What is nuclear medicine ?

• How does it work?
• Therapy & Diagnosis
• PET & SPECT - Oncology
• Radiopharmaceuticals

PET & SPECT - Oncology

Imaging tools in Nuclear Medicine: a guide to the typical procedures and applications involved, and to their advantages over one another in specific investigation areas.

by Prof. M. Hacker

In a nuclear medicine investigation an endogenous molecule is coupled to a radioactive substance (usually technetium) and injected into the patient. This complex enriches itself over the bloodstream in the organ which can be imaged:. Already after short time leaves itself with the help of a highly sensitive special camera (a so-called gamma camera) the radioactive marked molecule can be detected.

Knowledge is lacking about use of radioactive radiation for medical application especially in Nuclear Medicine Departments, this often leads to unfounded fears from patients. They do not notice no more than the injection in their vane done by the physician usually (similar as with a blood withdrawal). In many cases the treatment and investigation with radioactive substances are even substantially more carefully performed as any other operational procedures or complex catheter investigations.

" The  x-ray image of an tissue (for example a bone image) shows only its anatomical structure. Whether it still lives or already died, remains uncertain"  as stated by the nuclear physician Professor Hahn.
“If one wants to know more about the vitality of the tissue, it is necessary to transfer substances into the cell metabolism which makes the function visible. This is what happens exactly in the Nuclear Medicine"

The main operational area of PET is Oncology since many tumours (in particular the frequent tumours such as Bronchial- carcinomas or lymphomas showed a strongly increased glucose consumption, whereby tumours and metastasis can be imaged.

Positron-Emitting-Tomography (PET) is an imaging procedure using systemically applied tracers, which are labelled with so called positron emitters. These radiotracers enable three-dimensional imaging of organ function, metabolism or receptors in-vivo. PET scanners are equipped with a detectors ring that is able to simultaneously acquire the 511 keV gamma radiation emitted in 180 degrees angles by the positrons. Latest technology is based on hybrid technology, where PET is combined with CT or MRI units.
The most popular PET procedure is imaging of glucose metabolism using 18F-FDG as radiopharmaceutical. 18F-FDG is mostly used for whole body imaging in the context of staging and therapy monitoring in oncological patients.

In contrast to PET, single photon emission computer tomography (SPECT) instead of positron emitter uses radiopharmaceuticals labelled with gamma emitters with different gamma energies (like 99mTc or 123I) . SPECT also enables three dimensional imaging and there are today also hybrid SPECT/CT scanners available. Typical procedures are bone scans with
99mTc-bisphosphonates or myocardial perfusion imaging using 99mTc-Sestamibi.

Due to better image resolution and quantification, PET is frequently preferred, if approved tracers with the same characteristics as compared to the respective SPECT tracers are available. However, SPECT radionuclide’s are more widely available and have a longer physical half life, so that these radiopharmaceuticals are preferable for certain clinical investigations.