Basic SPECT Concepts

1. SPECT imaging (just the fundamentals)
1. SPECT is, in many ways, very much like a CT scan in radiology
2. The differences are:
   1. The radiation source is emission vs. CT is transmission
   2. Nuclear medicine looks at physiology, not anatomy
   3. SPECT resolution has a matrix size of 64 or 128, whereas CT is 512 or 1024
   4. Acquisition time in CT is VERY fast, but SPECT is VERY slow
   
   5. In helical CT, the x-ray tube spins around the patient as the table moves. This allows us to image a significant part of the human anatomy.
   6. SPECT's FOV is limited to the size of the detector
   7. The computer algorithm or image reconstruction that produces tomographic slices is similar in both systems

3. The above image shows how a detector or a set of detectors collects information within a 360 radius around the organ of interest

4. The acquired data is then reconstructed via a filtered backprojection protocol, where the images are projected back at each angle acquired
5. Most SPECT systems have two detectors, however, three detectors systems are available
6. The following acquisition parameters are used and will vary pending the type of procedure being acquired:
1. One-hundred-eighty degree rotation, cardiac only
2. Usually, cardiac is imaged at a 64 matrix with 32 stops
3. Most 360-degree acquisitions are set at a matrix 64 with 64 stops
4. In certain procedures, a 128 matrix may be applied, and usually 128 stops are acquired
5. As a general rule, acquisition time should be no more than 30-minutes

7. Once the data is collected, the raw data can be displayed in a cine format, as seen above
8. The above acquisition is of a pediatric brain scan
9. Raw data is the reconstructed/processed that will produce the tomographic slices
1. Filtered backprojection is applied, and imaging filters are used to enhance image quality
2. The goal of filtering is to remove background counts and reduce noise
3. Can you recall the definition of image noise?
4. The goal is to only keep the true counts

5. Transverse, sagittal, and coronal images are generated and "centered," as seen in the displayed above
6. Again, it is essential to realize that the concept presented today is fundamental

10. From the above rotating SPECT images, the three types of slices are displayed (see above image)
11. It should be noted that these slices are only 2 pixels thick and have approximately 15 slices per each angle that are not being displayed (transverse, sagittal, and coronal)
12. Here is another example of ALL the slices you would see in a normal brain scan
13. From the acquired data, the lack of uptake in the frontal lobe of the brain is demonstrated
14. Moya Moya disease may starts with pediatric patients where calcification within the arterial structure of the brain occurs. The result is a loss of blood flow to specific areas of the brain
15. Moya Moya disease - in Japanese, it means "puff of smoke." Refer to the link
2. Acquisition settings to consider when acquiring a SPECT Bone Scan
   1. Collimation - HR or UHR
   2. Energy Setting - 140 keV with 20% window
   3. Rotation - 360 elliptical or body contour
   4. Matrix 64 with 64 slices
   5. Matrix 126 with 128 slices
   6. Two heads are better than one
   
   7. Time per slice calculation - In general, you should never image longer than 30 minutes and a 2-headed SPECT system is preferred
   8. Calculate the time per stop on a 30-minute acquisition - see above
   9. Other points of interest
      1. Why does SPECT have fewer counts than a spot view?
      2. Even though a SPECT scan may have more total counts, the resolution is based on the number of counts acquired in a single stop
         

      3. Is image shows the position of transverse, sagittal, and coronal angles
      
      4. Here is an example of where a spot view on a bone scan seems normal, however, when SPECT images are taken abnormal uptake is seen
         



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