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Buxton & District Science Discussion Medical Scanners Marge Rose 16th November 2012 Buxton & District Introduction • Confusion – they all look the same • CT, MR, SPECT, PET, Ultrasound • A plethora of names • Why a scan? Science Discussion Buxton & District Names • • • • Science Discussion CT – computed tomography (was CAT) SPECT – nuclear medicine (was radioisotopes) MR(I) is based on NMR PET stands for positron emission tomography Buxton & District Why a scan? • • • • • • • An aid to diagnosis Localisation Screening Assessment of function Treatment planning and monitoring Research Reassurance Science Discussion Buxton & District For each modality We’ll look at • History • Importance • Probe • Signal – few natural ones • Detector – match to signal • What is it detecting? Science Discussion Buxton & District EM spectrum Science Discussion Buxton & District Ionisation Certain types of radiation can ionise atoms Science Discussion Buxton & District Ultrasound • Sound is experienced by our ears • Caused by longitudinal pressure waves • We can hear from 20 Hz to 20 kHz • Above 20 kHz - ultrasound Science Discussion Buxton & District Ultrasound scan Science Discussion 1980 Buxton & District CT scan – uses x-rays Science Discussion They were discovered in 1895 by Röntgen. 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. Buxton & District X-ray tube and image But x-ray tubes and images have improved a great deal in over 100 years Science Discussion Buxton & District High Voltage Generator The naked CT Science Discussion Cooling heat exchanger Cooling oil pump Detector Array Detector Amplifiers & A/D Converters X-Ray tube 120-140kV Collimator Buxton & District Tomography Science Discussion “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” X-ray tube Reconstruction of the data by Back projection Patient Grid Buxton & District CT slice through abdomen Science Discussion Probe 120kV X-ray Interaction Photoelectric, Compton Property X-ray attenuation Image 3D reconstruction from multiple projections Buxton & District SPECT – uses γ rays Science Discussion 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 Buxton & District Gamma camera detector Gamma Camera detector computer Light guide Crystal collimator Lead shield (~60) PhotoMultiplier Tubes + pre-amp + ADC (Analog to Digital Convertor) Science Discussion 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 Buxton & District Nuclear Medicine Science Discussion 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) Buxton & District Whole body imaging A type of static imaging – A whole body bone scan is a very common example Science Discussion Gated images – the MUGA Series1 Series1 Series1 R-R interval 24 1 2 3 Frame or bin 4 Buxton & District SPECT studies – Myocardial perfusion scan Science Discussion Probe Gamma emitting isotope Interaction Uptake of radiopharmaceutical Property Concentration of pharmaceutical in organ Image Spatial distribution of counts SPECT – 3D PET – Positron Emission Tomography Buxton & District Antimatter Science Discussion • 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 Buxton & District Positron annihilation 511 keV e.g.18F b+ e- 511 keV Coincidence Unit Science Discussion Buxton & District PET images Science Discussion Normal Pre-therapy Post-therapy Buxton & District MR scanner Science Discussion An MR(I) Scanner Buxton & District MR – souped up NMR Science Discussion • A hydrogen nucleus has spin • 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 Buxton & District Gradient coils Science Discussion Buxton & District MR Science Discussion • Probe – EM pulses • Interaction – Resonant energy exchange changes nucleus spin state • Property – proton density, proton microenvironment • Image – Map EM signal – 3D reconstruction Buxton & District Artifacts, Hybrid scans Science Discussion The End
