환자들에게많은영향을주기때문에적절한대책이필요할것으로판단된다. 따라서 2가지방법을모두사용하면자기장의세기가 3T인 D Source 를제외하고는 dB(A) 로나타나환자에게영향을주지않는정도로소음레벨이낮아졌다. 뿐만아니라 3T의 D Source 의경우도 dB(A) 로나타나폭로시간이길지않을경우환자들에게큰영향을미치지는않을것으로판단된다. 따라서 MRI실내부의흡음력을증가시키고방음보호구를착용할경우 MRI 진료를받는환자들에게안정적인진료환경을제공할수있을것으로판단된다. 이러한소음저감대책방안은향후 MRI 작동소음의저감대책을수립하는데유용한자료로활용될수있을것으로사료된다. 핵심용어 : MRI실, MRI 작동소음, 소음저감, 방음보호구 Ⅰ. 서론 현대의학에쓰이는 MRI(Magnetic Resonance Imaging) 는자기장을발생하는자기공명장치에인체를넣고고주파를발생시켜신체와공명하는데이때나오는신호의차이를측정하여컴퓨터로영상화시키는장치로기존의 X선촬영이나 CT와는달리비전리방사선인고주파를이용하는검사로인체에해가없고, 다양한정보를한번에볼수있다는장점이있어많이사용되어지는의료진단기기이다. 그러나 MRI 는자기장을발생하기위해코일이움직이는과정에서지속적인심각한소음이발생하여검사를받는환자들에게심리적인불안감을주며이로인해검사의정확도도떨어질수있다. 이러한관점에서최근 MRI 작동소음특성및저감을위한연구들이발표되었다. 1,2) 따라서본연구에서는이러한연구자료를토대로 MRI 작동소음저감을위해 MRI실내부의흡음요소를증 가시키는방법과방음보호구를착용하는방법에따른소음저감효과를분석하고자하였으며이러한소음이환자에게어느정도영향을미치는지알아보았다. Ⅱ. MRI 실내부흡음력증가에따른소음저감 2.1. MRI실의개선전 후제원연구대상인 MRI실의제원및장비규격은 Table 1과같고, MRI실내부를모델링한것은 Fig. 1과같다. 또한 MRI실내부의흡음요소증가를위해개선전 후마감재료의변화를나타낸것은 Table 2와같다. Table 2와같이 MRI실내부의변경가능한부위의마감재료를흡음률이높은마감재료인 벽산미네랄울 T 로변경하였다. 이는선행 J. of the Korean Society for Environmental Technology, Vol. 19, No. 3, 18

P1 P1 P1 P1 2 장희라 김재수 Table 1. Specifications and equipment standards of MRI room Division Length(m) 5.3 6. 7.2 1.1 Specifica tions MRI Standard Width(m) 4.4 4.5 5.4 5. Ceiling(m) 2.6 2.8 2.7 2.

Magnetic field area(m) 2. 2.5 2.5 3.9 2.4 3.8 3. 5.2 (a) J (b) I (c) W(1, 2) Fig. 1. Modeling of MRI room. (a) J (b) I (c) W-1 (d) W-2 Fig. 2. Ray-tracing of MRI Room.

따라서본연구에서는음선추적법 (Ray-tracing method) 과허상법 (Image model method) 에의한 3차원컴퓨터시뮬레이션 (Odeon 14.3) 을이용하여음향성능평가지수를분석하였다. 음향시뮬레이션을이용한각 MRI실의음선추적도는 Fig. 2 와같다. 음향시뮬레이션을이용하여개선전 후소음레벨의변화를파악해보면 Table 3과같다.

3 P1 P1 P1 P1 2 장희라 김재수 Table 1. Specifications and equipment standards of MRI room Division Length(m) Specifica tions MRI Standard Width(m) Ceiling(m) Area(m 2 ) Volume(m 3 ) Name of device Hitach AIRIS Ⅱ SIEMENS harmony PHILIPS Intera Achieva PHILIPS Intera Magnetic intensity(t) Magnetic field area(m) (a) J (b) I (c) W(1, 2) Fig. 1. Modeling of MRI room. (a) J (b) I (c) W-1 (d) W-2 Fig. 2. Ray-tracing of MRI Room. 연구 1) 에서 MRI Source 별 NR곡선의등급결정주파수가대부분 1,Hz로나타나이대역의소음을줄이는것이가장효과적이기때문이다 MRI실흡음력증가에따른소음저감 MRI실에서사용되는 MRI 기기는강한자기장을발생시키고있어소음측정장비를반입할경우오작동및파손으로인해현장실험을통한 음향성능평가가불가능하였다. 따라서본연구에서는음선추적법 (Ray-tracing method) 과허상법 (Image model method) 에의한 3차원컴퓨터시뮬레이션 (Odeon 14.3) 을이용하여음향성능평가지수를분석하였다. 음향시뮬레이션을이용한각 MRI실의음선추적도는 Fig. 2 와같다. 음향시뮬레이션을이용하여개선전 후소음레벨의변화를파악해보면 Table 3과같다. Table 3에서추출된소음레벨개선량은음향시뮬레이션을통한개선전 후음압레벨의변화량이다. 따라서이러한개선량을토대로개선전 MRI 작동시발생하는소음레벨과 MRI실내부흡음력을증가시킨후 MRI Source 별소음레벨의변화를파악해보면 Fig. 3과같다. 또한사용된 MRI Sourec 는 WN(MRI 기계의자력과온도유지를위해사용 ), T 1 ( 해부학적정보가필요할경우사용 ), T 2 ( 병리학적정보가필요할경우사용 ), D ( 뇌졸중의진행단계와치유과정을관측하는데사용 ), G( 출혈을진단하는데사용 ) 등 5가지이며본연구에서는 WN Source 는개선전모두 소음의건강보전한계 인 6dB(A) 이하로나타나분석에서제외하였다. 소음이인체에미치는영향은 Table 4와같고, MRI 작동시발생하는소음을이러한기준과비교해보면 Table 5와같다. Table 5를보면마감재료변경을통해내부흡음력증가시자기장의세기가.3T 로가장작은 한국환경기술학회지 ( 논문 ), 제 19 권제 3 호, 18

4 MRI 실의음향성능개선및방음보호구착용을통한 MRI 소음저감대책 221 Table 2. Finishing materials and absorption coefficient data before and after improvement Division Finishing Material Area Frequency(Hz) ( ) k 2k 4k NRC carpet Floor Wood venter on plywood finish Tektum 25T MRI machine Soundproof door Wall Heavy plate glass J furniture Wood venter on plywood finish Plastic illumination plates Ceiling Plywood 12T wood molding Ventilator Floor Vinyl floor tiles Gypsum board painted finish MRI machine Wall Heavy plate glass I Baseboard Soundproof door furniture Gypsum board painted Ceiling finish Ventilator Floor Vinyl floor tiles Before Aluminum sheet panel improvement Sandwich panel Wall MRI machine Soundproof door W-1 Heavy plate glass Nawang Baseboard Sound absorbing plate Ceiling Gypsum board painted finish Ventilator Floor Vinyl floor tiles Wood tailboard Sound absorbing plate Sliced veneer sheet Fabric Sound absorbing plate Wall Aluminum sheet panel MRI machine Nawang Baseboard W-2 Heavy plate glass Soundproof door Sound absorbing plate Fabric Sound absorbing material Ventilator Ceiling Gypsum board painted finish Plastic illumination plates After Byucksan mineral wool 4 MRI Rooms impreovement T : Changing material area J. of the Korean Society for Environmental Technology, Vol. 19, No. 3, 18

5 222 장희라 김재수 Table 3. Amount of improvement of Sound Power Level according to increased internal Absorbing power in MRI room Category SPL (db(a)) Hospital Before After Amount of improvement improvement improvement J I W W Table 4. Effect that noise influences to human body Effect to human body Division 9 Urine quantity increase, Arises hearing difficulty 8 Possible early rupture of water bag 75 Begin to arise hearing loss Peripheral blood vessel contraction, Adrenocortical hormone decrease. 6 Health preservation limit of noise Increased respiratory / pulse rate, decreased depth of sleep (sleeping time 8% longer than 35dB(A) required) Sleep Depth Decrease (35dB(A) % longer sleep time than required) Damage assessment standard Befor improvement Increase absorption power Befor improvement Increase absorption power (a) T 1 sequence (b) T 2 sequence Befor improvement Increase absorption power Befor improvement Increase absorption power (c) Diffusion (d) Gradient Fig. 3. Changes in MRI operating noise according to increased internal absorbing power in MRI room. 한국환경기술학회지 ( 논문 ), 제 19 권제 3 호, 18

MRI 실의음향성능개선및방음보호구착용을통한 MRI 소음저감대책 223 Table 5. Effect in MRI operating noise according to increased internal absorbing power in MRI room Type Hospital T 1 53.7 8.1 65.2 69.9 T 2 56.8 74.6 81.7 86.

Specifications of hearing protection devices Item Ear plugs Ear cover Product name 11 H6A Product Material Polyurethane PVC+ABS Noise reduction rate (NRR) 28dB 21dB J의경우모든 Source 가 6dB(A)

6 MRI 실의음향성능개선및방음보호구착용을통한 MRI 소음저감대책 223 Table 5. Effect in MRI operating noise according to increased internal absorbing power in MRI room Type Hospital T T D G : Noise exceeding 6dB(A), the Health preservation limit of noise Table 6. Specifications of hearing protection devices Item Ear plugs Ear cover Product name 11 H6A Product Material Polyurethane PVC+ABS Noise reduction rate (NRR) 28dB 21dB J의경우모든 Source 가 6dB(A) 보다낮게나타나환자에게영향을미치지않는수준으로나타났다. 그러나자기장의세기가 1T가넘는 I는 dB(A), W-1 는 dB(A), W-2는 dB(A) 로모두소음의건강보전한계를초과하는것으로나타났다. 또한자기장이 3T로가장큰 W-2 의 D Source 는소음저감후에도 94.dB(A) 로 소음량증가, 난청발생 의기준을초과하므로심각한피해를줄것으로판단된다. 따라서 MRI 작동소음을저감하는데 MRI 실내부의흡음요소를증가시키는것만으로는많은한계가있을것으로사료되며, 방음보호구사용과같은보다적극적인대책이필요할것으로사료된다. 보호구를사용시실제소음을통해차음치를평가해야한다. 실제현장에서사용되는방음보호구차음치의적합성평가법은 NIOSH, EPA, OSHA 세가지가있으며 EPA, OSHA 방법의경우계산시안전계수를사용하는데 MRI작동소음의경우장시간고소음에폭로되는작업현장이아니므로본연구에서는안전계수를사용하지않는미국산업안전보건연구원에서제안한 NIOSH 방법을사용하였다. NIOSH 방법은주파수별 MRI작동소음과방음보호구의주파수별차음치를이용한계산방법으로 MRI실에서발생하는소음에대한방음보호구의소음감소율을예측하는데적합할것으로사료된다. Ⅲ. 방음보호구착용에따른소음저감 3.1. 방음보호구의제원및차음성능방음보호구는환자가직접소음을차단할수있는장치로써현재상용화된방음보호구는크게귀마개 귀덮개가있다. 본연구에서는일반적으로많이사용되고있는 3M사의방음보호구를선정하였으며, 방음보호구의대표모델은가장기본적이고대중화되는모델을선정하였다. 방음보호구의제원은 Table 6과같고, 선정된모델의주파수별차음치와표준편차는 Table 7과같다. Table 6과같이방음보호구는제품별소음감소율 (NRR) 을가지고있으며이는제조회사에서명시한실험적인값으로실제현장에서방음 NIOSH Forecast method 1. Measure MRI operating noise. (Refer to previous research 1) ) 2. Obtain the auditory correction A weighted sound level(db(a)) by each frequency correction. 3. Obtain sound insulation difference and standard deviation by each frequency from the protection manufacturer.(see Table 7) 4. Obtain the sound pressure level (db(a)) each frequency when wearing protection device. MRI Operating noise db(a) - Sound insulation difference + (2 standard deviation) 6. Add up the sum of the noise. 7. Calculate the noise reduction rate of the hearing protection device against MRI noise. MRI Operating noise db(a) - Sound pressure level when wearing protection device db(a) J. of the Korean Society for Environmental Technology, Vol. 19, No. 3, 18

7 224 장희라 김재수 Table 7. Sound insulation difference and standard deviation of hearing protection device by frequency Type Ear plugs Ear cover Frequency(Hz) k 2k 4k 8k Average stdev Average stdev Table 8. Noise reduction rate by NIOSH method(db(a)) Hospital Type T Ear T plugs D G Ear cover T T D G Table 9. Effect of MRI operating noise when wearing hearing protection device Hospital Type T Ear T plugs D G Ear cover T T D G : Noise exceeding 6dB(A), the "Health preservation limit of noise" NIOSH 방법을통해계산된방음보호구의소음감소율은 Table 8과같다 방음보호구착용에의한소음영향평가 환자가직접소음을차단할수있는방음보 호구착용을통한 MRI 작동소음의저감량및환자에게미치는영향을평가한것은 Fig. 4, Table 9와같다. Fig. 4, Table 9를보면방음보호구착용을통한소음저감의경우귀덮개보다는외이도를직접막을수있는귀마개의소음저감량이크게나타났다. 또한자기장의세기가.3T로가장작은 J의경우방음보호구사용만으로모든 Source 에서피해판정기준보다낮게나타났다. 그러나자기장의세기가 1T 3T의경우귀마개착용시 dB(A), 귀덮개착용시 dB(A) 로나타나대부분의 Source 가 6dB(A) 이상으로피해판정기준보다높게나타났다. 따라서자기장의세기가.3T인경우방음보호구만으로도환자에게영향을미치지않는정도로소음을저감할수있지만자기장의세기가 1T 이상일경우에는방음보호구착용만으로는한계가있으므로방음보호구착용과함께 MRI실내부흡음력을증가시키는방법을통한대책수립이병행되어야할것으로사료된다. Ⅳ. MRI 실흡음력증가와방음보호구착용에따른소음저감 MRI 작동소음을효과적으로저감하기위해서는 MRI실의내부의흡음력을증가시키는방법과함께동시에방음보호구를착용했을때가장효과가클것으로판단된다. 따라서 2가지방법을모두사용했을경우 MRI작동소음저감량및환자에게미치는영향을평가한것은 한국환경기술학회지 ( 논문 ), 제 19 권제 3 호, 18

8 MRI 실의음향성능개선및방음보호구착용을통한 MRI 소음저감대책 Ear plugs Ear cover Ear plugs + Increase absorption power Ear cover + Increase absorption power (a) T 1 sequence (a) T 1 sequence Ear plugs Ear cover Ear plugs + Increase absorption power Ear cover + Increase absorption power (b) T 2 sequence (b) T 2 sequence Ear plugs Ear cover Ear plugs + Increase absorption power Ear cover + Increase absorption power (c) Diffusion (c) Diffusion Ear plugs Ear cover Ear plugs + Increase absorption power Ear cover + Increase absorption power (d) Gradient Fig. 4. Size of MRI operating noise when wearing an Ear protection device. Fig. 5, Table 1과같다. Fig. 5, Table 1을보면 MRI실내부흡음력을증가시키는방법과함께방음보호구를착용할경우자기장의세기가 1T 3T의경우자 (d) Gradient Fig. 5. Changes in MRI operating noise when using both methods. 기장의세기가가장큰 W-2의 D Source 를제외한모든소음이 dB(A) 로피해판정기준인 6dB(A) 이하로나타나환자에게영향을미치지않는수준으로소음이감소하였 J. of the Korean Society for Environmental Technology, Vol. 19, No. 3, 18

9 226 장희라 김재수 Table 1. Effect of MRI operating noise when using both methods Hospital Type T Ear T plugs D G Ear cover T T D G : Noise exceeding 6dB(A), the "Health preservation limit of noise" 다. 또한 W-2의 D Source 의경우 dB(A) 로높지않은소음레벨과폭로시간이짧아환자에게심각한영향을주지는않을것으로사료된다. 따라서 MRI실내부의흡음요소를증가시키는방법과함께일반적인방음보호구를착용할경우자기장의세기가 3T 미만일때 MRI작동소음이낮아져환자에게영향을주지않는수준으로소음을저감할수있는것으로나타났다. Ⅴ. 결론 본연구는 MRI 작동소음을저감하기위해 MRI실내부의흡음요소를증가시키는방법과방음보호구착용을통한소음저감방안에대해그효과및영향을평가한연구로그결과는다음과같다. 1) MRI 자기장의세기가.3T 인경우 MRI 실내부의흡음력을증가시키는방법이나방음보호구를착용하는방법중한가지만사용할경우 MRI 작동소음이모든 Source 에서 6dB(A) 이하로나타나환자에게영향을주지않고있다. 따라서한가지방법만사용하여도 MRI 작동소음으로인한영향을최소화할수있다. 2) MRI 자기장의세기가 1 3T의경우 MRI 실내부의흡음력을증가시키면 MRI 작동소 음은 dB(A), 귀마개착용은 db(a), 귀덮개착용은 dB(A) 로나타나외이도를직접막을수있는귀마개착용이가장효과적이었다. 그러나 MRI 작동소음이대부분 6dB(A) 이상으로나타나환자에게피해가예상되므로이에대한대책마련이필요하다. 3) MRI 자기장의세기가 1 3T의경우 MRI 작동소음을저감하기위해서 MRI실내부의흡음력증가와방음보호구착용의 2가지방법을동시에사용하면자기장의세기가 3T인 D Source 를제외하고는모두 dB (A) 로나타났다. 또한 D Source 도 dB(A) 로나타나소음레벨이높지않고폭로시간도짧아환자들에게큰영향을주지는않을것으로사료된다. 따라서 MRI작동소음저감을위해 2가지방법을동시에사용할경우환자들에게안정적인진료환경을제공할수있을것으로판단된다. References 1. Jang, H, L., Kim, J, S., The Characteristics and Evaluation of the Noises from MRI Operation at Hospitals, proceeding of the Society of Air-conditioning and Refrigerating Engineers of Korea, SAREK, 13 19, Lee, Y, N., Kim, J, S., Analysis of Acoustic Performance on MRI Room using Acoustic Simulation, proceeding of the Society of Air-conditioning and Refrigerating Engineers of Korea, SAREK, , Kim, J, S.,The Characteristics of Noise Generated at High Noise Workshop, J. of Korean Society of Environmental Technology, 17(4), 362 3, Kim, D, G., Lee, S, Y., Kim, J, S., A Study on the Response Evaluation 한국환경기술학회지 ( 논문 ), 제 19 권제 3 호, 18

10 MRI 실의음향성능개선및방음보호구착용을통한 MRI 소음저감대책 227 comparison which follows Hearing Protective equipment use at Loud Noise Workplace, proceeding of the Korean Society for Noise and Vibration Engineering Annual Conference, KSNVE, , Oh, C. H., Methods and Applications of Magnetic Resonance Imaging, J. of the Korean Magnetics Society, Vol. 6, No. 4, , Lee, N. H., Park, Y. J., Park, Y. S., MRI Noise Reduction using the Repeatability, J. of the Korean Society for Noise and Vibration Engineering, Vol. 13, No. 4, , Cho, Z. H., Park, S. H., Chung, S. T., Analysis of Acoustic Noise in MRI, ISMRM 6th Annual Meeting, Kim, J, S., Architectural Acoustic Design (3rd edition), Sejin Co., , Kim, J, S., Sound and Vibration(4th edition), Sejin Co., 18 7, Vern, O. Kundsen., Cyril, M. Harris., Acoustical Designing in Architecture, John Wiley & Sons, Inc., , M, David. Egan., Concepts in Architectural Acoustics, McGRAW-Hill Book Company, , William, J. Cavanaugh., Joseph, A. Wilks., Architectural Acoustics, JOHN WILEY & SONS.INC, , William, J. Cavanaugh., Joseph, A. Wilks., Architectural Acoustics, JOHN WILEY & SONS.INC, , Lewis H. Bell, Trumbull, Connecticut, Industrial Noise Control, Marcel Dekker, Inc., , J. of the Korean Society for Environmental Technology, Vol. 19, No. 3, 18

19권 2호.hwp

19권 2호.hwp J. of the Korean Society for Environmental Technology Vol. 9, No. 2, April 28, pp. 29~38 ISSN 229-8425 http://dx.doi.org/.265/jkset.9.2.5 흡음요소변경을통한 MRI 실의음향성능개선및변화 장희라 이현재 김재수 원광대학교건축공학과 Hee-La Jang Hyun-Jae