An imaging examination (also known as scan) is the term used for non-invasive (i.e. no surgical intervention) visualization of structures and processes in our body. In cancer, and other disease types, imaging can be divided into two main types, serving two main objectives:
Anatomical imaging: This allows doctors to see (assessment of presence, structure & size) and localize tumors, that is examine where they are in the body and the extent to which they have spread (metastasized) to other parts, for example lymph nodes, liver, brain
Functional imaging: This type enables the interrogation of many aspects of tumor physiology, molecular pathology and biochemistry, so tells us something about what the tumors are doing or how they are behaving
This information is altogether useful for the detection and staging of disease, and longitudinal assessment (over time) of tumor evolution including monitoring of response to treatment and recurrence
There are several techniques available in the clinic for imaging of patients with cancer. The most widely available and commonly known methods are ultrasound and X-ray imaging but for a full body scan and/or a more advanced assessment, scanning techniques such as computed tomography (CT), magnetic resonance imaging (MRI), ingle photon emission computed tomography (SPECT) and positron emission tomography (PET) are also available in most cancer centers.
PET and SPECT are both nuclear imaging methods based on the injection of a radio-labelled tracer and monitoring of its body and tissue distribution and accumulation.
Imaging examinations can involve different types of scans (known as multi-modality imaging) and each scanning method can measure several different parameters (also referred to as multi-parametric imaging); these can be endogenous (inherent) tissue properties (tissue cellular density, water content) or contrast-enhanced features (blood perfusion, uptake of certain drugs or metabolites).
The choice of the technique to be used and parameter to be tested are carefully chosen and largely depend on the question under investigation and the availability of the technology in a particular cancer center.
The main differences between the main types of imaging modalities can be thought of in terms of type of the waves/rays used to obtain an image, image data quality, imaging depth (how far from the body surface), safety and of course cost; these are summarized as follows
Imaging techniques have different attributes/limitations but are mostly complementary. If combined they can provide a wealth of clinically-meaningful information about disease biology and behaviour, with the added advantage of being non-invasive.
