By Dr Abdul Jalil Nordin

Trend in Diagnostic Imaging
Routine workflow for a patient seeking treatment in a hospital involve several medical investigations before the final diagnosis is achieved. This include medical imaging. In general, diagnostic medical imaging consists of Diagnostic Radiology and Diagnostic Nuclear Imaging.

Diagnostic Imaging in Radiology
Diagnostic Imaging in Radiology is a study of cross sectional anatomy of different organs in every systems. The function of this modality is to seek any forms of anatomical abnormalities to the organs studied.
Various forms of imaging modalities commonly available in hospitals including plain radiography, fluoroscopy, ultrasound, mammography, Interventional Radiology, Computed Tomography and Magnetic Resonance Imaging.

In some circumstances especially studies using Computed Tomography and Magnetic Resonance Imaging, chemical in liquid form called ‘contrast agents’ is injected in to the patients. The purpose of this injection is to acquire more specific information during the study.
Generally tumours and inflammations are more evident through demonstration of specific tissue characterisation following contrast injection. This should lead to the clinician close to the diagnosis.

Diagnostic Nuclear Imaging
In Malaysia, the utilisation of nuclear imaging in diagnosis is limited by its availability. In theory, various forms of Diagnostic Nuclear Imaging techniques are available.

This include diagnostic works involving gamma camera, gamma camera with single photon emission, computed tomography (SPECT), positron emission photography (PET), positron emission photography computed tomography (PET/CT) and single photon emission computed tomography /computed tomography (SPECT/CT).
The function of this modalities depend on the availability of radioisotopes and its tagging agents.

In principle, this study utilises the physics property of unstable elements called ‘radioisotopes’
Due to its instability, these elements will continuously decay until they reach a stabilized form. During the process of transformation, energy is being released in the form of ionising ray.

In medical imaging, majority of the emitted rays utilised are the gamma rays.
Positron Emission Tomography Computed Tomography (PET/CT)
The latest nuclear imaging tool available in Malaysia is the fusion integrated combined imaging technique, PET/CT.
This diagnostic imaging modality is a combined tool between both modality is a combined tool between both modalities.

In general, there are 2 important principles in this imaging modality that need to be understood in order to know how PET/CT works at molecular level.
First a special chemical resembling glucose molecule has been developed to be utilised in PET modality called ‘floro deox glucose’ (FDG).

Since glucose is an essential elements to all living cells for energy production, this agent when tagged with a suitable radioisotope for PET imaging will demonstrate the road map to tissues with high metabolic activities.

In Malaysia, most common radioisotope available for PET imaging is 18-flourine (18F).
Secondly, cancer tissues contain numerous abnormal cells with abnormally large capability to reproduce. These cancerous cells are metabolically active in comparison to normal cells.

During PET imaging, metabolically active abnormal cells will demonstrate high 18F-FDG uptake.

These tissues will be readily visible and prominent against the normal tissue activity in the background.

For this reason, PET is also known as a functional imaging modality.
However, PET alone is unable to provide previce information on the locations of these lesions. CT on the contrary, gives best information on cross sectional anatomy.
When both modalities are combined, the information gathered will increase the accuracy at diagnosis as the precise location of the abnormal cells can be identified.