Intraoperative Spinal Cord Remote Monitoring with a Modified US A-Scope

Research Article

Austin J Clin Case Rep. 2021; 8(7): 1219.

Intraoperative Spinal Cord Remote Monitoring with a Modified US A-Scope

Zaaroor M1, Sviri G2, Sinai A3, Constantinescu M4 and Halevy-Politch J5*

1Department of Neurosurgery, Rambam HCC and The School of Medicine at the Technion I.I.T, Haifa, Israel

2Department of Neurosurgery, Rambam HCC and The School of Medicine at the Technion I.I.T, Haifa, Israel

3Department of Biomedical Eng., with Specialization in Neurophysiology, Rambam HCC, Haifa, Israel

4Department of Neurosurgery, Rambam HCC, Haifa, Israel

5Department of Aerospace Eng., Technion I.I.T., Haifa, Israel

*Corresponding author: Jacob Halevy-Politch, Department of Aerospace Engineering, Technion I.I.T, Technion City, Haifa 32000, Israel

Received: May 20, 2021; Accepted: June 10, 2021; Published: June 17, 2021


Materials and Methods: The motivation for this feasibility study were: (i) to modify the ultrasonic A-scope in order to monitor remotely, intraoperatively and in real-time tumor’s depth and size, before cutting its dura and to control tumor’s residual thickness while its resection and (ii) to demonstrate these abilities during several spinal-cord surgeries.

Results: The ultrasonic A-scope was modified for these purposes, to a noncontact, intraoperative and real-time device. It was successfully applied during several human spinal cord clinical trials. Its data were compared with those of a pre-operative MRI (of the same person), where a good similarity was obtained between them, with a difference less than 1mm, in most cases.

Conclusions: The modified A-Scope advantages: (i) remote, intraoperative and real-time monitoring; (ii) accurate and objective data was obtained; (iii) there is no direct contact between the US transducer and the monitored tissue, as the ultrasound propagates through a free stream of normal saline; (iv) the length of the free stream is few mm, at least; (v) the handpiece enables to monitor in a confined area, as it has a small foot-print; (vi) it is simple to operate the device; (vii) it enables to define intraoperatively tumor edges, before cutting and opening the dura.

Consequently, this modified device seems to be a valuable and useful tool to define intraoperatively tumor’s location and its complete removal and reducing potential damages to healthy tissues surrounding it.

Keywords: Ultrasound; Remote monitoring; Spinal-cord; Tumor


The first application of the ultrasonic (US) A-scope (also named “US B-Scan”), was in Neurosurgery [1], for monitoring tumor-inbrain. Since the US Imaging System (IS) was developed, it replaced the US A-Scope that was not further developed. Although, the US IS are feasible, they have drawbacks, as: (i) are time consuming; (ii) provide suboptimal results [2,3]; (iii) the size of a US transducer limits its applicability in many neurosurgical cases [4] and also for tumor resection in confined areas. It is essential that in these cases, the residual tumor thickness should be monitored Intraoperatively (IO) and in Real-Time (RT). A good US conductivity is essential, which is solved by a thin layer of Normal Saline (NS) [5%, 25°C]). This thin layer of NS is produced by pouring the NS on the tissue to be monitored. A process that requires to stop the surgery; moreover, this solution is not feasible for confined areas. It was also recognized that specialization is essential [4] for a proper operation of an US IS and its image analysis; furthermore, some of these ISs are expensive [1,2,4,5].

A spinal cord surgery, is known as a sensitive and delicate one, with a high risk of post-surgical adverse effects [6-8]. These surgeries are planned, using data from images of a pre-operative Computer Tomography Image’s (CTI) and/or Magnetic Resonance Image’s (MRI) [9,10] and also from a Planar X-ray Image (PXI) (performed at the beginning of the surgery, when the patient is already anesthetized and in the ‘surgical position’). More information is obtained from neurophysiological intra-operative monitoring of spinal tracts [11-13], obtained by electrical stimulation of the motor cortex and recording responses of muscles, as known as (AKA) ‘Motor Evoked-Potentials’ (MEP’s) [14,15], or by stimulating the peripheral nerves and recording the subcortical and cortical responses, AKA ‘Somatosensory Evoked-Potentials’ (SEP’s). However, there is no IO device that provides data in RT and monitors it remotely.

A preliminary study using US was reported on newborns [7,8], for in-vitro studies, where a complete tumor resection was reported [16]. It was also applied during laminoplasty, as it is a useful method for evaluating spinal cord decompression status [12].

As known, CTI and MRI are applied during the pre-operative stages, for anatomic analysis and planning the surgery [9,15]. These IS are rarely used IO in the Operating Room (OR), and even then-they don’t provide the data in RT. Moreover, their price is much higher than the US IS and require dedicated trained personnel in the OR that measures and calculates the data from these images. Therefore, this data is “operator dependent” and subjective (‘operator’s decision’ where to start and stop the measurement on the image).

It will be shown here that the Improved US A-Scope (IUS) is the only true IO and RT monitoring device operating during a spinal cord surgery. IUS allows neurosurgeons to visualize and monitor soft tissue anatomic thicknesses instantly and continuously [6-8]. Although the conventional US ISs are simpler to operate compared to CTI and MRI, their quantitative information (data) is also not obtained in RT [6,7,16] and is also subjective.

Due to the following reasons the conventional US IS, used during tumor-in-brain neurosurgeries, are not suitable always for spinal cord surgery: (a) the size of an US transducer is too large in close vicinity to dura, or in a confined area; (b) the Active Surface (AS) of the US transducer and the examined tissue, should be in good US contact; (c) the size of the US transducer is too large for monitoring the residual tumor thickness during its resection; (d) it is not a RT measuring method, since time is required for processing [13], followed by a quantitative thicknesses evaluation; (e) the estimated error in depth (or thickness), as obtained for US IS, is in the range of 1.0 to 2.5 mm. (f) A thin layer of NS is required that prevents monitoring continuously. While resecting, these drawbacks may cause a damage to a healthy tissue in tumor’s vicinity. The motivation to overcome these drawbacks have led to improve the US A-Scope abilities by developing the IUS (Figure 1) that operates IO, in RT, remotely and provides simultaneously and objectively tumor’s depth, thickness and its residual thickness.