Why the Need for PET/CT

Medical diagnosis imaging technologies have always focused on one aspect of a disease process. The diagnosis method would only ever look at either:

• Anatomical structure – Location of internal organs and suspicious masses
• Functional change – Areas of cancerous growth

Whether a patient underwent a PET scan, MRI or CT scan, only one modality at a time could be looked at and this caused many problems, especially if a surgeon needed to overlap PET and CT scans to get more information on how to treat a tumour. The main problems with individual scans were therefore:

• Limited accuracy

Firstly separate PET and CT scans, although beneficial, only showed their specific requirements: either anatomical location of a mass, or area of cancer growth.

Accurate imaging of the exact location with the cancerous growth highlighted was therefore difficult, as two separate techniques were required to be superimposed onto each other.

This caused great frustration for physicians, especially cancer surgeons, who needed to know the exact location and extent of cancer growth to prepare for surgery.

The time delay between taking separate CT and PET scans, which could sometimes be weeks apart, meant that involuntary movement of internal organs between scans and the variability of patient positioning in the two scanners made superimposing PET and CT scans difficult.

As a result of the difficulties with separate PET and CT scan, the exact location of a cancerous growth was difficult to tell and other than an informed guess exploratory surgeries were sometimes needed by a surgeon to gather the information they need. Not only was this time consuming it was also more expensive overall.

• Labour intensive

Having two separate scans (PET and CT) meant that more time was needed to collect all of the data that was needed for surgery. Also because PET and CT use different types of medical diagnosis techniques separate technicians were required to perform each scan and also separate physicians were required to separately read and interpret the scans as different training is needed to understand CT and PET scans.

All of these parts were labour intensive and required more time and money especially when two surgeons had to consult each other over the results of each scan.

• Impractical

To increase the probability of success from 90% to 93% (only a 3 percent increase, i.e. an extra 3 cases out of 100) by overlapping a PET scan and a CT scan was sometimes unjustifiable and impractical in terms of the cost of each scan. These costs included things such as time for the scanner, technical costs, patient time and surgeon consultation.

Other problems with separate PET and CT scans were that PET scan registration software was primarily designed for diagnosing brain conditions and its usefulness in full body diagnosis, which CT scans were usually needed for was therefore limited.

Because of these deficiencies with using the two technologies of PET and CT separately the advantages of a combined Positron Emission Tomography/ Computed Tomography (PET/CT) was recognized early on.