Transcript Document

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
.
BACKGROUND
Hepatocellular 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).
FINDINGS
Diagnostic Accuracy
Until
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).
AIM
Accessibility
Contrast Contraindications
There 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).
In 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.
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.
To 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.
METHODOLOGY
This 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).
.
(9)
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.
CONCLUSION
Ultrasound, 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.
Technological Advances
While 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).
Claustrophobia
The 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).
REFERENCES
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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 ContrastEnhanced CT Predominantly in Patients With Hepatocellular Carcinoma and Chronic Liver
Disease”, Investigative Radiology, Vol. 45(3), pp.133-141, (2010)
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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)
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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]
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http://www.ispub.com/ostia/index.php?xmlFilePath=journals [Accessed: 20 March, 2011]
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