Open Access

Image reconstruction using small-voxel size improves small lesion detection for positron emission tomography

Sebastijan Rep
Sebastijan Rep
, 
Petra Tomse
Petra Tomse
, 
Luka Jensterle
Luka Jensterle
, 
Leon Jarabek
Leon Jarabek
, 
Katja Zaletel
Katja Zaletel
 and 
Luka Lezaic
Luka Lezaic
   | Apr 13, 2022
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Article Category: Research Article
Published Online: Apr 13, 2022
Page range: 142 - 149
Received: Feb 01, 2022
Accepted: Feb 16, 2022
DOI: https://doi.org/10.2478/raon-2022-0015
© 2022 Sebastijan Rep, Petra Tomse, Luka Jensterle, Leon Jarabek, Katja Zaletel, Luka Lezaic, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1

NEMA body (A) and the Micro Hollow-Sphere phantom (C), filled in the sphere-to-background radioactivity ratio 2:1, 3:1, 4:1, 8:1, and reconstructed with 2 mm (top row) and 4 mm (bottom row) in-line pixel size. Axial CT images with phantom spheres diameter of NEMA body (B) and the Micro Hollow-Sphere phantom (D).
NEMA body (A) and the Micro Hollow-Sphere phantom (C), filled in the sphere-to-background radioactivity ratio 2:1, 3:1, 4:1, 8:1, and reconstructed with 2 mm (top row) and 4 mm (bottom row) in-line pixel size. Axial CT images with phantom spheres diameter of NEMA body (B) and the Micro Hollow-Sphere phantom (D).

Figure 2

Measurements of contrast-to-noise ratio (CNR)max/mean (top row) and contrast recovery coefficient (CRC)max/mean (bottom row) in all NEMA body and the Micro Hollow-Sphere phantom spheres for all radioactivity concentration ratios with 2 mm and 4 mm in-line pixel size.
Measurements of contrast-to-noise ratio (CNR)max/mean (top row) and contrast recovery coefficient (CRC)max/mean (bottom row) in all NEMA body and the Micro Hollow-Sphere phantom spheres for all radioactivity concentration ratios with 2 mm and 4 mm in-line pixel size.

Figure 3

Graphically represented contrast recovery coefficient (CRC)max/mean and contrast-to-noise ratio (CNR)max/mean of the 2 mm and 4 mm in-line pixel sizes.
Graphically represented contrast recovery coefficient (CRC)max/mean and contrast-to-noise ratio (CNR)max/mean of the 2 mm and 4 mm in-line pixel sizes.

Contrast-to-noise ratio (CNR)max, CNRmean, of the four Micro Hollow Sphere phantom and the six NEMA body phantom spheres filled with sphere-to-background radioactivity concentration ratios of 2:1, 3:1, 4:1, 8:1 for both 2 mm and 4 mm voxel size reconstructions, including relative changes in %

Micro Hollow Sphere phantom - sphere diameter (mm) NEMA body phantom - sphere diameter (mm)
Ratio 8:1 4 mm 5 mm 6 mm 8 mm 10 mm 13 mm 17 mm 22 mm 28 mm 37 mm
2 mm max 12.53 34.82 71.23 134.50 104.68 157.51 159.30 162.70 152.06 148.02
4 mm max N/A 25.58 44.71 84.76 84.32 151.31 181.45 169.86 167.41 161.28
% change 36 59 59 24 4 -12 -4 -9 -8
2 mm mean 11.99 24.84 55.10 75.80 55.69 76.75 89.86 100.92 108.16 115.50
4 mm mean N/A 17.41 40.95 55.58 54.73 78.83 93.99 107.44 116.37 123.83
% change 43 35 36 2 -3 -4 -6 -7 -7
Ratio 4:1 4 mm 5 mm 6 mm 8 mm 10 mm 13 mm 17 mm 22 mm 28 mm 37 mm
2 mm max N/A 6.33 20.19 41.57 31.20 59.06 68.97 65.49 66.91 67.42
4 mm max N/A N/A 17.13 37.28 30.46 57.33 80.41 77.47 76.63 71.95
% change 18 12 2 3 -14 -15 -13 -6
2 mm mean N/A 5.73 16.51 24.55 17.42 29.96 34.68 38.24 43.13 48.28
4 mm mean N/A N/A 16.04 23.93 16.91 29.57 39.95 42.28 47.14 53.26
% change 3 3 3 1 -13 -10 -9 -9
Ratio 3:1 4 mm 5 mm 6 mm 8 mm 10 mm 13 mm 17 mm 22 mm 28 mm 37 mm
2 mm max N/A N/A 7.72 23.53 18.69 32.87 44.04 41.32 42.66 41.87
4 mm max N/A N/A N/A 16.13 18.18 31.84 45.27 49.36 48.04 47.15
% change 46 3 3 -10 -8 -9 -9
2 mm mean N/A N/A 6.11 13.45 11.28 16.93 21.28 22.58 25.55 28.23
4 mm mean N/A N/A N/A 10.66 11.01 16.91 23.39 25.56 28.58 31.47
% change 26 2 0 9 -9 -9 -9
Ratio 2:1 4 mm 5 mm 6 mm 8 mm 10 mm 13 mm 17 mm 22 mm 28 mm 37 mm
2 mm max N/A N/A N/A N/A 5.49 15.68 19.40 22.51 22.90 22.73
4 mm max N/A N/A N/A N/A 4.00 15.08 20.40 24.89 25.48 24.94
% change 37 4 -5 -10 -10 -9
2 mm mean N/A N/A N/A N/A 1.64 6.93 7.59 9.95 11.97 13.85
4 mm mean N/A N/A N/A N/A 1.37 6.54 8.44 11.18 13.32 15.18
% change 20 6 -10 -11 -10 -9

Median, minimum and maximum values of contrast-to-noise ratio (CNR)max and CNRmean over all spheres-to-background ratios for all spheres, smaller (≤ 13 mm) spheres and larger (≥ 17 mm) spheres. The values are given for images reconstructed with 2 mm and 4 mm in-line pixel size

Number of spheres Median Minimum Maximum
CNRmax 2 mm 30 42.26 5.49 162.60
CNRmax4 mm 30 46.21 4.00 181.45
CNRmean 2 mm 30 25.56 1.64 115.50
CNRmean 4 mm 30 27.15 1.37 123.83
CNRmax 2 mm; ≤ 13 mm 14 33.84 5.49 157.51
CNRmax 4 mm; ≤ 13 mm 14 31.15 4.00 151.31
CNRmean 2 mm; ≤ 13 mm 14 20.98 1.64 76.75
CNRmean 4 mm; ≤ 13 mm 14 17.16 1.37 78.73
CNRmax 2 mm; ≥ 17 mm 16 54.76 19.40 162.70
CNRmax 4 mm; ≥ 17 mm 16 60.65 20.40 181.45
CNRmean 2 mm; ≥ 17 mm 16 31.45 7.59 115.50
CNRmean 4 mm; ≥ 17 mm 16 35.71 8.44 123.83

Median, minimum and maximum values of contrast recovery coefficient (CRC)max and CRCmean over all for all spheres, spheres ≤ 13 mm and spheres ≥ 17 mm. The values are given for images reconstructed with 2 mm and 4 mm voxel size

Number of spheres Median Minimum Maximum
CRCmax 2 mm 30 0.88 0.16 0.98
CRCmax 4 mm 30 0.87 0.13 1.03
CRCmean 2 mm 30 0.60 0.14 0.75
CRCmean 4 mm 30 0.59 0.13 0.76
CRCmax 2 mm; ≤ 13 mm 14 0.56 0.16 0.92
CRCmax 4 mm; ≤ 13 mm 14 0.52 0.13 0.84
CRCmean 2 mm; ≤ 13 mm 14 0.40 0.14 0.60
CRCmean 4 mm; ≤ 13 mm 14 0.38 0.13 0.60
CRCmax 2 mm; ≥ 17 mm 16 0.94 0.87 0.98
CRCmax 4 mm; ≥ 17 mm 16 0.94 0.87 1.03
CRCmean 2 mm; ≥ 17 mm 16 0.66 0.57 0.75
CRCmean 4 mm; ≥ 17 mm 16 0.66 0.56 0.76

Contrast recovery coefficient (CRC)max, CRCmean, of the four Micro Hollow Sphere phantom and the six NEMA body phantom spheres filled with sphere-to-background radioactivity concentration ratios of 2:1, 3:1, 4:1, 8:1 for both 2 mm and 4 mm in-line pixel size reconstructions, including relative changes in %

Micro Hollow Sphere phantom - sphere diameter (mm) NEMA body phantom - sphere diameter (mm)
Ratio 8:1 4 mm 5 mm 6 mm 8 mm 10 mm 13 mm 17 mm 22 mm 28 mm 37 mm
2 mm max 0.11 0.16 0.24 0.38 0.65 0.92 0.93 0.95 0.89 0.87
4 mm max N/A 0.15 0.21 0.33 0.51 0.84 0.99 0.93 0.92 0.89
% change 2 14 17 26 10 -5 2 -2 -2
2 mm mean 0.10 0.14 0.20 0.25 0.39 0.50 0.57 0.63 0.67 0.71
4 mm mean N/A 0.13 0.19 0.24 0.37 0.49 0.56 0.63 0.67 0.71
% change 4 2 3 6 3 2 0 0 0
Ratio 4:1 4 mm 5 mm 6 mm 8 mm 10 mm 13 mm 17 mm 22 mm 28 mm 37 mm
2 mm max N/A 0.21 0.28 0.40 0.57 0.87 0.98 0.94 0.96 0.96
4 mm max N/A N/A 0.26 0.38 0.53 0.80 1.03 1.00 1.00 0.95
% change 6 5 8 9 -5 -6 -4 2
2 mm mean N/A 0.20 0.26 0.30 0.41 0.55 0.60 0.64 0.70 0.75
4 mm mean N/A N/A 0.26 0.30 0.39 0.52 0.63 0.64 0.70 0.75
% change 0 0 5 6 -4 -1 0 -1
Ratio 3:1 4 mm 5 mm 6 mm 8 mm 10 mm 13 mm 17 mm 22 mm 28 mm 37 mm
2 mm max N/A N/A 0.28 0.38 0.57 0.78 0.94 0.90 0.92 0.91
4 mm max N/A N/A N/A 0.36 0.53 0.71 0.89 0.94 0.93 0.91
% change 7 7 9 6 -1 0 0
2 mm mean N/A N/A 0.26 0.31 0.64 0.54 0.61 0.62 0.67 0.71
4 mm mean N/A N/A N/A 0.31 0.43 0.51 0.60 0.63 0.67 0.71
% change 1 5 5 1 -1 0 0
Ratio 2:1 4 mm 5 mm 6 mm 8 mm 10 mm 13 mm 17 mm 22 mm 28 mm 37 mm
2 mm max N/A N/A N/A N/A 0.57 0.79 0.87 0.94 0.95 0.94
4 mm max N/A N/A N/A N/A 0.53 0.74 0.85 0.93 0.95 0.93
% change 8 6 3 0 0 1
2 mm mean N/A N/A N/A N/A 0.48 0.60 0.61 0.66 0.71 0.75
4 mm mean N/A N/A N/A N/A 0.47 0.58 0.61 0.67 0.71 0.74
% change 2 4 0 -1 0 1
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