Tactical audio and acoustic rendering in biomedical applications.

Complexity of biomedical data requires novel sophisticated analysis and presentation methods. Sonification is used as a new information display in augmented reality systems to overcome problems of existing human-computer interface (e.g., opaque or heavy head-mounted displays, slow computer graphics, etc.). A novel taxonomy of sonification methods and techniques is introduced. We present our experience with tactical audio and acoustic rendering in biomedical applications. Tactical audio as an audio feedback is used as support for precise manual positioning of a surgical instrument in the operating room. Acoustic rendering is applied as an additional information channel and/or warning signal in biomedical signal analysis and data presentation.

Audio-guided blind biopsy needle placement.

We discuss an implementation of an audio user interface for assisting surgical placement tasks. We assembled and tested an apparatus for evaluating the potential benefit of using audio guidance for assisting blind biopsy needle placement tasks. This system improves upon an earlier system we demonstrated (see [1]) by employing three dimensional audio processing as well as a facility for algorithmically-motivated arbitrary waveform synthesis. Using this apparatus an operator attempted to manually follow a predetermined biopsy needle insertion path (trajectory) with an instrumented biopsy needle. This trajectory intercepted a target object embedded within a custom biopsy phantom. The target was invisible to the operator. Audio feedback provided the only means of trajectory and target localization.

Study of human occipital alpha rhythm: the alphon hypothesis and alpha suppression.

Alpha rhythm of the parieto-occipital area is comprised of a parade of short-lived cortical excitations (alphons), each of which exhibits oscillations having a stable period within the alpha bandwidth. Strong alpha rhythm is produced by alphons extending over a larger cortical area, although an enhanced cortical current density may also contribute. Local suppression of alpha rhythm indicates when specific cortical areas become engaged in sensory or cognitive functions. Examples are provided for mental imagery, visual memory, auditory memory, and silent rhythming.

Surgical navigation using audio feedback.

Current medical visualization technology intended for positional guidance in surgical applications may only ever have limited utility in the operating room due to the preexisting visual requirements of surgical practice. Additionally, visual systems impose limits as a result of their high latency, poor image resolution, problems with stereopsis and physical strain upon the user. Audio technology is relatively unexamined in the broad range of available methodologies for medical devices. The potential to translate surgical instrument position into audio feedback presents a novel solution to the human factors and engineering problems faced by visual display technology because audio technology employs a rich and as yet unburdened sensory modality. We describe an experimental system we have developed for investigating this new interface design approach using commercially available hardware.

Tonotopic organization of human auditory association cortex.

Neuromagnetic studies of responses in human auditory association cortex for tone burst stimuli provide evidence for a tonotopic organization. The magnetic source image for the 100 ms component evoked by the onset of a tone is qualitatively similar to that of primary cortex, with responses lying deeper beneath the scalp for progressively higher tone frequencies. However, the tonotopic sequence of association cortex in three subjects is found largely within the superior temporal sulcus, although in the right hemisphere of one subject some sources may be closer to the inferior temporal sulcus. The locus of responses for individual subjects suggests a progression across the cortical surface that is approximately proportional to the logarithm of the tone frequency, as observed previously for primary cortex, with the span of 10 mm for each decade in frequency being comparable for the two areas.

Advantages and limitations of magnetic source imaging.

The term "magnetic source image" (MSI) describes the distribution of neuronal activity in the brain that can be deduced from measurements of the field pattern it produces across the scalp. The signals which provide the basis for an MSI are obtained from the magnetoencephalogram (MEG) which is conventionally recorded with superconducting detectors. Advances in MSI techniques during the past decade have revealed numerous aspects of the functional organization of human sensory systems that were previously unknown. In addition, studies of spontaneous signals, such as those in the alpha bandwidth, have identified specific cortical areas that support rhythmic activity. Extensions of this approach to cognitive research are able to determine the active cortical areas where spontaneous activity is suppressed when a person is engaged in a task such as mental imagery and auditory memory recall. Because only the component of the intracellular current tangential to the overlying skull contributes to the extracranial field, a confined source--modeled as a current dipole--has a characteristic field pattern that simplifies the pattern recognition problem of identifying the underlying sources. This advantage is illustrated by the identification of simultaneously active sources in auditory primary and association cortex. Their separate localization makes it possible to characterize their functional differences. Because the source strength in an MSI may be inferred without knowledge of the electrical conductivities of intervening tissue, it is also possible to estimate the extent of cortical involvement. From the tangential source strength in an MSI, it is possible in most cases to determine the total source strength by taking account of the orientation of the cortical surface. This provides an objective, quantitative measure of the strength of neuronal activity. At present, the major limitation in more extensive use of MSI is the cost of instrumentation. While it requires no contact with the head, and measurements can commence within a few minutes of the arrival of the subject or patient, the present cost of a large array of sensors is two to three million dollars.

Three-dimensional input of body surface data using a laser light scanner.

This article presents a device for automated input of three-dimensional body surface data using a laser light scanner. The device scans the surface in a few seconds. The data are available immediately in digital form for computer-aided presentation and analysis. Although the initial cost is moderately high, the cost per patient and processing time are low. This device makes possible the quantitative evaluation of plastic surgical procedures that are designed to alter body surface form.