Image quality assessment of automatic three-segment MR attenuation correction vs. CT attenuation correction

Abstract

The purpose of this study is to systematically evaluate the usefulness of Positron emission tomography/Magnetic resonance imaging (PET/MRI) images in a clinical setting by assessing the image quality of Positron emission tomography (PET) images using a three-segment MR attenuation correction (MRAC) versus the standard CT attenuation correction (CTAC). We prospectively studied 48 patients who had their clinically scheduled FDG-PET/CT followed by an FDG-PET/MRI. Three nuclear radiologists evaluated the image quality of CTAC vs. MRAC using a Likert scale (five-point scale). A two-sided, paired t-test was performed for comparison purposes. The image quality was further assessed by categorizing it as acceptable (equal to 4 and 5 on the five-point Likert scale) or unacceptable (equal to 1, 2, and 3 on the five-point Likert scale) quality using the McNemar test. When assessing the image quality using the Likert scale, one reader observed a significant difference between CTAC and MRAC (p=0.0015), whereas the other readers did not observe a difference (p=0.8924 and p=0.1880, respectively). When performing the grouping analysis, no significant difference was found between CTAC vs. MRAC for any of the readers (p=0.6137 for reader 1, p=1 for reader 2, and p=0.8137 for reader 3). All three readers more often reported artifacts on the MRAC images than on the CTAC images. There was no clinically significant difference in quality between PET images generated on a PET/MRI system and those from a Positron emission tomography/Computed tomography (PET/CT) system. PET images using the automatic three-segmented MR attenuation method provided diagnostic image quality. However, future research regarding the image quality obtained using different MR attenuation based methods is warranted before PET/MRI can be used clinically.

Keywords: FDG; PET/CT; PET/MRI; attenuation correction; hybrid imaging; image quality.

Figure 1

Distribution of the artifact prevalence in CTAC as well as MRAC for each individual reader.

Figure 2

Representative image quality instances in MRAC using the Likert scale. In panel A an MRAC is shown which was rated as 5 on the Likert scale (meaning excellent defined as “no artifacts exist”). The upper row shows the non attenuation corrected image, whereas the lower row shows the attenuation corrected image. In panel B an MRAC is shown which was rated as 4 on the Likert scale (meaning good defined as “minor artifacts which do not affect clinical use”). Mild attenuation artifact across the neck is appreciated on this image. The upper row shows the non attenuation corrected image whereas the lower row shows the attenuation corrected image.

Figure 3

The mean image quality values for CTAC and MRAC are shown for each reader. The error bars indicate the standard deviation from the mean value. The mean value is calculated as an average from the scores assigned to each of the CTAC or MRAC images by each individual reader. A significant difference was found for reader 1 between CTAC and MRAC (p= 0.0015), whereas for readers 2 and 3 no significant differences were detected (p=0.8924 and p=0.1880, respectively) using a two-sided, paired t-test.

Figure 4

The number of cases ranked in according to the image quality categories 1 to 5 are depicted over all readers.