Faculty: Health Sciences And Technology
Department: Radiology


Adejoh, T
Nzotta, C.C


In Anambra State specifically, and in Nigeria as a whole, diagnostic reference levels (DRLs) for CT are not readily available. The aim of the study was therefore, to establish diagnostic reference levels for computed tomography of the human head for the adult population of Anambra State of Nigeria. The design of the study was mixed, with both a prospective and a retrospective cross-sectional components. The survey was undertaken between October 2015 and May 2017 and involved four CT centres, and a head CT population of 1,104 subjects. Formula was used to derive a sample size of 300, comprising 162 male and 138 female digital folders of subjects aged 18 – 93 years. Their images were analyzed in order to establish diagnostic reference levels in Anambra State. The subjects were followed up prospectively as they came into the CT suite and their anthropometric parameters were measured and recorded at the back of their request cards. When they were scanned subsequently, their dose data were stored automatically by the CT scanner on the computer console. These were then retrieved immediately after the scan. Confidentiality of the subjects was maintained by the activation of partial data anonymity features of the scanner. A dose survey sheet was used for data collection. The sheet was designed to extract patient anthropometric characteristics such as age, height weight, and gender. It also allows for collection of information related to imaging parameters such as scan mode, tube potential (kVp), tube current and time (mAs), gantry rotation time, pitch, and slice thickness. To enable head CT dose comparison between centres, only the DLP and CTDIvol of non-contrast scans in centres that performed contrast-enhanced brain CT scans were used. The CT Dose Index volume (CTDIvol) and the Dose-Length-Product (DLP) were also recorded. The total DLP and the mean CTDIvol were used to represent the dose received by each patient. The diagnostic reference levels (DRLs) for the examinations was then calculated based on the mean and 75th percentiles. Whilst the 75th percentile represent the recommended dose values that should not be exceeded, the mean provided dose levels that facilities should strive towards. Effective doses (E) for these examinations were estimated using the k conversion factor as described in the ICRP publication 103 (EDLP= k × DLP), Where k = tissue weighting factor (head: 0.0023). Data was analyzed with the aid of computer software, SPSS version 20.0 (SPSS Incorporated, Chicago, Illinois, USA). Descriptive statistical tools such as frequency, mean, percentages and percentiles were used in the analysis. Pearson’s correlation analysis was also done to establish relationships between dose outputs and measured anthropo-technical parameters. Level of significance was set at p < 0.05. The centre - specific 75th percentile of the dose output had a range of 24 - 94 mGy (CTDIvol) and 337 - 1982 (DLP), respectively. The combined 75th percentile of the CTDIvol and the DLP were 67 mGy and 1500, respectively. A comparison with other local and foreign works showed remarkable variations in dose outputs (2 - 43 %, CTDIvol; 2 – 47 %, DLP). Correlation analyses of DLP with CTDIvol yielded a significant, strong and positive relationship (r = 0.770, p = 0.001), but a weak relationship with other anthropo-technical parameters (r ≤ 0.241, p > 0.05). In conclusion, the diagnostic reference levels for adult head CT scans for Anambra State are 67 mGy and 1500 mGy-cm, respectively. A DRL that is lower than our values is achievable in the locality, if regular dose audits are implemented and sustained

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