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Influences of RF Transmit Field (B₁+) of Un-shielded Birdcage Coil at 7 Tesla
Phil Heo(허필),Sun Young Chae(채선영),Julius Juhyun Chung(정주현),Jung Hee Lee(이정희) 대한전기학회 2014 정보 및 제어 심포지엄 논문집 Vol.2014 No.10
Despite the effect of radio frequency (RF) shield on the birdcage coil leading to degradation of RF signal sensitivity in the imaging region, RF shield has to be considered for preventing the electro-magnetic field interaction between RF coil and MR scanner. Although the RF shield decreases overall transverse magnetic field (B₁) and RF transmit (B₁+) sensitivity compared to un-shielded volume coil, optimal RF shield configuration and positioning are critical issues in small-animal MR scanner. In this study, we demonstrated that improper positioning of un-shield RF birdcage (BC) coil leads to inhomogeneous B₁ + distribution at 7 Tesla. The flip angle (FA) map and the S-parameter measurement of custom-built 8-leg BC coil were performed when rotating its coil by 5° in the azimuthally angle. The results clearly show that an inhomogeneous FA map was measured in all cases due to the coil-subject interaction and improper positioning of BC coil. The mean valuesfor reference angles at 55°, +100° and + 220° of BC coil were 56.9, 54.5 and 58.3, respectively. Standard deviation (SD) value of for reference angles at 55°, +100° and + 220° of BC coil were measured to be 2.5, 2.7 and 2.3. The differentiation of mean and SD value of rotating angles indicate inhomogeneity and their sensitivity of B₁+ field. The proper positioning of BC coil in the MR scanner is crucial in shielding RF in the small-animal MR scanner.
Phil Heo,Han-Joong Kim,Soobum Kim,Donghyuk Kim,Kyoung-Nam Kim 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.5
In this computational analysis-based study, we proposed an overlapping birdcage (BC) coil with a particular interval distance along the z-axis in order to provide an artificial circular-polarized (CP) magnetic flux (B1) field based on a linear-polarized (LP) B1 field given by two single-channel BC coils. Overlapping BC coils were spaced at a specific overlapping distance in the main magnetic field (B0) direction by two identical BC coils through electromagnetic (EM) calculations and compared with B1 field and pointing vector distribution for the non-overlapping region at 7 Tesla of 297.2 MHz. These results clearly show that, unlike the general method for generating the CP mode using the quadrature driving method, overlapping LP modes that are individually used do not form a perfect CP mode, but instead a quasi-CP mode, in the form of an elliptical-polarized (EP) mode.
적혈구 형광현미경검사로 진단한 적혈구 조혈성 프로토포르피린증
허은필(Eun Phil Heo),이원섭(Won Sup Lee),윤태진(Tae Jin Yoon),김태흥(Tae Heung Kim),김성언(Seong Eon Kim) 대한피부과학회 2002 대한피부과학회지 Vol.40 No.1
Erythropoietic protoporphyria (EPP), caused by decreased activity of the enzyme ferrochelatase, is characterized clinically by burning photosensitivity beginning from childhood, and chemically by excessive amounts of red blood cell protoporphyrins. 1-10% of EPP patients develop potentially fatal protoporphyric hepatic failure. The diagnosis of EPP had been missed in many cases when traditional solvent extraction qualitative screening test was used for blood porphyrins, and use of fluorescence microscopy improved this problem. We report a case of EPP screened by fluorescence microscopy of erythrocytes in a 50-year-old man complaining of photosensitivity. We recommend fluorescence microscopy could be the screening test of choice for the detection of increased red blood cell porphyrins. (Korean J Dermatol 2002;40(1):63~67)
허은필 ( Eun Phil Heo ),민준홍 ( Joon Hong Min ),최종원 ( Chong Won Choi ),이가영 ( Ga Young Lee ),박수홍 ( Soo Hong Park ),김원석 ( Won Serk Kim ),김계정 ( Kea Jeung Kim ) 대한피부과학회 2011 대한피부과학회지 Vol.49 No.10
Background: Scabies is an ectoparasite caused by the mite Sarcoptesscabiei var. hominis, an obligate human parasite. Although the incidence of scabies is decreased nowadays, it is not rare and it is difficult to diagnose without experience. Objective: We conducted this study to evaluate clinical aspects of patients diagnosed with scabies in the last 4 years. Methods: We evaluated 56 patients who were diagnosed with scabies with a skin biopsy or with the mineral oil test. Medical records and telephone-interviews were used for more information. Results: There were 56 scabies patients, 28 males and 28 females. The mean age of the patients was 54 (male; 44.4/ female; 62.9) and 39.3% of patients were over 65 years. The most common affected site was the groin; common cutaneous lesions were pruritic papules and burrow. There was no seasonal variation in occurrence. The majority of suspected routes of infection were unknown but, nosocomial infection and communal living were also major causes. On average, 102 days were required to confirm scabies, which suggests the difficulty in early diagnosis of scabies. Conclusion: We suggest that dermatologists should consider scabies infection in patients who show pruritis that does not improve with ordinary treatment. (Korean J Dermatol 2011;49(10):882∼886)
Aggressive Digital Papillary Adenoma 1 예
허은필(Eun Phil Heo),김지연(Chi Yeon Kim),오지원(Chee Won Oh) 대한피부과학회 2002 대한피부과학회지 Vol.40 No.7
Aggressive digital papillary adenoma is a rare neoplasm of eccrine sweat gland origin. We report a case of aggressive digital papillary adenoma with literature reviews. Pathogenesis of this tumor is unclear but, according to his past history, possible induction by defoliants could not be ruled out. Several immunohistochemical studies were done to confirm tumoral origin and to evaluate histological potential of malignancy.
Acitretin 치료로 호전된 비호지킨 림프종과 병발한 사마귀양 표피이형성증 1 예
허은필(Eun Phil Heo),엄성희(Sung Hee Um),오지원(Chee Won Oh) 대한피부과학회 2002 대한피부과학회지 Vol.40 No.8
Epidermodysplasia verruciformis(EV) is a rare disease characterized by a unique susceptibility to widespread infection with human papilloma virus. It induces flat papular skin lesions, characterized by large vacuolated cells in the upper epithelial layers. We report a patient of EV in association with non-Hodgkins lymphoma(NHL) improved with systemic acitretin treatment. A 69-year-old man presented multiple red flat-topped papules and plaques on his face and upper extremities for 12 years. Past various therapeutic modalities including DPCP sensitization were entirely ineffective. Several years ago, NHL of cervical lymph node was diagnosed. With the treatments with chemotherapy and radiotherapy, he is now in remission state. His skin biopsy specimen showed extensive vacuolation of upper malpighian layer. Bleomycin IL trial showed no response. Only 1 week after oral acitretin administration, his lesions began to exfoliate and became much flatter. Acitretin was effective but not suitable for maintenance therapy.
허은필(Eun Phil Heo),이원섭(Won Sup Lee),오지원(Chee Won Oh) 대한피부과학회 2002 대한피부과학회지 Vol.40 No.5
Subcutancous panniculitie. T-cell lymphoma(SPTCL) is a rare subtype of peripheral T-call lymphoma that clinically and histologically mimies benign panniculids. It represents subeutaneous nodules prdominantly on extremities and turck and himophagoeytic syndromc almost leading to death. Recent reports suggest that cytophagic histocyde pammieulitis(CHP) and SPTCL may span a clinieopathologic spectrum in which there is a natural disease progression from CHP to SPTCL. We reprot a 41-year-old Korean man who prescnted with recurrent tender crythematous subeutancous mokules on the buttock and extremites for 13 years history. There was no hipatosplenomegaly or lymphadenopathy. Laboratory data revealed mild ancmia, lcukopinia, and clevated alanine transterase. Epstein-Barr virus(EBV) scrlolgical values evidenced chronic active infection. His skin biopsy spceimen showed lobular pammiculitis with atypical lymphohistiocytic inflammatory infiloates. The inflammatory infilltrates expressed CK45RO, CD3, CD4, CD8, and CD68, But CD20 and CD56 were negative. In situ hybridizstion studies for the EBV ginome showed megative finding. This case presints SPTCL that had eluded diagnosis for a long time. It also suggests the improtance of comtinued follow-up with repeated biopsy, in case of long course of recurrent tender crythematous nokules and histological lobular lymphocytic pammiculitis.