Reproducibility of MR-Based Attenuation Maps in PET/MRI and the Impact on PET Quantification in Lung Cancer

• Published in: Journal of Nuclear Medicine Vol. 59; no. 6; pp. 999 - 1004
• Main Authors: Olin, Anders, Ladefoged, Claes N, Langer, Natasha H, Keller, Sune H, Löfgren, Johan, Hansen, Adam E, Kjær, Andreas, Langer, Seppo W, Fischer, Barbara M, Andersen, Flemming L
• Format: Journal Article
• Language: English
• Published: United States Society of Nuclear Medicine 01-06-2018
• Subjects: Alternating current; Attenuation; Cancer; Cancer therapies; Coefficient of variation; Data acquisition; Fluorine isotopes; Image detection; Image reconstruction; Inspection; Lung cancer; Magnetic resonance imaging; Medical imaging; Medical personnel; NMR; Nuclear magnetic resonance; Patients; Physicians; Positron emission; Positron emission tomography; Reliability analysis; Reproducibility; Thorax; Tomography; Tumors; Variation; non-small cell lung cancer; MR-based attenuation correction; PET/MR; reproducibility
• ISSN: 0161-5505; 1535-5667; 2159-662X
• DOI: 10.2967/jnumed.117.198853

Quantitative PET/MRI is dependent on reliable and reproducible MR-based attenuation correction (MR-AC). In this study, we evaluated the quality of current vendor-provided thoracic MR-AC maps and further investigated the reproducibility of their impact on
F-FDG PET quantification in patients with non-small cell lung cancer.
Eleven patients with inoperable non-small cell lung cancer underwent 2-5 thoracic PET/MRI scan-rescan examinations within 22 d.
F-FDG PET data were acquired along with 2 Dixon MR-AC maps for each examination. Two PET images (PET
and PET
) were reconstructed using identical PET emission data but with MR-AC from these intrasubject repeated attenuation maps. In total, 90 MR-AC maps were evaluated visually for quality and the occurrence of categorized artifacts by 2 PET/MRI-experienced physicians. Each tumor was outlined by a volume of interest (40% isocontour of maximum) on PET
, which was then projected onto the corresponding PET
SUV
and SUV
were assessed from the PET images. Within-examination coefficients of variation and Bland-Altman analyses were conducted for the assessment of SUV variations between PET
and PET
Image artifacts were observed in 86% of the MR-AC maps, and 30% of the MR-AC maps were subjectively expected to affect the tumor SUV. SUV
and SUV
resulted in coefficients of variation of 5.6% and 6.6%, respectively, and scan-rescan SUV variations were within ±20% in 95% of the cases. Substantial SUV variations were seen mainly for scan-rescan examinations affected by respiratory motion.
Artifacts occur frequently in standard thoracic MR-AC maps, affecting the reproducibility of PET/MRI. These, in combination with other well-known sources of error associated with PET/MRI examinations, lead to inconsistent SUV measurements in serial studies, which may affect the reliability of therapy response assessment. A thorough visual inspection of the thoracic MR-AC map and Dixon images from which it is derived remains crucial for the detection of MR-AC artifacts that may influence the reliability of SUV.