Calibration/Standardization of Short-Duration Stimuli

This article provides a brief summary of issues relevant to the calibration and standardization of acoustic transients.     

Ultrasound imaging in neurosurgery: approaches to minimize surgically induced image artefacts for improved resection control

Background

Intraoperative ultrasound imaging is used in brain tumor surgery to identify tumor remnants. The ultrasound images may in some cases be more difficult to interpret in the later stages of the operation than in the beginning of the operation. The aim of this paper is to explain the causes of surgically induced ultrasound artefacts and how they can be recognized and reduced.

Methods

The theoretical reasons for artefacts are addressed and the impact of surgery is discussed. Different setups for ultrasound acquisition and different acoustic coupling fluids to fill up the resection cavity are evaluated with respect to improved image quality.

Results

The enhancement artefact caused by differences in attenuation of the resection cavity fluid and the surrounding brain is the most dominating surgically induced ultrasound artefact. The influence of the artefact may be reduced by inserting ultrasound probes with small footprint into the resection cavity for a close-up view of the areas with suspected tumor remnants. A novel acoustic coupling fluid developed for use during ultrasound imaging in brain tumor surgery has the potential to reduce surgically induced ultrasound artefacts to a minimum.

Conclusions

Surgeons should be aware of artefacts in ultrasound images that may occur during brain tumor surgery. Techniques to identify and reduce image artefacts are useful and should be known to users of ultrasound in brain tumor surgery.     

Threshold of hearing (0.125-20 kHz) in children and youngsters.

Pure-tone air-conduction audiometry has been performed in three groups of children and youngsters aged 10, 14 and 18 years old. The complete frequency range of 0.125 to 20 kHz was measured, and number of different questions were raised. Firstly, the hearing threshold in the conventional frequency range was compared to the international standard ISO 389. Significant differences from ISO zero were found for all groups and at all frequencies of 0.125 to 8 kHz. Secondly, possible noise damage, shown as dips in the audiograms at 3, 4 or 6 kHz was examined; and thirdly, high-frequency (8-20 kHz) sensitivity between groups was compared. Only a few audiograms, the majority being in the youngest age group, were found to be a result of possible noise damage, and in the extra-high-frequency range, a systematic decrease in sensitivity was found for the two older groups compared to the 10-year-old children at frequencies higher than 14 kHz.     

Low-frequency hearing loss: auditory brainstem response-derived band analysis

Conventional (0.125-8 kHz) and high-frequency (8-20 kHz) audiometry, together with brainstem response audiometry supplemented with derived-band studies have been performed in 6 patients with sensorineural hearing loss: 1 with narrow-band, 3-4 kHz, and 5 with low-frequency threshold elevations. The derived-band results in the latter indicate that the low-frequency audiometric thresholds are spurious, and represent the low-frequency tails of viable high-frequency neurons. Threshold preservation in the 4- to 8-kHz frequency band proved necessary for generation of a normal auditory brainstem response at suprathreshold stimulus levels.     

Frequency specificity of the auditory brainstem responses in the cat

The auditory brainstem responses evoked by click, noise-burst and tone-bursts have been recorded in the cat, and octave-wide derived bands obtained at 20 and 50 dB RL intensity levels. At near-threshold intensity both the 2 and 4 kHz tone-bursts are frequency specific, while the click and noise-burst ABR contain no contributions below 2 kHz. The principal contribution to the 1 kHz ABR comes from the 2-4 kHz band, while at 0.5 kHz almost the entire response is generated basally. Higher stimulus intensity produces a spread of activity into other bands. Low frequency cochlear function cannot be assessed by this technique.     

Development of surface-recorded cochlear and early neural potentials in the cat

Summary The development of the surface-recorded cochlear and early neural potentials has been studied in the cat from birth to the 8th post-natal week. CM, SP, and each of the neural waves has a characteristic temporal developmental pattern and mature threshold. Wave IV is the most resistant to reduction in stimulus intensity levels, while the thresholds of both cochlear potentials are high. Animals with hereditary unilateral deafness constitute a most convenient model for the study of functional maturation in the auditory pathways, particularly with regard to precise latency estimations.Supported by grant no. C.37.59-001 from the Norwegian Research Council for Science and the Humanities     

CustusX: an open-source research platform for image-guided therapy

Purpose

CustusX is an image-guided therapy (IGT) research platform dedicated to intraoperative navigation and ultrasound imaging. In this paper, we present CustusX as a robust, accurate, and extensible platform with full access to data and algorithms and show examples of application in technological and clinical IGT research.

Methods

CustusX has been developed continuously for more than 15 years based on requirements from clinical and technological researchers within the framework of a well-defined software quality process. The platform was designed as a layered architecture with plugins based on the CTK/OSGi framework, a superbuild that manages dependencies and features supporting the IGT workflow. We describe the use of the system in several different clinical settings and characterize major aspects of the system such as accuracy, frame rate, and latency.

Results

The validation experiments show a navigation system accuracy of \(<\)1.1 mm, a frame rate of 20 fps, and latency of 285 ms for a typical setup. The current platform is extensible, user-friendly and has a streamlined architecture and quality process. CustusX has successfully been used for IGT research in neurosurgery, laparoscopic surgery, vascular surgery, and bronchoscopy.

Conclusions

CustusX is now a mature research platform for intraoperative navigation and ultrasound imaging and is ready for use by the IGT research community. CustusX is open-source and freely available at http://www.custusx.org.

     

Validation of a hybrid Doppler ultrasound vessel-based registration algorithm for neurosurgery

Purpose

We describe and validate a novel hybrid nonlinear vessel registration algorithm for intra-operative updating of preoperative magnetic resonance (MR) images using Doppler ultrasound (US) images acquired on the dura for the correction of brain-shift and registration inaccuracies. We also introduce an US vessel appearance simulator that generates vessel images similar in appearance to that acquired with US from MR angiography data.

Methods

Our registration uses the minimum amount of preprocessing to extract vessels from the raw volumetric images. This prevents the removal of important registration information and minimizes the introduction of artifacts that may affect robustness, while reducing the amount of extraneous information in the image to be processed, thus improving the convergence speed of the algorithm. We then completed 3 rounds of validation for our vessel registration method for robustness and accuracy using (i) a large number of synthetic trials generated with our US vessel simulator, (ii) US images acquired from a real physical phantom made from polyvinyl alcohol cryogel, and (iii) real clinical data gathered intra-operatively from 3 patients.

Results

Resulting target registration errors (TRE) of less than 2.5?mm are achieved in more than 90?% of the synthetic trials when the initial TREs are less than 20?mm. TREs of less than 2?mm were achieved when the technique was applied to the physical phantom, and TREs of less than 3?mm were achieved on clinical data.

Conclusions

These test trials show that the proposed algorithm is not only accurate but also highly robust to noise and missing vessel segments when working with US images acquired in a wide range of real-world conditions.     

Damage and functional recovery of the Atlantic cod (Gadus morhua) inner ear hair cells following local injection of gentamicin

This study addresses the ultrastructural and functional damage and subsequent recovery of the inner ear in the Atlantic cod following intrasaccular gentamicin injection. Inner ear damage was assessed using SEM and measurements of AEP following 250-Hz pure-tone stimuli. Data from gentamicin-treated fish were compared with control (no injection) and sham (injection of saline) fish. Control fish had normal response thresholds associated with well-developed hair cell bundles in their macula sacculi. Sham fish had higher response thresholds compared with control fish during the first week post-intervention, but response thresholds were subsequently normal. Treated fish displayed significant inner ear damage associated with an increased average AEP threshold on the third day following treatment. Thereafter, inner ear tissue displayed signs of progressive regeneration until it was comparable to controls from the 14th day. Response thresholds were similar to those of control fish from the 17th day following treatment. These observations suggest that the macula sacculi of Atlantic cod can regenerate towards a near-complete functional and ultrastructural recovery within 17–21 days following ototoxic gentamicin treatment.