- The example used is a renal study where a radiopharmaceutical passes though the kidney and is excreted within the bladder
- Following the collection of data, images are displayed
- ROIs are then drawn over the right and left kidneys
- ROIs are also drawn below the lower poles of both kidneys and are defined as background (bkg)
- Bkg is then subtracted from each ROI calculation of both kidneys
- Computer then calculated the activity passing through each kidney
- This data is then displayed as a time-activity curve which shows the radiopharmaceutical passing though the kidneys over time
- This type of quantification defines renal function
- The name of the radiopharmaceutical used is Tc99mMAG-3
- SPECT is in many ways very much like a CT scan in radiology
- The differences are: the radiation source and physiology vs. anatomy
- The above image shows how a how a detector or a set of detectors collect information on a 360 radius around the organ of interest
- A SPECT system can have one to three detectors
- The following acquisition parameters are used, however, this data will vary pending what you are imaging:
- 64 stops (in a 360 degree rotation)
- 30 seconds per stop
- 64 by 64 matrix
- Once the data is collected it can be displayed in a cine format which are all 64 planner images rotating on an axis (The exam used here is a Brain SPECT)
- Basic comments on processing
- Images are the backprojected onto each other
- Backprojection is lined up along the same matrix of each image
- The results is a sum of all projections respective to all angles (64) that allows for processing a new images at any angle
- Usually the angles are defined as: transverse (frontal), sagittal, and coronal
- In is important to realized that the concept presented today is very basic
- Images can be filtered to smooth out the data, reducing noise and scatter
- From the above rotating SPECT images the three types of slices are displayed (see above image)
- It should be noted that the these slices are only 2 pixels thick and that 20 additional slices per each transverse, sagittal, and coronal projections where generated
- Note the lack of uptake in the frontal lobe of the brain
- Moya Moya disease is usually a childhood disease that is caused by the lack of blood flow to certain parts of the brain
 |
- PET detects gamma radiation that occurs from positron decay
- F-18 FDG is the most common radiopharmaceutical used for this type of study
- FDG goes to any site in the body that has high glucose turnover
- Brain, myocardium, and many types of cancer utilize a lot of glucose
- As F-18 decays by the release of a positrons, at rest mass it emits two gammas at 180 degrees with 511 keV of energy
- By the process of coincidence detection, a PET system detects and will record any two incoming gammas that strike the crystal at opposite ends, at the same time
- Hence, this imaging system records exactly where the annihilation reaction occurred
- Types of PET systems
- Detected system - Looks a lot like a CT camera, however, it is composed of a ring of crystals
- Modified SPECT/PET system uses two detectors heads that are places at 180 degrees of each other
- Note: A SPECT system must be modified before it can use in coincidence detection
- While this radiographic instrument stands alone in acquiring anatomical "slices of the body" nuclear medicine can also apply this technology
- SPECT and/or PET equipment can be combined with a CT unit
- Creates a concept known as fusion - combining two procedures into one
- Allows to analyze the area of interest by overlaying anatomical and physiological images
- CT can also be used to correct for gamma ray attenuation within the area of interest. This is known as attenuation correction
