No abstract

This paper presents a correction algorithm for metal artefacts in CT images using a novel technique known as dual-step adaptive thresholding (DSAT). The proposed artefact correction algorithm was applied to selected artefactual phantom and clinical CT images. The missing projection data due to metal is detected and extracted by double-thresholding technique. The DSAT-based algorithm allows significant reduction of the artefact and preserves most of the anatomical structures in the corrected CT images.

The concept of diagnostic reference range (DRR) is introduced to address the balance between a patient’s risk (radiation dose) and benefit (image quality necessary for an accurate diagnosis). R provides a minimum estimated dose that covers 25–75% range of dose distribution. The International Commission on Radiological Protection, ICRP (2017) recommended the 75th percentile as the upper d 25th percentile as the lower limit of DRR [1]. Dose below the lower range should compromise accurate interpretation of the image and dose above the upper range may be in excess and need to be reviewed. Meanwhile, Diagnostic Reference Levels (DRLs) are set at the 75th percentile of dose distribution and recommended by ICRP as a guidance to identify any unusual computed tomography (CT) procedures that consistently exceed the established DRLs. The aim of this study was to establish the local DRR for CT scanning based on clinical indications associated to thorax, abdomen, and pelvic regions in adult patients at Department of Radiology, Hospital Universiti Sains Malaysia (HUSM), Kelantan. This study involved a retrospective survey on data of adult patients underwent CT scanning based on 5 most common clinical indications related to thorax, abdomen, and pelvic regions at two departments, Radiology and Trauma Department, HUSM. This study obtained human ethical approval from the university ethical committee (Protocol code: USM/JEPeM/22010025). The CT dose metrics (dose length product, DLP and total DLP) and associated technical factors were collected. Results showed that the five most common clinical indications were cancer staging, coronary artery disease, pulmonary embolism, stones (CTU protocol) and stones (KUB protocol). The DLP values were varied based on their clinical indications and CT scanner types.  Figure 1 shows boxplots representing the DRRs of DLP based on five most common clinical indications associated to CT scans of thorax, abdomen, and pelvic regions for Toshiba and Siemens CT scanners. The highest total DLP values was 4722 mGy.cm observed from CT scanning of cancer staging using Siemens scanner. While the lowest DLP value is 40 mGy.cm for stones scanning using the KUB protocol also using Siemens scanner. The main factor that contributes to higher DLP is the longer scanning length. This study demonstrates that the dose descriptor values, DLP and total DLP were varied for similar anatomical region based on different image quality requirement for each clinical indication. Thus, utilisation of both DRR and DRL are crucial to minimise the unnecessary dose to patient and ensure the optimum image quality is produced by each CT scanning.

The aim of this study was to evaluate the application of monoenergetic (ME) extrapolation technique of dual-energy computed tomography (DECT) for metal artefact reduction using phantom study. This study involved phantom study with a customized phantom consisting different types of metal implant such as titanium and stainless steel. The phantom was scanned using a single-source DECT scanner (SOMATOM Definition AS+, Siemens Healthcare, Germany) with dual-energy mode of 140/80 kV spectrum. The commercially available post-processing software (Syngo DE, Siemens) was applied to generate ME image datasets with different extrapolated energies ranged from 55 to 160 keV. The reduction of artefacts was measured qualitatively and quantitatively using region of interests (ROIs) statistical analysis. The results show 60% of metal streak regions were reduced significantly at higher extrapolated energy which is 160 keV. Quantitative analysis also resulted in lower HU readings within the region of artefact for 160 keV. However, higher extrapolated energy resulted in higher noise and lower signal-to-noise (SNR) value. ME images at 160 keV appear noisier while ME images at 64, 70 and 80 keV appear smoother. Metal artefacts induced by both metal implants were reduced significantly using DECT ME extrapolation and diagnostic quality of CT images also improved. It can be achieved by using higher ME of DECT. However, image noise is higher, and SNR is reduced with higher ME extrapolated energy.

Diagnostic reference range (DRR) were introduced to help manage image quality as well as patient dose by providing minimum estimated dose that covers 25–75% range of dose distribution. The International Commission on Radiological Protection (ICRP) (2017) recommended 75th percentile as upper boundary and 25th percentile as lower boundary of DRR [1]. Dose below the lower range should compromised accurate interpretation of the image and dose above the upper range may be in excess and need to be reviewed. Meanwhile, Diagnostic Reference Levels (DRLs) also recommended by ICRP as a guidance to identify any uncommon high dose delivered by computed tomography (CT) scanner. DRLs are established at 75th percentile of dose distribution and should be implemented at international, regional, or local level for dose management.   This study aims to establish a local DRR based on five most common clinical indications for adult head CT scanning at Department of Radiology, Hospital Universiti Sains Malaysia (HUSM), Kelantan. This study involved a retrospective survey on adult patient data undergone head CT scan with two CT scanners, Toshiba CT scanner at Trauma Department and Siemens CT scanner at Radiology Department, HUSM. The related data regarding the scanning protocols and dose descriptor (dose length product, DLP) were recorded for the most common clinical indication in head CT scans.   Results showed the five most common clinical indication related to head CT scans were abscess, bleeding, stroke, trauma, and tumour. The DLP values were varied based on their clinical indications and CT scanner types.  Figure 1 shows boxplots representing the DRRs of dose length product (DLP) based on the five most common clinical indications in head CT scans for Toshiba and Siemens CT scanners. From the figure, the DLP ranges for Toshiba CT scanner were slightly higher than Siemens CT scanners. The lowest DLP value was observed for tumour indication and the highest DLP was bleeding and trauma indications. Clinical indication that requires higher image resolution and details and longer scan length, recorded higher DLP distribution. This study demonstrates that the dose descriptor values, CTDIvol and DLP were varied for similar anatomical region based on different image quality requirement for each clinical indication. Therefore, DRR and DRL should be established based on specific clinical indication and routine dose audit is essential to ensure patients safety.