Terahertz pulse imaging: a pilot study of potential applications in dentistry

The improvement in the detection of caries offers the possibility for dramatic improvement in dental healthcare. Current caries detection rates suggest that there may be scope for improvement. This paper describes a preliminary study to examine applications of terahertz pulse imaging (TPI) to caries detection. We present results for the detection of early stage caries in the occlusal enamel layer of a range of human tooth cross sections using TPI. Higher attenuation of terahertz radiation was observed in carious enamel as compared with healthy enamel. Hypomineralised enamel had different absorption spectra and contrast compared to carious enamel in TPI images. These results have important implications for extending TPI to other medical imaging applications where both early diagnosis and safety issues are important.

Surface visualization of electromagnetic brain activity

Advances in hardware and software have made possible the reconstruction of brain activity from non-invasive electrophysiological measurements over a large part of the brain. The appreciation of the information content in the data is enhanced when relevant anatomical detail is also available for visualization. Different neuroscientific questions give rise to different requirements for optimal superposition of structure and function. Most available software deal with scalar measures of activity, especially hemodynamic changes. In contrast, the electrophysiological observables are generated by electrical activity, which depends on the synchrony of neuronal assemblies and the geometry of the local cortical surface. We describe methods for segmentation and visualization of spatio-temporal brain activity, which allow the interplay of geometry and scalar as well as vector properties of the current density directly in the representations. The utility of these methods is demonstrated through displays of tomographic reconstructions of early sensory processing in the somatosensory and visual modality extracted from magnetoencephalography (MEG) data. The activation course characteristic to a specific area could be observed as current density or statistical maps independently and/or contrasted to the activity in other areas or the whole brain. MEG and functional magnetic resonance imaging (fMRI) activations were simultaneously visualized. Integrating and visualizing complementary functional data into a single environment helps evaluating analysis and understanding structure/function relationships in normal and diseased brain.

Systematic design of phononic band-gap materials and structures by topology optimization

Phononic band-gap materials prevent elastic waves in certain frequency ranges from propagating, and they may therefore be used to generate frequency filters, as beam splitters, as sound or vibration protection devices, or as waveguides. In this work we show how topology optimization can be used to design and optimize periodic materials and structures exhibiting phononic band gaps. Firstly, we optimize infinitely periodic band-gap materials by maximizing the relative size of the band gaps. Then, finite structures subjected to periodic loading are optimized in order to either minimize the structural response along boundaries (wave damping) or maximize the response at certain boundary locations (waveguiding).

Characterization of the magnetic fields around walk-through and hand-held metal detectors

Magnetic field strength measurements were made around eight hand-held and 10 walk-through metal detectors. The method was similar to that used in previous research for Electronic Article Surveillance units except a Cartesian rather than cylindrical coordinate system was used. Special magnetic field probes specifically designed for metal detector measurements were used. A non-metallic positioning apparatus was designed and fabricated. Magnetic field strength measurements were collected on one hand-held metal detector in the laboratory. The remaining data were collected at airport terminals, federal and state government buildings, and a local high school. Walk-through metal detectors had considerably higher magnetic field strengths [up to 299 Am(-1) p-p (3,741 mG)] than hand-held metal detectors [up to 6 Am(-1) p-p (76 mG)]. The frequencies of the magnetic field signal for walk-through detectors were between 0.1 kHz and 3.5 kHz while those for hand-held detectors were between 89 kHz and 133 kHz. Waveforms for all hand-held metal detectors were sinusoidal; those for walk-through metal detectors varied with most being saw-toothed or pulsed. Due to their higher field strengths and the pulsed nature of their magnetic fields, walk-through metal detectors likely pose a higher risk for medical device electromagnetic interference than do hand-held units. Root mean squared magnetic field strengths were calculated from the peak-to-peak values and compared to occupational and general public exposure limits. None of these limits were exceeded. Measurement repeatability was examined for one hand-held and two walk-through metal detectors. For the hand-held metal detector measurements at the location of the maximum magnetic field strength, measurements by three individuals had a repeatability (percent standard deviation) of 5.9%. Limited repeatability data were collected for on-site measurements of walk-through detectors. One unit showed repeatability of 0.1 to 4.5%; a multi-zone unit showed repeatability of 2.7 to 67.5%.

Transcranial magnetic stimulation in the treatment of depression

OBJECTIVE

Transcranial magnetic stimulation (TMS) is a noninvasive and easily tolerated method of altering cortical physiology. The authors evaluate evidence from the last decade supporting a possible role for TMS in the treatment of depression and explore clinical and technical considerations that might bear on treatment success.

METHOD

The authors review English-language controlled studies of nonconvulsive TMS therapy for depression that appeared in the MEDLINE database through early 2002, as well as one study that was in press in 2002 and was published in 2003. In addition, the authors discuss studies that have examined technical, methodological, and clinical treatment parameters of TMS.

RESULTS

Most data support an antidepressant effect of high-frequency repetitive TMS administered to the left prefrontal cortex. The absence of psychosis, younger age, and certain brain physiologic markers might predict treatment success. Technical parameters possibly affecting treatment success include intensity and duration of treatment, but these suggestions require systematic testing.

CONCLUSIONS

TMS shows promise as a novel antidepressant treatment. Systematic and large-scale studies are needed to identify patient populations most likely to benefit and treatment parameters most likely to produce success. In addition to its potential clinical role, TMS promises to provide insights into the pathophysiology of depression through research designs in which the ability of TMS to alter brain activity is coupled with functional neuroimaging.

Task-dependent modulation of excitatory and inhibitory functions within the human primary motor cortex

We evaluated motor evoked potentials (MEPs) and duration of the cortical silent period (CSP) from the right first dorsal interosseous (FDI) muscle to transcranial magnetic stimulation (TMS) of the left motor cortex in ten healthy subjects performing different manual tasks. They abducted the index finger alone, pressed a strain gauge with the thumb and index finger in a pincer grip, and squeezed a 4-cm brass cylinder with all digits in a power grip. The level of FDI EMG activity across tasks was kept constant by providing subjects with acoustic-visual feedback of their muscle activity. The TMS elicited larger amplitude FDI MEPs during pincer and power grip than during the index finger abduction task, and larger amplitude MEPs during pincer gripping than during power gripping. The CSP was shorter during pincer and power grip than during the index finger abduction task and shorter during power gripping than during pincer gripping. These results suggest excitatory and inhibitory task-dependent changes in the motor cortex. Complex manual tasks (pincer and power gripping) elicit greater motor cortical excitation than a simple task (index finger abduction) presumably because they activate multiple synergistic muscles thus facilitating corticomotoneurons. The finger abduction task probably yielded greater motor cortical inhibition than the pincer and power tasks because muscles uninvolved in the task activated the cortical inhibitory circuit. Increased cortical excitatory and inhibitory functions during precision tasks (pincer gripping) probably explain why MEPs have larger amplitudes and CSPs have longer durations during pincer gripping than during power gripping.

Calculation and measurement of the magnetic field in a large diameter electromagnetic flow meter

An idealized magnet model previously used in a simple coil configuration is applied to a more complicated engineering design problem, where an electromagnetic flow meter in diameter of 500 mm is used with five pairs of coils. The numerical results are compared with measurement data. The difference between theory and experiment and the possible causes of errors are discussed. It is shown that the idealized magnet model is practical for the design and the analysis of the flow meter. The work also shows that the traditional uniform field design based on two dimensional (2D) analysis is not suitable for this kind of flow meter. Thus nonuniform field and 3D analysis is needed.

Local detection of electromagnetic energy transport below the diffraction limit in metal nanoparticle plasmon waveguides

Achieving control of light-material interactions for photonic device applications at nanoscale dimensions will require structures that guide electromagnetic energy with a lateral mode confinement below the diffraction limit of light. This cannot be achieved by using conventional waveguides or photonic crystals. It has been suggested that electromagnetic energy can be guided below the diffraction limit along chains of closely spaced metal nanoparticles that convert the optical mode into non-radiating surface plasmons. A variety of methods such as electron beam lithography and self-assembly have been used to construct metal nanoparticle plasmon waveguides. However, all investigations of the optical properties of these waveguides have so far been confined to collective excitations, and direct experimental evidence for energy transport along plasmon waveguides has proved elusive. Here we present observations of electromagnetic energy transport from a localized subwavelength source to a localized detector over distances of about 0.5 microm in plasmon waveguides consisting of closely spaced silver rods. The waveguides are excited by the tip of a near-field scanning optical microscope, and energy transport is probed by using fluorescent nanospheres.

[Plasticity of motor maps in primates: recent advances and therapeutical perspectives]

In the past decade, there have been considerable advances in understanding the neuronal bases of sensory and motor map reorganisation in adults and it is now clear that cortical representations are not invariant and stable, but rather, are dynamic and can continuously be modified. In human subjects, substantial advances in this field have been possible because of the spectacular development of non-invasive imaging and brain stimulation techniques. This review addresses specific questions about the capacity of motor maps in adult primates, including man, to change in response to behaviourally relevant experiences or as a result of central or peripheral lesion. The first part of this review deals with recent progress in understanding the role of the primary motor cortex (M1) in both motor control and cognition. The organisation and function of multiple "non-primary" motor areas located rostrally to the primary motor cortex and in the cingulate cortex are also discussed. This review then focuses on advances made in understanding motor cortex plasticity in different conditions. Firstly, since representations in M1 have been shown to change after motor learning, the contribution of M1 in motor learning has been insinuated; arguments against and in favour of this view are discussed. In addition, data suggesting that intracortical circuitry of M1 may play a role in map reorganisation following motor learning are also evaluated. Secondly, a large body of evidence from both animal and human observations is reviewed that confirms that M1 representations can also be altered as a result of changes in availability of effectors or following sensory deprivation. The mechanisms underlying such a plasticity of cortical maps following peripheral lesions are increasingly well understood. Thirdly, we discuss data showing that a corticospinal system lesion can lead to a complete reorganisation of the area allocated to the hand representation in the primary motor cortex or to a reorganization of the whole network of motor areas responsible for voluntary movements. As a conclusion, therapeutical perspectives that result from a better understanding of those various mechanisms responsible for motor map plasticity are briefly discussed.

Improvement of central motor conduction after bone marrow transplantation in adrenoleukodystrophy

The case is described of a 20-year-old man with adrenoleukodystrophy who showed right spastic hemiparesis and gait disturbance. Brain magnetic resonance imaging disclosed predominant involvement of the left corticospinal pathway. The clinical symptoms improved after bone marrow transplantation. Transcranial magnetic stimulation disclosed significant improvement in various parameters of central motor conduction.

Information for assistants of repeated transcranial magnetic stimulation

Repeated transcranial magnetic stimulation (rTMS) is an exciting new technology being used in psychiatric and neurological research in many centres around the world. rTMS has been accepted as a routine treatment of depression in Canada and Israel. To this point, it has been exclusively conducted by medical officers. As knowledge and experience grows, it is probable that professionals with other backgrounds will have the opportunity to play a role. The aim of this paper is to provide information that will be valuable to assistants. Electromagnetic principles are harnessed to deliver electric currents to localized regions of the cortex. rTMS does not involve anaesthesia or seizure. Side-effects appear to be few. Much remains uncertain, however, even including the most appropriate treatment parameters.

A four coil exposure system (tetracoil) producing a highly uniform magnetic field

We propose a magnetic field exposure system (tetracoil) for in vitro and in vivo experiments, composed of two couples of circular coils satisfying a spherical constraint, whose characteristics are chosen in order to maximize the uniformity region of the magnetic field. Analytical calculations and computer simulations show that our system, as compared to the other most largely used magnetic field exposure systems, represents an optimal compromise in terms of field uniformity, accessibility for biological experiments, and ratio between overall dimension and uniformity region.

A novel method of studying total body water content using a resonant cavity: experiments and numerical simulation

A novel electromagnetic method of obtaining total body water is proposed, in which the water content is obtained from the dielectric properties as measured by a resonant perturbation technique. A screened room acts as a radio-frequency cavity, in our case resonating at 59 MHz, a frequency at which both real and imaginary parts of the complex permittivity of tissues are correlated to their moisture content. The presence of a human subject in the room leads to both a negative shift in the room's resonant frequency and a reduction in its Q-factor. We simulated the room and the body using the transmission line matrix (TLM) method, a computational electromagnetic code which models the problem in the time domain. Experiment and numerical model showed good agreement for two orientations of the subject. The sensitivity of the technique was investigated by measuring the response before and after the subject drank a small quantity of water, less than 2% of body mass. The resulting change in the resonant frequency was significant, and was also predicted by the numerical model. The proposed technique for studying body composition is simple, non-invasive and employs non-ionizing radio waves at low power.

Evaluation of sLORETA in the Presence of Noise and Multiple Sources

The standardized Low Resolution Brain Electromagnetic Tomography method (sLORETA) can be used to compute statistical maps from EEG and MEG data that indicate the locations of the underlying source processes with low error. These maps are derived by performing a location-wise inverse weighting of the results of a Minimum Norm Least Squares (MNLS) analysis with their estimated variances. In this contribution, we evaluate the performance of the method under the presence of noise and with multiple, simultaneously active sources. It is shown that the sLORETA method localizes well, as compared to other linear approaches such as MNLS and LORETA. However, simultaneously active sources can only be separated if their fields are distinct enough and of similar strength. In the context of a strong or superficial source, weak or deep sources remain invisible, and nearby sources of similar orientation tend not to be separated but interpreted as one source located roughly in between.

Neck mobility measurement by means of the 'Flock of Birds' electromagnetic tracking system

OBJECTIVE

To establish the accuracy and reliability of a six-degrees-of-freedom electromagnetic tracking device, the "Flock of Birds", for measuring neck rotations and to identify the main sources of error.

DESIGN

Ten human subjects made the same types of maximal neck rotation, both actively and passively: axial rotation in neutral position, from a flexed position and from an extended position, flexion/extension and lateral flexion. The same movements were mimicked in a 'dummy head' set-up.

METHODS

One Flock of Birds receiver was mounted on the thorax, one on the head. By means of a third receiver, mounted on a stylus, bony landmarks on head and thorax were palpated. These served to define two anatomically based local coordinate systems, to which the rotations were referred.

RESULTS

Measurements were accurate with a maximal measurement error of 2.5 degrees. No significant difference between active and passive rotation was seen. The intra-subject variation was low within the same session, SD between 2 degrees and 4 degrees. Between sessions the variability was considerable, SD between 5 degrees and 16 degrees.

CONCLUSION

The Flock of Birds method is reliable and sufficiently precise. The variability in measured range of motion between sessions is a point of concern in interpreting follow-up studies in patients.

RELEVANCE

A reduced range of neck motion is a major complaint in pathologies of the cervical spine or the shoulder. A method is described in which neck rotations are related to well-defined bony landmarks. In combined rotations, e.g. flexion combined with axial rotation, the measured range of motion can sometimes fluctuate strongly (up to 30 degrees ) between measurements, without apparent pathology.

Repetitive transcranial magnetic stimulation (rTMS): new tool, new therapy and new hope for ADHD

Attention-deficit hyperactivity disorder (ADHD) is the most common developmental disorder that is associated with environmental and genetic factors. Neurobiological evidence suggests that fronto-striatum-cerebellum circuit abnormalities, mainly in the right hemisphere, are responsible for most of the disturbed sensorimotor integration; dopamine seems to be the main neurochemical alteration underlying these morphological abnormalities. Different conventional treatments have been employed on ADHD; however, repetitive transcranial magnetic stimulation (rTMS), a new and useful option for the clinical/research investigation of several neuropsychiatric disorders involving dopamine circuits, has yet to be considered as a therapeutic tool and possible drug-free option for ADHD. Here the authors explore the available evidence that makes this tool a rational therapeutic possibility for patients with ADHD, calling attention to safety issues, while highlighting the potentials of such an approach and the new hope it may bring for patients, parents, researchers and clinicians. The authors advocate carefully conducted clinical trials to investigate efficacy, safety, cost-effectiveness and clinical utility of rTMS for ADHD patients - in comparison to both placebo and standard treatments.

[Methods of prevention and reduction of delayed muscle soreness (DOMS)]

This review describes the methods of reducing the effects of delayed onset muscle soreness (DOMS) as a result of muscle contractions, including the cryotherapy, physical and pharmacological therapies. Concentric and eccentric exercise and some pharmacological agents are also described as the methods of DOMS prevention.

Lack of a therapeutic effect of a 2-week sub-threshold transcranial magnetic stimulation course for treatment-resistant depression

Stimulation parameters seem to strongly influence the efficacy of repetitive transcranial magnetic stimulation (rTMS) in the management of treatment-resistant depressed patients. The most effective and safest parameters are yet to be defined. Moreover, systematic follow-up data available to document the duration of the therapeutic effects remain sparse. Twenty-one treatment-resistant depressed patients were randomized to either active rTMS (N=12) or to sham (N=9) treatment in a double-blind design. Patients were kept on their medications. Sub-motor-threshold (MT) stimulation (80% MT) was delivered for 10 consecutive work days (20 Hz, 2-s trains, 20 trains). Subjects meeting pre-set criteria for responding were entered into a follow-up phase for up to 5 months. Utilizing the above stimulation parameters, we found no significant difference between groups. Six patients in the active group and one subject in the sham group met criteria for the follow-up phase. The period of time before subjects met criteria for relapse was highly variable ranging from 2 to 20 weeks. Sub-threshold rTMS stimulation for 2 weeks is not significantly superior to sham treatment for treatment-resistant depressed patients. The duration of the therapeutic effects of rTMS delivered to the left prefrontal cortex using the above-described parameters is highly variable.

Abnormal somatotopic arrangement of sensorimotor interactions in dystonic patients

The aim of the study was to detect abnormalities of sensorimotor interactions and their topographic distribution in the hand muscles of dystonic patients. We investigated the effect of electrical stimulation of the second (D2) and fifth (D5) fingers on the amplitude of motor evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES) in the relaxed first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles on both sides of eight patients with unilateral hand dystonia (HD) and in four patients with cervical dystonia (CD). Six Parkinson's disease patients were used as the disease control group and 10 healthy subjects served as normal controls. For each muscle, the digital stimulation was applied to a contiguous finger (CF) and to a non-contiguous finger (NCF). The digital stimulation was set at three times the sensory threshold and preceded TMS or TES at intervals ranging from 10 to 100 ms. In normal subjects, a somatotopic inhibitory effect was detected, since the CF stimulation was significantly more powerful in determining the reduction of MEPs in response to TMS at intervals ranging from 20 to 50 ms. In dystonic patients, on the contrary, the somatopic effect was not present, because both CF and NCF stimulation evoked a consistent MEP inhibition and no significant difference was detected between the conditioning effect of CF and NCF stimulation. These abnormalities were present in the muscles of both the affected and unaffected hands of HD patients, as well as in CD patients. TES conditioning provoked MEP inhibition only at interstimulus intervals (ISIs) <40 ms. Significant MEP potentiation was found at ISIs of 20-40 ms to CF stimulation in Parkinson's disease patients, while there was no effect after NCF stimulation. These data suggest that MEP suppression in response to digital stimulation is preserved in dystonia, but the somatotopically distributed input-output organization of the sensorimotor interactions is lost in dystonic patients' hands. The comparison between TMS and TES experiments indicates that abnormalities may be present at both the spinal and the cortical level, at least in some patients. These findings suggest that a mechanism that normally operates in order to focus the effect of somatosensory afferences on the motor system may be impaired in dystonia. This abnormality seems specific to dystonia.

Terahertz wave imaging: horizons and hurdles

Terahertz (THz) science will profoundly impact biotechnology. It has tremendous potential for applications in imaging, medical diagnosis, health monitoring, environmental control and chemical and biological identification. THz research will become one of the most promising research areas in the 21st century for transformational advances in imaging, as well as in other interdisciplinary fields. However, terahertz wave (T-ray) imaging is still in its infancy. This paper discusses the uniqueness and limitations of T-ray imaging, identifies the major challenges impeding T-ray imaging and proposes solutions and opportunities in this field. It also concentrates on the generation, propagation and detection of T-rays by the use of femtosecond optics.