It is a versatile imaging tool

Date:14/02/2008 URL: http://www.thehindu.com/thehindu/seta/2008/02/14/stories/
2008021450031500.htm



It is a versatile imaging tool

Scanners that use combined positron emission tomography (PET) and computed tomography (CT) have been proving their potential as versatile medical imaging tools since 2000 when they became commercially available.

A PET scanner uses small amounts of radioactive pharmaceuticals targeted at specific organs, bone or tissues. Development of radiopharmaceuticals such as fluoro-deoxyglucose (FDG) which can act as a marker for sugar metabolism enhanced its potential u se. FDG contains Fl-18, a positron emitting radionuclide, whose presence will help to trace and locate the sites where the molecules get accumulated.
Special camera

A special camera that works with a computer provides pictures of the area of the body being imaged. Cancer cells often grow and multiply uncontrollably. They consume enormous amounts of energy. Basically, this energy comes from burning glucose.

Cancer cells metabolise sugar at higher rates than normal cells, and the radiopharmaceutical is drawn in higher amounts to cancerous areas (Society of Nuclear Medicine [SNM] Release, December 12, 2007)

PET scans produce three-dimensional images of the precise distribution of FDG in the body; FDG plays the role of a marker for the disease and its spread. CT scans on the other hand show the details of the anatomical structures.

Since 2000, when Beyer, Townsend and others introduced the concept of PET-CT imaging, state-of-the–art CT imaging technology has been combined with high-end PET systems (The Journal of Nuclear Medicine [JNM], January 2007).

Recently, researchers claimed that PET-CT imaging is superior to conventional imaging in detecting cancers in children (JNM, December 2007). The modality provides additional information, possibly sparing young patients from being overtreated.
Plaque inflammation

PET-CT offers a superior view of atherosclerosis plaque inflammation — a process in which deposits of fats, cholesterol, cellular waste products and other substances, collectively called plaque, builds up in the inner linings of the artery and limits the flow of blood through it (innovations-report.com, June 6, 2006).

PET-CT may be able to assess biologically active plaques; these are of concern as they may lead to “deadly consequences when they misbehave.”

Disease processes may obstruct blood vessels. Specialists insert prosthetic grafts to restore and ensure blood circulation.

According to Ora Israel, director of nuclear medicine and research operations at Rambam Health Care Campus, in Haifa, Israel, graft infection is a rare, but potentially severe complication occurring at a rate ranging between 0.5 and 5 per cent following prosthetic vascular reconstruction (ZAMP Bionews, June 5th, 2007).

Infection imaging

PET-CT imaging effectively diagnoses and differentiates infection, Israeli researchers noted at the 54th Annual Meeting of the SNM. Surgeons remove the infected blood vessel grafts in a complex surgical procedure.

“Sparing unnecessary high risk operations in patients…is of major significance” Dr Israel clarified. “PET-CT imaging can effectively diagnose graft involvement and differentiate it from infection that affects only soft tissue…in its vicinity,” she added (ZAMP Bionews, June 5th 2007)
Cancer screening

Can we justify using PET-CT for population screening for cancer? “Recommendations and decisions regarding cancer screening should be based on reliable data, not good intention, assumptions or speculation …”

“…We conclude from the available data that neither CT nor PET-CT cancer screening is currently warranted…The clinical and statistical relevance of occasionally detected cancers is likely too low to justify population wide screening efforts with these modalities” (The JNM, Supplement, January 2007).

The Journal of Nuclear Medicine, the scientific publication of the Society of Nuclear Medicine (SNM), U.S., published two supplements on PET-CT, one in 2005 and the second in January 2007. Both are available on the web.

As on January 2007, specialists are using more than 1700 PET and PET-CT units in the U.S. India has 15 PET scanners, nine of them are PET-CT; more will be installed in the near future.

Indian nuclear medicine specialists have been providing excellent service though the facilities available in India are too meagre.

Diagnostic nuclear medicine services are admittedly lucrative. Nuclear medicine physicians must collaborate and initiate well focused clinical research and development programmes to improve their professional competence and to create more specialists in the country.

K.S. PARTHASARATHY

Former Secretary, AERB
ksparth@yahoo.co.uk

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