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RAD 466-L 8 by Dr. Halima Hawesa. SPECT/CT TECHNOLOGY & FACILITY DESIGN. Objective. To become familiar with basic SPECT/CT technology, and review considerations in establishing a new SPECT/CT facility. Content. SPECT cameras Image Quality & C amera QA SPECT/CT scanners

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rad 466 l 8 by dr halima hawesa

RAD 466-L 8byDr. Halima Hawesa

SPECT/CT

TECHNOLOGY & FACILITY DESIGN

objective
Objective

To become familiar with basic SPECT/CT technology, and review considerations in establishing a new SPECT/CT facility

slide3

Content

  • SPECT cameras
  • Image Quality & Camera QA
  • SPECT/CT scanners
  • Design of SPECT/CT facilities
what is spect camera
What is SPECT Camera

gamma cameras.

  • The most widely used gamma cameras are the so-called Anger cameras, in which a series of phototubes detects the light emissions of a large single crystal, covering the field of view of the camera.
  • SPECT imaging systems consist of single- or multiple-head gamma cameras which rotate around the patient, thereby acquiring the projections necessary for reconstruction of axial slices.
  • SPECT stand for Single Positron Emitting Computing Tomography.
slide5

SPECT Camera Components

  • Collimator
  • NaI(Tl) crystal
  • Light Guide (optical coupling)
  • PM-Tube array
  • Pre-amplifier
  • Position logic circuits (differential & addition etc.)
  • Amplifier (gain control etc)
  • Pulse height analyser
  • Display (Cathode Ray Tube etc).
scintillators
Scintillators

Density

Z

Decay

Light

Atten

.

(g/cc)

time

yield

length

(ns)

(% NaI)

(mm)

Na(Tl)

I

3.67

51

230

100

30

BGO

7.13

75

300

15

11

LSO

7.4

66

47

75

12

GSO

6.7

59

43

22

15

  • Na(Tl) I works well at 140 keV, and is the most common scintillator used in SPECT cameras
scintillation detector
Scintillation detector

Amplifier

PHA

Scaler

pulse height analyzer
Pulse height analyzer

Pulse height (V)

UL

LL

Time

The pulse height analyzer allows only pulses of a certain height

(energy) to be counted.

counted

not counted

gamma camera
Gamma camera

Used to measure the spatial and temporal distribution of a radiopharmaceutical

gamma camera principle of operation
Gamma camera(principle of operation)

Position X

Position Y

Energy Z

PM-tubes

Detector

Collimator

Types of collimator

Pinhole

Parallel hole

Diverging

Converging collimators.

gamma camera2
GAMMA CAMERA

Photons are selected by a collimator, hits the detector crystal, which produce light flashes that are detected and amplified by the photomultipliers, then send to digitizer, and then to computer processor for image reconstruction, then to display on monitor.

pm tubes
PM-tubes

Detect and amplify the light flash produced by the scintillation crystal.

gamma ray scintillation detector

Light

gamma-Rays

GAMMA-ray Scintillation Detector
  • gamma-ray energy converted to light
  • Light converted to electrical signal

Photomultiplier Tube

Electrical

Signal

Scintillation

Crystal

photomultiplier tubes
Photomultiplier Tubes
  • Light incident on Photocathode of PM tube
  • Photocathode releases electrons

+

-

Light

gamma-Rays

Scintillation

Crystal

Photocathode

PM

Tube

Dynodes

photomultiplier tubes1
Photomultiplier Tubes
  • Electrons attracted to series of dynodes
    • each dynode slightly more positive than last one

+

+

+

-

+

+

Light

gamma-Rays

Scintillation

Crystal

Photocathode

PM

Tube

Dynodes

gamma camera data acquisition
Gamma cameraData acquisition
  • Static
  • Dynamic
  • ECG-gated
  • Wholebody scanning
  • Tomography
  • ECG-gated tomography
  • Wholebody tomography
factors affecting image formation
Factors affecting image formation
  • Distribution of radiopharmaceutical
  • Collimator selection and sensitivity
  • Spatial resolution
  • Energy resolution
  • Uniformity
  • Count rate performance
  • Spatial positioning at different energies
  • Center of rotation
  • Scattered radiation
  • Attenuation
  • Noise
spatial resolution
SPATIAL RESOLUTION

Sum of intrinsic resolution and the collimator resolution

Intrinsic resolution depends on the positioning of the

scintillation events (detector thickness, number of PM-tubes, photon energy)

Collimator resolution depends on the collimator geometry (size, shape and length of the holes)

spatial resolution1
SPATIAL RESOLUTION

Object

Image

Intensity

non uniformity
NON-UNIFORMITY

(Contamination of collimator)

non uniformity ring art i facts
NON UNIFORMITYRING ARTIFACTS

Good uniformity Bad uniformity

Difference

non uniformity1
NON-UNIFORMITY

Defect collimator

scattered radiation
Scattered radiation

Scattered

photon

photon

electron

the amount of scattered photons registered
The amount of scattered photons registered

Depends on

1- Patient size

2- Energy resolution of the gammacamera

3- Window setting

pulse height distribution

Counts

140

120

100

80

Tc99m

60

40

20

0

120

100

140

160

20

60

Energy

Pulse height distribution

Full energy peak

Scattered

photons

The width of the full energypeak (FWHM) is determined by the energy resolution of thegamma camera. There willbe an overlap between thescattered photon distributionand the full energy peak,meaning that some scatteredphotons will be registered.

FWHM

Overlappingarea

window width
Window width

20%

40%

10%

Increased window width will result in an increased number ofregistered scattered photons and hence a decrease in contrast

attenuation correction
ATTENUATION CORRECTION
  • Transmission measurements
  • Sealed source
  • CT
attenuation correction1
ATTENUATION CORRECTION

Ficaro et al Circulation 93:463-473, 1996

noise
NOISE

Count density

gamma camera3
Gamma camera
  • Operational considerations
      • Collimator selection
      • Collimator mounting
      • Distance collimator-patient
      • Uniformity
      • Energy window setting
      • Corrections (attenuation, scatter)
      • Background
      • Recording system
      • Type of examination
qc gamma camera
QC GAMMA CAMERA

Acceptance Daily Weekly Yearly

Uniformity P T T P

Uniformity, tomography P P

Spectrum display P T T P

Energy resolution P P

Sensitivity P T P

Pixel size P T P

Center of rotation P T P

Linearity P P

Resolution P P

Count losses P P

Multiple window pos P P

Total performance phantom P P

P: physicist, T:technician

slide41

Sensitivity

  • Expressed as counts/min/MBq and should be measured for each collimator
  • Important to observe with multi-head systems that variations among heads do not exceed 3%
multiple window spatial registration
Multiple Window Spatial Registration
  • Performed to verify that contrast is satisfactory for imaging radionuclides, which emit photons of more than one energy (e.g. Tl-201, Ga-67, In-111, etc.) as well as in dual radionuclides studies
count rate performance
Count Rate Performance
  • Performed to ensure that the time to process an event is sufficient to maintain spatial resolution and uniformity in clinical images acquired at high-count rates
total performance
Total performance

Total performance phantom. Emission or transmission.

Compare result with reference image.

phantoms for qc of gamma cameras
Phantoms for QC ofgamma cameras
  • Bar phantom
  • Slit phantom
  • Orthogonal hole phantom
  • Total performance phantom
quality control analogue images
QUALITY CONTROLANALOGUE IMAGES

Quality control of film processing: base & fog, sensitivity,

contrast

quality assurance computer evaluation
QUALITY ASSURANCECOMPUTER EVALUATION

Efficient use of computers can

increase the sensitivity and

specificity of an examination.

* software based on published and

clinically tested methods

* well documented algorithms

* user manuals

* training

* software phantoms

typical spect ct configuration
TYPICAL SPECT/CT CONFIGURATION

The most prevalent form of SPECT/CT scanner involves a dual-detector SPECT camera with a 1-slice or 4-slice CT unit mounted to the rotating gantry; 64-slice CT for SPECT/CT also available

spect ct
SPECT/CT
  • Accurate registration
  • CT data used for attenuation correction

Localization of abnormalities

  • Parathyroid lesions (especially for ectopic lesions)
  • Bone vs soft tissue infections
  • CTCA fused with myocardial perfusion for 64-slice CT scanners
the ct scanner
The CT Scanner

X ray tube

X ray emission in

all directions

collimators

a look inside a rotate rotate ct
A look inside a rotate/rotate CT

Detector Array

and Collimator

X Ray

Tube

a look inside a slip ring ct
A Look Inside a Slip Ring CT

Note:

how most

of the

electronics is

placed on

the rotating

gantry

X Ray

Tube

Detector

Array

Slip Ring

what are we measuring in a ct scanner
What are we measuring in a CT scanner?
  • We are measuring the average linear attenuation coefficient µ between tube and detectors
  • The attenuation coefficient reflects how the x ray intensity is reduced by a material
conversion of to ct number
Conversion of  to CT number
  • Distribution of  values initially measured
  •  values are scaled to that of water to give the CT number
nuclear medicine application according to type of radionuclide
Nuclear medicine applicationaccording to type of radionuclide

Radionuclide

Diagnostics

Therapy

  • Pure  emitter  ()
  • e.g. ; Tc99m, In111, Ga67, I123
  • Positron emitters (ß+)  
  • e.g. : F-18
  • , ß- emitters 
  • e.g. : I131, Sm153
  • Pure ß- emitters  
  • e.g. : Sr89, Y90, Er169
  •  emitters  
  • e.g. : At211, Bi213
radiopharmaceuticals
RADIOPHARMACEUTICALS
  • Radiopharmaceuticals used in nuclear medicine can be classified as follows:
  • ready-to-use radiopharmaceuticals
  • e.g. 131I- MIBG, 131I-iodide, 201Tl-chloride, 111In- DTPA
  • instant kits for preparation of products
  • e.g. 99mTc-MDP, 99mTc-MAA, 99mTc-HIDA, 111In-Octreotide
  • kits requiring heating
  • e.g. 99mTc-MAG3, 99mTc-MIBI
  • products requiring significant manipulation
  • e.g. labelling of blood cells, synthesis and labelling of radiopharmaceuticals produced in house
99 mo 99m tc generator
99Mo-99mTc GENERATOR

Technetium-99m is a metastable nuclear isomer of technetium-99, symbolized as 99mTc. The "m" indicates that this is a metastable nuclear isomer

87.6%

99mTc

99Mo

Molybdenum 99

 140 keV

T½ = 6.02 h

12.4%

ß- 442 keV

 739 keV

T½ = 2.75 d

99Tc

ß- 292 keV

T½ = 2*105 y

99Ru stable

technetium generator
Technetium generator

Mo-99 Tc-99m Tc-99

66 h 6h

NaCl

AlO2

Mo-99

+Tc-99m

Tc-99m

radiopharmaceuticals1
Radiopharmaceuticals

Radionuclide Pharmaceutical Organ Parameter

+ colloid Liver RES

Tc-99m + MAA Lungs Regional

perfusion

+ DTPA Kidneys Kidney

function

summary of s pet ct
SUMMARY OF SPET/CT
  • SPECT cameras are scintillation cameras, also called gamma cameras, which image one gamma ray at a time, with optimum detection at 140 KeV, ideal for gamma rays emitted by Tc-99m
  • SPECT cameras rotate about the patient in order to determine the three-dimensional distribution of radiotracer in the patient
  • SPECT/CT scanners have a CT scanner immediately adjacent to the SPECT camera, enabling accurate registration of the SPECT scan with the CT scan, enabling attenuation correction of the SPECT scan by the CT scan and anatomical localization of areas of unusually high activity revealed by the SPECT scan
spect ct clinical allplications
SPECT/CT CLINICAL ALLPLICATIONS
  • Refer to the pdf file included with this lecture (spect-appl-L8)