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AJR Am J Roentgenol. 2018 Oct;211(4):896-900. doi: 10.2214/AJR.18.19620. Epub 2018 Aug 14.

Does Extended PET Acquisition in PET/MRI Rectal Cancer Staging Improve Results?

Author information

1
1 Department of Radiology and Biomedical Imaging, University of California, San Francisco, 505 Parnassus Ave, San Francisco, CA 94143.
2
2 Department of Medicine, Division of Hematology and Oncology, University of California, San Francisco, San Francisco, CA.
3
5 Henry Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA.
4
3 Department of Surgery, University of California, San Francisco, San Francisco, CA.
5
4 Department of Radiology, San Francisco VA Medical Center, San Francisco, San Francisco, CA.

Abstract

OBJECTIVE:

The purpose of this study was to determine if extended PET acquisition times in the pelvis during PET/MRI increase detection rates of potentially metastatic lymph nodes in patients with rectal cancer.

MATERIALS AND METHODS:

Our study was approved by the institutional review board of the University of California, San Francisco. Twenty-two patients with biopsy-proven rectal cancer underwent imaging via simultaneous 3-T time-of-flight PET/MRI, with seven undergoing two separate PET/MRI examinations, for a total of 29 studies. Each examination included both a whole-body PET/MRI and a dedicated pelvic PET/MRI with both 3- and 15-minute PET acquisitions for the pelvis. Three radiologists interpreted each examination with PET only, MRI only, then combined PET and MRI examinations, using all available images. Additionally, the 3- and 15-minute PET acquisitions of the pelvis were reviewed separately by a single radiologist.

RESULTS:

A total of 94 lymph nodes were identified as abnormal on PET, all with MRI anatomic correlates. Of these, 37 (39.4%) were seen only on the dedicated 15-minute acquisition. Fifty-seven (60.6%) nodes measured 5 mm or less, including 29 (30.9%) seen only on the 15-minute acquisition. Thirty-one (33.0%) nodes measured 5.1-10 mm, including eight (25.8%) seen only on the 15-minute acquisition. Of the 17 subjects imaged for initial staging, 11 (64.7%) were upstaged as a result of the increased PET acquisition time (10 from N1 to N2 and one from N0 to N1).

CONCLUSION:

Longer PET acquisition times during PET/MRI for rectal cancer increases the number of FDG-avid lymph nodes detected without increasing scan time.

KEYWORDS:

PET/MRI; acquisition time; rectal cancer

PMID:
30106609
DOI:
10.2214/AJR.18.19620

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