PRINCIPLES & APPLICATIONS OF PET - CT

Presentated BY-

Abdulkader Helwan

Submitted to: Dr. Zafer Topukcu

PET/CT

• Medical Imaging Technique

• Both systems in one Gantry

• Aquired image combined into a coregistered image

• Functional imaging by PET

• Anatomical imaging by CT-Scanner

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PET/CT

• Combines the functional information with the anatomical detail

• Accurate anatomical registration

• Higher diagnostic accuracy than PET or CT alone

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Fused PET/CT images

PET

• Stands for positron emission tomography

• Machine that can image biological and chemical activities

• For ex: imaging brain activity when there is a scary event

• Active part of brain can’t be imaged using x-ray of only CT

• It can be imaged using PET

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Principles of PET

• Inject a radioactive tracer bind with glucose

• The active part of brain absorbs it more than other inactive parts

• The radioactive tracer is:

Fluorine-18-deoxyglucose (FDG), a radionuclide labeled glucose analogue is injected into the organ that would be imaged

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PET tracer: FDG

• Fluorodeoxyglucose is a glucose analog. Its full chemical name is 2-fluoro-2-deoxy-D-glucose, commonly abbreviated to FDG.

• Radioactive fluoride atom produced in a cyclotron is attached to a molecule of glucose.

• The FDG molecule is absorbed by various tissues just as normal glucose would be.

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FDG

CH2HO

HO

HO

O

OH

18F

CH2HO

HO

HO

O

OH

OH

glucose

2-deoxy-2-(F-18) fluro-D-glucose

• Most widely used PET tracer

• Glucose utilization

• Taken up avidly by most tumours

• It is absorbed by various tissues as normal glucose would be.

By Eng. Abdulkader Helwan

Figure 3. Uptake of FDG. FDG is a glucose analog that is taken up by metabolically active cells by means of facilitated transport via glucose transporters (Glut) in the cell

membrane.

Kapoor V et al. Radiographics 2004;24:523-543

©2004 by Radiological Society of North America

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FDG Metabolism

FDG FDG -6-P

Radio- active

Glucose 18F-FDG

Radioactive Glucose 18F-FDG

X

Glucose Glucose

Glucose

Glucose-6-Phosphate

Unlike glucose, FDG is trapped

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PET Radiopharmaceuticals

Nuclide Half-life Tracer Application

O-15 2 mins Water Cerebral blood flow

C-11 20 mins Methionine Tumour protein synthesis

N-13 10 mins Ammonia Myocardial blood flow

F-18 110 mins FDG Glucose metabolism

Ga-68 68 min DOTANOC Neuroendocrine imaging

Rb-82 72 secs Rb-82 Myocardial perfusion

Positron and Photons Emission

Kapoor V et al. Radiographics 2004;24:523-543

©2004 by Radiological Society of North America

Annihilation Reaction

• The positron annihilates with an electron to release energy in the form of coincident photons :

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Coincidence Detection

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Figure 5. Photograph (frontal view) of a hybrid PET-CT scanner shows the PET ring detector system (red ring).

Kapoor V et al. Radiographics 2004;24:523-543

©2004 by Radiological Society of North America 17

CRYSTALS USED IN PET

BaF2

– Barium Flouride(0.8ns)

BGO – Bismuth Germinate Oxide(300ns)

LSO – Lutetium Orthosilicate(40ns)

GSO – Gadolineum Orthosilicate(60ns)

YLSO – Yttrium Lutetium Orthosilicate(40ns)

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Data Acqusition

• The detection of photon pairs by opposing crystals create one event (LOR)

• Millions of these event will be stored with in sinograms and used to reconstruct the image

• Spatial resolution is determined by the size of crystal and their separation and is typically 3-5mm

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Interpretation of Images

PET provides images of quantitative uptake of the radionuclide

injected that can give the concentration of radiotracer activity in

kilobecquerels per milliliter .

Methods for assessment of radiotracer uptake –

• visual inspection

• standardized uptake value (SUV)

• glucose metabolic rate

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SUV

• Standardized Uptake Value

• The SUV is a semiquantitative assessment of the radiotracer uptake from a static (single point in time) PET image.

• Malignant tumors have an SUV of greater than 2.5–3.0, whereas normal tissues such as the liver, lung, and marrow have SUVs ranging from 0.5 to 2.5.

• The SUV of a given tissue is calculated with the following formula:

Limitations of PET/CT

• FDG is not cancer specific and will accumulate in any

areas of high rates of metabolism and glycolysis.

• Therefore, increased uptake can be expected in all sites

of hyperactivity at the time of FDG administration (e.g.

muscles and nervous system tissues); at sites of active

inflammation or infection

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The distribution of FDG within a normal individual (MIP).

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Physiologic FDG uptake

Figure 17b.

Kapoor V et al. Radiographics 2004;24:523-543

©2004 by Radiological Society of North America

Figure 18. Non-small cell lung carcinoma in a 78-year-old man with enlarged hilar and mediastinal lymph nodes.

Kapoor V et al. Radiographics 2004;24:523-543

©2004 by Radiological Society of North America

Figure 20. Large cell lung cancer in a 54-year-old woman.

Kapoor V et al. Radiographics 2004;24:523-543

©2004 by Radiological Society of North America

Identification of distant metastatic disease

Top Tip Evidence suggests that the removal of a solitary adrenal deposit at the time of resection of the lung primary results in an increased life expectancy. Liver, adrenal, brain and bony deposits are common with lung cancer but many of the lesions are undetected in the course of conventional staging

• ASSESSMENT OF TREATMENT RESPONSE

Pretherapy and post therapy studies showing a complete metabolic response to therapy.

PET in Neurology

The Active Human Brain

Hypo metabolism in left temporal lobe secondary to epilepsy

THANK YOU new ideas make work interesting

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