Sains Malaysiana 39(2)(2010): 299–303

Pengoptimuman Parameter Dedahan dalam Mamografi Digital Medan Penuh menggunakan Rajah Merit

(Optimization of Exposure Parameters in Full Field Digital  Mammography using Figure of Merit)

Laila Suryani Elias*^,1, Eng May Lin¹, Ang Wee Chin¹, Abd Aziz Tajuddin², Shantini A. Arasaratnam³, Suraya Aziz⁴, Khairul Osman⁵ & Kanaga Kumari Chelliah¹

¹Program Pengimejan Diagnostik dan Radioterapi, Fakulti Sains Kesihatan Bersekutu

Universiti Kebangsaan Malaysia, Jalan Raja Muda Abd Aziz, 50300 Kuala Lumpur, Malaysia

²Pusat Pengajian Sains Fizik, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia

³Jabatan Radiologi, Hospital Kuala Lumpur, Jalan Pahang, 50300, Kuala Lumpur, Malaysia

⁴Jabatan Radiologi, Hospital Universiti Kebangsaan Malaysia

Jalan Yaacub Latif, Bandar Tun Razak, 56000, Cheras, Kuala Lumpur, Malaysia

⁵Program Sains Forensik, Fakulti Sains Kesihatan Bersekutu

Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Malaysia

Received: 14 April 2009 / Accepted: 13 July 2009

ABSTRAK

Mamografi digunakan sebagai alat penskrinan dalam pengesanan awal kanser payudara. Walau bagimanapun, dos radiasi yang digunakan perlulah serendah mungkin bagi meminimumkan sebarang kesan pada wanita asimptomatik di samping mengekalkan kualiti imej bernilai diagnostik memandangkan ia digunakan setiap tahun. Kajian ini dijalankan bagi menentukan parameter dedahan optimum dalam kawalan dedahan automatik (AEC) untuk dua kombinasi anod/penuras iaitu molibdenum/molibdenum (Mo/Mo) dan molibdenum/rhodium (Mo/Rh) menggunakan sistem mamografi digital Lorad Selenia di Klinik Payudara Wanita, Pusat Kebangsaan Kanser Malaysia (NCS). Satu fantom kajian mamografi CIRS012A berketebalan 4 cm dengan 50% kandungan tisu glandular didedahkan pada projeksi kranio-kaudal (cc). TLD 100H telah digunakan untuk mengukur kerma udara kemasukan permukaan (ESAK). Nilai AGD ditentukan daripada nilai ESAK, melibatkan tiga faktor pembetulan (g, c and s) mengikut protokol Euref. Kualiti imej pula dinilai menggunakan nisbah isyarat kepada hingar (SNR) yang diperoleh dari sistem terbabit. Rajah merit (FOM) iaitu nisbah kuasa dua SNR kepada AGD menunjukkan 30 kVp adalah parameter dedahan optimum untuk fantom berketebalan 4 cm menggunakan kombinasi anod/penuras Mo/Rh dan Mo/Mo. Ujian korelasi Spearman tak parametrik menunjukkan hubungan linear negatif antara AGD dan SNR dengan peningkatan nilai voltan tiub untuk kedua-dua kombinasi anod/penuras.

Kata kunci: Dedahan; dos glandular purata; fantom CIRS012A; mamografi digital medan penuh

ABSTRACT

Mammography is used as a screening tool for early detection of breast cancer. However, the radiation dose used should be as low as possible to minimize any effects on asymptomatic woman while maintaining the diagnostic value of the image as mammography is done annually. This study was done to determine the optimum exposure parameter in exposure control mode (AEC) for two combinations of anode/filter which were molybdenum/molybdenum (Mo/Mo) and molybdenum/rhodium (Mo/Rh) using the Lorad Selenia digital mammography system at the Women’s Breast Clinic, National Cancer Society (NCS). A CIRS012A mammography research of phantom 4 cm thickness with 50% glandularity was exposed in the cranio-caudal projection. TLD 100H was used to measure the entrance surface air kerma (ESAK). The AGD values were then calculated from the ESAK values, incorporating three correction factors (g, c and s) according to Euref protocol. Image quality was evaluated using signal to noise ratio (SNR). Figure of Merit (FOM) which is the ratio of the square of SNR to the AGD shows that 30 kVp is the optimum exposure parameter for a 4 cm thickness phantom with the use of Mo/Rh and Mo/Mo anode/filter combination. Non-parametric Spearman correlation test showed a negative linear relationship between AGD and SNR with increasing tube voltage for both anode/filters.

Keywords: Average glandular dose; CIRS012A phantom; exposure; full field digital mammography

REFERENCES

Aichinger, H., Dierker, J., Joite-barfub, S. & Sabel, M. 2004. Radiation Exposure and Image Quality in X-ray Diagnostic Radiology, Physical Principles and Clinical Applications. Berlin Heidelberg: Springer-verlag 91-94.

Baldelli, P., Phelan, N. & Egan, G. 2008. Effect of Anode/Filter Combination on the Dose and Image Quality of a Digital Mammography System Based on an Amorphous Selenium Detector. Digital Mammography 716-723.

Bor, D., Tukel, S., Olgar, T., Toklu, T., Aydin, E. & Akyol, O. 2008. Investigation of mean glandular dose versus compressed breast thickness relationship for mammography. Radiat. Prot. Dosimetry 129(1-3): 160-4.

Burell, H.C., Pinder, S.E., Wilson, A.R., Evans, A.J., Yeoman, L.J., Elston, C.W. & Ellis, I.O. 1996. The positive redictive value of mammographic signs: a review of 425 nonpalpable breast lesions. Clin. Radiol. 51(4): 277-81.

Dance, D.R., Skinner, C.L., Young, K.C., Becktt, J.R. & Kotre, C.J. 2000. Additional factors for the estimation of mean glandular breast dose using UK mammography dosimetry protocol. Phys. Med. Biol. 45(11): 3225-3240.

Gram, I.T., Funkhouser, E. & Tabar, L. 1997. The Tabar classification of mammographic parenchymal patterns. Eur. J. Radiol. 24(2): 131-6.

Harmmerstein, G.R., Miller, D.W., White, D.R., Masterson, M.E., Woodard, H.Q. & Laughlin, J.S. 1979. Absorbed dose in mammography. Radiology 130:485-491.

Hemdal, B., Herrnsdorf, L., Andersson, I., Bengtsson, G., Heddson, B. & Olsson, M. 2005. Average Glandular Dose According to American and European Dose Protocols Using a Sectra MicroDose Mammography Unit. www.rti.se/dealer/downloads/documents/scientific/996icmp2005hemdal.pdf.

Jamal, N., Ng, K. H., McLean, D., Looi, L. M., & Moosa, F. 2004. Mammographic Breast Glandularity in Malaysian Women: Data Derived from Radiography. AJR 182: 713-717.

Kerlikowske, K., Grady, D., Rubin, S.M., Sandrock, C. & Ernster, V.L. 1995. Efficacy of screening mammography: A meta-analysis. J. Am. Med. Assoc. 273(2): 149-54.

Lee, C.H. 2002. Screening mammography:proven benefit, continued controversy. Radiol. Clin. North Am. 49: 395-407.

Letton, A.H., Mason, E.M. & Ramshaw, B.J. 1996. Twenty year review of a breast cancer screening project:ninety-five percent survival of patients with nonpalpable cancers. Cancer 77: 104-106.

Ng, K.H., Jamal, N. & DeWerd, L. 2006. Global quality control perspective for the physical and technical aspects of screen-film mammography-image quality and radiation dose. Radiation Protection Dosimetry 121(4): 445-451.

Radiology Info. 2007. The radiology information resource for patients. Radiological Society of North America, Inc. http://www.radiologyinfo.org/en/info.cfm?pg=mammo&bhcp=1 [21 Ogos 2007].

Tabar, L. & Dean, P. B. 1982. Mammographic parenchymal pattern: risk indicator for breast cancer? J. Am. Med. Assoc. 247: 185-9.

Van Engen, R., Young, K., Bosmans, H. & Thijssen, M. 2003. Addendum on digital mammography to chapter 3 of the European guidelines for quality assurance in mammography screening, Versi 1.0 (Belgium: EUREF).

Williams, M.B., Raghunathan, P., Seibert, A., Kwan, A., Lo, J., Samei, E., Fajardo, L., Maidment, A.D.A., Yaffe, M. & Bloomquist, A. 2006. Beam Optimization for Digital Mammography – II. Digital Mammography 273-280.

*Corresponding author; email: elayani85@yahoo.com