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PubMed1990

Effects of level on nonspectral frequency difference limens for electrical and acoustic stimuli.

The purpose of this experiment was to study the effects of stimulus level on discrimination of frequency as represented in the temporal waveforms of acoustic and electrical signals. The subjects were four nonhuman primates in which one ear had been deafened and implanted with an electrode array and the other ear was untreated. Frequency difference limens for 100 Hz electrical sinusoidal stimulation via a cochlear implant in the deafened ear were compared to those for 100 Hz sinusoidally amplitude-modulated white noise (SAM noise) acoustic stimuli to the normal-hearing contralateral ear. To correct for loudness cues, levels of the test stimuli were varied relative to the reference-stimulus level. The test-stimulus levels at which the percent responses were minimum were determined. These levels were used to measure the frequency difference limens. Frequency difference limens for the electrical stimuli decreased as a function of reference-stimulus level through most of the dynamic range, while those for the acoustic stimuli reached a minimum at 20 dB to 40 dB above threshold. For the electrical stimuli the slopes and relative positions of the frequency difference limen vs. level functions varied from subject to subject, and with changes in electrode configuration within a subject. These differences were related to threshold level and dynamic range. At higher levels of stimulation, frequency difference limens for acoustic and electrical stimuli fell in the same range. The slopes and relative positions of the frequency difference limen vs. level functions for electrical stimuli did not parallel those of level difference limen vs. level functions collected simultaneously from the same ears. The data suggest that nonspectral frequency discrimination may depend on the number of nerve fibers stimulated. With prostheses in cochleas with less than a full complement of auditory nerve fibers, the data suggest that stimulation level is an important variable influencing discriminability.

Acoustic Stimulation↗
PubMed1997

ZSD: a universal parameter for precision in the ultrasonic assessment of osteoporosis.

There are now several commercial systems available for the ultrasonic assessment of osteoporosis, differing in anatomical location (calcaneus, tibia and phalanges), measurement parameters (broadband ultrasonic attenuation, BUA, and velocity) and their respective calculation algorithms. Comparison of system performance to date has centred upon precision (reproducibility) defined as coefficient of variation (CV%). It has been shown by both theoretical and in vivo studies that the computational algorithm implemented in the calculation of BUA of the calcaneus may have a significant effect upon CV%. The CV% for BUA is inherently inferior to the CV% for velocity by a factor of approximately seven since no allowance is made for population dynamic range. This note proposes and validates a novel parameter for precision, the standard deviation of the Z-score (ZSD). The precision of ultrasound velocity, even when expressed as ZSD, is superior to BUA by a factor of approximately two in the calcaneus. Since precision defined as ZSD is automatically sealed for both mean value and population dynamic range, and is dimensionless, it may be applied to all densitometric technologies. There is a broad range of precision values within the population and future work should investigate the causes of the variability.

Age Factors↗
PubMed1993

Quantitative PCR for hepatitis B virus with colorimetric detection.

A novel, sensitive colorimetric test is described for quantification of the initial number of hepatitis B virus (HBV) genomes amplified in PCR. The viral genomes are amplified together with a synthetic internal standard (IS) to correct for the variability of the efficiency factor. One of the two primers is biotinylated, and the amplified mixtures of HBV and IS DNAs are bound to streptavidin-coated microtiter plates for quantitative detection. The ratio of HBV to IS DNA is determined for each sample by hybridization with DNP-containing probes and immunoenzymatic detection. The colorimetric detection is quantitative, rapid, and accurate with a dynamic range from approximately 10(8) to > 10(11) DNA molecules. The initial number of HBV genomes in a clinical sample is interpreted from the signal ratio HBV/IS by using a standard curve, obtained from coamplification of known quantities of synthetic HBV templates with IS. The assay quantified 15 viral genomes from 10 microliters of serum, and its dynamic range was up to five orders of magnitude. After the amplification step, the assay takes > 2 hr, and the method is applicable to automation.

Base Sequence↗
PubMed2001

Comparison of dissociation-enhanced lanthanide fluorescent immunoassays to enzyme-linked immunosorbent assays for detection of staphylococcal enterotoxin B, Yersinia pestis-specific F1 antigen, and Venezuelan equine encephalitis virus.

The dissociation-enhanced lanthanide fluorescent immunoassays (DELFIA) were developed for the detection of staphylococcal enterotoxin B, Yersinia pestis-specific F1 antigen, and Venezuelan equine encephalitis virus. These assays were compared to previously developed enzyme-linked immunosorbent assays (ELISAs) by determining the sensitivity or limit of detection (LOD), the dynamic range, and the reproducibility of each assay in a number of different sample matrices. The sensitivity and specificity of each assay were then determined by using a small panel of blinded spiked and nonspiked samples. All three DELFIAs demonstrated at least 1 log greater sensitivity than corresponding ELISAs utilizing the same reagents and showed an increase in dynamic range of at least 2 log(10) concentrations. This increased LOD resulted in higher sensitivity rates for the DELFIA. The specificity of all of the assays evaluated was 100%, and no sample matrix effects were observed in either format. However, the reproducibility of the DELFIA was poor due to randomly distributed wells exhibiting excessive background signal (hot wells), which occurred throughout the evaluation. As this technology matures, the reproducibility of these assays should improve, as will the ability to identify hot wells. Despite its sensitivity, the logistical burden associated with the DELFIA and the technical expertise required to complete assays and interpret the data limit the application of this technology to reference or large clinical laboratories.

Animals↗
PubMed2006

Specific and quantitative detection of human polyomaviruses BKV and JCV by LightCycler real-time PCR.

BACKGROUND: BK virus (BKV) and JC virus (JCV) are the only two known human polyomavirus that typically establish subclinical persistent infections. In immunocompromised hosts reactivation of the JCV infection is the cause of the central nervous system disease progressive multifocal leucoencephalopathy (PML), while BKV may cause renal nephropathy and haemorrhagic cystitis. OBJECTIVES: The goal of this study was to develop a specific quantification assay for each polyomavirus by LightCycler real-time polymerase chain reaction (PCR) based on SYBR Green I detection. STUDY DESIGN: DNA fragments of 138bp and 233bp from the "large T antigen" region of JCV and BKV, respectively, were amplified. The ability of the designed primer sets to separately quantify BKV DNA or JCV DNA and the PCR efficiency were assessed on reference DNA samples. Known amounts of cloned JCV DNA and BKV DNA from TEBU-BIO nv (Boechout, Belgium) were used to generate standard curves for the quantification assays. Species-specificity of the PCR was evaluated with cloned DNA and with DNA from patient samples. RESULTS: The assay allowed a specific quantification over a 7log dynamic range. Seventeen copies each of the viral genes were reproducibly and accurately detected. The primer sets generated specific DNA fragments for each virus confirmed by agarose gel analysis and by cycle sequencing. The similarities of the amplified gene sequences by BLAST analysis were 99% and 100% for BKV and JCV, respectively. There was no cross-reactivity within the dynamic range of the standard dilutions. CONCLUSIONS: We developed LightCycler real-time PCR assay based on SYBR Green I detection that provided rapid and specific quantification of polyomavirus load.

BK Virus↗
PubMed2006

Regional and segmental flexibility of antibodies in interaction with antigens of different size.

The interaction of antibodies (Abs) with protein antigens (Ags) of different size, such as hen egg white lysozyme, ovalbumin, and bovine serum albumin, was examined using analytical ultracentrifugation, electrospray ionization time-of-flight mass spectrometry, and surface plasmon resonance in order to estimate regional and segmental Ab flexibility. When both Abs and Ags were free in solution, sedimentation equilibrium and surface plasmon resonance analyses showed the formation of an Ag(2)Ab(1) complexes regardless of Ag size, suggesting that the Fab arms were able to move to avoid interference between Ags bound to Ab combining sites. The Ag(2)Ab(1) complex, as well as the Ag(1)Ab(1) complex, was observed by MS. However, when Abs were immobilized on the surface of a sensor chip through the Fc region, the stoichiometry of the Ag-Ab complex was dependent on the Ag size; Ag(2)Ab(1) forming with hen egg white lysozyme and Ag(1)Ab(1) with ovalbumin and bovine serum albumin. These results indicated that immobilization of the Fc region reduces the dynamic range of the Fab arms and results in interference from the first Ag bound to either combining site, which in turn prevents the binding of the second Ag to the other combining site. Our results allow us to propose that the Fab arms of B-cell receptors whose Fc regions are immobilized on cell surface have a reduced dynamic range.

Animals↗
PubMed2003

Reproducibility of HPV 16 and HPV 18 viral load quantitation using TaqMan real-time PCR assays.

A reproducibility study was designed to assess within-assay, between-day, and interlaboratory variability of three real-time PCR assays targeting HPV 16, HPV 18, and the human glyceraldehyde-3-phosphate dehydrogenase (GAPDH) pseudogenes. Fifteen HPV 16 and fifteen HPV 18 cervical swab samples were amplified in triplicate by GAPDH and HPV 16 and by GAPDH and HPV 18 assays, respectively. All samples were amplified undiluted and at a 1:10 dilution on 2 separate days in the same laboratory, and the same samples were amplified in a separate laboratory. HPV 16 and HPV 18 normalized viral load is reported as the number of HPV genomes per 20000 GAPDH copies. The analytic specificity of the HPV 16 and 18 assays was 100 and 97%, respectively. The intraclass correlation coefficients (ICC) were 0.99, 0.97, and 0.98 for HPV 16, HPV 18, and GAPDH, respectively, indicating that the variability due to experimental error was very low. Ten-fold differences in viral load could be readily discriminated across a six order of magnitude dynamic range (ca. 5-5x10(6) copies). Power of discrimination was increased at higher target concentrations (>5000 copies). The correlation of normalized HPV 16 and 18 viral load was high between the two laboratories (Spearman rho (rho)=0.96 and 0.87, respectively). These HPV 16 and HPV 18 quantitative PCR assays with GAPDH normalization are reproducibly quantitative over a broad linear dynamic range allowing for application in epidemiologic studies for measurement of viral load.

Cervix Uteri↗
PubMed2001

FRET-based in vivo Ca2+ imaging by a new calmodulin-GFP fusion molecule.

Intracellular Ca2+ acts as a second messenger that regulates numerous physiological cellular phenomena including development, differentiation and apoptosis. Cameleons, a class of fluorescent indicators for Ca2+ based on green fluorescent proteins (GFPs) and calmodulin (CaM), have proven to be a useful tool in measuring free Ca2+ concentrations in living cells. Traditional cameleons, however, have a small dynamic range of fluorescence resonance energy transfer (FRET), making subtle changes in Ca2+ concentrations difficult to detect and study in some cells and organelles. Using the NMR structure of CaM bound to the CaM binding peptide derived from CaM-dependent kinase kinase (CKKp), we have rationally designed a new cameleon that displays a two-fold increase in the FRET dynamic range within the physiologically significant range of cytoplasmic Ca2+ concentration of 0.05-1 microM.

Animals↗
PubMed2002

Improving DNA array data quality by minimising 'neighbourhood' effects.

Gene expression studies using cDNA arrays require robust and sensitive detection methods. Being extremely sensitive, radioactive detection suffers from the influence of signals positioned in each other's vicinity, the 'neighbourhood' effect. This limits the gene density of arrays and the quality of the results obtained. We have investigated the quantitative influence of different parameters on the 'neighbourhood' effect. By using a model experimental system, we could show that the effect is linear and depends only on the intensity of the hybridisation signal. We identified a common factor that can describe the influence of the neighbour spots based on their intensities. This factor is <1%, but it has to be taken into account if a high dynamic range of gene expression is to be detected. We could also derive the factor, although with less precision, from comparison of duplicate spots on arrays of 4565 different clones and replication of the hybridisation experiments. The calculated coefficient applied to our actual experimental results not only revealed previously undetected tissue or cell-specific expression differences, but also increased the dynamic range of detection. It thus provides a relatively simple way of improving DNA array data quality with few experimental modifications.

Gene Expression Profiling↗
PubMed1986

Encoding timing and intensity in the ventral cochlear nucleus of the cat.

Physiological response properties of neurons in the ventral cochlear nucleus have a variety of features that are substantially different from the stereotypical auditory nerve responses that serve as the principal source of activation for these neurons. These emergent features are the result of the varying distribution of auditory nerve inputs on the soma and dendrites of the various cell types within the nucleus; the intrinsic membrane characteristics of the various cell types causing different responses to the same input in different cell types; and secondary excitatory and inhibitory inputs to different cell types. Well-isolated units were recorded with high-impedance glass microelectrodes, both intracellularly and extracellularly. Units were characterized by their temporal response to short tones, rate vs. intensity relation, and response areas. The principal response patterns were onset, chopper, and primary-like. Onset units are characterized by a well-timed first spike in response to tones at the characteristic frequency. For frequencies less than 1 kHz, onset units can entrain to the stimulus frequency with greater precision than their auditory nerve inputs. This implies that onset units receive converging inputs from a number of auditory nerve fibers. Onset units are divided into three subcategories, OC, OL, and OI. OC units have extraordinarily wide dynamic ranges and low-frequency selectivity. Some are capable of sustaining firing rates of 800 spikes/s at high intensities. They have the smallest standard deviation and coefficient of variation of the first spike latency of any cells in the cochlear nuclei. OC units are candidates for encoding intensity. OI and OL units differ from OC units in that they have dynamic ranges and frequency selectivity ranges much like those of auditory nerve fibers. They differ from one another in their steady-state firing rates; OI units fire mainly at the onset of a tone. OI units also differ from OL units in that they prefer frequency sweeps in the low to high direction. Primary-like-with-notch (PLN) units also respond to tones with a well-timed first spike. They differ from onset cells in that the onset peak is not always as precise as the spontaneous rate is higher. A comparison of spontaneous firing rate and saturation firing rate of PLN units with auditory nerve fibers suggest that PLN units receive one to four auditory nerve fiber inputs. Chopper units fire in a sustained regular manner when they are excited by sound.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1992

Performance characteristics and image fidelity of gray-scale monitors.

Gray-scale monitors are an essential element of electronic radiology, and their ability to provide images that are perceived to be identical to those available on conventional or laser-printed film is crucial to success of electronic radiology. Image fidelity is measured in physical characteristics (luminance, dynamic range, distortion, resolution, and noise) and with psychophysical techniques, including receiver operator characteristics analysis with clinical images and testing with contrast-detail patterns to determine threshold contrast. Currently, laser-printed images facilitate greater information transfer than does a gray-scale monitor because of their higher absolute luminance (500 ft-L vs 60 ft-L), greater perceived dynamic range, and better spatial resolution. In the near future, the developments of gray-scale monitors with 150-200 ft-L luminance, a display standard based on just noticeable differences, and algorithms to improve similarities between gray-scale display images and laser-printed images will help increase the acceptability of monitors as a means to make primary diagnoses.

Computer Peripherals↗
PubMed2001

Long-range reactive dynamics in myoglobin.

We report the complete vibrational spectrum of the probe nucleus 57Fe at the oxygen-binding site of the protein myoglobin. The Fe-pyrrole nitrogen stretching modes of the heme group, identified here, probe asymmetric interactions with the protein environment. Collective oscillations of the polypeptide, rather than localized heme vibrations, dominate the low frequency region. We conclude that the heme "doming" mode is significantly delocalized, so that distant sites respond to oxygen binding on vibrational time scales. This has ramifications for understanding long-range interactions in biomolecules, such as those that mediate cooperativity in allosteric proteins.

Animals↗
PubMed2005

Specific and quantitative detection of human polyomaviruses BKV, JCV, and SV40 by real time PCR.

BACKGROUND: The polyomaviruses that infect humans, BK virus (BKV), JC virus (JCV), and simian virus 40 (SV40), typically establish subclinical persistent infections. However, reactivation of these viruses in immunocompromised hosts is associated with renal nephropathy and hemorrhagic cystitis (HC) caused by BKV and with progressive multifocal leukoencephalopathy (PML) caused by JCV. Additionally, SV40 is associated with several types of human cancers including primary brain and bone cancers, mesotheliomas, and non-Hodgkin's lymphoma. Advancements in detection of these viruses may contribute to improved diagnosis and treatment of affected patients. OBJECTIVE: To develop sensitive and specific real time quantitative polymerase chain reaction (RQ-PCR) assays for the detection of T-antigen DNA sequences of the human polyomaviruses BKV, JCV, and SV40 using the ABI Prism 7000 Sequence Detection System. STUDY DESIGN: Assays for absolute quantification of the viral T-ag sequences were designed and the sensitivity and specificity were evaluated. A quantitative assay to measure the single copy human RNAse P gene was also developed and evaluated in order to normalize viral gene copy numbers to cell numbers. RESULTS: Quantification of the target genes is sensitive and specific over a 7 log dynamic range. Ten copies each of the viral and cellular genes are reproducibly and accurately detected. The sensitivity of detection of the RQ-PCR assays is increased 10- to 100-fold compared to conventional PCR and agarose gel protocols. The primers and probes used to detect the viral genes are specific for each virus and there is no cross reactivity within the dynamic range of the standard dilutions. The sensitivity of detection for these assays is not reduced in human cellular extracts; however, different DNA extraction protocols may affect quantification. CONCLUSION: These assays provide a technique for rapid and specific quantification of polyomavirus genomes per cell in human samples.

BK Virus↗
PubMedDate not supplied

Achromatic parvocellular contrast gain in normal and color defective observers: Implications for the evolution of color vision.

The PC pathway conveys both chromatic and achromatic information, with PC neurons being more responsive to chromatic (L-M) than to achromatic (L+M) stimuli. In considering the evolution of color vision, it has been suggested that the dynamic range of chromatic PC-pathway processing is tuned to the chromatic content of the natural environment. Anomalous trichromats, with reduced separation of their L- and M-cone spectral sensitivities, have diminished chromatic input to PC-pathway cells. Dichromats, with absent L or M cones, should have no chromatic input to PC-pathway cells. Therefore, the PC-pathway dynamic range of color defectives should be released from any constraint imposed by the chromatic environment. Here we ask whether this results in compensatory enhancement of achromatic PC-pathway processing in color defectives. This study employed a psychophysical method designed to isolate PC-pathway processing using achromatic stimuli. In a pulsed-pedestal condition, a four-square stimulus array appeared within a uniform surround. During a trial, one of the test squares differed from the other three, and the observer's task was to choose the square that was different. A four-alternative, forced-choice method was used to determine thresholds as a function of the contrast of the four-square array to the surround. Seven color defective and four normal observers participated. Results showed no systematic differences between normals and color defectives. There was no enhancement of achromatic processing as compensation for reduced chromatic processing in the PC-pathway system in color defectives. From physiological recordings, PC-pathway achromatic contrast gains of dichromatic and trichromatic New World primates and trichromatic Old World macaques have also been shown to be similar to each other. Our study and the animal studies imply that PC-pathway contrast gain parameters were regulated by factors other than the environmental chromaticity gamut, and may have arisen in a nontrichromatic common ancestor to both Old and New World primates.

Animals↗
PubMed2004

Bidirectional modulation of windup by NMDA receptors in the rat spinal trigeminal nucleus.

Activation of afferent nociceptive pathways is subject to activity-dependent plasticity, which may manifest as windup, a progressive increase in the response of dorsal horn nociceptive neurons to repeated stimuli. At the cellular level, N-methyl-d-aspartate (NMDA) receptor activation by glutamate released from nociceptive C-afferent terminals is currently thought to generate windup. Most of the wide dynamic range nociceptive neurons that display windup, however, do not receive direct C-fibre input. It is thus unknown where the NMDA mechanisms for windup operate. Here, using the Sprague-Dawley rat trigeminal system as a model, we anatomically identify a subpopulation of interneurons that relay nociceptive information from the superficial dorsal horn where C-fibres terminate, to downstream wide dynamic range nociceptive neurons. Using in vivo electrophysiological recordings, we show that at the end of this pathway, windup was reduced (24 +/- 6%, n = 7) by the NMDA receptor antagonist AP-5 (2.0 fmol) and enhanced (62 +/- 19%, n = 12) by NMDA (1 nmol). In contrast, microinjections of AP-5 (1.0 fmol) within the superficial laminae increased windup (83 +/- 44%, n = 9), whereas NMDA dose dependently decreased windup (n = 19). These results indicate that NMDA receptor function at the segmental level depends on their precise location in nociceptive neural networks. While some NMDA receptors actually amplify pain information, the new evidence for NMDA dependent inhibition of windup we show here indicates that, simultaneously, others act in the opposite direction. Working together, the two mechanisms may provide a fine tuning of gain in pain.

Action Potentials↗
PubMed2006

Repeatability of normal multifocal VEP: implications for detecting progression.

PURPOSE: To assess the repeatability of the multifocal visual evoked potential (mfVEP) and to compare it with the repeatability of standard automated perimetry (SAP) in the same group of 50 normal controls retested after 1 year. Our second aim was to assess the repeatability of false alarm rates determined previously for the mfVEP using various cluster criteria. METHODS: Fifty individuals with normal vision participated in this study (33 females and 17 males). The age range was 26.7 to 77.9 years and the group average age (+/- SD) was 51.4 (+/- 12.1) years. Pattern-reversal mfVEPs were obtained using a dartboard stimulus pattern in VERIS and two 8-minute runs per eye were averaged. The average number of days between the first and second mfVEP tests was 378 (+/- 58). SAP visual fields were obtained within 17.4 (+/- 20.3) days of the mfVEP using the SITA-standard threshold algorithm. Repeatability of mfVEPs and SAP total deviation values were evaluated by calculating point-wise limits of agreement (LOA). Specificity (1-false alarm rate) was evaluated for a range of cluster criteria, whereby the number and probability level of the points defining a cluster were varied. RESULTS: Point-wise LOA for the mfVEP signal-to-noise ratio (SNR) ranged from 2.0 to 4.3 dB, with an average of 2.9 dB across all 60 locations. For SAP, LOA ranged from 2.4 to 8.9 dB, with an average of 4.0 dB (excluding the points immediately above and below the blind spot). Clusters of abnormal points were not likely to repeat on either mfVEP or SAP. When an mfVEP abnormality was defined as the repeat presence (confirmation) of a 3-point (P < 0.05) cluster anywhere within a single hemifield, only 1 (of 200) monocular hemifield was deemed abnormal. Although the LOA of the mfVEP were similar throughout the field, the limited dynamic range of SNR at superior field locations will limit the ability to follow progression in "depth" at those locations. CONCLUSIONS: Repeatability of the mfVEP was slightly better than SAP visual fields in this group of controls with a 1-year retest interval. This suggests that progression in early stages should be more easily detectable by mfVEP. However, in certain field locations (eg, superior periphery), the relatively more narrow dynamic range of the SNR of the mfVEP may limit detection of progression to just 1 event. Confirmation of a 3-point cluster abnormality is highly suggestive of a true defect on the mfVEP.

Adult↗
PubMed1987

Postsynaptic inhibition mediates high-frequency selectivity in the cricket Teleogryllus oceanicus: implications for flight phonotaxis behavior.

The frequency selectivity of the identified auditory interneuron, Int-1, in the cricket Teleogryllus oceanicus was examined using intracellular recording and staining techniques. Previous behavioral assays showed that crickets discriminate the low frequencies of the species calling song (4-5 kHz) from the high frequencies contained in the vocalizations of insectivorous bats (Nolen and Hoy, 1986a). Int-1 was excited by frequencies between 3 and 40 kHz, being similar, therefore, to the tympal organ (ear) in its broad range sensitivity; however, it responded differentially to high and low frequencies in terms of the number of action potentials evoked per stimulus tone pulse, the average discharge rate, and the latency of response. It was especially responsive to ultrasound (greater than 20 kHz), discharging at rates up to 400 spikes/sec (average rate), with 10 msec latencies; its response to pulses of the calling song was less than 150 spikes/sec, with 30 msec latencies. Int-1's dynamic range for ultrasound was also quite large, about 50 dB, compared to 20 dB for the calling song frequency. In addition, it responded well to trains of short, batlike pulses of ultrasound. These results are consistent with previous behavioral experiments showing that during flight, Int-1 was both necessary and sufficient for the ultrasound avoidance steering behavior (Nolen and Hoy, 1984), as long as it discharged above a rate of 180 spikes/sec. Ultrasound readily produced such high rates, whereas calling song rarely did; ultrasound reliably evoked avoidance steering over a wide dynamic range, while tone pulses of the calling song rarely did so (Nolen and Hoy, 1986a). A unique source of ipsilaterally mediated inhibition, tuned to the calling song frequency, accounted for the poor response to calling song and hence the neuron's high-frequency selectivity, and the behavioral and physiological effects of 2-tone suppression of high frequencies by the calling song (Nolen and Hoy, 1986b). These results further strengthen Int-1's proposed role as a "bat-detector" during flight and suggest only a limited role in other contexts such as social behavior.

Action Potentials↗
PubMed1996

[Magnetic resonance with fat-saturation sequences in studying the upper abdomen: the normal semeiological aspects].

The fat-saturation (FAT-SAT) MR technique decreases the signal intensity of fat in tissues, though yielding the T1, T2 and proton-density (PD) information available on spin-echo (SE) sequences. To investigate the potentials of FAT-SAT sequences in MRI of the upper abdomen, the authors carried out a prospective study including 129 subjects, namely 12 normal volunteers and 117 patients with different abdominal conditions. The patients were submitted to T1-weighted SE sequences (TR 500-600 ms, TE 15 ms), T2W SE (TR 1600-1730 ms, TE 80 ms) and PD SE (TR 1600-1730 ms, TE 20 ms). The images obtained with and without fat suppression were compared both qualitatively and quantitatively, with a special emphasis on the normal anatomy of the upper abdomen: we investigated the efficacy of subcutaneous and retroperitoneal fat suppression (116/129 cases, 90%), the reduction in respiratory and chemical shift artifacts (112/129 cases, 87%) and the better visualization of parenchyma (119/129 cases, 93%) and of other abdominal structures. Concerning the quantitative study, we calculated the signal-to-noise ratio (S/N) for liver, spleen, pancreas, adrenal glands, renal cortex and medulla, the improvement of contrast in these organs after retroperitoneal fat suppression (conspicuity) and the increase in contrast between organs (dynamic range). The statistical analysis showed significant differences between the sequences with and those without fat suppression. Correlations were found between observers' and quantitative evaluations, suggesting that the better yield of FAT-SAT sequences is probably due to three factors: 1) retroperitoneal and subcutaneous fat suppression; 2) increase in S/N ratio for pancreas and renal cortex on T1W images; 3) reduction in the dynamic range of signal intensity, which increases contrast between pancreas, adrenal glands and renal cortex relative to adjacent structures, especially on T2W or PD sequences. The results of this study suggest that FAT-SAT sequences are useful because fat suppression increases contrast and improves image quality, reducing respiratory and chemical shift artifacts.

Abdomen↗