At Ankara University Medical School, Department of Nuclear Medicine, we have utilized SIGNA™ PET/MR in more than 2,000 oncology patients for staging and treatment planning.
Two recent studies conducted in our institution, one for the detection of liver metastases from colorectal cancer and the other for peritoneal recurrence of ovarian cancer, demonstrate that the addition of PET imaging increases the diagnostic power of MR in suspicious lesions. We are currently recruiting patients for an International Atomic Energy Agency (IAEA) coordinated research project (CRP) on breast PET/MR patients for the evaluation of treatment response to neoadjuvant chemotherapy in breast carcinoma.
Currently, PET/MR is performed in patients with a hepatocellular cancer (HCC) or colorectal cancer diagnosis for staging of disease. PET/MR is utilized for planning in patients who receive transarterial radioembolization (TARE) for primary or secondary liver tumors.
In uterine cervical carcinoma or endometrium carcinoma cases, PET/MR is used for radiation therapy planning. Debulking surgery is planned using the data from PET/MR in ovarian carcinoma patients.
We utilize dedicated, anatomic-specific MR protocols for PET/MR imaging rather than whole-body imaging. After acquiring a whole-body PET/CT, we immediately obtain PET/MR imaging for the corresponding body/anatomic area with the same FDG injection. In addition, contrast-enhanced MR sequences are utilized to enable evaluation, along with the FDG uptake. All MR sequences are reviewed by an experienced MR radiologist, and an experienced MR technologist acquires the PET/MR imaging data.
Case 1
Patient history
A 62-year-old male underwent a right lung biopsy in October 2021. Initial diagnosis was small-cell lung carcinoma. In November 2021, pathology from a right lung inferior lobectomy and lymph node dissection indicated high-grade neuroendocrine carcinoma and lymphovascular invasion. Patient underwent chemotherapy and radiation therapy.
Follow-up CT exam in August 2022 indicated suspected metastasis in the liver, segment 5. Patient was referred for 18F-FDG PET/CT and 18F-FDG PET/MR for re-staging (Figures 1 and 2).
Figure 1.
Case 1. PET/CT exam depicting liver metastases. (A) Fused coronal PET/CT; (B) axial CT; (C) axial PET/CT with attenuation correction (AC); and (D) fused axial PET/CT AC.
Figure 2.
Case 1. PET/MR exam. (A) Coronal T2 SSFSE 1.2 x 1.2 x 6 mm, 2:12 min.; (B) axial T2 PROPELLER FSE 1.2 x 1.2 x 5 mm, 2:12 min.; (C) DISCO Lava post-contrast 1.2 x 1.8 x 4 mm, 11 sec.; (D) respiratory triggered DWI b800, 2.6 x 2.2 x 5 mm, 2:54 min.; (E) MAGiC DWI b1500; and (F) ADC.
Protocol
Dedicated MR protocols for PET/MR were developed for oncology cases. In PET/MR liver cancer imaging, we utilize coronal T2-weighted SSFSE, axial T2-weighted FSE, axial T2-weighted fat-suppressed FSE, axial dual echo, and diffusion-weighted imaging with echo-planar imaging and b-values of 50 and 800 s/mm2 post-contrast. DISCO, a 3D dynamic T1 sequence, is performed with gadoterate meglumine (Clariscan™, GE Healthcare).
Results
This study demonstrates the high sensitivity of the SIGNA™ PET/MR solid-state detectors and utilization of Q.Clear to help improve resolution, contrast recovery and SNR improvement (Figure 3).
Figure 3.
Case 1. (A) PET/MR with Q.Clear and AC demonstrates focal liver uptake of SUVmax 4.4; (B) delayed enhancement, fused PET AC and T2 PROPELLER; (C) PET/CT AC; and (D) fused PET AC/CT.
Case 2
Patient history
A 58-year-old female underwent breast ultrasound in March 2022. Initial diagnosis was a 25 mm retroareolar lesion, BI-RADS® 5, in the left breast and corresponding 15 mm axillar lymphadenopathy. Biopsy pathology confirmed grade 2 invasive ductal carcinoma. Patient underwent 18F-FDG PET/CT and 18F-FDG PET/MR for staging (Figures 4 and 5).
Figure 4.
Case 2. (A) Axial 3D T2 Cube, 1 x 1 x 1 mm, 8:25 min.; (B) axial T1 FSE, 0.9 x 1 x 4 mm, 3:12 min.; and (C) axial dynamic VIBRANT, 0.8 x 1 x 1 mm, 7 phases, 7:45 min.
Figure 5.
Case 2. (A) Axial DWI b1500, 2.8 x 2.8 x 4 mm, 6:03 min.; (B) ADC; and (C) VIBRANT DCE and corresponding kinetic curve.
Protocol
Breast PET/MR imaging includes the use of a 3-plane localizer, axial T2, axial T1, axial DWI and dynamic 3D contrast enhancement of both breasts at three or four time points. Patient is in the prone position with the use of dual breast coils.
Results
18F-FDG PET/MR images demonstrate strong uptake in mass and lymphadenopathy correlating with aggressive tumor biology.
Figure 6.
Case 2. (A, B) PET/MR AC and (C, D) fused 3D T2 Cube with PET/MR AC.
Discussion
Based on our experience, PET/MR can detect additional lesions that can change the treatment strategy.
