Sains Malaysiana 45(10)(2016): 1525–1530

 

Optimization of Number of Scans for a Sparse Temporal Sampling (STS) Functional Magnetic Resonance Imaging (fMRI)

(Pengoptimuman Bilangan Imbasan untuk Pengimejan Resonans Magnet Kefungsian (fMRI) Pensampelan Temporal Berjarak (STS))

AHMAD NAZLIM YUSOFF¹*, KHAIRIAH ABDUL HAMID², HAMDI HAMZAH³, MAZLYFARINA MOHAMAD¹, SITI ZAMRATOL-MAI SARAH MUKARI^4,5 & WAN AHMAD KAMIL WAN ABDULLAH⁶

 

¹Diagnostic Imaging & Radiotherapy Program, School of Diagnostic and Applied Health Sciences

Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Malaysia

 

²Medical Imaging Department, School of Health Sciences,  KPJ University College

Lot PT 17010, Persiaran Seriemas, Kota Seriemas, 71800 Nilai, Negeri Sembilan, Malaysia

 

³KPJ Ipoh Specialist Hospital, 26, Jalan Raja Dihilir, 30350 Ipoh, Perak Darul Ridzuan

Malaysia

 

⁴Audiology Program, School of Rehabilitation Sciences, Faculty of Health Sciences

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

 

⁵Institute of Ear, Hearing and Speech, Faculty of Health Science, Universiti Kebangsaan Malaysia, Jalan Temerloh, 53200 Kuala Lumpur, Malaysia

 

⁶Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan Darul Naim, Malaysia

 

Received: 8 October 2015/Accepted: 19 February 2016

 

ABSTRACT

High sensitivity signal detection for a sparse temporal sampling (STS) functional magnetic resonance imaging (fMRI) is compensated by the increase in the number of scans (Ns) and consequently the scan time. A long scan time would result in fatigue and restlessness in participants, while a short scan time is undesirable for an STS-fMRI due to insufficient Ns for averaging. The purpose of this study was to determine the Ns practically sufficient for a sparse fMRI study. Eighteen participants were presented with white noise during a sparse fMRI scan. The height extent of activation was determined via t statistics and region of interest (ROI) based percentage of signal change (PSC). The t statistics and PSC for Heschl’s gyrus (HG) and superior temporal gyrus (STG) during which the participants listened to the white noise were calculated for different number of scans which were 6, 12, 18, 24, 30 and 36. The t statistics and PSC values calculated for the bilateral HG and STG qualitatively indicated a minimal change over Ns = 12 to 36. Both ROIs showed a consistent common right lateralization of activation for all Ns, indicating the right-hemispheric dominance of auditory cortex in processing white noise stimulus. It was proposed that for a sparse fMRI study, Ns may practically fall between 12 and 36.

 

Keywords: Auditory cortex; functional MRI; percentage of signal change; SPM; t statistics

 

ABSTRAK

Pengesanan isyarat berkepekaan tinggi bagi pengimejan resonans magnet kefungsian (fMRI) pensampelan temporal berjarak (STS) dipampas oleh peningkatan bilangan imbasan (Ns) dan seterusnya masa imbasan. Masa imbasan yang lama boleh mengakibatkan kelesuan dan resah gelisah dalam diri pesakit, manakala masa imbasan yang singkat tidak diterima dalam STS-fMRI disebabkan bilangan Ns yang tidak mencukupi untuk pemurataan. Tujuan kajian ini adalah untuk menentukan Ns yang secara praktiknya mencukupi untuk kajian fMRI berjarak. Lapan belas peserta kajian diperdengarkan bunyi hingar putih semasa imbasan fMRI berjarak. Takat tinggi pengaktifan ditentukan melalui statistik t dan peratus perubahan isyarat (PSC) berasaskan kawasan diminati (ROI). Statistik t dan PSC untuk girus Heschl (HG) dan girus temporal superior (STG) semasa peserta kajian mendengar hingar putih dihitung untuk bilangan imbasan berbeza iaitu 6, 12, 18, 24, 30 dan 36. Statistik t dan PSC yang dihitung untuk HG dan STG bilateral secara kualitatif menunjukkan perubahan minimum merentasi Ns = 12 ke 36. Kedua-dua ROI memperlihatkan pengaktifan lateralisasi kanan biasa yang tekal untuk semua Ns, menunjukkan kedominanan hemisfera kanan bagi korteks auditori dalam memproses stimulus hingar putih. Dicadangkan bahawa untuk kajian fMRI berjarak, Ns secara praktiknya boleh mengambil nilai antara 12 dan 36.

 

Kata kunci: Korteks auditori; MRI kefungsian; peratus perubahan isyarat; SPM; statistik t

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*Corresponding author; email: nazlimtrw@ukm.edu.my