nuclear medicine contents imaging - unibas.ch · 2016-10-05 · principles of medical imaging oct...

Nuclear MedicineImaging

Principles of Medical Imaging

Prof. Dr. Philippe Cattin

MIAC, University of Basel

Oct 31st, 2016

Oct 31st, 2016Principles of Medical Imaging

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Prof. Dr. Philippe Cattin: Nuclear Medicine Imaging

Contents

Abstract

1 Introduction

Introduction

Introduction (2)

2 Scintigraphy

Scintigraphy

Scintigraphy (2)

Radiopharmaceuticals

99mTc Radiopharmaceuticals in Routine Applications

Bone Scintigraphy Examples

Causes of Image Degradation

3 Collimator

Collimator

Collimator Designs

Collimator Examples

Resolution and Efficiency

Resolution vs Depth

4 Single Photon Emission Tomography

Single Photon Emission Tomography

Single Photon Emission Tomography (2)

SPECT Applications

Early Clinical SPECT Systems

Today's Clinical SPECT Systems

Attenuation Correction

Attenuation Correction (2)

SPECT/CT

SPECT/CT System

5 Positron Emission Tomography

Positron Emission Tomography

PET Radiopharmaceuticals

PET Radiopharmaceuticals (2)

PET Scanning PrincipleOct 31st, 2016Principles of Medical Imaging

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PET Projections

PET/CT and PET/MRI

PET/CT Scan Protocol

PET/CT Example


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(2)


Abstract

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Introduction


(4)Introduction

The methods of Nuclear Medicine are a coalition of

Physics

To produce the radio nuclei (radiotracers)

Chemistry

Synthesising radiopharmaceuticals from the tracers

Physiology/Medicine

To understand and interpret the radionuclide distribution

Engineering

To operate/maintain and process the acquired data

Nuclear medicine differs from most other imaging modalities in that thetests primarily show the physiological function of the system beinginvestigated as opposed to traditional anatomical imaging such as CT orMRI.

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Introduction

(5)


Introduction (2)

The → Washington University in St. Louis [http://wustl.edu] has a → nice collection[http://gamma.wustl.edu/allknown.html] of nuclear medicine cases split by study type anddiagnosis.

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Scintigraphy


(7)Scintigraphy

Scintigraphy or planar imaging is anuclear medicine imaging modalityoften used in diagnosis. It consists ofthe following main steps

The radionuclides are combined with

chemical compounds →

radiopharmaceuticals

The radiopharmaceutical is

administered to the patient

Wait for the radiopharmaceutical to

distribute in the body

External gamma cameras capture

the photons and form an image

representing the distribution of the

radionuclides i.e. the

radiopharmaceuticals

Since the energy of the photons is

known, scattered photons can be

rejected

Fig. 7.1: Principle of scintigraphy

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Scintigraphy

(8)


Scintigraphy (2)

Scintigraphy is used to diagnose

Cancer and metastases

Bone fractures caused e.g. by fatigue

and are difficult or impossible to see

under planar X-ray

Myocardial ischemia

...

Fig. 7.2: Gamma camera of the scintigraph

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Scintigraphy

(9)


Radiopharmaceuticals

Although multiple radionuclides are available for nuclear medicine, thepredominant nuclei is as its generator can be stored for weeks and isimmediately available.

All the radiopharmaceuticals are constructed such that they mimic a certainfunctional compound of the human physiology.

Depending on the age of the patient, the type of investigation and the appliedradiopharmaceutical one has to wait for several minutes and up to an hour beforescanning the patient.

Fig. 7.3: MAG3 forrenal investigations

Fig. 7.4: Brainseeking

complex

Fig. 7.5: Brainseeking

complex

Fig. 7.6: Complexfor imaging the

neuronal dopaminetransport

Fig. 7.7: Complexfor imaging the

neuronal dopaminetransport

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Scintigraphy

(10)


99mTc Radiopharmaceuticals inRoutine Applications

The table below shows some based radiopharmaceuticals and their use inroutine clinical applications on adults in Scintigraphy and SPECT.

Organ Agent Application

Bone MDP Metastases

HMDP Fractures

Brain DTPA Tumour

HMPAO Perfusion

Cardiac MIBI Myocardium

Terfosmin pyrophosphate Infarct

Kidney DTPA GFR

MAG3 Function

DMSA Function

Lung MAA Perfusion

Aerosols Ventilation

Liver/spleen Colloid Function

EHIDA Biliary

Bone marrow Colloid Metastases

Lymph Colloid Function

Whole body HMPAO Infection

Whole body White cells Tc-DMSA Tumour sites

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Scintigraphy

(11)


Bone Scintigraphy Examples

[http://gamma.wustl.edu/bs116te144.html]

Fig. 7.8: (20.8 mCi Tc-99m MDP i.v), 30 year oldfemale, four weeks post motor vehicle accidentwith continued pain in the sternum, back, and

right ribs

Fig. 7.9: Scintigraphy of a patient with advancedstages of bone cancer (black areas)

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Scintigraphy

(12)


Causes of Image Degradation

In nuclear imaging, the photons are emittedisotropically. Figure 7.10 shows possible fates of thesephotons:

Photons can be absorbed or scattered within the

tissue of the patient

Many of the photons escaping the patient are not

detected because they are emitted in directions away

from the detector

The collimator absorbs the vast majority of the

photons that reach it → only 1 or 2 in 10'000 reaches

the detector

Well over of the emitted photons are wasted

Photons can penetrate the collimator septa without

interaction

Photons reaching the detector crystal can scatter or

pass through without interacting

Multiple scattered photons can also mimic a single

photon within the allowed energy window

The relative probability of these resolution limitingevents depends on the photon energy.

Fig. 7.10: Photon fates innuclear medicine

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Collimator


(14)Collimator

The Collimator is at the heart of anyScintigraphy and/or SPECT system:

The collimator has the biggest impact on the

SNR (signal-to-noise ratio) and image blur

The collimator defines the direction along

which the -rays are allowed to propagate

Lens systems similar to visible light are not

possible with -rays

Absorbing lead collimators are typically used

Fig. 7.11: Design of a parallel holecollimator

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Collimator

(15)


Collimator Designs

Fig. 7.12: Highly sensitive collimator with a lowerspatial resolution

Fig. 7.13: High spatial resolution collimator

Fig. 7.14: Converging collimator Fig. 7.15: Diverging collimator

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Collimator

(16)


Collimator Examples

Fig. 7.16: Example parallel (cast) collimator afterrepair (scratches)

Fig. 7.17: Example parallel (foil) collimator

Fig. 7.18: Cast vs. foil design. Whereas the cast design has an even thickness, the foil design has anuneven septa thickness

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Collimator

(17)


Resolution and Efficiency

The spatial resolution of a parallel hole collimator isapproximately given by

(7.1)

and the Efficiency is approximately

(7.2)

Fig. 7.19: Parallel hole collimator

We can state that

spatial resolution improves when the diameter of the hole is reduced but the

efficiency of the collimator decreases with

spatial resolution and efficiency is best for objects close to the collimator, thus

small

the efficiency decreases rapidly with collimator-to-object distance

spatial resolution decreases with increasing gamma energy because of septal

penetration!

We have to find good compromise between resolution, efficiency, applied dose.

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Collimator

(18)


Resolution vs Depth

Fig. 7.20: Resolution vs depth in dependence of the collimator depth , the hole diameter and thedistance to the object

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Single Photon EmissionTomography


(20)Single Photon Emission Tomography

Similar to planar X-ray and CT, → Single PhotonEmission Tomography (SPECT) [http://en.wikipedia.org

/wiki/Single_photon_emission_computed_tomography] is the3-dimensional version of the 2-dimensional Scintigraphy.

Because SPECT acquisition is very similar to the planarScintigraphy, the same → radiopharamceuticals[http://en.wikipedia.org/wiki/Radiopharmaceuticals] may be used.

The concept of SPECT was introduced by → David E.Kuhl [http://en.wikipedia.org/wiki/David_E._Kuhl] and Roy Edwardsin the late 1950's. This was even before the developmentof X-ray computed tomography (CT) in 1970's.

SPECT combines Scintigraphy with reconstructionmethods as used in Computed Tomography (CT) to getthe 3D distribution of the radionuclide.

Fig. 7.21: MultipurposeSPECT scanner

Fig. 7.22: SPECT scanner formainly cardiac applications

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(21)


Single Photon Emission Tomography(2)

The gantry allows to rotate the gamma

camera around the patient.

The camera takes a series of images

(projections) in a step-and-shoot mode.

The non-circular gantry rotation reduces

the patient/camera distance and thus

improves image quality.

Sensitivity can be significantly improved

by using 2 or 3 camera heads or even a

ring of detectors.

An angular sampling interval of is

typical.

Image acquisition time can range from

minutes to an hour or more.

Fig. 7.23: Principle of SPECT

Fig. 7.24: Three head systems increaseefficiency

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(22)


SPECT Applications

Brain

Perfusion (stroke, epilepsy, schizophrenia, dementia,...)

Heart

Coronary artery disease

Myocardial infarcts

Respiratory problems

Liver

Kidney

Cancer/Metastases

Bone fractures

...

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(23)


Early Clinical SPECT Systems

Fig. 7.25: Clinical SPECT imaging system from General Electric ca 1980s

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(24)


Today's Clinical SPECT Systems

(a)

(b)

(c)

Fig. 7.26: (a) General Electric Millennium VG, (b) Philips Cardio 60, (c) Siemens

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(25)


Attenuation Correction

Attenuation of the gamma rays within the patient canlead to significant underestimation of activity in deeptissues, compared to superficial tissues or even to awrong diagnosis.

The attenuations are not always easily recognisable andcould thus be mistaken as a pathology.

Approximate correction is possible, based on relativeposition of the activity and assuming attenuation values

e.g. a constant value.

Modern SPECT equipment has a possibility for atransmision scan or even an integrated CT scanner tomeasure the attenuation coefficients. This data can beincorporated into the SPECT reconstruction to correctfor attenuation.

Fig. 7.27: Some photons

are already absorbed withinthe patient. Although source'B' has twice the activity than'A' it only appears as half asactive due to absorption in

the tissue

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(26)


Attenuation Correction (2)

The photon attenuation in tissue causessignificant problems whenreconstructing SPECT images.

Figure 7.28 shows a simulation for photons in water with an

attenuation of andhomogeneous objects of varyingdiameter.

Attenuation produces distortions thatincrease with object size.

Fig. 7.28:Effect of attenuation on homogeneousdiscs (of varying diameter) in water

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SPECT/CT

Having the gamma camera andCT scanner on the same gantryallows straightforward fusion ofthe two data sets. The CTprovides accurate anatomicallocalisation of the functionalinformation within the gammacamera scan. In addition, the CTdata can be used for generatingattenuation correction maps toincrease the accuracy of thegamma camera data. It isclaimed that the accuracy ofradionuclide therapy planningcan be increased by using theCT attenuation correctedSPECT data. Applications indevelopment include combinedcoronary CT angiography andmyocardial perfusion imaging.

Fig. 7.29: Philips Precedence SPECT/CT

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SPECT/CT System

Fig. 7.30: Siemens Symbia Fig. 7.31: GE Discovery NM/CT 570c forcardiac SPECT/CT

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Positron EmissionTomography


(30)Positron Emission Tomography

Positron Emission Tomography (PET) relies on -decaythat produces two -photons ( ) in oppositedirection when the positron annihilates with a near byelectron.

As the two photons hit the gamma camera quasisimultaneously, no collimation is required.

PET offers the highest sensitivity of all nuclear medicineimaging techniques as

it does not require a collimator and

tissue absorption is less due to the higher energy

photons.

The spatial resolution of PET is higher than in SPECTand modern systems often achieve a resolution of

Fig. 7.32: PET principle

Fig. 7.33: Open PET scanner

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PET Radiopharmaceuticals

In contrast to the radionuclei used for Scintigraphy and SPECT, radionuclei forPET must undergo -decay and thus emit a positron. The most common isotopesused in PET investigations are

Element Half-life Energy

Due to their short half-lifes, they must be produced in an on-site cyclotron.

Before the positron annihilates, it has to lose its kinetic energy throughcollisions. The end-to-end distance of this random walk can be upto awayfrom where it was emitted, limitting the achievable resolution.

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PET Radiopharmaceuticals (2)

The most common radiopharmaceutical used in PET is-labelled fluorodeoxyglucose of FDG. It is extensively

used in tumour, brain and heart imaging studies.

In the example below e.g. the lung nodule (arrow) showsan increased uptake of FDG which turned out to be lungcancer.

Fig 7.34: (A) CT image, (B) PET image. The PET image shows anincreased uptake of FDG indicating a tumour

Fig 7.35: d-Glucose

Fig 7.36: -FDG

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PET Scanning Principle

Fig 7.37: Animation of the PET scanning principle

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PET Projections

Fig 7.38: Animation of projections in PET

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PET/CT and PET/MRI

As the co-registration of thefunctional PET and theanatomical CT images is nottrivial, PET scans areincreasingly read alongside CT(or MR) scans, giving both theanatomic and metabolicinformation in immediatesequence without moving thepatient → more-preciselyregistered data.

Fig. 7.39: Philips Gemini TF PET/CT scanner

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PET/CT Scan Protocol

Fig. 7.40: PET/CT example scan protocol

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PET/CT Example

The bright red/yellow masses show hypermetabolic areas of the pelvis withmetastases of a previous, surgically removed colon carcinoma in a 69-yrs oldwoman. Photo: Renato M.E. Sabbatini, PhD, Cancer Hospital of São Paulo, Brazil

Fig. 7.41: CT image Fig. 7.42: PET image Fig. 7.43: Registered PET/CTimage

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nuclear medicine contents imaging - unibas.ch · 2016-10-05 · principles of medical imaging oct...

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