'Field of gold' scanner cuts children's radiation risk

“A new method for scanning children's livers for tumours could prevent them being exposed to unnecessary radiation,” BBC News reports.

The scanner, based on ultrasound technology, successfully identified liver tumours (which are rare in children).

Usually the liver is initially examined using a standard “grey scale” ultrasound, but this often does not give enough diagnostic information.

The next option in these types of cases is a computerised tomography (CT) scan. A CT scan involves the use of ionising radiation that carries a potential, if unproven, risk to the child.

There is also the option of using an MRI scanner but this is often upsetting to a child (many find the combination of a being in an enclosed space and being exposed to loud noises traumatic) and many children require sedation.

So an accurate alternative would be a useful advancement.

The technique being studied is called contrast enhanced ultrasonography (CEUS) and is currently available for use in adults only. It involves using a combination of an ultrasound scanner and a contrast agent.

The contrast agent "lights up" healthy tissue on the scan – hence the reference to a "field of gold" in the BBC's headline. In contrast, abnormal sections of tissue, such as tumours, appear as black holes.

The study found that CEUS was highly accurate, agreeing with the diagnoses made by CT or MRI scanning in 85% of cases, with no adverse effects observed. It was able to reliably differentiate harmless from cancerous lesions.

So far the number of children examined by this technique has been small, though this is unavoidable given the rarity of liver conditions among the child population as a whole. Further study in larger numbers of children undergoing diagnostic imaging for liver lesions is required.

Overall, the results seem promising.

Where did the story come from?

The study was carried out by researchers from King’s College Hospital, London, and was published in the peer-reviewed medical journal European Journal of Ultrasound. No sources of funding are reported.

BBC News gives reliable coverage of this study and provides some useful commentary from the lead researcher.

What kind of research was this?

This was a diagnostic study looking at how effective contrast enhanced ultrasonography (CEUS) was at examining liver lesions (for example, a tumour) compared to the standard diagnostic methods of standard “grey scale” ultrasound, CT or MRI scan, or laboratory examination of biopsy samples removed from the liver.

As the researchers say, primary liver lesions (that is, tumours originating in the liver, rather than metastatic cancer which spreads from elsewhere in the body) are rare in children, accounting for only 1-2% of all tumours that occur in children. Two-thirds of liver tumours identified in children will be benign (non-cancerous), and the remaining third will be cancerous.

The researchers say that standard “grey scale” ultrasound is the first-line diagnostic tool to investigate liver lesions in both children and adults. However, a follow-up CT or MRI scan is nearly always necessary because the ultrasound can’t give a clear enough look at any identified lesions.

If a CT scan is used this involves exposing the individual to ionising radiation, and the potential risks from exposing children to the radiation of CTs is still largely unknown. MRI is an alternative, but an MRI can be more traumatic for the child and often requires the use of sedation, which can limit the use of this technique.

However, contrast enhanced ultrasonography (CEUS) – where a contrast agent is injected into the bloodstream – is an imaging technique that can give better definition of liver lesions than standard ultrasound. CEUS is reported to have an excellent safety record in adults, with minimal side effects.

The researchers say that it is not known whether CEUS performs better than standard ultrasound for looking at liver lesions in children, or how it compares to CT, MRI or laboratory examination of biopsy specimens.

Therefore this study aimed to look at its accuracy compared to the standard techniques.

What did the research involve?

This study involved 44 children (23 male, average age 11.5 years) who were referred over the course of a five-year period for further CEUS assessment of an indeterminate liver lesion that had been identified by standard ultrasound.

“Indeterminate” meant that it was unclear from the standard ultrasound whether the lesion was benign or cancerous, which therefore prevented any further management decisions without the use of further diagnostic tools.

The majority (30) of the children in the sample were known to have chronic liver disease and were undergoing routine ultrasound scans for monitoring purposes when the lesion had been identified.

Experienced operators performed CEUS, and any adverse effects following injection of the contrast (such as nausea and vomiting, pain, breathlessness, or low blood pressure) were monitored. All children then also received the standard hospital protocol following identification of an indeterminate liver lesion on standard ultrasound: that is, either CT or MRI scan at the clinician’s discretion, followed by liver biopsy and laboratory examination if this was considered necessary. Follow-up ultrasounds were also performed in most cases to monitor those children with chronic liver disease.

What were the basic results?

CEUS was successfully performed in all 44 children, with no adverse reactions to injection of the contrast. Following this, 34 children received CT or MRI imaging (14 had CT, 30 MRI, and 10 received both). Biopsy of the liver lesion, followed by laboratory examination, was performed in eight children.

Ten children required no further CT or MRI imaging because diagnoses related to chronic liver disease could be made through either further ultrasound follow-up or biopsy (six of these children had biopsy of the “background” liver, i.e. not a specific lesion).

Of the children who received CEUS followed by standard CT or MRI imaging, the diagnosis made following CEUS agreed with the diagnosis made following CT or MRI in 85% of cases (29/34). In the five cases where there was disagreement, CEUS picked out four liver lesions that were thought to be fatty liver change. These lesions were not picked up by CT or MRI, and remained unchanged at further ultrasound follow-up.

CEUS had a 98% specificity for identifying benign lesions, which means that 98% of non-cancerous lesions were correctly identified as being non-cancerous by the test. There was one case where all the imaging modalities – CEUS, MRI and CT – were wrong, as they all suggested a cancerous lesion, which was shown to be benign following biopsy.

How did the researchers interpret the results?

The researchers conclude that their study suggests CEUS is useful for examining focal liver lesions that are indeterminate on standard “grey scale” ultrasound in children. This potentially reduces the risk of exposure to ionising radiation. 

Conclusion

This is a valuable diagnostic study that demonstrates the potential value of using contrast enhanced ultrasonography (CEUS) to examine liver tumours in children. As the researchers say, the liver would normally be initially examined using standard “grey scale” ultrasound, but as this often does not give enough diagnostic information, this has to be followed by further imaging using CT or MRI. CT involves the use of ionising radiation, which still carries uncertain risk for the child, while MRI can be difficult for the child and require sedation.

Therefore an accurate alternative would be a good advancement. It would not only reduce potential risks or harm to the child, but could also have potential benefits in terms of reducing healthcare costs and use of resources.

This study demonstrates the accuracy of CEUS compared to standard imaging techniques, with no adverse effects observed. It was able to reliably differentiate benign from cancerous lesions, which is beneficial in avoiding unnecessary anxiety. The one case where a cancerous lesion was missed, the other standard imaging techniques missed it too. So far the sample of children examined by this technique has been small – 44 children over a five year period at one hospital. However, this is unavoidable given the rarity of liver conditions among the child population as a whole.

CEUS is not currently licensed for use among children. As only a small case series of children at one hospital have so far been examined, further study in larger numbers of children undergoing diagnostic imaging for liver lesions is required.

As Professor Sidhu, one of the researchers involved the study, concludes: “This is an exciting breakthrough, but it now needs multicentre trials probably involving up to a couple of thousand patients.”