An important monthly test for CT scanners is the CT constancy test,
which is performed by using the CT quality phantom. The following factors
are checked by this test: position of the light marker, laser slice thickness,
homogeneity and noise of kV values, MTF, and the table position. The
manufacturer provides the appropriate software to conduct these tests.
Questions
- Describe the principles of single photon emission computed tomogra-
phy (SPECT). - Explain how SPECT images are reconstructed by the filtered back-
projection technique. - Elucidate different factors that affect SPECT images.
- What is the optimum angular sampling for the SPECT system?
- How does the center of rotation affect the SPECT image and from what
does it originate? What is the ideal location of COR in a 64 ×64 matrix? - With a multihead camera, does the sensitivity of an imaging device
increase or decrease? - What are the different types of common filters used in the reconstruc-
tion of images in SPECT? - Which of the following acquisition matrices would give better spatial
resolution: a 64 ×64 matrix or a 128 ×128 matrix? - What are the different factors that affect the uniformity of an imaging
device? Describe the methods to improve uniformity. - In the filtered backprojection method, the Fourier method is preferred
to the convolution method. Why? - What is edge packing and how is it rectified?
- High-frequency data represent noise in SPECT image reconstruction.
True or False? - A filter with a low cut-off frequency should be used for noisy data and
low count density studies in order not to curtail image detail. True or
False? - A gamma camera has a NaI(Tl) detector of 38-cm diameter. Data of a
study are acquired in a 64 ×64 matrix. What is the Nyquist frequency? - Describe the OSEM method of reconstruction of SPECT images.
References and Suggested Readings
Bacharach SL. Image analysis. In: Wagner HN Jr, Szabo Z, Buchanan JW, eds.Prin-
ciples of Nuclear Medicine. Philadelphia: W.B. Saunders; 1995; 393–404.
Brooks RA, DiChiro G. Theory of image reconstruction in computed tomography.
Radiology. 1975; 117:561–572.
Cherry SR, Sorensen JA, Phelps ME. Physics in Nuclear Medicine. 3rd ed.
Philadelphia; W.B. Saunders: 2003.
180 12. Single Photon Emission Computed Tomography