Real-time, image-based slice-to-volume registration for ultrasound-guided spinal intervention

Real-time fusion of magnetic resonance (MR) and ultrasound (US) images could facilitate safe and accurate needle placement in spinal interventions. We develop an entirely image-based registration method (independent of or complementary to surgical trackers) that includes an efficient US probe pose initialization algorithm. The registration enables the simultaneous display of 2D ultrasound image slices relative to 3D pre-procedure MR images for navigation. A dictionary-based 3D-2D pose initialization algorithm was developed in which likely probe positions are predefined in a dictionary with feature encoding by Haar wavelet filters. Feature vectors representing the 2D US image are computed by scaling and translating multiple Haar basis filters to capture scale, location, and relative intensity patterns of distinct anatomical features. Following pose initialization, fast 3D-2D registration was performed by optimizing normalized cross-correlation between intra- and pre-procedure images using Powell's method. Experiments were performed using a lumbar puncture phantom and a fresh cadaver specimen presenting realistic image quality in spinal US imaging. Accuracy was quantified by comparing registration transforms to ground truth motion imparted by a computer-controlled motion system and calculating target registration error (TRE) in anatomical landmarks. Initialization using a 315-length feature vector yielded median translation accuracy of 2.7 mm (3.4 mm interquartile range, IQR) in the phantom and 2.1 mm (2.5 mm IQR) in the cadaver. By comparison, storing the entire image set in the dictionary and optimizing correlation yielded a comparable median accuracy of 2.1 mm (2.8 mm IQR) in the phantom and 2.9 mm (3.5 mm IQR) in the cadaver. However, the dictionary-based method reduced memory requirements by 47×  compared to storing the entire image set. The overall 3D error after registration measured using 3D landmarks was 3.2 mm (1.8 mm IQR) mm in the phantom and 3.0 mm (2.3 mm IQR) mm in the cadaver. The system was implemented in a 3D Slicer interface to facilitate translation to clinical studies. Haar feature based initialization provided accuracy and robustness at a level that was sufficient for real-time registration using an entirely image-based method for ultrasound navigation. Such an approach could improve the accuracy and safety of spinal interventions in broad utilization, since it is entirely software-based and can operate free from the cost and workflow requirements of surgical trackers.

Current paradigms for metastatic spinal disease: an evidence-based review

INTRODUCTION

Management of metastatic spine disease is quite complex. Advances in research have allowed surgeons and physicians to better provide chemotherapeutic agents that have proven more efficacious. Additionally, the advancement of surgical techniques and radiosurgical implementation has altered drastically the treatment paradigm for metastatic spinal disease. Nevertheless, the physician-patient relationship, including extensive discussion with the neurosurgeon, medicine team, oncologists, radiation oncologists, and psychologists, are all critical in the evaluation process and in delivering the best possible care to our patients. The future remains bright for continued improvement in the surgical and nonsurgical management of our patients with metastatic spine disease.

METHODS

We include an evidence-based review of decision making strategies when attempting to determine most efficacious treatment options. Surgical treatments discussed include conventional debulking versus en bloc resection, conventional RT, and radiosurgical techniques, and minimally invasive approaches toward treating metastatic spinal disease.

CONCLUSIONS

Surgical oncology is a diverse field in medicine and has undergone a significant paradigm shift over the past few decades. This shift in both medical and surgical management of patients with primarily metastatic tumors has largely been due to the more complete understanding of tumor biology as well as due to advances in surgical approaches and instrumentation. Furthermore, radiation oncology has seen significant advances with stereotactic radiosurgery and intensity-modulated radiation therapy contributing to a decline in surgical treatment of metastatic spinal disease. We analyze the entire spectrum of treating patients with metastatic spinal disease, from methods of diagnosis to the variety of treatment options available in the published literature.

Adult lumbar scoliosis: underreported on lumbar MR scans

BACKGROUND AND PURPOSE

Adult lumbar scoliosis is an increasingly recognized entity that may contribute to back pain. We investigated the epidemiology of lumbar scoliosis and the rate at which it is unreported on lumbar MR images.

MATERIALS AND METHODS

The coronal and sagittal sequences of lumbar spine MR imaging scans of 1299 adult patients, seeking care for low back pain, were reviewed to assess for and measure the degree of scoliosis and spondylolisthesis. Findings were compared with previously transcribed reports by subspecialty trained neuroradiologists. Inter- and intraobserver reliability was calculated.

RESULTS

The prevalence of adult lumbar scoliosis on MR imaging was 19.9%, with higher rates in ages >60 years (38.9%, P < .001) and in females (22.6%, P = .002). Of scoliotic cases, 66.9% went unreported, particularly when the scoliotic angle was <20 degrees (73.9%, P < .001); 10.5% of moderate to severe cases were not reported. Spondylolisthesis was present in 15.3% (199/1299) of cases, demonstrating increased rates in scoliotic patients (32.4%, P < .001), and it was reported in 99.5% of cases.

CONCLUSIONS

Adult lumbar scoliosis is a prevalent condition with particularly higher rates among older individuals and females but is underreported on spine MR images. This can possibly result in delayed 1) identification of a potential cause of low back pain, 2) referral to specialized professionals for targeted evaluation and management, and 3) provision of health care. The coronal "scout images" should be reviewed as part of the complete lumbar spine evaluation if dedicated coronal sequences are not already part of the spine protocol.

CT fluoroscopically guided percutaneous placement of transiliosacral rod for sacral insufficiency fracture: case report and technique

Treatment of sacral insufficiency fractures (SIFs) has traditionally been conservative, but several patients have been treated with percutaneous sacroplasty. Unfortunately, in the setting of severe, bilateral SIFs, cement may not withstand shear forces present at the lumbosacral junction, and surgical hardware may not provide adequate fixation in osteoporotic, cancellous bone of the sacrum, leading to eventual pseudarthrosis. Thus, we propose a novel technique in which guidance with CT fluoroscopy allows placement of a transiliosacral bar in conjunction with sacroplasty.

Efficient coupling of ligand binding to channel opening by the binding domain of a modulatory (beta) subunit of the olfactory cyclic nucleotide-gated channel

CNG channels in vivo are heteromers of homologous alpha and beta subunits that each contain a six-transmembrane segment domain and a COOH-terminal cytoplasmic cyclic nucleotide binding domain (BD). In heterologous expression systems, heteromeric alphabeta channels activate with greater sensitivity to ligand than do homomeric alpha channels; however, ligand-gating of channels containing only beta subunit BDs has never been studied because beta subunits cannot form functional homomeric CNG channels. To characterize directly the contribution of the beta subunit BD to ligand-gating, we constructed a chimeric subunit, X-beta, whose BD sequence was that of the beta subunit CNG5 from rat, but whose sequence outside the BD was derived from alpha subunits. For comparison, we constructed another chimera, X-alpha, whose sequence outside the BD was identical to that of X-beta, but whose BD sequence was that of the alpha subunit CNG2 from catfish. When expressed in Xenopus oocytes, X-beta and X-alpha each formed functional homomeric channels activated by both cAMP and cGMP. This is the first demonstration that the beta subunit BD can couple ligand binding to activation in the absence of alpha subunit BD residues. Notably, both agonists activate X-beta more effectively than X-alpha (higher opening efficacy and lower K(1/2)). The BD is believed to comprise two functionally distinct subdomains: (1) the roll subdomain (beta-roll and flanking A- and B-helices) and (2) the C-helix subdomain. Opening efficacy was previously believed to be controlled primarily by the C-helix, but when we made additional chimeras by exchanging the subdomains between X-beta and X-alpha, we found that both subdomains contain significant determinants of efficacy and agonist selectivity. In particular, only channels containing the roll subdomain of the beta subunit had high efficacy. Thermodynamic linkage analysis shows that interaction between the two subdomains accounts for a significant portion of their contribution to activation energetics.