Assist. Prof. Dr. Ilker Ozsahin Oct 9 2017 SPECT Assist. Prof. Dr. Ilker Ozsahin Oct 9 2017

Questions Which radiations can be stopped in which medium or material and at what thickness? Why is this important? What is the mostly used scintillation crystal, and their properties, e.g. NaI(Tl) Thallium-doped Sodium Iodide and its density, atomic number, etc.? Spatial Resolution & Sensitivity Formula? Compton Kinematics? Characteristics of Scintillation Detectors: Energy Resolution, Decay Time, Efficiency, Effective Z, Density, Photon Yield, Relative Light Output, Attenuation Coefficient?

Commonly used single photon emitting radionuclides

Parallel hole collimator Most common designs are Low Energy All-Purpose (LEAP), Low Energy High-Resolution (LEHR) and Medium- and High Energy Collimators.  LEAP collimators have holes with a large diameter. The sensitivity is relatively high as where the resolution is moderate (larger diameter holes allow more scattered photons). The average sensitivity of a LEAP is approx. 500,000 cpm for a 1-uCi source, and the resolution is 1.0cm at 10cm from the patent side of the collimator.  LEHR collimators have higher resolution images than the LEAP. They have more holes that are both smaller and deeper. The sensitivity is approx. 185,000 cpm for 1-uCi source, and the resolution is higher with 0.65cm at 10cm from the patient side of the collimator.  Medium Energy Collimators are used for medium energy photons of nuclides such as Krypton81 (190keV), Gallium67, Indium111. High Energy Collimators are used for Iodine131(606keV) and F-18FDG. These collimators have thicker septa than LEAP and LEHR collimators (mainly used with Technetium 99m) in order to reduce septal penetration by the higher energy photons.

Electromagnetic Spectrum

Spatial Resolution  

Full Width at Half Maximum (FWHM)

Efficiency

Physical properties of common SPECT scintillator detector

Comparison of scintillator materials

Physical properties of common SPECT semiconductor detector

Compton Kinematics

Good Absorbers Alpha Sheet of paper Beta Thin sheet of aluminum Gamma a few cm of Lead or meters of concrete Gamma 122keV Gamma 140keV Gamma 511keV

Single-photon emission computed tomography (SPECT) Single-photon emission computed tomography (SPECT) cameras acquire multiple planar view of the radioactivity in an organ. The data are then processed mathematically to create cross sectional views of the organ. SPECT utilizes the single photons emitted by gamma-emitting radionuclides such as 99mTc, 67Ga, 111In, and 123I. This is in contrast to positron emission tomography (PET), which utilizes the paired 511-keV photons arising from positron annihilation. PET

Single-photon emission computed tomography (SPECT) The simplest camera design for SPECT imaging is similar to that of a planar camera but with two additional features. First, the SPECT camera is constructed so that the head can rotate either stepwise or continuously about the patient to acquire multiple views. Second, it is equipped with a computer that integrates the multiple images to produce the cross sectional views of the organ.

Single/Double/Triple Headed SPECT  

Two Headed SPECT Two-headed cameras can have a fixed, parallel configuration or fixed, perpendicular configuration Fixed, parallel heads (opposing heads) can be used for simultaneous anterior and posterior planar imaging or can be rotated as a unit for SPECT acquisition. Fixed, perpendicular heads, in an L-shaped unit, are used almost exclusively for cardiac or brain SPECT imaging.

Two Headed SPECT