3-Tesla High-Field Magnetic Resonance Neurography for Guiding Nerve Blocks and Its Role in Pain Management

The role of imaging in focal neuropathies

Electrodiagnostic testing (EDX) has been the diagnostic tool of choice in peripheral nerve disease for many years, but in recent years, peripheral nerve imaging has been used ever more frequently in daily clinical practice. Nerve ultrasound and magnetic resonance (MR) neurography are able to visualize nerve structures reliably. These techniques can aid in localizing nerve pathology and can reveal significant anatomical abnormalities underlying nerve pathology that may have been otherwise undetected by EDX. As such, nerve ultrasound and MR neurography can significantly improve diagnostic accuracy and can have a significant effect on treatment strategy. In this chapter, the basic principles and recent developments of these techniques will be discussed, as well as their potential application in several types of peripheral nerve disease, such as carpal tunnel syndrome (CTS), ulnar neuropathy at the elbow (UNE), radial neuropathy, brachial and lumbosacral plexopathy, neuralgic amyotrophy (NA), fibular, tibial, sciatic, femoral neuropathy, meralgia paresthetica, peripheral nerve trauma, tumors, and inflammatory neuropathies.

Selective MR neurography-guided lumbosacral plexus perineural injections: techniques, targets, and territories

The T12 to S4 spinal nerves form the lumbosacral plexus in the retroperitoneum, providing sensory and motor innervation to the pelvis and lower extremities. The lumbosacral plexus has a wide range of anatomic variations and interchange of fibers between nerve anastomoses. Neuropathies of the lumbosacral plexus cause a broad spectrum of complex pelvic and lower extremity pain syndromes, which can be challenging to diagnose and treat successfully. In their workup, selective nerve blocks are employed to test the hypothesis that a lumbosacral plexus nerve contributes to a suspected pelvic and extremity pain syndrome, whereas therapeutic perineural injections aim to alleviate pain and paresthesia symptoms. While the sciatic and femoral nerves are large in caliber, the iliohypogastric and ilioinguinal, genitofemoral, lateral femoral cutaneous, anterior femoral cutaneous, posterior femoral cutaneous, obturator, and pudendal nerves are small, measuring a few millimeters in diameter and have a wide range of anatomic variants. Due to their minuteness, direct visualization of the smaller lumbosacral plexus branches can be difficult during selective nerve blocks, particularly in deeper pelvic locations or larger patients. In this setting, the high spatial and contrast resolution of interventional MR neurography guidance benefits nerve visualization and targeting, needle placement, and visualization of perineural injectant distribution, providing a highly accurate alternative to more commonly used ultrasonography, fluoroscopy, and computed tomography guidance for perineural injections. This article offers a practical guide for MR neurography-guided lumbosacral plexus perineural injections, including interventional setup, pulse sequence protocols, lumbosacral plexus MR neurography anatomy, anatomic variations, and injection targets.

MRI-guided sacroiliac joint injections in children and adults: current practice and future developments

Common etiologies of low back pain include degenerative arthrosis and inflammatory arthropathy of the sacroiliac joints. The diagnostic workup revolves around identifying and confirming the sacroiliac joints as a pain generator. Diagnostic sacroiliac joint injections often serve as functional additions to the diagnostic workup through eliciting a pain response that tests the hypothesis that the sacroiliac joints do or do not contribute to the patient's pain syndrome. Therapeutic sacroiliac joint injections aim to provide medium- to long-term relief of symptoms and reduce inflammatory activity and, ultimately, irreversible structural damage. Ultrasonography, fluoroscopy, computed tomography, and magnetic resonance imaging (MRI) may be used to guide sacroiliac joint injections. The populations that may benefit most from MRI-guided sacroiliac joint procedures include children, adolescents, adults of childbearing age, and patients receiving serial injections due to the ability of interventional MRI to avoid radiation exposure. Most clinical wide-bore MRI systems can be used for MRI-guided sacroiliac joint injections. Turbo spin echo pulse sequences optimized for interventional needle display visualize the needle tip with an error margin of < 1 mm or less. Published success rates of intra-articular sacroiliac joint drug delivery with MRI guidance range between 87 and 100%. The time required for MR-guided sacroiliac joint injections in adults range between 23-35 min and 40 min in children. In this article, we describe techniques for MRI-guided sacroiliac joint injections, share our practice of incorporating interventional MRI in the care of patients with sacroiliac joint mediated pain, discuss the rationales, benefits, and limitations of interventional MRI, and conclude with future developments.

Selective MR neurography-guided anterior femoral cutaneous nerve blocks for diagnosing anterior thigh neuralgia: anatomy, technique, diagnostic performance, and patient-reported experiences

OBJECTIVE

To evaluate the clinical utility of selective magnetic resonance neurography-(MRN)-guided anterior femoral cutaneous nerve (AFCN) blocks for diagnosing anterior thigh neuralgia.

MATERIALS AND METHODS

Following institutional review board approval and informed consent, participants with intractable anterior thigh pain and clinically suspected AFCN neuralgia were included. AFCN blocks were performed under MRN guidance using an anterior groin approach along the medial sartorius muscle margin. Outcome variables included AFCN identification on MRN, technical success of perineural drug delivery, rate of AFCN anesthesia, complications, total procedure time, patient-reported procedural experiences, rate of positive diagnostic AFCN blocks, and positive subsequent treatment rate.

RESULTS

Eighteen MRN-guided AFCN blocks (six unilateral and six bilateral blocks) were performed in 12 participants (6 women; age, 49 (30-65) years). Successful MRN identified the AFCN, successful perineural drug delivery, and AFCN anesthesia was achieved in all thighs. No complications occurred. The total procedure time was 19 (10-28) min. Patient satisfaction and experience were high without adverse MRI effects. AFCN blocks identified the AFCN as the symptom generator in 16/18 (89%) cases, followed by 14/16 (88%) successful treatments.

CONCLUSION

Our results suggest that selective MR neurography-guided AFCN blocks effectively diagnose anterior femoral cutaneous neuralgia and are well-tolerated.

MRI-guided lumbar spinal injections with body-mounted robotic system: cadaver studies

INTRODUCTION

This paper reports the system integration and cadaveric assessment of a body-mounted robotic system for MRI-guided lumbar spine injections. The system is developed to enable MR-guided interventions in closed bore magnet and avoid problems due to patient movement during cannula guidance.

MATERIAL AND METHODS

The robot is comprised by a lightweight and compact structure so that it can be mounted directly onto the lower back of a patient using straps. Therefore, it can minimize the influence of patient movement by moving with the patient. The MR-Conditional robot is integrated with an image-guided surgical planning workstation. A dedicated clinical workflow is created for the robot-assisted procedure to improve the conventional freehand MRI-guided procedure.

RESULTS

Cadaver studies were performed with both freehand and robot-assisted approaches to validate the feasibility of the clinical workflow and to assess the positioning accuracy of the robotic system. The experiment results demonstrate that the root mean square (RMS) error of the target position to be 2.57 ± 1.09 mm and of the insertion angle to be 2.17 ± 0.89°.

CONCLUSION

The robot-assisted approach is able to provide more accurate and reproducible cannula placements than the freehand procedure, as well as to reduce the number of insertion attempts.

Evaluation of MR-neurography in diagnosis and treatment in peripheral nerve surgery of the upper extremity: A matched cohort study

INTRODUCTION

"Watch and wait"-strategies from 3 to 6 months for peripheral nerve injuries are standard of care in specialized centers. However, this contradiction between delayed decision-making and the demand for fast reinnervation, especially of the motoric endplate, has not yet been overcome. Therefore, this study aimed to investigate the time-sparing effects by accelerated decision-making due to the complementary MR-neurography application combined with established diagnostics like electroneurography and neurosonography from the first admission to the determination of the treatment plan.

PATIENTS AND METHODS

A retrospective matched-pair chart review analysis with Supplementary MR-neurography in the period between 2014 and 2017 was designed. Matching was performed by the parameters of nerve type, localization of the nerve injury, patient age, and treatment of the injury. Twenty-nine patients were included and matched in the study. MR-neurography imaging was performed by a 3T magnetic resonance imaging with a sampling perfection with application optimized contrasts using different flip angle evolution short tau inversion recovery sequence for the brachial plexus and gradient echo accurate fast imaging with steady-state free precession sequence for the upper extremity. Time to decision-making was investigated for or against a surgical intervention for patients with or without a Supplementary MR-neurography.

RESULTS

In general, MR-neurography accelerated decision-making for 28 days, with results of 37.5 + 5.4 days with Supplementary MR-neurography and 65.3 + 9.7 days without Supplementary MR-neurography (p = .05). Within the first 90 days following trauma, patients with MR-neurography (38.2 ± 7.7 days) benefit under a significant faster decision-making (p = .05) than patients without MR-neurography (79.0 + 14.2 days). After 90 days, no evidence of accelerated decision-making was found with the addition of MR-neurography (p = .6). In 10 of the 29 patients, despite additional electroneurography and neurosonography, no decision could be made and the MR-neurography has been used primarily as a diagnostic tool.

CONCLUSION

MR-neurography has significant time-sparing effects on the decision-making for approximately 4 weeks within the first 90 days after the trauma. This may help overcome the paradigm of "watch and wait"-strategies during the first 3-6 months after the peripheral nerve injury.

The Value of 3 Tesla Field Strength for Musculoskeletal Magnetic Resonance Imaging

ABSTRACT

Musculoskeletal magnetic resonance imaging (MRI) is a careful negotiation between spatial, temporal, and contrast resolution, which builds the foundation for diagnostic performance and value. Many aspects of musculoskeletal MRI can improve the image quality and increase the acquisition speed; however, 3.0-T field strength has the highest impact within the current diagnostic range. In addition to the favorable attributes of 3.0-T field strength translating into high temporal, spatial, and contrast resolution, many 3.0-T MRI systems yield additional gains through high-performance gradients systems and radiofrequency pulse transmission technology, advanced multichannel receiver technology, and high-end surface coils. Compared with 1.5 T, 3.0-T MRI systems yield approximately 2-fold higher signal-to-noise ratios, enabling 4 times faster data acquisition or double the matrix size. Clinically, 3.0-T field strength translates into markedly higher scan efficiency, better image quality, more accurate visualization of small anatomic structures and abnormalities, and the ability to offer high-end applications, such as quantitative MRI and magnetic resonance neurography. Challenges of 3.0-T MRI include higher magnetic susceptibility, chemical shift, dielectric effects, and higher radiofrequency energy deposition, which can be managed successfully. The higher total cost of ownership of 3.0-T MRI systems can be offset by shorter musculoskeletal MRI examinations, higher-quality examinations, and utilization of advanced MRI techniques, which then can achieve higher gains and value than lower field systems. We provide a practice-focused review of the value of 3.0-T field strength for musculoskeletal MRI, practical solutions to challenges, and illustrations of a wide spectrum of gainful clinical applications.

Cryoanalgesia of the anterior femoral cutaneous nerve (AFCN) for the treatment of neuropathy-mediated anterior thigh pain: anatomy and technical description

OBJECTIVE

To describe and illustrate the magnetic resonance imaging (MRI) anatomy of the anterior femoral cutaneous nerve (AFCN) and a new technique for cryoanalgesia of the AFCN for long-term analgesic treatment of recalcitrant AFCN-mediated neuropathic pain.

MATERIALS AND METHODS

Using a procedural high-resolution MRI technique, we describe the MRI anatomy of the AFCN. Three patients (mean age, 48 years; range, 41-67 years) with selective nerve block-verified recalcitrant AFCN-mediated anterior thigh pain were enrolled to undergo cryoanalgesia of the AFCN. Procedures were performed under MRI guidance using clinical wide-bore MR imaging systems and commercially available cryoablation system with MR-conditional probes. Outcome variables included technical success, clinical effectiveness including symptom relief measured on an 11-point visual analog scale, frequency of complications, and procedure time.

RESULTS

Procedural MRI allowed to successfully demonstrate the course of the AFCN, accurate cryoprobe placement, and monitoring of the ice ball, which resulted in technically successful iceball growth around the AFCN in all cases. All procedures were clinically effective, with median pain intensity decreasing from 8 (7-9) before the procedure to 1 (0-2) after the procedure. The cryoanalgesia effect persisted during a 12-month follow-up period in all three patients. No major complications occurred. The average total procedure time was 98 min (range, 85-125 min).

CONCLUSION

We describe the MRI anatomy of the AFCN and a new technique for cryoanalgesia of the AFCN using MRI guidance, which permits identification of the AFCN, selective targeting, and iceball monitoring to achieve long-term AFCN-mediated neuropathic pain relief.

Neurolysis of the Dorsal Nerve to the Penis to Restore Function After Trauma

BACKGROUND

Loss of penile sensation or development of a painful penis and erectile dysfunction can occur after injury to the dorsal branch of the pudendal nerve. Although recovery of genital sensibility has been discussed frequently in transmen, this subject has been reported rarely in cismen. The purpose of this report is to review our experience with recovery of sensation in men after decompression of the dorsal branch of the pudendal nerve after trauma.

METHODS

A retrospective chart review of men who have had decompression of the dorsal branch of the pudendal nerve was carried out from 2014 to 2018. Patients were included in the cohort if they had a loss of penile sensation or the development of a painful penis after trauma. Primary outcomes measured were the change in penile symptoms, including erection, ejaculation, ejaculatory pain, erogenous sensation, numbness, and penile pain.

RESULTS

For the 7 men included in this study, the mean follow-up time was 57 weeks (range, 28-85 weeks). Bilateral surgery was done in 71% (5/7). Of the 6 patients with loss of penile sensation, complete recovery of erogenous sensibility occurred in 5 (83%) patients, with partial relief in 1 (17%) patient. Of the 3 men who had erectile dysfunction, normal erections were restored in 2 (67%) patients. Of the 2 patients unable to ejaculate, 1 (50%) patient regained ejaculatory function. Of the 4 patients with ejaculatory pain, complete relief of pain occurred in 2 (50%) patients, with partial relief in 2 (50%) patients. Of the 6 patients with penile pain in the absence of ejaculation, complete relief of pain occurred in 3 (50%) patients, with partial relief in 3 (50%) patients.

CONCLUSION

Neurolysis of the dorsal nerve to the penis at the inferior pubic ramus canal can be successful in relieving pain, and restoring sensation and erectile function in men who sustained an injury along the inferior pubic ramus.

Interventional Techniques for Bone and Musculoskeletal Soft Tissue Tumors: Current Practices and Future Directions - Part I. Ablation

Musculoskeletal (MSK) image-guided oncologic intervention is an established field within radiology. Numerous studies have described its clinical benefits, safety, cost effectiveness, patient satisfaction, and improved quality of life, thereby establishing image-guided oncologic intervention as a preferred pathway in treating patients presenting with specific benign MSK tumors. But there is a paradigm shift on the horizon because these techniques may also support established pillars (surgery, systemic treatment, radiotherapy) in the treatment of malignant MSK tumors. Unlike benign tumors, where they are used as primary therapy lines with curative intent, such interventions can be selected for malignant tumors as adjuvant treatment in painful or unstable bone or soft tissue lesions or as more palliative therapy strategies. Using examples from our clinical practices, we elaborate on the benefits of applying a multidisciplinary approach (traditionally involving MSK radiologists, oncologists, orthopaedic surgeons, microbiologists, pathologists, physiotherapists, and pain management experts), ideally within a sarcoma treatment center to deliver a patient-specific therapy plan and illustrate methods to assess the benefits of this model of care.In this article, we review the current repertoire of ablation techniques, demonstrate why such procedures offer value-based alternatives to conventional treatments of specific tumors, and reflect on future directions. Additionally, we review the advantages and limitations of each technique and offer guidance to improve outcomes.

Fully Actuated Body-Mounted Robotic System for MRI-Guided Lower Back Pain Injections: Initial Phantom and Cadaver Studies

This paper reports the improved design, system integration, and initial experimental evaluation of a fully actuated body-mounted robotic system for real-time MRI-guided lower back pain injections. The 6-DOF robot is composed of a 4-DOF needle alignment module and a 2-DOF remotely actuated needle driver module, which together provide a fully actuated manipulator that can operate inside the scanner bore during imaging. The system minimizes the need to move the patient in and out of the scanner during a procedure, and thus may shorten the procedure time and streamline the clinical workflow. The robot is devised with a compact and lightweight structure that can be attached directly to the patient's lower back via straps. This approach minimizes the effect of patient motion by allowing the robot to move with the patient. The robot is integrated with an image-based surgical planning module. A dedicated clinical workflow is proposed for robot-assisted lower back pain injections under real-time MRI guidance. Targeting accuracy of the system was evaluated with a real-time MRI-guided phantom study, demonstrating the mean absolute errors (MAE) of the tip position to be 1.50±0.68mm and of the needle angle to be 1.56±0.93°. An initial cadaver study was performed to validate the feasibility of the clinical workflow, indicating the maximum error of the position to be less than 1.90mm and of the angle to be less than 3.14°.

Image-guided Sports Medicine and Musculoskeletal Tumor Interventions: A Patient-Centered Model

The spectrum of effective musculoskeletal (MSK) interventions is broadening and rapidly evolving. Increasing demands incite a perpetual need to optimize services and interventions by maximizing the diagnostic and therapeutic yield, reducing exposure to ionizing radiation, increasing cost efficiency, as well as identifying and promoting effective procedures to excel in patient satisfaction ratings and outcomes. MSK interventions for the treatment of oncological conditions, and conditions related to sports injury can be performed with different imaging modalities; however, there is usually one optimal image guidance modality for each procedure and individual patient. We describe our patient-centered workflow as a model of care that incorporates state-of-the-art imaging techniques, up-to-date evidence, and value-based practices with the intent of optimizing procedural success and outcomes at a patient-specific level. This model contrasts interventionalist- and imaging modality-centered practices, where procedures are performed based on local preference and selective availability of imaging modality or interventionalists. We discuss rationales, benefits, and limitations of fluoroscopy, ultrasound, computed tomography, and magnetic resonance imaging procedure guidance for a broad range of image-guided MSK interventions to diagnose and treat sports and tumor-related conditions.

Diagnostic and interventional magnetic resonance neurography diagnosis of brachytherapy seed-mediated pudendal nerve injury: a case report

Injury to the pudendal nerve in men presents with pain, paresthesia, or numbness of the perineum, and/or scrotum, and/or penis. There is evidence implicating the brachytherapy seeds used to treat prostate cancer as source of pudendal nerve injury. Compared to surgical prostatectomy, brachytherapy has the advantage of being less invasive, but seeds may not only lead to well-established complications such as urinary, bowel, and erectile dysfunction, but also injury to the sensory branches of the pudendal nerve. We report and document a case of pudendal nerve injury secondary to brachytherapy seeds diagnosed with magnetic resonance (MR) neurography, nerve blocks, and histopathological examination; and successful treatment via sensory branch neurectomy.

MRI-guided percutaneous sclerotherapy of venous malformations: initial clinical experience using a 3T MRI system

PURPOSE

Venous malformations (VMs) are low-flow vascular anomalies that are commonly treated with image-guided percutaneous sclerotherapy. Although many VMs can be safely accessed and treated using ultrasonography and fluoroscopy, some lesions may be better treated with magnetic resonance imaging (MRI)-guided sclerotherapy. The aim of this study is to evaluate the feasibility, efficiency, and outcomes of MRI-guided sclerotherapy of VMs using a 3T MRI system.

METHODS

Six patients with VMs in the neck (n = 2), chest (n = 1), and extremities (n = 3) underwent sclerotherapy with 3T MRI guidance. Feasibility was assessed by calculating the technical success rate and procedural efficiency. Efficiency was evaluated by using planning, targeting, intervention, and total procedure times. Outcomes were assessed by measuring VM volumes before and after sclerotherapy, patient-reported pain scores, and occurrence of complications.

RESULTS

Technical success was achieved in all 6 procedures. There was a non-significant 30% decrease in mean VM volume after the procedure (P = .350). The procedure resulted in a decrease in mean pain score (on an 11-point scale) of 2.6 points (P = .003). After the procedure, 4 patients reported complete pain resolution, 1 reported partial pain resolution, and 1 reported no change in pain. Procedural efficiency was consistent with similar sclerotherapy procedures performed at our institution. There were no major or minor complications.

CONCLUSION

3T MRI guidance is feasible for percutaneous sclerotherapy of VMs, with promising initial technical success rates, procedural efficiency, and therapeutic outcomes without complications.

Persistent Genital Arousal Disorder: Review of Pertinent Peripheral Nerves

INTRODUCTION

Persistent genital arousal disorder (PGAD) is a condition that is still poorly understood. Etiologies reported for PGAD are vascular, neurological, pharmacological, and psychological. Determining the neurophysiological etiology of PGAD began with developing an understanding of the underlying biomechanics of the pudendal nerve and the female sexual response.

AIM

To summarize the anatomy, physiology, etiologies, diagnostics, and treatments of the pertinent peripheral nerves involved in the pathology of PGAD.

METHODS

We performed a PubMed, Cochrane, Embase, Web of Science, and Google Scholar search for English-language articles in peer-reviewed journals with no predefined time period for inclusion. Terms included "humans"[All Fields] AND "persistent"[All Fields] AND/OR ("genitalia"[All Fields] OR "genital"[All Fields]) AND/OR "arousal"[All Fields] AND/OR ("disease"[All Fields] OR "disorder"[All Fields]) AND/OR "nerve"[All Fields]. The main outcomes of the papers were reviewed.

MAIN OUTCOME MEASURE

The main outcome measures were the anatomy and physiology, etiologies, history and physical examination, diagnostic imaging, and current evidence for the treatment of PGAD related to the peripheral nervous system.

RESULTS

Most of the literature for PGAD originates from case studies. The diagnosis of PGAD itself is still a debated topic of discussion. More recent data published indicate that this disease affects males, as well.

CONCLUSION

Nerve entrapment may be a source of continuous arousal. Associated PGAD symptoms would depend on the segment of the nerve involved. Unwelcomed or unwanted arousal has been observed as the most common detrimental symptom. Pelvic 3-tesla magnetic resonance imaging is recommended in all patients with suspected nerve entrapment. Lumbosacral 3-tesla magnetic resonance imaging is recommended if a Tarlov cyst or a herniated intervertebral disc is suspected. If the peripheral nerve is the source of the pathology, surgical intervention may be curative. A multidisciplinary team approach consisting of a medical provider, pelvic floor physical therapist, and sex therapist has demonstrated benefits. There are currently no Food and Drug Administration-approved evidenced-based treatments for PGAD. Klifto KM, Dellon AL. Persistent Genital Arousal Disorder: Review of Pertinent Peripheral Nerves. Sex Med Rev 2020;8:265-273.

3D reconstruction of MR-visible Fe3 O4 -mesh implants: Pelvic mesh measurement techniques and preliminary findings

AIMS

To develop MR-based measurement technique to evaluate the postoperative dimension and location of implanted magnetic resonance (MR)-visible meshes.

METHODS

This technique development study reports findings of six patients (A-F) with cystoceles treated with anterior vaginal MR-visible Fe₃ O₄ -polypropylene implants. Implanted meshes were reconstructed from 3 months and/or 1 year postsurgical MR-images using 3D Slicer®. Measurements including mesh length, distance to the ischial spines, pudendal, and obturator neurovascular bundles and urethra were obtained using software Rhino® and a custom Matlab® program. The range of implanted mesh length and their placements were reported and compared with mesh design and implantation recommendations. With the anterior/posterior-mesh-segment-ratio mesh shrinkage localization was evaluated.

RESULTS

Examinations were possible for patients A-D 3 months and for A, C, E, and F 1 year postsurgical. The mesh was at least 40% shorter in all patients 3 months and/or 1 year postoperatively. A, B showed shrinkage in the anterior segment, D, E in the posterior segment (Patients C, F not applicable due to intraoperative mesh trimming). Patient E presented pain in the area of mesh shrinkage. In Patient C posterior mesh fixations were placed in the iliococcygeal muscle rather than sacrospinous ligaments. Arm placement less than 20 mm from the pudendal neurovascular bundles was seen in all cases. The portion of the urethra having mesh underneath it ranged from 19% to 55%.

CONCLUSIONS

MRI-based measurement techniques have been developed to quantify implanted mesh location and dimension. Mesh placement variations possibly correlating with postoperative complications can be illustrated.

High Isotropic Resolution T2 Mapping of the Lumbosacral Plexus with T2-Prepared 3D Turbo Spin Echo

PURPOSE

Isotropic high-resolution three-dimensional (3D) magnetic resonance neurography (MRN) is increasingly used to depict even small and highly oblique nerves of the lumbosacral plexus (LSP). The present study introduces a T2 mapping sequence (T2-prepared 3D turbo spin echo) that is B1-insensitive and enables quantitative assessment of LSP nerves.

METHODS

In this study 15 healthy subjects (mean age 28.5 ± 3.8 years) underwent 3 T MRN of the LSP area three times. The T2 values were calculated offline on a voxel-by-voxel basis and measured at three segments (preganglionic, ganglionic, postganglionic) of three LSP nerves (S1, L5, L4) by two independent investigators (experienced and novice). Normative data for the different nerves were extracted and intraclass correlation coefficients (ICCs) were calculated to assess reproducibility and interobserver reliability of T2 measurements.

RESULTS

The T2 mapping showed excellent reproducibility with ICCs ranging between 0.99 (S1 preganglionic) and 0.89 (L5 postganglionic). Interobserver reliability was less robust with ICCs ranging between 0.78 (S1 preganglionic) and 0.44 (L5 postganglionic) for S1 and L5. A mean T2 value of 74.6 ± 4.7 ms was registered for preganglionic segments, 84.7 ± 4.1 ms for ganglionic and 65.4 ± 2.5 ms for postganglionic segments, respectively. There was a statistically significant variation of T2 values across the nerve (preganglionic vs ganglionic vs postganglionic) for S1, L5, and L4.

CONCLUSION

Our approach enables isotropic high-resolution and B1-insensitive T2 mapping of LSP nerves with excellent reproducibility. It might reflect a robust and clinically useful method for future diagnostics of LSP pathologies.

1.5 T augmented reality navigated interventional MRI: paravertebral sympathetic plexus injections

PURPOSE

The high contrast resolution and absent ionizing radiation of interventional magnetic resonance imaging (MRI) can be advantageous for paravertebral sympathetic nerve plexus injections. We assessed the feasibility and technical performance of MRI-guided paravertebral sympathetic injections utilizing augmented reality navigation and 1.5 T MRI scanner.

METHODS

A total of 23 bilateral injections of the thoracic (8/23, 35%), lumbar (8/23, 35%), and hypogastric (7/23, 30%) paravertebral sympathetic plexus were prospectively planned in twelve human cadavers using a 1.5 Tesla (T) MRI scanner and augmented reality navigation system. MRI-conditional needles were used. Gadolinium-DTPA-enhanced saline was injected. Outcome variables included the number of control magnetic resonance images, target error of the needle tip, punctures of critical nontarget structures, distribution of the injected fluid, and procedure length.

RESULTS

Augmented-reality navigated MRI guidance at 1.5 T provided detailed anatomical visualization for successful targeting of the paravertebral space, needle placement, and perineural paravertebral injections in 46 of 46 targets (100%). A mean of 2 images (range, 1-5 images) were required to control needle placement. Changes of the needle trajectory occurred in 9 of 46 targets (20%) and changes of needle advancement occurred in 6 of 46 targets (13%), which were statistically not related to spinal regions (P = 0.728 and P = 0.86, respectively) and cadaver sizes (P = 0.893 and P = 0.859, respectively). The mean error of the needle tip was 3.9±1.7 mm. There were no punctures of critical nontarget structures. The mean procedure length was 33±12 min.

CONCLUSION

1.5 T augmented reality-navigated interventional MRI can provide accurate imaging guidance for perineural injections of the thoracic, lumbar, and hypogastric sympathetic plexus.

Artifact-reduced imaging of biopsy needles with 2D multispectral imaging

PURPOSE

Magnetic resonance (MR) guidance for biopsy procedures requires high intrinsic soft-tissue contrast. However, artifacts induced by the metallic needle can reduce its localization and require low-susceptibility needle materials with poorer cutting performance. In a proof of concept, we demonstrate the feasibility of 2D multispectral imaging (2DMSI) for both needle tracking and for needle artifact reduction for more precise needle localization and to enable the usage of needle materials with higher susceptibility.

METHOD

We applied 2DMSI for imaging of MR-compatible biopsy needles, conventional stainless-steel needles, and mixed-material needles and compared it to conventional techniques. In addition, we exploited intrinsic off-resonance information for passive needle tracking.

RESULTS

2DMSI achieved a stronger reduction of the needle artifact compared to conventional techniques. For the mixed-material needles, the artifact was reduced to a level below that for MR-compatible needles with conventional imaging. The passive tracking also improved the ability to pinpoint the needle.

CONCLUSION

2DMSI is promising for both needle tracking and artifact-reduced imaging of biopsy needles for a more precise needle localization. 2DMSI may be particularly promising for needles inducing large distortions or for targeting of small lesions. In addition, it may enable the use of needle materials with higher susceptibility and potentially better sampling performance. Magn Reson Med 80:655-661, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Diagnostic Evaluation of Chronic Pelvic Pain

Chronic pelvic pain can result from various intra- and extra-pelvic etiologies. Although patient history and physical examination may narrow the differential diagnosis, frequently, the different etiologies have overlapping presentations. Imaging examinations such as US and/or MR imaging may help delineate the cause of pain, particularly when related to intra-pelvic organs, pelvic floor dysfunction or prolapse, synthetic material such as pelvic mesh or slings, and in some cases of neuropathic pain. Etiologies of neuropathic pain can also be assessed with non-imaging tests such as nerve conduction studies, electromyography, and testing of sacral reflexes.

MRI-guided cryoablation of the posterior femoral cutaneous nerve for the treatment of neuropathy-mediated sitting pain

Neuropathy of the posterior femoral cutaneous nerve may manifest as pain and paresthesia in the skin over the inferior buttocks, posterior thigh, and popliteal region. Current treatment options include physical and oral pain therapy, perineural injections, and surgical neurectomy. Perineural steroid injections may provide short-term pain relief; however, to our knowledge, there is currently no minimally invasive denervation procedure for sustained pain relief that could serve as an alternative to surgical neurectomy. Percutaneous cryoablation of nerves is a minimally invasive technique that induces a sustained nerve conduction block through temporary freezing of the neural layers. It can result in long-lasting pain relief, but has not been described for the treatment of neuropathy-mediated PFCN pain. We report a technique of MR-guided cryoablation of the posterior femoral cutaneous nerve resulting in successful treatment of PFCN-mediated sitting pain. Cryoablation of the posterior femoral cutaneous nerve seems a promising, minimally invasive treatment option that deserves further investigation.

Magnetic Resonance Neurography of the Pelvic Nerves

Chronic pelvic pain syndrome is commonly caused by nerve injury, inflammation, or entrapment. Owing to the complex anatomy and branching patterns of pelvic nerves, pelvic neuropathies are often difficult to illustrate and diagnose. High-resolution 3-T magnetic resonance neurography is a promising technique for the evaluation of peripheral neuropathy. In this article, the authors discuss the normal anatomy of major pelvic nerves, technical considerations of high-resolution imaging, and normal and abnormal imaging appearances with relevant case examples.

Sacrotuberous Ligament Healing following Surgical Division during Transgluteal Pudendal Nerve Decompression: A 3-Tesla MR Neurography Study

Pelvic pain due to chronic pudendal nerve (PN) compression, when treated surgically, is approached with a transgluteal division of the sacrotuberous ligament (STL). Controversy exists as to whether the STL heals spontaneously or requires grafting. Therefore, the aim of this study was to determine how surgically divided and unrepaired STL heal. A retrospective evaluation of 10 patients who had high spatial resolution 3-Tesla magnetic resonance imaging (3T MRI) exams of the pelvis was done using an IRB-approved protocol. Each patient was referred for residual pelvic pain after a transgluteal STL division for chronic pudendal nerve pain. Of the 10 patients, 8 had the STL divided and not repaired, while 2 had the STL divided and reconstructed with an allograft tendon. Of the 8 that were left unrepaired, 6 had bilateral surgery. Outcome variables included STL integrity and thickness. Normative data for the STL were obtained through a control group of 20 subjects. STL integrity and thickness were measured directly on 3 T MR Neurography images, by two independent Radiologists. The integrity and thickness of the post-surgical STL was evaluated 39 months (range, 9-55) after surgery. Comparison was made with the native contra-lateral STL in those who had unilateral STL division, and with normal, non-divided STL of subjects of the control group. The normal STL measured 3 mm (minimum and maximum of absolute STL thickness, 2-3 mm). All post-operative STL were found to be continuous regardless of the surgical technique used. Measured at level of Alcock's canal in the same plane as the obturator internus tendon posterior to the ischium, the mean anteroposterior STL diameter was 5 mm (range, 4-5 mm) in the group of prior STL division without repair and 8 mm (range, 8-9 mm) in the group with the STL reconstructed with grafts (p<0.05). The group of healed STLs were significantly thicker than the normal STL (p<0.05). We conclude that a surgically divided STL will heal spontaneously and will be significantly thicker after healing.