68Ga PSMA PET/MRI
No additional preparation was requested from the patients prior to
68Ga-PSMA PET/MRI. PET/MRI was performed on the prostate gland and the
entire body simultaneously from the vertex to the toe approximately 50
min after 5 mCi (185 MBq) 68(Ga)-PSMA-11 was injected intravenously. An
integrated 3T PET/MR camera (GE Signa PET/MRI; GE Healthcare, Waukesha,
WI, USA) with a time-of-flight (TOF) feature was used for PET/MRI.
Imaging of the prostate gland was performed in a single-bed position.
After the first 16-s localiser image, 18-s axial two-point Dixon 3D
T1-weighted gradient echo sequences (GESs) were obtained for anatomical
registration and attenuation correction maps based on magnetic resonance
(MR) images. Subsequently, sagittal (2 min 29 s), axial (3 min 29 s),
and coronal (3 min 27 s) high-resolution T2-weighted images were taken.
In addition, 5 min 5 s for b = 50, 400, and 800 s/mm2 and 4 min 5 s for
b = 50, 1400, and 1800 s/mm2 of DWIs were obtained for the prostate
gland, respectively. PET data were taken simultaneously during the
imaging of the MR sequences. High-resolution imaging for the prostate
gland took 20 min. Then the whole-body imaging was performed in a nine
bed position with a 3-minute acquisition time per bed position. After
the first 60-s localiser image, 18-s axial two-point Dixon 3D
T1-weighted GESs were obtained at each bed position for anatomical
registration and attenuation correction maps based on MR images. In
addition, 20-s axial T1-weighted images were taken for each bed
position. For the first five bed positions, 1 min 34 s axial DWIs were
taken at each bed position. In addition, 33-s coronal T2-weighted
imaging was performed for the first, third, and fifth bed positions.
Simultaneous PET data was obtained during the imaging of the MR
sequences. Dixon MR sequences and PET acquisitions were obtained in the
same bed position at the same time to ensure optimal temporal and
spatial overlap. MR images were segmented to different tissue types for
attenuation correction. Reconstruction of PET images was performed using
the ordered subset expectation maximisation (OSEM) protocol (two
iterations and 28 subsets), and TOF reconstructed images were obtained.
PET/MR images were visually and quantitatively evaluated by a nuclear
medicine specialist with 9 years of experience. In the PET-avid lesions,
pathological uptake of 68Ga-PSMA-11 was reported with an SUVmax value
according to the regional anatomy of the prostate (left/right anterior
zone and left/right posterior zone). SUVmax was calculated by drawing a
volume of interest automatically over the intraprostatic tumour with the
highest 68Ga-PSMA-11 uptake in each patient with PET-avid lesions.
Region of interest (ROIs) around PET-avid prostatic tumours were defined
as a 42% isocontour threshold of the SUVmax within the focal lesions.
PET data were analysed with only T1-weighted MRI sequence for anatomical
correlation.