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Truncation Artifact on PET/CT: Impact on Measurements of Activity Concentration and Assessment of a Correction Algorithm

Osama Mawlawi1, Jeremy J. Erasmus2, Tinsu Pan1, Dianna D. Cody1, Rachelle Campbell2, Albert H. Lonn3, Steve Kohlmyer3, Homer A. Macapinlac2 and Donald A. Podoloff1

1 Department of Imaging Physics, M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Box 56, Houston, TX 77030.
2 Department of Diagnostic Imaging, M. D. Anderson Cancer Center, Houston, TX.
3 GE Healthcare, Waukesha, WI.


Figure 1
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  		Fig. 1A —48-year-old man with lymphoma. CT image with truncation of arms (A) and CT attenuation-corrected PET scan (B) show truncation artifact. Truncation artifact causes rim of high attenuation values at edge of CT field of view (FOV), leaving objects beyond edge with no attenuation. These artifacts result in overestimation of 18F-FDG activity concentration in rim region (arrows, B) and underestimation in regions beyond edge (asterisks, B) of CT FOV. Note marked uptake of 18F-FDG in chest wall mass (M).

 

Figure 2
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  		Fig. 1B —48-year-old man with lymphoma. CT image with truncation of arms (A) and CT attenuation-corrected PET scan (B) show truncation artifact. Truncation artifact causes rim of high attenuation values at edge of CT field of view (FOV), leaving objects beyond edge with no attenuation. These artifacts result in overestimation of 18F-FDG activity concentration in rim region (arrows, B) and underestimation in regions beyond edge (asterisks, B) of CT FOV. Note marked uptake of 18F-FDG in chest wall mass (M).

 

Figure 3
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  		Fig. 2A —Phantom 1. CT image of cylindric phantom with inserts positioned centrally in scanner field of view (FOV).

 

Figure 4
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  		Fig. 2B —Phantom 1. and C, CT (left) and PET (right) images show phantom positioned at edge of FOV to cause truncation in three inserts before correction (B) and after correction (C).

 

Figure 5
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  		Fig. 2C —Phantom 1. CT (left) and PET (right) images show phantom positioned at edge of FOV to cause truncation in three inserts before correction (B) and after correction (C).

 

Figure 6
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  		Fig. 2D —Phantom 1. Placement of regions of interest (roi) for quantitative evaluation of correction algorithm is shown.

 

Figure 7
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  		Fig. 3A —Phantom 2. CT image of RSD-Alderson chest phantom with simulated arm (asterisk) while positioned centrally in scanner field of view (FOV).

 

Figure 8
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  		Fig. 3B —Phantom 2. and C, CT (left) and PET (right) images of same phantom positioned at edge of FOV to cause truncation in simulated arm (asterisk) before (B) and after (C) truncation correction.

 

Figure 9
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  		Fig. 3C —Phantom 2. CT (left) and PET (right) images of same phantom positioned at edge of FOV to cause truncation in simulated arm (asterisk) before (B) and after (C) truncation correction.

 

Figure 10
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  		Fig. 3D —Phantom 2. Images show placement of regions of interest (circles) on background water and bone insert for quantitative evaluation before (top) and after (bottom) truncation correction.

 

Figure 11
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  		Fig. 4A —55-year-old man with history of metastatic melanoma. Reprinted from [23]. Coronal CT (left), PET (middle), and coregistered PET/CT (right) images obtained before (A) and after (B) truncation correction. Metastasis (arrow) in upper right extremity is located in truncated region of CT image. Before truncation correction, maximum standard uptake value (SUV) measurement in 1.5-cm region of interest drawn on metastasis was 3.25, and after truncation correction maximum, SUV was 6.05—a difference of 86%.

 

Figure 12
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  		Fig. 4B —55-year-old man with history of metastatic melanoma. Reprinted from [23]. Coronal CT (left), PET (middle), and coregistered PET/CT (right) images obtained before (A) and after (B) truncation correction. Metastasis (arrow) in upper right extremity is located in truncated region of CT image. Before truncation correction, maximum standard uptake value (SUV) measurement in 1.5-cm region of interest drawn on metastasis was 3.25, and after truncation correction maximum, SUV was 6.05—a difference of 86%.

 

Figure 13
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  		Fig. 5A —64-year-old man with history of diffuse large B-cell lymphoma. Coronal CT (left), PET (middle), and coregistered PET/CT (right) images obtained before (A) and after (B) truncation correction. Before truncation correction, four measurements of 18F-FDG-avid tumor (within ellipse, A) had maximum standard uptake value (SUV) range of 1.3-2.8 (2.51, 1.28, 1.31, 2.74). After truncation correction, maximum SUV range (within ellipse, B) was 3.6-11.1 (3.59, 7.94, 7.13, 11.12)—an average difference of 328%.

 

Figure 14
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  		Fig. 5B —64-year-old man with history of diffuse large B-cell lymphoma. Coronal CT (left), PET (middle), and coregistered PET/CT (right) images obtained before (A) and after (B) truncation correction. Before truncation correction, four measurements of 18F-FDG-avid tumor (within ellipse, A) had maximum standard uptake value (SUV) range of 1.3-2.8 (2.51, 1.28, 1.31, 2.74). After truncation correction, maximum SUV range (within ellipse, B) was 3.6-11.1 (3.59, 7.94, 7.13, 11.12)—an average difference of 328%.

 

Figure 15
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  		Fig. 6A —35-year-old man with osteosarcoma of left thigh. Coronal oblique CT, PET, coregistered PET/CT, and CT attenuation maximum-intensity-projection images from left to right, respectively. Patient was unable to extend leg and this resulted in truncation artifact. Before truncation correction (A), maximum standard uptake value (SUV) of tumor in truncated region (arrow, A) was 3.37, and after truncation correction (B), maximum SUV was 12.74 (arrow, B)—an increase of 278%.

 

Figure 16
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  		Fig. 6B —35-year-old man with osteosarcoma of left thigh. Coronal oblique CT, PET, coregistered PET/CT, and CT attenuation maximum-intensity-projection images from left to right, respectively. Patient was unable to extend leg and this resulted in truncation artifact. Before truncation correction (A), maximum standard uptake value (SUV) of tumor in truncated region (arrow, A) was 3.37, and after truncation correction (B), maximum SUV was 12.74 (arrow, B)—an increase of 278%.

 

Figure 17
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  		Fig. 7A —Large 73-year-old woman with lymphoma. Coronal CT (left), PET (middle), and coregistered PET/CT (right) images obtained before (A) and after (B) truncation correction. Truncation artifact affects soft tissue only, and truncated area on CT shows rim of increased attenuation value with corresponding decrease in 18F-FDG activity concentration. Before truncation correction, maximum standard uptake (SUV) value of soft tissue was 0.32 (arrow, A), and after truncation correction, maximum SUV was 0.79 (arrow, B)—an increase of 147%.

 

Figure 18
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  		Fig. 7B —Large 73-year-old woman with lymphoma. Coronal CT (left), PET (middle), and coregistered PET/CT (right) images obtained before (A) and after (B) truncation correction. Truncation artifact affects soft tissue only, and truncated area on CT shows rim of increased attenuation value with corresponding decrease in 18F-FDG activity concentration. Before truncation correction, maximum standard uptake (SUV) value of soft tissue was 0.32 (arrow, A), and after truncation correction, maximum SUV was 0.79 (arrow, B)—an increase of 147%.

 

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