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. 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. 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. 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 (less than or equal to2mm) 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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
To evaluate the initial results of predicting lymph node metastasis in rectal cancer patients detected in-vivo with USPIO-enhanced MRI at 3 T compared on a node-to-node basis with histopathology.
Ten ...rectal cancer patients of all clinical stages were prospectively included for an in-vivo 0.85 mm3 isotropic 3D MRI after infusion of Ferumoxtran-10. The surgical specimens were examined ex-vivo with an 0.29 mm3 isotropic MRI examination. Two radiologists evaluated in-vivo MR images with a classification scheme to predict lymph node status. Ex-vivo MRI was used for MR-guided pathology and served as a key link between in-vivo MRI and final histopathology for the node-to-node analysis.
138 lymph nodes were detected by reader 1 and 255 by reader 2 (p = 0.005) on in-vivo MRI with a median size of 2.6 and 2.4 mm, respectively. Lymph nodes were classified with substantial inter-reader agreement (κ = 0.73). Node-to-node comparison was possible for 55 lymph nodes (median size 3.2 mm; range 1.2–12.3), of which 6 were metastatic on pathology. Low true-positive rates (3/26, 11 % for both readers) and high true negative rates were achieved (14/17, 82 %; 19/22, 86 %). Pathological re-evaluations of 20 lymph nodes with high signal intensity on USPIO-enhanced MRI without lymph node metastases (false positives) did not reveal tumor metastasis but showed benign lymph node tissue with reactive follicles.
High resolution MRI visualizes a large number of mesorectal lymph nodes. USPIO-enhanced MRI was not accurate for characterizing small benign versus small tumoral lymph nodes in rectal cancer patients. Suspicious nodes on in-vivo MRI occur as inflammatory as well as metastatic nodes.
Accurate detection of lymph node (LN) metastases in prostate cancer (PCa) is a challenging but crucial step for disease staging. Ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic ...resonance imaging (MRI) enables distinction between healthy LNs and nodes suspicious for harboring metastases. When combined with MRI at an ultra-high magnetic field, an unprecedented spatial resolution can be exploited to visualize these LNs.
The aim of this study was to explore USPIO-enhanced MRI at 7 T in comparison to 3 T for the detection of small suspicious LNs in the same cohort of patients with PCa.
Twenty PCa patients with high-risk primary or recurrent disease were referred to our hospital for an investigational USPIO-enhanced 3 T MRI examination with ferumoxtran-10. With consent, they underwent a 7 T MRI on the same day. Three-dimensional anatomical and T2*-weighted images of both examinations were evaluated blinded, with an interval, by 2 readers who annotated LNs suspicious for metastases. Number, size, and level of suspicion (LoS) of LNs were paired within patients and compared between field strengths.
At 7 T, both readers annotated significantly more LNs compared with 3 T (474 and 284 vs 344 and 162), with 116 suspicious LNs on 7 T (range, 1-34 per patient) and 79 suspicious LNs on 3 T (range, 1-14 per patient) in 17 patients. For suspicious LNs, the median short axis diameter was 2.6 mm on 7 T (1.3-9.5 mm) and 2.8 mm for 3 T (1.7-10.4 mm, P = 0.05), with large overlap in short axis of annotated LNs between LoS groups. At 7 T, significantly more suspicious LNs had a short axis <2.5 mm compared with 3 T (44% vs 27%). Magnetic resonance imaging at 7 T provided better image quality and structure delineation and a higher LoS score for suspicious nodes.
In the same cohort of patients with PCa, more and more small LNs were detected on 7 T USPIO-enhanced MRI compared with 3 T MRI. Suspicious LNs are generally very small, and increased nodal size was not a good indication of suspicion for the presence of metastases. The high spatial resolution of USPIO-enhanced MRI at 7 T improves structure delineation and the visibility of very small suspicious LNs, potentially expanding the in vivo detection limits of pelvic LN metastases in PCa patients.
Purpose
In this work, a combined body coil array with eight transmit/receive (Tx/Rx) meander elements and with 24 receive‐only (Rx) loops (8Tx/32Rx) was developed and evaluated in comparison with an ...8‐channel transmit/receive body array (8Tx/Rx) based on meander elements serving as the reference standard.
Methods
Systematic evaluation of the RF array was performed on a body‐sized phantom. Body imaging at 7T was performed in six volunteers in the body regions pelvis, abdomen, and heart. Coil characteristics such as signal‐to‐noise ratio, acceleration capability, g‐factors, S‐parameters, noise correlation, and B1+ maps were assessed. Safety was ensured by numerical simulations using a coil model validated by dosimetric field measurements.
Results
Meander elements and loops are intrinsically well decoupled with a maximum coupling value of −20.5 dB. Safe use of the 8Tx/32Rx array could be demonstrated. High gain in signal‐to‐noise ratio (33% in the subject's center) could be shown for the 8Tx/32Rx array compared to the 8Tx/Rx array. Improvement in acceleration capability in all investigations could be demonstrated. For example, the 8Tx/32Rx array provides lower g‐factors in the right–left and anterior–posterior directions with R = 3 undersampling as compared to the 8Tx/Rx array using R = 2. Both arrays are very similar regarding their RF transmit performance. Excellent image quality in the investigated body regions could be achieved with the 8Tx/32Rx array.
Conclusion
In this work, we show that a combination of eight meander elements and 24 loop receive elements is possible without impeding transmit performance. Improved SNR and g‐factor performance compared to an RF array without these loops is demonstrated. Body MRI at 7T with the 8Tx/32Rx array could be accomplished in the heart, abdomen, and pelvis with excellent image quality.
High resolution MR imaging of pelvic lymph nodes at 7 Tesla Philips, Bart W. J.; Fortuin, Ansje S.; Orzada, Stephan ...
Magnetic resonance in medicine,
September 2017, 2017-Sep, 2017-09-00, 20170901, Letnik:
78, Številka:
3
Journal Article
Administration of lactate during hypoglycemia suppresses symptoms and counterregulatory responses, as seen in patients with type 1 diabetes and impaired awareness of hypoglycemia (IAH), presumably ...because lactate can substitute for glucose as a brain fuel. Here, we examined whether lactate administration, in a dose sufficient to impair awareness of hypoglycemia, affects brain lactate levels in patients with normal awareness of hypoglycemia (NAH). Patients with NAH (n = 6) underwent two euglycemic-hypoglycemic clamps (2.8 mmol/L), once with sodium lactate infusion (NAH w|lac) and once with saline infusion (NAH w|placebo). Results were compared to those obtained during lactate administration in patients with IAH (n = 7) (IAH w|lac). Brain lactate levels were determined continuously with J-difference editing 1H-MRS. During lactate infusion, symptom and adrenaline responses to hypoglycemia were considerably suppressed in NAH. Infusion of lactate increased brain lactate levels modestly, but comparably, in both groups (mean increase in NAH w|lac: 0.12 ± 0.05 µmol/g and in IAH w|lac: 0.06 ± 0.04 µmol/g). The modest increase in brain lactate may suggest that the excess of lactate is immediately metabolized by the brain, which in turn may explain the suppressive effects of lactate on awareness of hypoglycemia observed in patients with NAH.
In various cancer types, the first step towards extended metastatic disease is the presence of lymph node metastases. Imaging methods with sufficient diagnostic accuracy are required to personalize ...treatment. Lymph node metastases can be detected with ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic resonance imaging (MRI), but this method needs validation. Here, a workflow is presented, which is designed to compare MRI-visible lymph nodes on a node-to-node basis with histopathology.
In patients with prostate, rectal, periampullary, esophageal, and head-and-neck cancer, in vivo USPIO-enhanced MRI was performed to detect lymph nodes suspicious of harboring metastases. After lymphadenectomy, but before histopathological assessment, a 7 Tesla preclinical ex vivo MRI of the surgical specimen was performed, and in vivo MR images were radiologically matched to ex vivo MR images. Lymph nodes were annotated on the ex vivo MRI for an MR-guided pathological examination of the specimens.
Matching lymph nodes of ex vivo MRI to pathology was feasible in all cancer types. The annotated ex vivo MR images enabled a comparison between USPIO-enhanced in vivo MRI and histopathology, which allowed for analyses on a nodal, or at least on a nodal station, basis.
A workflow was developed to validate in vivo USPIO-enhanced MRI with histopathology. Guiding the pathologist towards lymph nodes in the resection specimens during histopathological work-up allowed for the analysis at a nodal basis, or at least nodal station basis, of in vivo suspicious lymph nodes with corresponding histopathology, providing direct information for validation of in vivo USPIO-enhanced, MRI-detected lymph nodes.
In vivo
H and
P magnetic resonance spectroscopic imaging (MRSI) provide complementary information on the biology of prostate cancer. In this work we demonstrate the feasibility of performing ...multiparametric imaging (mpMRI) and
H and
P spectroscopic imaging of the prostate using a
P and
H endorectal radiofrequency coil (ERC) in combination with a multitransmit body array at 7 Tesla (T).
An ERC with a
P transceiver loop coil and
H receive (Rx) asymmetric microstrip (
P/
H ERC) was designed, constructed and tested in combination with an external 8-channel
H transceiver body array coil (8CH). Electromagnetic field simulations and measurements and in vivo temperature measurements of the ERC were performed for safety validation. In addition, the signal-to-noise (SNR) benefit of the
H microstrip with respect to the 8CH was evaluated. Finally, the feasibility of the setup was tested in one volunteer and three patients with prostate cancer by performing T
-weighted and diffusion-weighted imaging in combination with
H and
P spectroscopic imaging.
Electromagnetic field simulations of the
P loop coil showed no differences in the E- and B-fields of the
P/
H ERC compared with a previously safety validated ERC without
H microstrip. The hotspot of the specific absorption rate (SAR) at the feed point of the
P/
H ERC loop coil was 9.42 W/kg when transmitting on
P at 1 W. Additional in vivo measurements showed a maximum temperature increase at the SAR hotspot of 0.7°C over 6 min on
P at 1.9 W transmit (Tx) power, indicating safe maximum power levels. When transmitting with the external
H body array at 40W for 2:30 min, the temperature increase around the ERC was < 0.3°C. Up to 3.5 cm into the prostate the
H microstrip of the ERC provided higher SNR than the 8CH. The total coil combination allowed acquisition of an mpMRI protocol and the assessment of
P and
H metabolites of the prostate in all test subjects.
We developed a setup with a
P transceiver and
H Rx endorectal coil in combination with an 8-channel transceiver external body array coil and demonstrated its safety and feasibility for obtaining multiparametric imaging and
H and
P MRSI at 7T in patients with prostate cancer within one MR examination.
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