AccessibilityThere is high demand on all imaging services which affects modality accessibility and waiting list times vary across Trusts due to differing demands. As ultrasound is the ‘Gold Standard’ for hepatic imaging, it could be assumed there is more demand on this modality however this is not always the case (10).

The table below demonstrates approximate scan times for each modality from the Cancer Research website (11). It was difficult to find published studies which included this information. It is deemed reasonable to cite this source as it is the UK’s leading cancer charity providing patients with information specific to liver cancer and the imaging processes involved to aid in diagnosis.

Technological AdvancesWhile faster scan times and better image quality are key factors of 3T scanners, patient safety is still a concern. Unlike ultrasound and CT, metallic implants can be contraindicated in MRI. However some materials that proved safe in 1.5T scanners may be contraindicated in 3T scanners and some implants and have yet to be tested (12).

ClaustrophobiaThe bore design of typical MRI scanners has proven to be undesirable for patients and claustrophobia has been a long term limitation to MRI scans (13). The issue of is evidently being address in recent scanner designs with a wider bore, reduced sound and quicker scan times offering an alternative to open scanners (14).

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Diagnosing Hepatocellular Carcinomas (HCC) and Hepatic Metastases: Should Magnetic Resonance Imaging (MRI) be the ‘Gold Standard’ Imaging Modality?

Megan Doherty and Janice St. John–Matthews, Faculty of Health and Life Sciences, University of the West of England, Bristol, UK

BACKGROUNDHepatocellular carcinoma (HCC) is the most common primary malignancy in the world with the liver being the most frequently observed site for metastases in the body (1) arising from primary tumours in the lung, breast, colon, pancreas and stomach (2, 3). Characterization of lesions is vital (4). Benign lesions, such as cysts and haemangiomas, can be mistaken as malignant, thus the use of an effective imaging technique is needed for accurate diagnosis and patient management (5). Improvements in imaging technology and contrast agents have made it easier to detect, locate and characterize liver lesions using various imaging modalities (6). Currently, the ‘Gold Standard’ for imaging suspected hepatic carcinomas and metastases is ultrasound. This may be followed by CT or MRI, if a suspicious abnormality is identified (7).

AIMTo explore why MRI is used in clinical practice as a problem solving tool as opposed to ultrasound, the ‘Gold Standard’, in the diagnosis process of HCC and hepatic metastases.

METHODOLOGYThis study was conducted as a literature review. Background reading, using textbooks and journals, was carried out to obtain relevant knowledge and familiarise the author with the subject in question. Key terms and phrases were identified during this process for use in database searches. Searches returned a large amount of data, thus an inclusion and exclusion criteria was set to ensure literature reviewed was relevant to the research problem. Grey literature was also used in this study in order to identify the ‘Gold Standard’ imaging modality used in hepatic imaging, making the study more relevant to practice in the UK. A system for critiquing literature was developed in order to avoid elements of bias (8).

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Contrast ContraindicationsIn patients with HCC and hepatic metastases, contrast media is important for accurate detection and characterization and therefore it is essential for all potential contraindications of contrast media to be known. In recent years there has been an increasing association between NSF and gadolinium based contrast agents however there are still gaps in literature relating to the impact of this when imaging patient’s in MRI and therefore further research is needed (15). This does however enhance the need for checks prior to imaging, such as blood tests for renal function.

CONCLUSIONUltrasound, CT and MRI are the mainstays of liver imaging with each contributing different information to the final clinical picture. Overall, the findings demonstrate ultrasound to be the cheapest, most accessible and safest modality, in comparison to CT and MRI. While Ultrasound remains the “Gold Standard” for diagnosing both pathologies, MRI provides the most information on tumour characterisation. Current and ,future technological developments in MRI i.e. DWI may further impact on the future role of MRI within the patient treatment pathway.

REFERENCES1.Reimer P. et al. “Clinical MR Imaging: A Practical Approach”, 3rd ed., Berlin: Springer, (2010)2.Patel, P. “Lecture Notes: Radiology”, 3rd ed., Oxford: Blackwell Publishing, (2010)3.Oliva, M et al. “Liver Cancer Imaging: Role of CT, MRI, US and PET” Cancer Imaging, Vol.4, pp.42-46, (2004)4.Ichikawa, T. et al. “Detection and Characterization of Focal Liver Lesions: A Japanese Phase III, Multicentre Comparison Between Gadocetic Acid Disodium-Enhanced MRI and Contrast-Enhanced CT Predominantly in Patients With Hepatocellular Carcinoma and Chronic Liver Disease”, Investigative Radiology, Vol. 45(3), pp.133-141, (2010)5.Ooi, C. Et al. “Diagnostic accuracy of contrast-enhanced ultrasound in differentiating benign and malignant focal liver lesions: A retrospective study”, Journal of Medical Imaging and Radiation Oncology, Vol: 54(5), pp.421-430, (2010)6.Choi, B. “Advances of Imaging for HCC, Oncology. Vol. 78, pp.46-52, (2010)7.Royal College of Radiologists, “Making the Best Use of the Radiology Department”, RCOR: London, 6th ed, (2008)8.LoBiondo-Wood, G. & Haber, J. “Nursing Research: Methods and Critical Appraisal for Evidence-Based Practice”, 6th ed. Missouri: Mosby Elsevier (2006)9.McRobbie, D. et al “MRI from Picture to Proton”, Cambridge University Press: Cambridge (2006)10.NHS Improvement. “Diagnostics Improvement: Radiology – Case Studies”. (online) Available from: http://www.improvement.nhs.uk/diagnostics/RadiologyCaseStudies/tabid/64/Default [Accessed: 12 April, 2011]11.Cancer Research UK. “Tests for Liver Cancer”. (online) Available from: http://www.cancerhelp.org.uk/type/liver-cancer/ [Accessed: 19 April, 2011]12. Jerrolds, J. & Keene, S. MRI Safety at 3T versus 1.5T. The Internet Journal of World Health and Social Politics. (online) . Available from: http://www.ispub.com/ostia/index.php?xmlFilePath=journals [Accessed: 20 March, 2011]13.Eshmed, I. et al. “Claustrophobia and Premature Termination of MRI examinations”, Journal of Magnetic Resonance Imaging, Vol.26, pp.401-404, (2007) 14.Hailey, D. “Open Magnetic Resonance Imaging Scanners”, Issues in Emerging Health Technologies. 92, pp.1-4, (2006) 15.Weinreb, J. “Which Study When? Is Gadolinium-enhanced MR Imaging Safer than Iodine-enhanced CT?”, Radiology, Vol.249, pp.3-8, (2008)

.FINDINGSDiagnostic AccuracyUntil recently CT was better fat demonstratingHCC lesions smaller than 15mm, than MRI gadolinium and liver-specific contrast enhanced studies. This is because size and the contrast used are both limiting factors in MRI. However, the advent of double contrast MRI studies, combining Diffusion Weighted Imaging (DWI) and Supra Paramagnetic Imaging Oxides (SPIOs) are proving to be more accurate than CT. This increases competition with ultrasound for which modality should be the ‘Gold Standard’. However, as this type of imaging is still new and evolving, for now, it is unable to replace ultrasound and further research is required to ensure patient safety (1).

Cost Implications Primary data was collected from 4 UK hospital Trusts, to find out the costing of the scans required for diagnosing the aforementioned pathologies It was not stated whether costs of resources, radiologist’s/ radiographer’s time and wear and tear of the machines are included in the overall quotes, therefore the documented price range for each modality should be regarded as an estimation.

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