Rachael McPhillips

Intraoperative Ultrasound-Guided Resection of Gliomas: A Meta-Analysis and Review of the Literature

BACKGROUND Image-guided surgery has become standard practice during surgical resection, using preoperative magnetic resonance imaging. Intraoperative ultrasound (IoUS) has attracted interest because of its perceived safety, portability, and real-time imaging. This report is a meta-analysis of intraoperative ultrasound in gliomas. METHODS Critical literature review and meta-analyses, using the MEDLINE/PubMed service. The list of references in each article was double-checked for any missing references. We included all studies that reported the use of ultrasound to guide glioma-surgery. The meta-analyses were conducted according to statistical heterogeneity between the studies using Open MetaAnalyst Software. If there was no heterogeneity, fixed effects model was used for meta-analysis; otherwise, a random effect model was used. Statistical heterogeneity was explored by χ(2) and inconsistency (I(2)) statistics; an I(2) value of 50% or more represented substantial heterogeneity. RESULTS A wide search yielded 19,109 studies that might be relevant, of which 4819 were ultrasound in neurosurgery; 756 studies used ultrasound in cranial surgery, of which 24 studies used intraoperative ultrasound to guide surgical resection and 74 studies used it to guide biopsy. Fifteen studies fulfilled our stringent inclusion criteria, giving a total of 739 patients. The estimated average gross total resection rate was 77%. Furthermore, the relationship between extent of surgical resection and study population was not linear. Gross total resection was more likely under IoUS when the lesion was solitary and subcortical, with no history of surgery or radiotherapy. IoUS image quality, sensitivity, specificity, and positive and negative predictive values deteriorated as surgical resection proceeded. CONCLUSION IoUS-guided surgical resection of gliomas is a useful tool for guiding the resection and for improving the extent of resection. IoUS can be used in conjunction with other complementary technologies that can improve anatomic orientation during surgery. Real-time imaging, improved image quality, small probe sizes, repeatability, portability, and relatively low cost make IoUS a realistic, cost-effective tool that complements any existing tools in any neurosurgical operating environment.

Progress towards a multi-modal capsule endoscopy device featuring microultrasound imaging

Current clinical standards for endoscopy in the gastrointestinal (GI) tract combine high definition optics and ultrasound imaging to view the lumen superficially and through its thickness. However, these instruments are limited to the length of an endoscope and the only clinically available, autonomous devices able to travel the full length of the GI tract easily offer only video capsule endoscopy (VCE). Our work seeks to overcome this limitation with a device (“Sonopill”) for multimodal capsule endoscopy, providing optical and microultrasound (μUS) imaging and supporting sensors1.μUS transducers have been developed with multiple piezoelectric materials operating across a range of centre frequencies to study viability in the GI tract. Because of the combined constraints of μUS imaging and the low power / heat tolerance of autonomous devices, a hybrid approach has been taken to the transducer design, with separate transmit and receive arrays allowing multiple manufacturing approaches to maximise system efficiency. To explore these approaches fully, prototype devices have been developed with PVDF, high-frequency PZT and PMN-PT composites, and piezoelectric micromachined ultrasonic transducer arrays. Test capsules have been developed using 3D printing to investigate issues including power consumption, heat generation / dissipation, acoustic coupling, signal strength and capsule integrity. Because of the high functional density of the electronics in our proposed system, application specific integrated circuits (ASICs) have been developed to realise the ultrasound transmit and receive circuitry along with white-light and autofluorescence imaging with singlephoton avalanche detectors (SPADs). The ultrasound ASIC has been developed and the SPAD electronics and optical subsystem have been validated experimentally. The functionality of various transducer materials.

Dual Orientation 16-MHz Single-Element Ultrasound Needle Transducers for Image-Guided Neurosurgical Intervention

Image-guided surgery is today considered to be of significant importance in neurosurgical applications. However, one of its major shortcomings is its reliance on preoperative image data, which does not account for brain deformations and displacements that occur during surgery. In this work, we propose to tackle this issue through the incorporation of an ultrasound device within the type of biopsy needles commonly used as an interventional tool to provide immediate feedback to neurosurgeons during surgical procedures. To identify the most appropriate path to access a targeted tissue site, single-element transducers that look either forward or sideways have been designed and fabricated. Micromolded 1-3 piezocomposites were adopted as the active materials for feasibility tests and epoxy lenses have been applied to focus the ultrasound beam. Electrical impedance analysis, pulse-echo testing, and wire phantom scanning have been carried out, demonstrating the functionality of the needle transducers at ~16 MHz. The capabilities of these transducers for intraoperative image guidance were demonstrated by imaging within soft-embalmed cadaveric human brain and fresh porcine brain.

15 MHz single element ultrasound needle transducers for neurosurgical applications

Image-guided surgery is today considered to be of significant importance in neurosurgical applications. However, one of its major shortcomings is its reliance on preoperative image data, which does not account for the intraoperative brain deformations and displacements that occur during surgery. In this work, we propose to tackle this issue with the incorporation of an ultrasound device within a biopsy needle that is commonly used as an interventional tool so as to provide immediate feedback to neurosurgeons during surgical procedures. In order to identify the most appropriate path to access a targeted tissue site, needle single element transducers that look both forwards and sideways have been designed and fabricated. Monolithic PZT plates and micro-moulded 1-3 piezocomposites have been adopted as the active materials for feasibility tests. Impedance analysis and pulse-echo testing have been carried out, demonstrating the functionality of the transducers at frequencies of ~15 MHz. The imaging capabilities of these transducers have been studied by wire phantom scans. Variations in the transducer properties as a result of the use of different active materials are discussed.

Advanced electrical array interconnections for ultrasound probes integrated in surgical needles

Real-time ultrasound guidance during neurosurgery is a novel and sought-after technique that enables imaging data to be acquired with improved precision during surgical intervention. Surgical needles that are inserted in the tissue of interest can be guided using the real-time graphical information collected by an embedded ultrasound transducer. The miniaturisation capabilities of modern manufacturing technologies allow the fabrication of ultrasound probes that are small enough to be fitted in needles conventionally used in surgical practices (down to ~2 mm inner diameter). High lateral resolution may in fact be achieved by producing miniaturised ultrasound transducer arrays with a series of emitting/receiving elements, each electrically isolated from the others. To guarantee the functionality of such devices, a series of independent electrical interconnections must be implemented that enables the external driving electronics of the imaging system to be connected to the miniaturised ultrasound probe array. This paper presents a novel interconnection scheme designed to interface ultrasound probes integrated in surgical needles with the driving electronics. The presented solution utilises a flexible printed circuit board carrying the electrical tracks and a bonding technique with an anisotropic conductive paste.

The fabrication and integration of a 15 MHz array within a biopsy needle

Microultrasound is a real-time imaging modality that can resolve features <200 μm using frequencies of 15 MHz and above. While attenuation limits the penetration depth, incorporating a miniature transducer within a biopsy needle enables in vivo imaging of structures deep within the body. Imaging from the tip of minimally invasive needles has potential in applications in guiding intervention and tissue characterisation for diagnosis, for example, accurate navigation of interventional neurosurgical tools, and high resolution diagnostic imaging of breast lesions and axillary lymph nodes.

Optimization and characterisation of bonding of piezoelectric transducers using anisotropic conductive adhesive

Microultrasound is of increasing interest in medicine due to the real-time, high-resolution images that can be acquired. The resulting low penetration depth of the image requires the use of multiple transducers laid out as an array and their integration into space-constrained form factors such as needles or capsules to enable minimally invasive access to the site of interest. Miniaturisation of the transducers is possible with modern manufacturing technology but challenges exist in the creation of a reliable interconnection scheme able to produce a series of robust, independent electrical connections between the transducers and external electronics. This paper describes work done to characterise and optimise a low process temperature bonding technology with anisotropic conductive adhesive (ACA) for the production of miniature ultrasound systems with satisfactory yield.

Translational trial outcomes for capsule endoscopy test devices

Endoscopy and colonoscopy are the clinically recognised standards for imaging and diagnosis of diseases of the gastrointestinal (GI) tract. While scope-based approaches combine optical and ultrasound imaging to allow both imaging of the surface and full thickness of the bowel wall, they are limited in their ability to access the full length of the GI tract particularly the small bowel. Wireless video capsule endoscopy (VCE) devices designed to transit the entire GI tract are currently limited to optical imaging of the superficial surface. Work is thus under way to implement additional capsule endoscopy (CE) functionality through the development of devices incorporating both optical and microultrasound imaging. Research to date has identified several gaps in the literature, which have been addressed through early translational trials in vivo. The areas of concern can be classified by sensing modality and necessary support circuitry, and resulting research questions addressed through bespoke, single system capsules.

A compact packaging technique for the integration of ultrasound probes in surgical needles

State-of-the-art neurosurgery intervention relies heavily on tissue imaging information taken at a pre-operative stage. The data retrieved prior to performing an opening in the patients skull, however, may present inconsistencies with respect to the tissue position observed by the surgeon during intervention, due to both the pulsing activity of the brain and possible displacements caused by movement of the patient and the pressure difference between the external and internal environment. The consequent uncertainty during the insertion of surgical tools into the treated tissue gives rise to great interest in real-time guidance techniques. In that respect, ultrasound imaging during neurosurgery is a promising method for imaging the tissue while inserting surgical tools, as it provides high lateral resolution images. While microelectromechanical systems (MEMS) manufacturing techniques have enabled the miniaturisation of ultrasound array devices to fit needle gauges down to 2 mm inner diameter, the challenge in scaling the probes for their integration in surgical needles lies in the development of adequate interconnection techniques to interface the microscale transducer at the tip of the needle with the macroscale driving electronic circuitry. This paper presents progress towards a novel packaging scheme that involves a thin flexible printed circuit interconnection wound inside a surgical needle and connected to the probe at the tip by means of a magnetically aligned anisotropic conductive paste. This bonding technology offers higher compactness compared to conventional wire bonding, as the individual electrical connections are isolated from one another within the volume of the paste line.

Ex-vivo navigation of neurosurgical biopsy needles using microultrasound transducers with M-mode imaging

A clinical need is evident in neurosurgery to facilitate portable, real-time image guidance of interventional tools such as biopsy needles. This work presents imaging studies with microultrasound transducers incorporated into neurosurgical biopsy needles. Two design orientations are shown with the intention to provide both a forward and side field of view to a neurosurgeon. To examine the performance of these needle devices, preliminary B-scans were obtained of resected lamb brain with an embedded target whereby the forward facing and side facing needles were mechanically scanned linearly and radially respectively. The results presented images indicating the feasibility of the transducers to identify a target within brain tissue. To further investigate the transducers potential application as a viable neurosurgical tool, real-time M-mode images were generated within ex vivo porcine brain tissue with an embedded target. Assessing the M-mode images produced by the forward and side facing transducers, the devices are seen to have the potential to offer simple but effective guidance for navigating and positioning the needle within brain tissue close to a target such as a cancerous lesion or in the ventricles.