Many different artefacts can occur during magnetic resonance imaging (MRI), some affecting the diagnostic quality, while others may be confused with pathology. An artefact is a feature appearing in an image that is not present in the original object. Artefacts can be classified as patientrelated, signal processing-dependent and hardware (machine)-related. This article presents an overview of MRI artefacts and possible rectifying methods. IntroductionArtefacts remain a problematic in magnetic resonance imaging (MRI). Some affect the quality of the examination, while others may be confused with pathology.An artefact is a feature appearing in an image that is not present in the original object. Depending on their origin, artefacts are typically classified as patient-related, signal processingdependent and hardware (machine)-related.It is important to recognise these artefacts and have a basic understanding of their origin, especially those mimicking pathology. In this article emphasis is placed on recognition of artefacts and possible rectifying methods. Patient-related MR artefacts Motion artefactsMotion is one of the most common artefacts in MR imaging, causing either ghost images or diffuse image noise in the phase-encoding direction. The reason for mainly affecting data sampling in the phase-encoding direction is the significant difference in the time of acquisition in the frequency-and phase-encoding directions. Frequency-encoding sampling in all the rows of the matrix (128, 256 or 512) takes place during a single echo (milliseconds). Phase-encoded sampling takes several seconds, or even minutes, owing to the collection of all the k-space lines to enable Fourier analysis. Major physiological movements are of millisecond to seconds duration and thus too slow to affect frequency-encoded sampling, but they have a pronounced effect in the phase-encoding direction.Periodic movements such as cardiac movement and blood vessel or CSF pulsation cause ghost images, while non-periodic movement causes diffuse image noise (Fig. 1). Ghost image intensity increases with amplitude of movement and the signal intensity from the moving tissue.Several methods can be used to reduce motion artefacts, including patient immobilisation, 1 cardiac and respiratory gating, 2 signal suppression of the tissue causing the artefact, 1 choosing the shorter dimension of the matrix as the phase-encoding direction, view-ordering or phase-reordering methods 3 and swapping phaseand frequency-encoding directions 1 to move the artefact out of the field of interest. FlowFlow can manifest as either altered intravascular signal (flow enhancement or flow-related signal loss), or flow-related artefacts (ghost images or spatial misregistration).Flow enhancement, also known as inflow effect, is caused by fully magnetised protons entering the imaged slice while the stationary protons have not fully regained their magnetisation. A short overview of MRI artefacts L J Erasmus MB ChB D Hurter MB ChB M Naudé MB ChB H G Kritzinger MB ChB

AIM: To determine the accuracy of Magnetic Resonance Cholangiopancreatography compared to the gold standard Endoscopic Retrograde Cholangiopancreatography in the diagnosis of bile duct disorders at our institution. PATIENTS AND METHODS: 52 patients with suspected pancreatobiliary pathology were included in this prospective observational study. MRCP was performed in the 24-hour period prior to the ERCP. RESULTS: MRCP had sensitivity, specificity, positive and negative predictive values of 87%, 80%, 83.3% and 84.2% respectively for choledocholitiasis which correlates well with results obtained in other parts of the world. CONCLUSION: At our institution, MRCP has high diagnostic accuracy for bile duct calculi. Due to a small study population, results for other biliary pathology were inconclusive

The KHR is an accurate, unifying clinical guideline that appears to optimise the utilisation of CTB in a resource-limited environment.

Giant peritoneal loose bodies are rare lesions, originating from auto-amputated appendices epiploicae. They may cause urinary or gastrointestinal obstruction and, should the radiologist not be familiar with the entity, can potentially be confused with malignant or parasitic lesions.Familiarity with their characteristic computed tomographic features is essential to prevent unnecessary surgery in the asymptomatic patient. We present a case of a 70-year-old man diagnosed with two giant peritoneal loose bodies.

Background: It has been well documented that ultrasound measurement of the optic nerve sheath diameter performed by an experienced operator shows good correlation with raised intracranial pressure, irrespective of the cause. Objective: To establish the accuracy of this technique performed by inexperienced operators.Method: A prospective analytical cross-sectional study was conducted. All patients ≥18 years of age who presented at our medical casualty and emergency departments with suspected meningitis were enrolled in the study. All patients were evaluated with the use of optic nerve sheath diameter ultrasound with or without computed tomography brain scan prior to lumbar puncture. Lumbar puncture opening pressure measurements were compared with the ultrasound measurements.Results: A total of 73 patients were enrolled in the study, of whom 14 had raised intracranial pressure. The study had a sensitivity of 50% (95% confidence interval (CI) 26.8%–73.2%) and specificity of 89.8% (95% CI 79.5%–95.3%) with a positive predictive value of 54.8% (95% CI 29.1%–76.8%) and negative predictive value of 88.3% (95% CI 77.8%–94.2%). The likelihood ratio of a positive test was 4.92 (95% CI 1.95–11.89) and that of a negative test 0.56 (95% CI 0.29–0.83). Cohen’s kappa value was 0.41 which indicates a moderate agreement. The receiver operating characteristic (ROC) curve had an area under the curve (AUC) of 0.73 (95% CI 0.51–0.95). Conclusion: Ultrasound measurement of the optic nerve sheath diameter can be used to exclude raised intracranial pressure, even in the hands of inexperienced operators.