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PubMed1985

Action potential patterns of isolated frog muscle spindle in response to sinusoidal stimulation.

Signal transfer in the isolated frog muscle spindle is investigated using the linear frequency domain analysis technique. Sinusoidal stretches of different amplitudes (20-120 micron) and frequencies (0.1-120 Hz) were applied at different levels of static prestretch, ranging from resting length (L0) up to L0 + 400 micron, so that the frequency-response characteristics were measured at different operating points within the dynamic range. The neuronal responses were recorded from the first node of the afferent stem fiber with a modified air-gap technique. By this means, subthreshold receptor potentials, prepotentials preceding the impulse, and the propagated action potentials were recorded simultaneously, thus providing a detailed insight into the encoding process. There is a well-defined dynamic range of receptor responses. At L0, the encoding site is depolarized to its firing level and discharges spontaneous stimulus-independent impulses. The upper limit is given by the saturation of the receptor potential, which keeps the depolarization maximum below the level of sodium inactivation. Therefore a "depolarization block" or "overstretch" does not exist in the muscle spindle; i.e., the receptor retains its ability to encode information over a large range of dynamic and static displacements. Since the dynamic curves of the receptor potential are not symmetrical about their static operating point, the impulse pattern remains modulated throughout the dynamic range, even if small sinusoids are superimposed on a large static prestretch. The afferent discharge pattern is mainly regulated by the modulated AC component of the receptor potential. At low stimulus frequencies (less than 1 Hz) the receptor potential modulates almost linearly about the mean membrane voltage, so that the evoked discharge pattern displays a smooth analog signal, which is close to sinusoidal. Increasing the static prestretch increases both the peak response and the modulation depth of the impulse pattern. In the intermediate frequency range (1-10 Hz), the cycle histogram disintegrates into discrete peaks separated by empty bins, because the nonlinear receptor potential elicites firmly phase-locked action potentials during its fast depolarization transient. Raising the prestretch level improves the precision of phase locking and increases the number of spikes elicited per cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2004

Attenuation of the neural response to sad faces in major depression by antidepressant treatment: a prospective, event-related functional magnetic resonance imaging study.

BACKGROUND: Depression is associated with interpersonal difficulties related to abnormalities in affective facial processing. OBJECTIVES: To map brain systems activated by sad facial affect processing in patients with depression and to identify brain functional correlates of antidepressant treatment and symptomatic response. DESIGN: Two groups underwent scanning twice using functional magnetic resonance imaging (fMRI) during an 8-week period. The event-related fMRI paradigm entailed incidental affect recognition of facial stimuli morphed to express discriminable intensities of sadness. SETTING: Participants were recruited by advertisement from the local population; depressed subjects were treated as outpatients. PATIENTS AND OTHER PARTICIPANTS: We matched 19 medication-free, acutely symptomatic patients satisfying DSM-IV criteria for unipolar major depressive disorder by age, sex, and IQ with 19 healthy volunteers. Intervention After the baseline assessment, patients received fluoxetine hydrochloride, 20 mg/d, for 8 weeks. MAIN OUTCOME MEASURES: Average activation (capacity) and differential response to variable affective intensity (dynamic range) were estimated in each fMRI time series. We used analysis of variance to identify brain regions that demonstrated a main effect of group (depressed vs healthy subjects) and a group x time interaction (attributable to antidepressant treatment). Change in brain activation associated with reduction of depressive symptoms in the patient group was identified by means of regression analysis. Permutation tests were used for inference. RESULTS: Over time, depressed subjects showed reduced capacity for activation in the left amygdala, ventral striatum, and frontoparietal cortex and a negatively correlated increase of dynamic range in the prefrontal cortex. Symptomatic improvement was associated with reduction of dynamic range in the pregenual cingulate cortex, ventral striatum, and cerebellum. CONCLUSIONS: Antidepressant treatment reduces left limbic, subcortical, and neocortical capacity for activation in depressed subjects and increases the dynamic range of the left prefrontal cortex. Changes in anterior cingulate function associated with symptomatic improvement indicate that fMRI may be a useful surrogate marker of antidepressant treatment response.

Affect↗

PubMed2004

Response properties of single auditory nerve fibers in the mouse.

The availability of transgenic and mutant lines makes the mouse a valuable model for study of the inner ear, and a powerful window into cochlear function can be obtained by recordings from single auditory nerve (AN) fibers. This study provides the first systematic description of spontaneous and sound-evoked discharge properties of AN fibers in mouse, specifically in CBA/CaJ and C57BL/6 strains, both commonly used in auditory research. Response properties of 196 AN fibers from CBA/CaJ and 58 from C57BL/6 were analyzed, including spontaneous rates (SR), tuning curves, rate versus level functions, dynamic range, response adaptation, phase-locking, and the relation between SR and these response properties. The only significant interstrain difference was the elevation of high-frequency thresholds in C57BL/6. In general, mouse AN fibers showed similar responses to other mammals: sharpness of tuning increased with characteristic frequency, which ranged from 2.5 to 70 kHz; SRs ranged from 0 to 120 sp/s, and fibers with low SR (<1 sp/s) had higher thresholds, and wider dynamic ranges than fibers with high SR. Dynamic ranges for mouse high-SR fibers were smaller (<20 dB) than those seen in other mammals. Phase-locking was seen for tone frequencies <4 kHz. Maximum synchronization indices were lower than those in cat but similar to those found in guinea pig.

Acoustic Stimulation↗

PubMed2004

Real time TaqMan PCR detection and quantitation of HBV genotypes A-G with the use of an internal quantitation standard.

BACKGROUND: Diagnostic assays for the accurate quantitation of hepatitis B virus (HBV) DNA levels from patients undergoing antiviral therapy are useful for monitoring and tailoring therapy. Such assays should give accurate results with all HBV genotypes, including a seventh genotype of hepatitis B virus, genotype G, that has recently been identified in specimens from HBV-positive patients in the United States and Europe. OBJECTIVES: To characterize the performance characteristics of a quantitative real time TaqMan PCR assay, the High Pure System Viral Nucleic Acid/COBAS TaqMan HBV Test, for the detection and quantitation of HBV genotypes A-G from patient plasma and serum. This test was evaluated for limit of detection, dynamic range, reproducibility, accuracy, and genotype inclusivity. STUDY DESIGN: Primers and TaqMan probes specific for HBV and an internal quantitation standard (QS) were designed and tested using a set of plasmid DNAs representing various genotyped specimens. In addition, sensitivity, dynamic range, precision, and correlation with the COBAS AMPLICOR HBV MONITOR Test were evaluated using HBV dilution panels and patient specimens. RESULTS AND CONCLUSIONS: A real time TaqMan assay was developed that detects and quantifies DNA from genotypes A-G equivalently. The assay has a limit of detection of <50 copies/ml with plasma and serum, a dynamic range up to 10(9) copies/ml, and good precision and accuracy. Titers obtained with this method without dilutions show good correlation across the dynamic range with titers obtained with the COBAS AMPLICOR HBV MONITOR Test.

DNA Primers↗

PubMed1987

Neuronal mechanisms of pain with special emphasis on visceral and deep somatic pain.

Pain has several dimensions: the sensory-discriminative, the motivational-affective, the cognitive and the motor and autonomic dimension. Each dimension can be roughly identified with certain brain areas. The sensory-discriminative dimension is also called the "nociceptive dimension" or, briefly, "nociception". 1. Noxious stimuli applied to the skin appear to be encoded quite specifically by certain types of nociceptive afferent units with group III (A) and IV (C) fibers. The impulse activity of these cutaneous primary afferents converges on spinal "nociceptive-specific" neurones, most of which seem to be located in lamina I of the dorsal horn, and together with the nonnociceptive information from the skin on "wide-dynamic range" (multisensory) neurones in the grey matter, most of which are situated in lamina V, but some also in adjacent laminae and lamina I. 2. Many of these "nociceptive-specific" and "wide-dynamic range" neurones project with their axons through the anterolateral tract to the nucleus ventralis posterolateralis (VPL) of the thalamus and also to other thalamic nuclei, to the mesencephalon and to the reticular formation of the brain stem. In the VPL of the thalamus, most neurones with nociceptive input have a wide-dynamic range property, very few are nociceptive-specific. 3. Noxious events leading to deep somatic pain are encoded by thin myelinated (A delta) and unmyelinated afferent fibers (e.g., from skeletal muscle, tendon and joint capsule). Besides these deep somatic "nociceptive" afferent units, other nonnociceptive deep somatic afferent units with fine afferents have been claimed to exist and it is believed that these are involved in functions other than nociception. The specificity of responses of these afferents, with respect to the natural stimuli, is only relative. 4. For the viscera nociceptive spinal visceral afferents, which are only activated when injurious or potentially injurious events in the visceral domain (which may lead to pain) occur, cannot be unambiguously shown to exist. It seems more likely that the activity in the same population of spinal visceral afferents is involved in nociceptive as well as in nonnociceptive sensory functions, in the regulation of visceral organs and in various types of reflexes. 5. No neurones in the spinal grey matter have been found which specifically transmit and process information from fine deep somatic and spinal visceral afferents. This information seems to converge not only on many "wide-dynamic range" (multisensory) spinal neurones but also on some "nociceptive-specific" neurones.(ABSTRACT TRUNCATED AT 400 WORDS)

Humans↗

PubMed1995

Measurement of the arc of digital flexion and joint movement ranges.

Dynamic digital flexion was examined by video recording healthy subjects making a fist. The arc of the fingertip sweep from full extension to full flexion was replayed frame by frame and plotted. A similar technique was employed to measure the MP, PIP and DIP joint angles throughout digital flexion. Graphs were plotted of MP against PIP, and PIP against DIP flexion. These results were related to a theoretical 45 degrees line. The fingertip appears to sweep through an elliptical pathway when flexing, rather than an equiangular curve. Graphs of joint flexion showed that male and female fingers flex in a similar fashion, as do the index and little finger. Graphs of PIP against DIP flexion suggest some limiting mechanism of either the extensor or flexor system. These graphs give useful insights into the complex mechanisms of dynamic digital flexion, and may be of diagnostic and prognostic importance.

Adult↗

PubMed2003

Changes over time in electrical stimulation levels and electrode impedance values in children using the Nucleus 24M cochlear implant.

OBJECTIVE: The present study was designed to evaluate changes in psycho-electric parameters, i.e. threshold levels, comfortable levels, dynamic range, and electrode impedance values during the 1st year post-implantation, in children using the Nucleus 24M cochlear implant system. METHODS: The maps of 25 pre-lingual children programmed with ACE strategy in Monopolar 1 + 2 mode were examined at five time points: connection, 1, 3, 6, and 12 months post-initial stimulation. Maps and electrode impedance values were analyzed according to three cochlear segments: basal, medial, and apical. RESULTS: Significant elevations of thresholds, comfortable levels, and dynamic range were found during the first few months of implant use. Specifically, threshold increased and dynamic range widened until the 3 months visit, whereas comfortable levels continued to increase until the 6 months visit, thereafter levels stabilized. Electrode impedance values decreased significantly from connection to the 1-month visit thereafter a stabilization of values was evident. In addition, thresholds and comfortable levels were found to be significantly lower in the apical segment, whereas dynamic range and electrode impedance values did not differ among the cochlear segments. CONCLUSIONS: Significant changes in psycho-electric parameters and electrode impedance values were evident during the first 6 months of implant use. Given the important role of an optimal map for speech perception, frequent programming sessions during the first few months of implant use are essential.

Acoustic Impedance Tests↗

PubMed2006

The effects of frequency range, vowel, dynamic loudness level, and gender on nasalance in amateur and classically trained singers.

This study addresses two questions: (1) How much nasality is present in classical Western singing? (2) What are the effects of frequency range, vowel, dynamic level, and gender on nasality in amateur and classically trained singers? The Nasometer II 6400 by KayPENTAX (Lincoln Park, NJ) was used to obtain nasalance values from 21 amateur singers and 25 classically trained singers while singing an ascending five-tone scalar passage in low, mid, and high frequency ranges. Each subject sang the scalar passage at both piano and mezzo-forte dynamic loudness levels on each of the five cardinal vowels (/a/, /e/, /i/, /o/, /u/). A repeated mixed-model analysis indicated a significant main effect for the amateur/classically trained distinction, dynamic loudness level, and vowel, but not for frequency range or gender. The amateur singers had significantly higher nasalance scores than classically trained singers in all ranges and on all vowels except /o/. Dynamic loudness level had a significant effect on nasalance for all subject groups except for female majors in the mid- and high-frequency ranges. The vowel, /i/, received significantly higher nasalance than all of the other vowels. Although results of this study show that dynamic loudness level, vowel, and level of training in classical singing have a significant effect on nasality, nasalance scores for most subjects were relatively low. Only six of the subjects, all of whom were amateur singers, had average nasalance scores that could be considered hypernasal (ie, a nasalance average of 22 or above).

Adolescent↗

PubMed1991

Small object contrast in AMBER and conventional chest radiography.

The ability of a commercially available scanning equalization system for chest radiography to render small object contrast in the lung-, mediastinum-, and subdiaphragm-equivalent regions of an acrylic chest phantom was quantitatively evaluated. Images from nine chest phantoms that represented a wide range of patient sizes and dynamic ranges of x-ray transmittance were analyzed. Subject contrast was measured with a photostimulable phosphor detector, and images were acquired in both equalized and nonequalized (conventional) imaging modes. Available subject contrast in the lung-equivalent region was 8%-15% lower in the equalized images compared with the nonequalized images in all phantoms (patient types); contrast in the mediastinum-, retro-cardiac-, and subdiaphragm-equivalent regions was 11%-63% higher in the equalized images, with the degree of improvement increasing as patient size and dynamic range increased. Images of each phantom were also acquired with the screen-film systems currently in use at the authors' institution, permitting an assessment of the relative performance (in terms of radiographic contrast) of these imagers with and without use of equalization.

Diaphragm↗

PubMed1984

Development of dose equivalent meters based on microdosimetric principles.

In this paper, the employment of microdosimetric dose-equivalent meters in radiation protection is described considering the advantages of introducing microdosimetric methods into radiation protection, the technical suitability of such instruments for measuring dose equivalent, and finally technical requirements, constraints and solutions together with some examples of instruments and experimental results. The advantage of microdosimetric methods in radiation protection is illustrated with the evaluation of dose-mean quality factors in radiation fields of unknown composition and with the methods of evaluating neutron- and gamma-dose fractions. --It is shown that there is good correlation between dose-mean lineal energy, yD, and the ICRP quality factor. --Neutron- and gamma-dose fractions of unknown radiation fields can be evaluated with microdosimetric proportional counters without recurrence to other instruments and methods. The problems of separation are discussed. The technical suitability of microdosimetric instruments for measuring dose equivalent is discussed considering the energy response to neutrons and photons and the sensitivity in terms of dose-equivalent rate. Then, considering technical requirements, constraints, and solutions, the problems of the large dynamic range in LET, the large dynamic range in pulse rate, geometry of sensitive volume and electrodes, evaluation of dose-mean quality factors, calibration methods, and uncertainties are discussed.

Gamma Rays↗

PubMed1991

Coding of interaural time differences of transients in auditory cortex of Rattus norvegicus: implications for the evolution of mammalian sound localization.

We obtained quantitative evidence on the coding of interaural time differences (ITDs) of click stimuli by 40 single neurons in the auditory cortex of anesthetized albino rats. Most of the neurons (31/40) received an excitatory input from the contralateral ear, and an inhibitory input from the ipsilateral ear (EI cells). These neurons expressed their sensitivity to ITDs in a sigmoidal relation between spike count and ITD, with maximal responses associated with contralateral-leading ITDs. The mean ITD dynamic range was 590 microseconds. The dynamic ranges typically encompassed at least part of the behaviorally-relevant range (about +/- 130 microseconds). Variations in ITD from 130 microseconds favoring one ear to 130 microseconds favoring the other ear caused spike response rate changes, on average, of 29.5%. These data are similar to those previously presented for the central auditory systems of larger mammals, whose auditory localization acuity is significantly better than that of the rat. We argue, therefore, that the sound localization mechanisms based on transient ITDs have not evolved in a fashion that covaries with interaural distance, and that there exists a mismatch between the ITDs the rat will encounter in the free field, and the ITDs which are encoded by its nervous system. This may be one reason why sound localization acuity has a roughly inverse relation to interaural distance.

Acoustic Stimulation↗

PubMed1988

Amplitude compression and profound hearing loss.

Nine subjects with prelingually acquired, sensorineural, hearing loss were given a three-interval, forced-choice, test of speech pattern contrast perception under two amplification conditions. The first involved adjustment of the low and high frequency outputs of a two-channel Master Hearing Aid to each subject's highest comfortable level, but without compression of the short-term dynamic range of the signal. The second involved the additional compression of a 30 dB input range into the subject's dynamic range of hearing, as measured by the difference between speech awareness threshold and highest comfortable level, in each of the two channels. One of the subjects performed much better with compression than without. Among the other eight, however, there was a small but significant reduction of performance when compression was introduced. It is proposed that the one positive result is due to the increased audibility of speech cues made possible by amplitude compression. It is further proposed that the negative results are due mainly to the distortions of time-intensity cues introduced by amplitude compression. The results suggest that, in terms of potential access to meaningful speech cues, the addition of amplitude compression, to an otherwise optimized signal, is unnecessary, or even detrimental, for most profoundly deaf subjects, but could be beneficial for some.

Adolescent↗

PubMed1999

[Study on the separation of optical chromatography].

The relationship between the particle radius with the intensity of the applied laser radiation force is theoretically studied using a ray-optics model by analyzing the forced-status of the separated particles in the mobile phase. The laser radiation force is proportional to the square of the particle radius when the particle radius is much smaller than the laser beam radius under the condition of using a single-transverse-mode laser beam with a Gaussian intensity distribution and the particle refractive index being larger than that of the mobile phase. The retention distance is calculated and the dynamic range is discussed. Theoretically, the dynamic range of the optical chromatography can be extended by increasing laser power, decreasing the flow rate of mobile phase and focusing the laser beam.

Chromatography↗

PubMed2002

Use of high flip angle in T1-prepared FAST sequences for myocardial perfusion quantification.

This study reports on the first use of high flip angle and radio-frequency (RF) spoiling in T1-prepared fast acquisition in steady state (FAST) sequence for myocardial perfusion in patients. T1 dynamic range was measured in vitro with a FAST, an RF FAST and a snapshot fast low-angle shot (FLASH) sequences with a 90 degrees flip angle. Myocardial perfusion was then measured twice in 6 patients during the same MR session. The RF FAST and FLASH, but not the FAST sequence, demonstrated an extended T1 dynamic range; however, the FLASH images were degraded by artifacts not present on the RF FAST images. The myocardial perfusion indices K1 (first-order transfer constant from the blood to the myocardium for the Gd-DTPA) and Vd (distribution volume of Gd-DTPA in myocardium) did not differ significantly between the two injections. K1 was 0.48+/-0.12 ml/min g(-1) and Vd was 12.5+/-2.9%. With an extended T1 dynamic range and the sensitivity required for myocardial perfusion quantification, the RF FAST sequence with a 90 degrees flip angle outperformed the snapshot FLASH sequence in terms of image quality and the FAST sequence in terms of contrast dynamic range.

Adult↗

PubMed1984

Effects of continuous noise backgrounds on rate response of auditory nerve fibers in cat.

This study describes the effects of broadband background noise on the average discharge rate to best-frequency (BF) tones of auditory nerve fibers in the cat. The effects of exposure to long-term continuous noise are compared to the effects of noise gated on and off simultaneously with test tones. Addition of background noise causes a shift of the dynamic portion of tone-evoked rate versus level functions to higher tone intensities. The shift occurs at a mean rate of 0.61 dB of shift for each 1-dB increment in noise level. The rate of shift is independent of best frequency and spontaneous discharge rate. The noise level at which the shift begins is frequency dependent and is consistent with the frequency-dependent bandwidths of auditory nerve fiber tuning curves. The adjustment of the dynamic range shows many similarities to two-tone suppression. Therefore, it is most likely that it is caused by suppression of the response to the BF test tone by energy present in the noise at surrounding frequencies. At high noise levels, the ability of auditory nerve fibers to respond to test tones is limited by the rate response to the noise. As noise level increases, the discharge rate it evokes approaches a fiber's saturation rate and ultimately eliminates the fiber's ability to respond to test tones. Low spontaneous rate fibers, which have been shown to have higher thresholds and wider dynamic range (17,29), are significantly more resistant to saturation by high noise levels. Exposure to broadband noise prior to onset of test tones produces an overall decrement in response rate. This phenomenon is similar to the effects of short-term adaptation (32) and seems to develop independently of the shift of dynamic range. At high noise levels, previous exposure to the noise produces a small dynamic range shift. This effect is similar to that produced by suppression but is smaller. The effect is occluded in continuous noise backgrounds by the adjustment of sensitivity produced by suppression.

Animals↗

PubMed1992

Sensitivity of neurons in cat primary auditory cortex to tones and frequency-modulated stimuli. II: Organization of response properties along the 'isofrequency' dimension.

The spatial distribution of neuronal responses to tones and frequency-modulated (FM) stimuli was mapped along the 'isofrequency' dimension of the primary auditory cortex (AI) of barbiturate-anesthetized cats. In each cat, electrode penetrations roughly orthogonal to the cortical surface were closely spaced (average separation approximately 130 microns) along the dorsoventral extent of a single 'isofrequency' strip in high frequency parts of AI (> 15 kHz). Characteristic frequency (CF), minimum threshold, sharpness of frequency tuning (Q10 and Q20), the dynamic range of the spike count-intensity function at CF, sensitivity to the rate of change of frequency (RCF) and to the direction of frequency-modulation (DS) were determined for contralaterally-presented tone and FM stimuli. Sharpness of tuning attained maximum values at central loci along the dorsoventral 'isofrequency' axis and values declined towards more dorsal and more ventral locations. Minimum threshold and dynamic range varied between high and low values in a similar and correlated periodic fashion. Their combined organization yielded an orderly spatial representation of response strength, relative to maximum, as a function of stimulus amplitude. The distributions of the most common forms of FM rate sensitivity (RCF response categories) and best RCF along 'isofrequency' strips were significantly non-random although there was a considerable degree of variability between cats. FM directional preference and sensitivity appeared to be randomly distributed. Sharpness of tuning may be related to the analysis of the spectral content of an acoustic stimulus, both minimum threshold and dynamic range are related to the encoding of stimulus intensity, and measures of FM rate and directional sensitivity assess the coding of temporal changes of stimulus spectra. The independent, or for minimum threshold and dynamic range dependent, topographic organizations of these neuronal parameters therefore suggest parallel and independent processing of these aspects of acoustic signals in AI.

Acoustic Stimulation↗

PubMed1991

Rate-level functions of neurons in the inferior colliculus of cats measured with the use of free-field sound stimuli.

1. The responses as a function of stimulus level of 125 single units in the inferior colliculus of anesthetized cats were studied with the use of free-field acoustic stimuli. 2. The characteristic frequency (CF; frequency at which threshold was lowest) of each unit was determined, and stimuli were presented from one of three speaker positions: 45 degrees contralateral to the midline, midline, and 45 degrees ipsilateral to the midline. 3. For each unit a variety of stimulus levels was presented at CF, and the total spike count was summed for 20 stimuli at each level. If time permitted, a similar series of levels of noise was presented. 4. Four classes of rate-level (RL) functions were observed. Monotonic increases in firing rate were observed in 10% of units stimulated with CF stimuli and 57% of units studied with noise. Nonmonotonic RL functions, for which firing first increased and then declined to less than 50% of the peak level, were observed in 61% of units responding to CF tones and in 10% responding to noise. Plateau functions, with shapes lying between these, accounted for 19% of CF responses and the remaining units excited by noise. Some very complex shapes that could not be categorized into the above groups were seen in the remaining 10% of the units responding to CF stimuli. 5. The RL functions of units studied with both noise and CF tones could belong to different classes; commonly, nonmonotonic RL functions to tones were associated with monotonic RL functions to noise. The noise thresholds averaged 10 dB, some 10-20 dB less sensitive than those to CF stimuli. 6. For the vast majority of both noise and tone responses, stimuli from the contralateral location were more effective than those from the other two positions in terms of a lower threshold, higher peak discharge rate, and, for nonmonotonic units, a lower sound level at which the function became nonmonotonic (turnover point). 7. The turnover points of nonmonotonic functions at any given CF could be spread broadly but, overall, tended to be concentrated between -6 and 44 dB. 8. The dynamic ranges (range of levels over which firing rate increased) were larger for monotonic and plateau functions than for nonmonotonic functions, which had dynamic ranges less than 45 dB. The median dynamic range for units stimulated with CF tones was 20 dB and for noise stimuli, 40 dB.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1996

Performance optimization in elastography: multicompression with temporal stretching.

A general theoretical framework known as the strain filter has been previously used to evaluate the performance in elastography. The strain filter describes the relationship among the resolution, dynamic range, sensitivity and elastographic SNR (SNRe), and may be plotted as a graph of the upper bound of the SNRe vs. the strain experienced by the tissue, for a desired elastographic axial resolution as determined by the data window length. The ideal strain filter has an infinitely high, flat all-pass characteristic shape in the strain domain, which means that all local tissue strains are displayed in the elastogram with infinite SNRe; it also means that the strain dynamic range in the elastogram is infinite as well. Practical strain filters obtained using a single tissue compression have a bandpass characteristic shape in the strain domain, where the -3 dB width of this bandpass characteristic may be defined as the elastographic dynamic range. In this paper, we present an optimal technique for stretching multicompression elastography, practiced by selecting the optimum incremental applied strain using the strain filter. Two techniques, temporal stretching and multicompression elastography, are combined in this paper to improve elastogram quality. Stretching multicompression elastography using the optimal applied strain increment alters the shape of the strain filter from its bandpass characteristic to a more desirable high-emphasis filter. The dynamic range of optimal stretching multicompress on elastography is limited only by tissue nonlinearities. This optimal applied strain increment minimizes signal decorrelation and achieves the maximum achievable elastographic SNRe.

Elastic Tissue↗