Transcript Effect of Software Version on Tomography Counts

Effect of Software Version
on Tomography Counts
WH Thomson
City Hospital , Birmingham
Software Versions
Version 8.5
 Version 9.4
 Version 8.9

“Software enhancements ensure that counts in
zoomed reconstructed images are
approximately equal to the counts in the
corresponding unzoomed images. “
Phantom

Plastic Cylinder 10cm long x 9.5cm diameter

Filled with Tc99m (80MBq), placed on bed

circular orbit, 20cm radius , 360 degrees, 60
frames , 10s per frame.

Hardware zoom factors
X1 , x1.33 , x1.6 . X2 , x2.6 , x3.2

also zoom x1 but 120 frames , 5s per frame
Software analysis

FBP Reconstruction , ramp only

x1 zoom reconstructed to give software zooms
of x1.33 , x1.6 . X2 , x2.6 , x3.2

Transverse images summed over phantom

ROI used (Display A) to give
– ROI counts
– Max Pixel value
Software Zoom
Zoom x3.2
x1
Zoom
x2
Width = 18.7cm
59.8cm
29.9cm
Quantification

Ramp only data used

summed all frames of phantom

ROI drawn on summed image
Counts in
Phantom
Summed images
ROI in Display A
- ROI counts
- Max Pixel
Software version 8.5
( Software zoom )
Max Pixel
ROI counts
1000
120
800
100
80
600
%
% 60
400
40
200
20
0
0
1
1.5
2
2.5
zoom factor
3
3.5
1
1.5
2
2.5
zoom factor
3
3.5
Software version 9.4
( Software zoom )
Max Pixel
ROI counts
120
120
100
100
80
80
% 60
% 60
40
40
20
20
0
0
1
1.5
2
2.5
zoom factor
3
3.5
1
1.5
2
2.5
zoom factor
3
3.5
Hardware v Software Zoom v9.4
ROI hardware zoom
hardware zoom max pix
ROI software zoom
software zoom max pix
12000
5000
10000
4000
total
K counts
8000
2000
6000
Max Pixel
value
3000
4000
1000
2000
0
0
1
1.5
2
2.5
zoom factor
3
3.5
1
1.5
2
2.5
zoom factor
3
3.5
60 frame v 120 frame (v9.4)
(Software zoom )
ROI counts 60 frames
ROI counts 120 frames
ROI counts 60 frames
3500
12000
3400
10000
ROI counts 120 frames
8000
3300
total
K counts
6000
Max Pixel
value
4000
3200
3100
2000
3000
0
1
1.5
2
2.5
zoom factor
3
3.5
1
1.5
2
2.5
zoom factor
3
3.5
Filter Effect

Change pixel size , need to change cut-off
Zoom
Factor
Pixel
size (mm)
cut-off
cycles/2 pixels
x1
x1.33
4.7
3.5
0.6
0.45
x1.6
x2
2.9
2.3
0.38
0.30
x2.6
x3.2
1.8
1.5
0.22
0.19
Butterworth and Wiener
hardware zoom
ROI counts - Wiener
ROI counts - Butterworth
160
160
140
140
120
120
100
100
% 80
% 80
60
60
40
40
20
20
0
0
1
1.5
2
2.5
zoom factor
3
3.5
1
1.5
2
2.5
zoom factor
3
3.5
Butterworth ROI counts
software zoom
ROI counts - software zoom
120
100
80
% 60
40
20
0
1
1.5
2
2.5
zoom factor
3
3.5
Conclusions
Older software versions scaled to
maximum pixel
 older versions give quantitative differences
with different zoom factors
 latest software maintains total counts
 check with high zoom factors though
 some count variation observed with Filters

Filter for Software Zoom
3D Postfilter now correctly filters data that
has been significantly zoomed in
Transverse Recon, Iterative Recon, or OffCenter Zoom.
This corrects the problem associated with
3D Postfilter that was identified in Warning
Letter PSN 27 05 22.
Phantom