Joseph D. Petruccelli

A Multiple-Threshold AR(1) Model

We consider the model Z, = +(0, k ) + +(I, k)Z,_, + a,(k) whenever r,_, < Z,_,S r,., 1S k k 1, with r, = -m and r, = m. Here {+(i, k); i =0 , l ; 1 5 k 5 1) is a sequence of real constants, not necessarily equal, and, for 1 5 k 5 I, {a,(k), t 2 1) is a sequence of i.i.d. random variables with mean 0 and with {a,(k), t 2 1) independent of {a,(j), t 2 1) for j # k. Necessary and sufficient conditions on the constants {+(i, k)} are given for the stationarity of the process. Least squares estimators of the model parameters are derived and, under mild regularity conditions, are shown to be strongly consistent and asymptotically normal. NON-LINEAR TIME SERIES; SETAR MODELS; AUTOREGRESSIVE MODELS; MARKOV CHAINS

Local Maximal Stress Hypothesis and Computational Plaque Vulnerability Index for Atherosclerotic Plaque Assessment

It is believed that atherosclerotic plaque rupture may be related to maximal stress conditions in the plaque. More careful examination of stress distributions in plaques reveals that it may be the local stress/strain behaviors at critical sites such as very thin plaque cap and locations with plaque cap weakness that are more closely related to plaque rupture risk. A “local maximal stress hypothesis” and a stress-based computational plaque vulnerability index (CPVI) are proposed to assess plaque vulnerability. A critical site selection (CSS) method is proposed to identify critical sites in the plaque and critical stress conditions which are be used to determine CPVI values. Our initial results based on 34 2D MRI slices from 14 human coronary plaque samples indicate that CPVI plaque assessment has an 85% agreement rate (91% if the square root of stress values is used) with assessment given by histopathological analysis. Large-scale and long-term patient studies are needed to further validate our findings for more accurate quantitative plaque vulnerability assessment.

Best-choice problems involving uncertainty of selection and recall of observations

This paper explores best choice problems which allow both recall of applicants and uncertainty of a current applicant accepting an offer of employment. Properties of optimal selection procedures are derived for the general case. Optimal procedures and the associated probabilities of obtaining the best applicant are found in two special cases. The results unify and extend those of Yang (1974) and Smith (1975). OPTIMAL STOPPING; SECRETARY PROBLEM: RELATIVE RANKS

Evaluation of anesthesia effects in a rat animal model using otoacoustic emission protocols

Anesthesia effects on otoacoustic emission (OAE) recordings were evaluated in a group of 72 Sprague-Dawley rats (mean weight 225+/-20 gr). Two anesthesia dosages (high and normal) and two anesthetic protocols (ketamine-xylazine, ketamine-xylazine-atropine) were tested. Transient evoked OAE (TEOAE) and distortion product OAE (DPOAE) responses were recorded in 10 min intervals, for a total period of 60 min. Analyses of the data with repeated measure models indicated the following: (1) The animals receiving a high dose of anesthesia (cumulative dose 66.6 mg of ketamine and 13.2 mg of xylazine/kg of body weight) presented significant alterations of the TEOAE response level and the signal to noise ratio at 3.0 kHz; (2) the animals receiving a normal dose of ketamine-xylazine anesthesia (cumulative dose 50 mg of ketamine and 10 mg of xylazine/kg of body weight) presented TEOAE and DPOAE responses invariant in terms of time; (3) significant differences were observed in the DPOAE responses from animals anesthetized with ketamine-xylazine and ketamine-xylazine-atropine. The data support the hypothesis that the ketamine anesthesia OAE suppressing mechanism is related to middle-ear mechanics.

Dose-dependent protection on cisplatin-induced ototoxicity – an electrophysiological study on the effect of three antioxidants in the Sprague-Dawley rat animal model

Summary Background Sprague-Dawley rats were used as an acute cisplatin ototoxicity model to compare the chemo-protective efficacy of 2 sulphur-containing antioxidants (D-methionine, N-L-acetylcysteine) and 1 seleno-organic compound (ebselen). Each putative chemo-protective agent was tested at 3 different dosages in order to assess the influence of dose on auditory preservation. Material/Methods A total of 40 Sprague-Dawley albino male rats were used in the study. Animals were divided into 10 groups, 3 groups of different doses for each protective agent and a cisplatin-treated control group. The animals were weight-matched before drug exposure to ensure similar weights in all groups. Auditory function was assessed with auditory brainstem responses and distortion product otoacoustic emissions at time zero and at 96 hours post-treatment. Results At the post-treatment follow-up no significant threshold change at 8 kHz was found in the D-Met- and NAC-treated groups. All ebselen-treated animals presented significant threshold elevations. At 12 and 16 kHz, only the groups treated with 300, 450 mg/kg of D-Met and 475 mg/kg of NAC presented thresholds comparable to the pre-treatment ABR data. The ebselen-treated animals presented significant threshold shifts and showed the highest threshold elevations. The DPOAE data analysis showed that only the animals from the 350 mg/kg D-met group presented lack of statistical differences between the pre and post recordings. Conclusions Considering the outcome from the ABR and DPOAE analyses together, only the 350 mg/kg D-met group presented a complete auditory preservation against the 14 mg/kg cisplatin administered i.v. Data from ebselen pre-treated Sprague-Dawley albino male rats demonstrate that ebselen dosages up to 12 mg/kg given by i.p. administration lack auditory preservation in this species.

A TEOAE screening protocol based on linear click stimuli: performance and scoring criteria.

In order to improve the quality of current TEOAE recording methodologies, we have conducted a comparison of TEOAE neonatal recordings acquired with linear protocols using click stimuli of 68 dB SPL and non-linear protocols using the ILO default stimulus values. From a theoretical standpoint it was expected that the linear recordings would generate responses characterized by higher S/N ratios due to the fact that the stimulus sequence contains four clicks of the same intensity and polarity. The project included recordings from 1,416 neonatal ears (age 48 h). The TEOAE data were compared in terms of correlation, response amplitude, noise, corrected response and S/N ratio in the 1.0-, 2.0-, 3.0-, 4.0- and 5.0-kHz bands, using a paired t-test criterion. We found that windowed (4-14 ms) responses evoked by a linear TEOAE protocol generated superior S/N estimates in the 2.0-, 3.0-, 4.0- and 5.0-kHz TEOAE bands, in addition to superior correlation estimates, and demonstrated lower levels of noise. Clear-cut scoring criteria were established for the S/N ratios at 2.0, 3.0 and 4.0 kHz, by constructing one-sided distribution-free tolerance boundaries.

A Bayesian Analysis of Autoregressive Time Series Panel Data

We describe a Bayesian hierarchical model to analyze autoregressive time series panel data. We develop two algorithms using Markov-chain Monte Carlo methods, a restricted algorithm that enforces stationarity or nonstationarity conditions on the series and an unrestricted algorithm that does not. Two examples show that restricting stationary series to be stationary provides no new information, but restricting nonstationary series to be stationary leads to substantial differences from the unrestricted case. These examples and a simulation study also show that, compared with inference based on individual series, there are gains in precision for estimation and forecasting when similar series are pooled.

Efficient otoacoustic emission protocols employed in a hospital-based neonatal screening program

Within the context of a hospital-based newborn hearing screening program, we have studied the application of two OAE protocols (TEOAE and DPOAE) on a group of 250 well babies. The main goal of this study was to evaluate the performance of DPOAE protocol in a relatively large population sample. using a preset number of five tested frequencies, in comparison with a default TEOAE screening protocol. The data were collected on the second day of life and during spontaneous sleep. The TEOAE recordings were acquired with linear protocols using click stimuli of 70-75 dB SPL and were used as indicators of normal cochlear function. The cubic distortion product DPOAE responses were evoked by an asymmetrical 75-65 dB SPL protocol, with a frequency ratio of 1.22. Five frequencies (referring to F2) were tested at 1.5, 2.0, 3.0, 4.0 and 5.0 kHz. The data from the DPOAE responses show a similar pass rate (similarity = 0.98) to the linear TEOAE protocol. The data presented suggest that a DPOAE cochlear evaluation, at 5 pre-selected frequencies, has clinical potential.Within the context of a hospital-based newborn hearing screening program, we have studied the application of two OAE protocols (TEOAE and DPOAE) on a group of 250 well babies. The main goal of this study was to evaluate the performance of DPOAE protocol in a relatively large population sample, using a preset number of five tested frequencies, in comparison with a default TEOAE screening protocol. The data were collected on the second day of life and during spontaneous sleep. The TEOAE recordings were acquired with linear protocols using click stimuli of 70-75 dB SPL and were used as indicators of normal cochlear function. The cubic distortion product DPOAE responses were evoked by an asymmetrical 75-65 dB SPL protocol, with a frequency ratio of 1.22. Five frequencies (referring to F2) were tested at 1.5, 2.0, 3.0, 4.0 and 5.0 kHz. The data from the DPOAE responses show a similar pass rate (similarity=0.98) to the linear TEOAE protocol. The data presented suggest that a DPOAE cochlear evaluation, at 5 pre-selected frequencies, has clinical potential.

Ototoxic effects of cisplatin in a Sprague-Dawley rat animal model as revealed by ABR and transiently evoked otoacoustic emission measurements.

The ototoxic effects of cisplatin in a Sprague-Dawley rat model were evaluated by recordings of auditory brainstem responses (ABR) and transiently evoked otoacoustic emissions (TEOAEs). The ABR responses were evoked from alternating clicks and 8, 10, 12, 16, 20 and 30 kHz tone pips in a range from 40 to 100 dB SPL range. The TEOAEs were recorded with a non-linear protocol, and were evoked by a 63.5 dB SPL click stimulus. Twenty five male Sprague-Dawley rats were used in the study, 20 animals were treated with cisplatin (16 mg/kg, body weight) and five animals served as controls. The data showed that 72 h after the cisplatin administration, the TEOAE and ABR variables were significantly altered. The relationship between the ABR and TEOAE variables was shown to be non-linear. The most significant relationships were observed between the TEOAE correlation and the ABR threshold values at 10, 12, and 16 kHz.

Comparison of the Return-to-the-Origin Probability and the Apparent Diffusion Coefficient of Water as Indicators of Necrosis in RIF-1 Tumors

Two model‐independent measures of diffusion, the apparent diffusion coefficient (ADC) and return‐to‐the‐origin probability enhancement (R) were compared for their ability to detect tissue necrosis in RIF‐1 murine tumors. Both reflect the degree of restriction experienced by the endogenous water molecules; however, the ADC is calculated from the initial linear slope of the diffusion attenuation curve, while R is calculated from data that includes the non‐monoexponential part of the curve. In spectroscopic studies (n = 9), neither the ADC nor R showed a strong correlation with tumor volume. In imaging studies (n = 14), ADC, R, and T2 were calculated on a pixel‐by‐pixel basis. There, the mean ADC and mean R for the entire imaging slice showed reasonable correlation with necrotic tumor fraction (r2 = 0.679 and −0.665, respectively). The mean T2 value yielded a poor correlation (r2 = 0.436). Regions‐of‐interest were chosen from areas identified as either necrotic or viable and the resulting sets of ADC and R‐values were subjected to discriminant analysis to determine the identification error rate. The error was greater for R than for the ADC (P < 0.001). Therefore, in this application, the use of the non‐monoexponential part of the diffusion attenuation curve does not provide additional identification power. Magn Reson Med 49:468–478, 2003.