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

 

Diserahkan: 14 April 2009 / Diterima: 13 Julai 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

 

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*Pengarang surat-menyurat; email: elayani85@yahoo.com