Departments

Medical Departments

PET CT Scan (Nuclear Medicine)

Clinical Benefit of a PET/CT scan

Background

The medical imaging field has known very significant technological progress over the past 10 years, especially in two areas : radiology with the development of the CT scan and the nuclear magnetic resonance, and nuclear medicine with the development of the SPECT and the PET. At the beginning, there was a kind of competition between these two areas. But they recently started to collaborate closely and now they even try to integrate the two techniques. Relationships between the two evolve because each of them provides complementary information : radiology gives information about organs' structure and anatomy, and nuclear medicine gives information on organs' function and on the metabolism of the cells which constitute them.
Besides, our most important industrial partners were right when they developed a new technology by combining a scan and a PET scan in only one device. The new camera was called PET/CT.

In July 2001, a PET camera was set up in Bordet Institute in the context of a collaboration between the IRIS network hospitals. It is a high-quality camera from General Electric (Advance). As we were setting it up, we already took into account the unit architecture just in case we should have to add a scanner and get a PET/CT in that way.

 

Benefits of the CT in the accurate anatomical localisation of lesions detected by PET

1) General remarks :
The metabolic images, like the ones provided by the FDG-F18 (PET), only give few anatomical references and thus prevent specialists from having an accurate localisation of abnormal images on the different sections. Several scientific studies showed that PET's diagnostic capacity was much better if the data were connected data from the CT. Three types of methods enable to correlate the images from the PET and the CT. The first one consists in a visual correlation by comparing the cross sections from the CT and the ones from the PET. In the case of an examination of the skull or of the thorax by FDG-F18, there is usually no problem since the visual correlation is sufficient most often. However, it is more difficult when it is question of neck or abdomen examinations, because there are less available anatomical references on PET images. Moreover, the duration between the two examinations PET and CT often implies that organs'anatomical position (bowels, bladder, ureters)is different on the two images, which makes precise correlation impossible.
The second method consists in mixing all the PET and CT images by computer, through a specialised software. The software is very useful for rigid part of the body such as the skull and the thorax but it is useless in parts of the body which move much more like the neck (flexion, rotation) or the abdomen (twisting). Moreover, like we previously said, the two examinations are separated in time and thus the images can't be superpimposed because of the changes that occur during the period of time.
The third method is more efficient : it consists in mixing the images resulting from both PET and CT at the same time, thanks to the physical association of the two scanners. In that way, we realise the two series of images at the same time (the whole body by PET and the whole body by CT) and thus the images exactly correspond to each other regarding position in space. A study of the benefit that such a device brings to the detection of lung tumours was recently published in the New England Journal of Medicine (see the appendix).

2) Specific clinical applications :

a. Tumor Staging : - Sensitivity and specificity of the diagnosis - Accurate localisation of PET lesions : impact on the staging and on the treatment schedule - Exact establishment of the tumour direct extension - optimisation of the algorithm to get a diagnosis	click here
b. Treatment Monitoring c. Radiotherapy scheduled d. Tracers developments	click here

 

Benefits of the CT regarding patient flow

One of the most important consequences of PET/CT upgrade is the significant increase in PET unit's capacity. It mainly results from a reduction of waiting time for getting the transmission data : they are provided by the scan in few minutes while the PET needs 20 to 30 minutes at the moment (it depends on the number of acquisition steps). Moreover, it also has a positive effect on the quantity of FDG-F18 we have to order.
  

Benefits of the PET/CT in the quantitative data analysis : click here

1) Attenuation correction
2) Adjust target organs in shot of the camera
3) Define target organs'outline accurately
4) "surrogate inputcurves"
5) Correct the partial volume effect

 

CONCLUSION

Having the CT upgrade for the PETscan Advance of IRIS network is justified by clinical arguments as well as scientific motivations. Indeed, it will not only enable to improve images quality but it will also provide clinicians with quantitative, rapid and reliable information because they are always looking for assessment measures of the effects of the treatments they prescribe. Even if we are expecting an increase in the number of staging PET scans in the future, it is clear that the new technology will be particularly useful in the field of treatments assessment, a field in which having a CT is essential.

The PET-CT will even more be a technique of reference in oncology as well as in other fields like neurology, infectiology and systemic diseases. This progress will probably be linked to the development of new radioactive markers and new treatments which will have to be exactly and rapidly assessed.

 

Person in charge : Pr Patrick Flamen

Last reading of this page : January 2008