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Partial-Volume Effect in PET Tumor Imaging^*

¹ UMR 678 INSERM-UPMC, CHU Pitié-Salpêtrière, Paris, France; ² Nuclear Medicine Department, HIA Val-de-Grâce, Paris, France; and ³ Department of Radiology, University of California, San Francisco, California

View larger version (33K): [in this window] [in a new window]   FIGURE 1.  Circular source (diameter of 10 mm) of uniform activity (100 arbitrary units) in nonradioactive background yields measured image in which part of signal emanating from source is seen outside actual source. Maximum activity in measured image is reduced to 85.

View larger version (21K): [in this window] [in a new window]   FIGURE 2.  Influence of image sampling on PVE. Pixels on edges of source include both source and background tissues. Signal intensity in these pixels is mean of signal intensities of underlying tissues. Part of signal emanating from source is seen outside actual object and therefore is described as spilling out.

View larger version (24K): [in this window] [in a new window]   FIGURE 3.  The measured image (D) of the activity distribution (A) results from mixture of spilling out (B) and spilling in (C). Image sampling affects background activity, creating spilling in within tumor (C). Resulting image is sum of spilling in and spilling out (D).

View larger version (24K): [in this window] [in a new window]   FIGURE 4.  (A) PET image. (B) Corresponding CT image. (C) PET/CT image. Discrepancy between tumor contours as seen on CT and PET images is clearly visible.

View larger version (42K): [in this window] [in a new window]   FIGURE 5.  Transverse PET slice of 6 radioactive spheres with different diameters (10, 12, 16, 22, 28, and 34 mm) and filled with same radioactivity concentrations in uniform radioactive background (left) and corresponding CT slice (right). PVE makes apparent uptake decrease when sphere size decreases.

View larger version (29K): [in this window] [in a new window]   FIGURE 6.  PET slice (left) and corresponding CT slice (right). Tumor is close to 3 types of tissues (lung, liver, and mediastinum).

View larger version (12K): [in this window] [in a new window]   FIGURE 7.  Transverse PET slices of same PET data reconstructed with ordered-subset expectation maximization with different numbers of iterations (8 subsets). SUVmax varies substantially at early iterations.

View larger version (19K): [in this window] [in a new window]   FIGURE 8.  Transverse PET slices from same patient with image sampling at 4 and 6 mm, resulting SUVmax, and corresponding CT slice.

View larger version (34K): [in this window] [in a new window]   FIGURE 9.  Different measurement methods yield different SUVs. SUVmax was calculated from maximum uptake in tumor. SUV75% and SUV50% were mean values in ROI corresponding to isocontours equal to 75% and 50% SUVmax, respectively. SUV15x15 was measured in fixed rectangular region of 15 x 15 mm. SUVmean was measured in manually drawn region (represented in red on CT slice [right]).

View larger version (29K): [in this window] [in a new window]   FIGURE 10.  Restored activity measured in actual contour of spheres in cold background as function of sphere diameter and spatial resolution of imaging system.

View larger version (22K): [in this window] [in a new window]   FIGURE 11.  Calculation of transfer coefficients for 2 compartments (tumor [t] and background [b]). Image of each binary compartment as seen by imaging system is obtained by modeling imaging system response. Resulting image is nonbinary image from which 4 transfer coefficients can be calculated. For example, Wtt corresponds to fraction of signal emanating from tumor and detected in tumor, whereas Wtb corresponds to fraction of signal emanating from tumor and detected in background.

View larger version (33K): [in this window] [in a new window]   FIGURE 12.  CT image (left), corresponding PET image (middle), and PET/CT image (right) of tumor with no uptake in center. Delineation of tumor from CT image would yield inappropriate definition of metabolically active part of tumor.

View larger version (43K): [in this window] [in a new window]   FIGURE 13.  CT (A and C) and PET (B and D) images corresponding to 2 slices through lung tumor. Compartment contours as drawn from CT are shown in red on PET images.