The distribution of scores comparing AD5 to AD3 in the first material are shown in Figure 1, where the material has been split in two halves corresponding to the first 250 (early) and last 250 (late) comparisons for each reader.
For the first image quality criterion (C1: liver parenchyma) and fifth criterion (C5: overall image quality), there was in the early comparisons a predominance of negative scores for AD5, which was more pronounced in the late comparisons, whereas no visually obvious change was found for the remaining criteria (C2: pancreas contour, C3: kidneys & ureters and C4: lymph nodes).
In the regression analysis, the effects of tube load and slice-thickness variables were strongly significant for all image quality criteria (Table 2). The values of these coefficients were identical to those obtained in the original analysis [6]. For the first criterion (C1: liver parenchyma), there was a strongly significant negative effect of AD5 and its interaction term, indicating that the initially negative evaluation of AD5 relative to AD3 became even stronger during the viewing sessions. Similar findings were observed for the fifth criterion (C5: overall image quality). For the third criterion (C3: kidneys & proximal ureters), there was a significant positive coefficient for AD5, but a significant negative coefficient of similar size for the interaction term, indicating a positive attitude to AD5 at the beginning of the reading session, which vanished during the review. For the remaining criteria (C2: pancreas contour and C4: lymph nodes), the interaction term had no significant effect.
In the second material, an analysis of all the scores comparing AD5 to either AD3 or FBP (Figure 2A) were performed. Here, predominantly negative scores for AD5 are seen with
Table 2. Visual Grading Regression (VGR) based on 2000 comparisons of tube load, reconstruction algorithms ADMIRE 3(AD3) and ADMIRE 5(AD5) and slice thickness for the first material [6]. The reference algorithm is AD3.
Criteria
|
Regression coefficients
|
Whole-model
p value
|
McFadden pseudo R2
|
log (mAs)
|
Slice 2mm
|
Slice 3mm
|
AD5
|
AD5
×
time
|
C1. Liver parenchyma
|
1.25***
|
0.49***
|
0.53***
|
–1.00***
|
–0.70**
|
<0.0001
|
0.083
|
C2. Pancreas contours
|
1.75***
|
0.47***
|
0.50***
|
0.16°
|
–0.22°
|
<0.0001
|
0.059
|
C3. Kidneys and proximal ureters
|
1.78***
|
0.55***
|
0.55***
|
0.49**
|
–0.56*
|
<0.0001
|
0.064
|
C4. Lymph nodes ≤15 mm
|
1.55***
|
0.51***
|
0.49***
|
0.65***
|
–0.34°
|
<0.0001
|
0.061
|
C5. Overall image quality
|
1.65***
|
0.71***
|
0.87***
|
–0.56***
|
–0.59*
|
<0.0001
|
0.077
|
***) p<0.001, **) p<0.01, *) p<0.05, °) not significant
|
C1 (liver parenchyma) and C6 (overall image quality). For C5 (image noise), on the other hand, the scores favourable for AD5 dominate. Both these patterns are slightly more apparent in the late assessments than in the early ones.
The regression analysis of the same material is presented in Table 3A, where both AD3 and AD5 are compared to FBP. The image quality of AD3 was rated as significantly superior to that of FBP, with no significant change over time for all criteria except C6 (overall image quality) for which, the initially positive attitude diminished over time. Still at the end of the review period, a clearly positive effect remained (0.94, p<0.001).
In addition, for AD5, a positive effect relative to FBP was seen initially for all criteria. For the reproduction of liver parenchyma (C1), this was overshadowed by a negative effect of the interaction between AD5 and time, so that at the end of the review period, there was a significant negative effect (−0.53, p<0.001). For image noise (C5), the initial strong positive effect became even stronger during the review. For overall image quality (C6), the initial positive effect diminished significantly over time, but even at the end of the review, a significant positive effect remained (0.67, p<0.001).
There was a strongly significant effect of tube load (categorical variables) for all criteria at tube loads 98 and 140 mAs relative to 42 mAs. The effect of 140 mAs was similar to that of 98 mAs, in line with the original analysis where an increase in dose from 98 to 140 mAs did not lead to a corresponding increase in image quality [7].
To produce results somewhat analogous to those of the first material (comparing AD5 to AD3), an analysis involving AD5 and AD3, split in two halves corresponding to the early and late viewings for each reader (Figure 2B) was carried out. Image criteria C1: liver parenchyma and C6: overall image quality, both show predominantly negative scores for AD5 with no obvious change in attitude between early and late assessments. However, for the remaining criteria C2 ̶ C5 there was a tendency to slight increase in the number of favourable scores for AD5 when comparing early and late viewings.
Table 3A. Visual Grading Regression (VGR) based on 3000 comparisons of tube load and reconstruction algorithms Filtered Back Projection (FBP), ADMIRE 3 (AD3) and ADMIRE 5 (AD5) in the second material [7]. The reference algorithm is FBP.
Criteria
|
Regression coefficients
|
Whole-model
p value
|
McFadden pseudo R2
|
98
mAs
|
140
mAs
|
AD3
|
AD3
×
time
|
AD5
|
AD5
×
time
|
C1. Liver parenchyma
|
2.19***
|
2.38***
|
1.02***
|
–0.35°
|
0.43**
|
–0.96***
|
<0.0001
|
0.178
|
C2. Pancreas contours
|
1.83***
|
1.94***
|
1.22***
|
0.27°
|
1.68***
|
0.34°
|
<0.0001
|
0.118
|
C3. Kidneys and proximal ureters
|
2.01***
|
2.16***
|
1.20***
|
0.42°
|
1.98***
|
0.32°
|
<0.0001
|
0.131
|
C4. Lymph nodes ≤15 mm
|
1.60***
|
1.68***
|
1.07***
|
0.31°
|
1.84***
|
0.30°
|
<0.0001
|
0.102
|
C5. Image noise
|
2.21***
|
2.59***
|
2.00***
|
–0.17°
|
2.98***
|
0.92***
|
<0.0001
|
0.198
|
C6. Overall image quality
|
2.31***
|
2.42***
|
2.02***
|
–1.08***
|
1.93***
|
–1.26***
|
<0.0001
|
0.177
|
***) p<0.001, **) p<0.01, *) p<0.05, °) not significant
|
Table 3B. Visual Grading Regression (VGR) based on 1500 comparisons of tube load and reconstruction algorithms ADMIRE 3(AD3) and 5 (AD5) for the second material [7]. The reference algorithm is AD3.
Criteria
|
Regression coefficients
|
Whole-model
p value
|
McFadden
pseudo R2
|
98
mAs
|
140
mAs
|
AD5
|
AD5
×
time
|
C1. Liver parenchyma
|
2.06***
|
1.99***
|
–0.70***
|
–0.65*
|
<0.0001
|
0.201
|
C2. Pancreas contours
|
1.87***
|
1.68***
|
0.29°
|
0.32°
|
<0.0001
|
0.120
|
C3. Kidneys and proximal ureters
|
2.14***
|
1.97***
|
0.68***
|
–0.03°
|
<0.0001
|
0.142
|
C4. Lymph nodes ≤15 mm
|
1.59***
|
1.35***
|
0.68***
|
–0.07°
|
<0.0001
|
0.091
|
C5. Image noise
|
2.45***
|
2.74***
|
1.20***
|
1.50***
|
<0.0001
|
0.187
|
C6. Overall image quality
|
2.31***
|
2.18***
|
0.05°
|
–0.40°
|
<0.0001
|
0.199
|
***) p<0.001, **) p<0.01, *) p<0.05, °) not significant
|
In the regression analysis (Table 3B), the only criteria showing a significant change over time (significant coefficient for the interaction term) were C1 (liver parenchyma), for which initially negative AD5 scores were more pronounced with time, and C5 (image noise), where the initially positive AD5 scores were reinforced over time. For C3 (kidneys & ureters) and C4 (lymph nodes), the initial positive evaluation for AD5 did not significantly change during the review. For C2 (pancreas contour) and C6 (overall image quality), finally, there was no significant difference between the algorithms, nor a change over time.