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Objective: The definition of an in vivo nodal anatomical baseline is crucial for validation of representative lymph node dissections and accompanying pathology reports of pelvic cancers, as well as for assessing a potential therapeutic effect of extended lymph node dissections. Therefore the number, size and distribution of lymph nodes in the pelvis were assessed with high-resolution, large field-of-view, 7 Tesla (T) magnetic resonance imaging (MRI) with frequency-selective excitation., Materials and Methods: We used 7 T MRI for homogeneous pelvic imaging in 11 young healthy volunteers. Frequency-selective imaging of water and lipids was performed to detect nodal structures in the pelvis. Number and size of detected nodes was measured and size distribution per region was assessed. An average volunteer-normalized nodal size distribution was determined., Results: In total, 564 lymph nodes were detected in six pelvic regions. Mean number was 51.3 with a wide range of 19-91 lymph nodes per volunteer. Mean diameter was 2.3 mm with a range of 1 to 7 mm. 69% Was 2 mm or smaller. The overall size distribution was very similar to the average volunteer-normalized nodal size distribution., Conclusions: The amount of in vivo visible lymph nodes varies largely between subjects, whereas the normalized size distribution of nodes does not. The presence of many small lymph nodes (≤2mm) renders representative or complete removal of pelvic lymph nodes to be very difficult. 7T MRI may shift the in vivo detection limits of lymph node metastases in the future., Competing Interests: The authors have declared that no competing interests exist.

Purpose: To evaluate the technical feasibility of high-resolution USPIO-enhanced magnetic resonance imaging of pelvic lymph nodes (LNs) at ultrahigh magnetic field strength., Materials and Methods: The ethics review board approved this study and written informed consent was obtained from all patients. Three patients with rectal cancer and three selected patients with (recurrent) prostate cancer were examined at 7-T 24-36 h after intravenous ferumoxtran-10 administration; rectal cancer patients also received a 3-T MRI. Pelvic LN imaging was performed using the TIAMO technique in combination with water-selective multi-GRE imaging and lipid-selective GRE imaging with a spatial resolution of 0.66 × 0.66 × 0.66mm 3 . T 2 * -weighted images of the water-selective imaging were computed from the multi-GRE images at TE = 0, 8, and 14 ms and used for the assessment of USPIO uptake., Results: High-resolution 7-T MR gradient-echo imaging was obtained robustly in all patients without suffering from RF-related signal voids. USPIO signal decay in LNs was visualized using computed TE imaging at TE = 8 ms and an R 2 * map derived from water-selective imaging. Anatomically, LNs were identified on a combined reading of computed TE = 0 ms images from water-selective scans and images from lipid-selective scans. A range of 3-48 LNs without USPIO signal decay was found per patient. These LNs showed high signal intensity on computed TE = 8 and 14 ms imaging and low R 2 * (corresponding to high T 2 * ) values on the R 2 * map., Conclusion: USPIO-enhanced MRI of the pelvis at 7-T is technically feasible and offers opportunities for detecting USPIO uptake in normal-sized LNs, due to its high intrinsic signal-to-noise ratio and spatial resolution., Key Points: • USPIO-enhanced MRI at 7-T can indicate USPIO uptake in lymph nodes based on computed TE images. • Our method promises a high spatial resolution for pelvic lymph node imaging.

Purpose: Pelvic lymph node (PLN) metastases are often smaller than 5 mm and difficult to detect. This work presents a method to perform PLN imaging with ultrahigh-field MRI, using spectrally selective excitation to acquire water and lipid-selective imaging at high spatial resolution., Methods: A 3D water-selective multigradient echo (mGRE) sequence and lipid-selective gradient echo (GRE) sequence were tested in six healthy volunteers on a 7 Tesla (T) MRI system, using time interleaved acquisition of modes (TIAMO) to improve image homogeneity. The size distribution of the first 10 iliac PLNs detected in each volunteer was determined, and the contrast-to-noise ratio (CNR) of these lymph nodes (LNs) was compared with the individual mGRE images, sum-of-squares echo addition, and computed T2*-weighted images derived from the T2* fits., Results: LN imaging was acquired robustly at ultrahigh field with high resolution and homogeneous lipid or water-selective contrast. PLNs down to 1.5-mm short axis were detected with mean ± standard error of the mean (SEM) short and long axes of 2.2 ± 0.1 and 3.7 ± 0.2 mm, respectively. Computed T2*-weighted imaging allowed flexibility in T2* contrast while featuring a CNR up to 90% of the sum-of-squares echo addition., Conclusion: Ultrahigh-field MRI in combination with TIAMO and frequency-selective excitation enables high-resolution, large field-of-view MRI of the lower abdomen, and may ultimately be suitable for detecting small PLN metastases. Magn Reson Med 78:1020-1028, 2017. © 2016 International Society for Magnetic Resonance in Medicine., (© 2016 International Society for Magnetic Resonance in Medicine.)