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Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

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Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012
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Page 1: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science Discussion

Medical Scanners

Marge Rose

16th November 2012

Page 2: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science Discussion

• Confusion – they all look the same

• CT, MR, SPECT, PET, Ultrasound

• A plethora of names

• Why a scan?

Introduction

Page 3: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science Discussion

• CT – computed tomography (was CAT)• SPECT – nuclear medicine (was radioisotopes) • MR(I) is based on NMR• PET stands for positron emission tomography

Names

Page 4: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science Discussion

• An aid to diagnosis• Localisation• Screening• Assessment of function• Treatment planning and monitoring• Research• Reassurance

Why a scan?

Page 5: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science Discussion

We’ll look at• History• Importance• Probe• Signal – few natural ones• Detector – match to signal• What is it detecting?

For each modality

Page 6: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionEM spectrum

Page 7: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionIonisation

Certain types of radiation can ionise atoms

Page 8: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionUltrasound• Sound is experienced by our ears• Caused by longitudinal pressure waves• We can hear from 20 Hz to 20 kHz • Above 20 kHz - ultrasound

Page 9: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionUltrasound scan

1980

Page 10: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science Discussion

CT scan – uses x-rays

Here is the very first x-ray – it shows his wife’s hand and was taken in 1895. The first medical use was just a few months later in 1896.

X-rays are the most important and widespread of the modalities we will look at in this talk.

The method of production is essentially unchanged.

They were discovered in 1895 by Röntgen.

Page 11: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionX-ray tube and image

But x-ray tubes and images have improved a great deal in over 100 years

Page 12: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionThe naked CT

X-Ray tube120-140kVDetector Array

Detector Amplifiers &A/D Converters

Cooling oil pump

Cooling heatexchanger

High Voltage Generator

Collimator

Page 13: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionTomography

“Atom” derived from Greek atomos meaning “uncut, indivisible”“Tomography” is from the Greek tomē meaning “cut” or tomos meaning

“section” and graphein meaning “to write”

Reconstruction of the data by Back projectionX-ray tube

Patient Grid

Page 14: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionCT slice through abdomen

Probe120kV X-ray

InteractionPhotoelectric, Compton

PropertyX-ray attenuation

Image3D reconstruction from multiple projections

Page 15: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionSPECT – uses γ rays

Becquerel discovered radioactivity in 1896

The Curies researched into it and Marie opened the first Radium Institute in 1914

Radioisotopes were first used in diagnosis after World War II when radioiodine became readily available

Rectilinear scanner appeared in 1951

Anger camera was invented in 1957

Page 16: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionGamma camera detector

First Anger camera I ever saw in use was in 1975

The most common radionuclide used is still Technetium 99m despite supply difficulties

Gamma ray energy 140keV

Half life of 6 hours

‘No’ beta emission

Flexible chemistry

Page 17: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionNuclear Medicine

X-ray images show anatomy whereas Nuclear Medicine images show function

Uses unsealed radioactive sources introduced into the patient. Patients can still be radioactive when they leave the hospital

Gamma cameras are much less common than x-ray machines

Very few Nuclear Medicine tests are diagnostic – generally they are highly sensitive but are of low specificity

‘Scans’ can comprise of static or dynamic images, whole body, gated images or SPECT (single photon emission computed tomography)

Page 18: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionWhole body imaging

A type of static imaging –

A whole body bone scan is a very common example

Page 19: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

R-R interval

24

1 2 3 4Frame or bin

Gated images – the MUGA

Page 20: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionSPECT studies – Myocardial perfusion scan

ProbeGamma emitting isotope

InteractionUptake of radiopharmaceutical

Property Concentration of pharmaceutical in organ

ImageSpatial distribution of countsSPECT – 3D

Page 21: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

PET – Positron Emission Tomography

Page 22: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionAntimatter

• Each fundamental particle has an antimatter equivalent• Same mass but opposite charge• Positrons are positive electrons• Collide with the first electron they come across to produce annihilation radiation

Page 23: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionPositron annihilation

e.g.18F

511 keV

511 keV

+

e- Coincidence Unit

Page 24: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionPET images

Normal Pre-therapy Post-therapy

Page 25: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionMR scanner

An MR(I) Scanner

Page 26: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionMR – souped up NMR

• If placed in a magnetic field, the nucleus precesses around in the direction of that field

• Direct in an RF (radiofrequency) pulse and the nucleus can flip to the higher energy state, opposing the field

• When it relaxes back, it gives off an RF signal which is dependent on the chemical environment

• A hydrogen nucleus has spin

Page 27: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionGradient coils

Page 28: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionMR

• Probe– EM pulses

• Interaction– Resonant energy exchange

changes nucleus spin state• Property

– proton density, proton microenvironment

• Image– Map EM signal– 3D reconstruction

Page 29: Buxton & District Science Discussion Medical Scanners Marge Rose 16 th November 2012.

Buxton & District

Science DiscussionArtifacts, Hybrid scans

The End


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