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Ultrasonic detection of bone fragment in mechanically deboned chicken breasts
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Innovative Food Science and Emerging Technologies 9 (2008) 109 – 115 www.elsevier.com/locate/ifset
Ultrasonic detection of bone fragment in mechanically deboned chicken breasts Lino R. Correia a , Gauri S. Mittal a,⁎, Otman A. Basir b a
b
School of Engineering, University of Guelph, Guelph, Ontario, Canada N1G 2W1 Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 Received 30 January 2007; accepted 14 June 2007
Abstract A piston and cylinder apparatus was designed and fabricated based on pulse–echo technique to perform ultrasound scans for both liquids and solid samples of variable heights. A short time fast Fourier transform program was used to reduce noise in the signal. This apparatus was tested with distilled water. Velocity was accurately measured, whereas values of amplitude ratio varied widely. Chicken breast muscles' density, velocity, impedance and amplitude ratio were determined. Amplitude ratio could successfully discriminate between uncut samples, cut samples, and cut samples with a bone fragment, regardless of bone fragment size from 6 mm2 to 16 mm2 projected area. The ratio of amplitude ratios of cut samples with bone fragment to that of cut (or uncut) samples decreased as the ratio of bone fragment projected area to transducer projected area increased. © 2007 Elsevier Ltd. All rights reserved. Keywords: Ultrasound; Foreign body detection; Bone fragment; Chicken breast; Food safety Industrial relevance: New hygiene regulations now require all food industries to implement a documented safety management system based on hazards analysis and critical control point (HACCP) principles. There is a need to detect and remove bone fragments from deboned poultry products before marketing. The technology developed in this research provides a non-invasive cost effective solution to a food safety concern that is causing production bottlenecks and hazardous situations in deboned poultry meat production.
1. Introduction Consumers expect food products to be free from biological, chemical, and physical contaminants. Mechanical deboning machines rapidly separate chicken breast muscles from the carcasses, sometimes breaking bones and leaving bone fragments in the fillets (Tao & Ibarra, 2000). In the Hazard Analysis and Critical Control Points (HACCP) for chicken breast fillets, the Canadian Food Inspection Agency (CFIA, 2004) identified, among others, knife chips, metal chips, pieces of equipment, bone and plastic particles as physical hazards. Hence, there is a need to detect and remove these physical hazards from deboned chicken products before marketing. Tao and Ibarra (2000) developed imaging algorithms to integrate thickness and X-ray images to produce a thickness⁎ Corresponding author. Tel.: +1 519 824 4120x52431; fax: +1 519 836 0227. E-mail address: [email protected] (G.S. Mittal). 1466-8564/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2007.06.004
compensated X-ray image for the detection of bone fragment signals in chicken products. Four types of plastic molds were used to simulate actual bone fragments. Experimental results from sample analyses demonstrated that the four types of frequent and hard-to-detect-bone fragments could be detected irrespective of location in the chicken meat of uneven thickness. McFarlane, Speller, Bull, and Tillett (2003) used X-ray backscatter to detect near-surface fragments of chicken clavicle, 2 cm long, and 20–60 mg in mass, in polystyrene phantoms and in samples of chicken breasts. Presently bone fragments in deboned poultry products are detected using conventional X-ray inspection systems. However, these machines are very costly and adequate precaution must be exercised to protect humans from the deleterious effects of X-rays. McClements (1997) conducted an extensive review of ultrasonic characterization of foods and drinks. Ultrasound systems are safe, non-destructive, low cost, hygienic (Wallin & Haycock, 1998) and can be operated in real time. Ultrasound
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technology is being increasingly used to detect and identify foreign bodies in food products (Hæggström & Luukkala, 2001). Cho and Irudayaraj (2003) used a non-contact air instability compensation ultrasound imaging technique to detect foreign objects in boneless chicken breast. The size of the glass and metal fragments used varied from 2 × 2 mm2 to 7 × 7 mm2. Results from image processing showed a good potential for non-destructive and rapid detection of foreign objects and defects in food material. However, they used different foreign bodies and sizes with regular shapes. Actual bone fragments were not used. Although a temperature compensation transducer reduced standard deviation of data, direct or watercoupled contact is preferable to air contact. Chanamai and McClements (1999) used a pulse–echo low-intensity ultrasonics to measure chicken composition. They used a sample holder with a fixed depth. However, they did not use the apparatus to detect foreign body in samples. Thus, not much work has been published on using a pulse–echo, direct or water-coupled, and low-intensity ultrasonic device to detect actual bone fragment in chicken breast fillet of variable heights. Thus, the objectives of this study were i) to design, fabricate and test a pulse–echo low-intensity ultrasonic apparatus for chicken breast fillet samples of variable thicknesses, ii) to measure ultrasonic properties of chicken breast muscle, iii) to evaluate the effect of various chicken bone fragment sizes on chicken breast ultrasonic properties, and iv) to study the effect of vertical location of a bone fragment size on chicken breast ultrasonic properties. 2. Materials and methods 2.1. Materials Boneless, skinless chicken breasts were purchased from a local grocery store at Guelph, ON, Canada. The breasts were equilibrated at ambient temperature (24 ± 0.5 °C) for at least 1 h prior to experimentation. A borer (or punch) of 25.4 mm (1″) inside diameter was used to obtain cylindrical samples from the thicker end of a chicken breast. Thus, the cross-sectional area of a bored chicken breast sample was 506.7 mm2. Bone fragments were produced by breaking a chicken bone into small pieces. The chicken breast with bones was cooked in boiling water for 20 min. After cooling the breast at room temperature, breast meat was manually removed from the pectoral bone system. The bones were heated in a convection oven at 93 ± 1 °C for 4 h. Any remnants of breast meat attached to the bone system were carefully removed. Bone fragments were produced from the rib by breaking this bone into small pieces (Tao & Ibarra, 2000). The “large” and “medium” sized bone fragments were approximately rectangular and square in shape, respectively, with major dimensions of 4.3 mm × 3.5 mm, and 3.0 mm × 3.0 mm, respectively. The “small” bone fragments were trapezoidal in shape with parallel dimensions of 2.6 mm and 3.9 mm, and perpendicular dimension of 1.9 mm. Thus, projected areas of the selected large, medium, and small bone fragments used were estimated to be 15.75, 9.92, and 6.18 mm2, respectively.
Fig. 1. Cross-sectional diagram of the piston and cylinder apparatus.
2.2. Methods 2.2.1. Piston and cylinder apparatus A Piston and cylinder (P&C) apparatus was developed to provide a chamber to perform pulse–echo based ultrasonic measurements for liquid or solid samples of variable heights (Fig. 1). This apparatus was an ultrasonic pulse–echo reflectometer based on the same principle of operation as provided by McClements and Fairley (1991). Essentially a cylinder of inside diameter of 32.75 mm (1.25″) and 3.175 mm (0.125″) thickness was attached to a plexiglass circular base plate. A stainless steel solid cylinder (density of 7927 kg/m3) was used to reflect ultrasonic pulses emitted and received by a piezoelectric transducer. If necessary, another stainless steel or plexiglass solid cylinder was placed below the reflecting stainless steel cylinder. A plexiglass pipe, 25.4 mm (1″) inside diameter, of a specified height, measured to the nearest 0.01 mm (Moore and Wright micrometer, Sheffield, UK) rested on the stainless steel reflector. The purpose of using a pipe of known height was to closely match sample height, thus limiting uniaxial sample compression. Plexiglass pipes of lengths ranging from 10 mm to 40 mm were cut for this study. A rexalite (cross-linked polystyrene) delay-line, cylindrical in shape (7.08 mm in length, 5.39 mm in diameter) (Technisonic Research, Fairfield, CT, USA) was housed in a plexiglass cylindrical piston 32.07 mm in diameter and 12.47 mm in height. The transducer could be screwed into a metal nut that was snugly fitted into the piston cavity, just above the delay-line. Prior to a scanning operation, the piston cavity was filled with distilled water. Then the transducer was screwed into the nut. A sample was placed between the bottom of the rexalitecentered plexiglass piston and the top of the stainless steel reflector cylinder at the bottom. To ensure adequate sample contact, a 1 kg mass was placed over the transducer (Fig. 2). After 30 s of stabilization, the sample was ultrasonically
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Fig. 3. Block diagram of the ultrasonic measurement system.
Fig. 2. Picture of the piston and cylinder apparatus during ultrasonic scanning of a chicken breast muscle sample.
scanned. Then the sample was again scanned twice in quick succession. An average of three scan readings were taken. Thus, the P&C apparatus provided a chamber wherein ultrasonic properties of liquid and solid samples of variable depths could be determined. 2.2.2. Sample preparations Appropriate sample preparations were required to investigate treatment effects. To ascertain effects of bone fragment sizes on ultrasonic characteristics, the cylindrical chicken breast samples were ultrasonically scanned several times as follows. Firstly, some breast samples were scanned. Secondly, the samples were horizontally cut approximately 80% of their circumferences at their mid-heights, and then ultrasonically scanned in the P&C apparatus. Thirdly, the samples were retrieved from the P&C apparatus, and a large, medium or small bone fragment was placed in the center of the bottom cut surface. A thin circular, gasket-type, rubber template with a center opening of 6.35 mm (0.25″) diameter was placed on the bottom cut surface to only guide placement of the bone fragment at the center of the bottom cut surface. A small chord segment of the template was cut-off near the circumference, to facilitate its placement near the uncut sample circumference. The samples inserted with large, medium or small bone fragments were sequentially scanned. Thus, the following five samples were ultrasonically scanned: uncut sample (u), horizontally cut sample (at its midheight) (c), cut sample with large bone fragment (l), cut sample with medium bone fragment (m), and cut sample with small bone fragment (s). There were 19 replications. To ascertain the effects of vertical location of bone fragment, the following sample preparations were conducted, before being ultrasonically scanned. Firstly, the samples were horizontally cut around approximately 80% of the circumference at two heights: a) one-third from the top surface, and b) two-thirds
from the top surface; then ultrasonically scanned in the P&C apparatus. Secondly, the samples were retrieved from the P&C apparatus, and the medium bone fragment was placed in the center of each uppercut sample. The circular template was used to only guide placement of the bone fragment at the center of the bottom surface. Thirdly, the medium bone fragment was removed from the upper cut bottom surface and placed at the center of the lower cut bottom surface. Thus, the following four samples were ultrasonically scanned: uncut sample (uc), horizontally cut (at two vertical locations) sample (cc), sample with the medium bone fragment placed at the center of the upper cut (mu), and the medium bone fragment placed at the center of the lower cut (md). There were 18 replications. 2.2.3. Ultrasound system The flat-focused ultrasonic transducer used (GRD-1502-HR, Technisonic Research, Fairfield, CT) had a nominal frequency of 15 MHz and 6.35 mm diameter. A pulse/receiver ultrasound card (SR 9000, Matec Instrument Co., Northborough, MA) was used to drive the transducer and to receive echo signals (Fig. 3). A pulse of 4 MHz peak frequency was produced by the SR9000 card at a repetition rate of 2 kHz (Zhao, Basir, & Mittal, 2003). The signal sampling frequency was 100 MHz. A typical raw signal plot of pressure amplitude (mV) versus time (μs) for a chicken breast sample is shown in Fig. 4a, wherein it is difficult to decipher peak amplitudes. Hence a Short Time Fourier Transform (STFT) algorithm (Jiang, Zhao, Basir, & Mittal, 2003) was implemented to enhance the signal-to-noise ratio. A Hamming window (Jiang et al., 2003) of 100-point
Fig. 4. Display of amplitude (mV) versus time: a) raw signal, b) processed signal.
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length was used to obtain a frequency of 4 MHz. A Labview 5.0 program (National Instruments, Cambridge, Ontario, Canada) was developed to control the SR-9000 card and to process the echo signals simultaneously. Fig. 4b shows a processed signal output of this program for a chicken breast sample clearly showing the two peak amplitudes. Digital values of amplitude and time data were also displayed in the output. 2.2.4. Property measurements A plexiglass pipe with an appropriate height equal to or slightly less than sample height was selected to ensure adequate sample contact with both the piston and with the stainless steel cylinder, yet minimizing uniaxial compression. Sample temperature was measured by inserting a digital thermocouple based thermometer (± 0.1 °C) into the sample after ultrasound scanning. Sample density was measured after ultrasonic scanning by determining a sample's mass and its volume. Ultrasonic velocity (m/s) was computed by dividing distance traveled in a sample by the corresponding travel time. Acoustic impedance (kg/(m2 s)) was computed as the product of ultrasonic velocity in the sample and corresponding sample density. For each scan, the ratio of the pressure amplitude (mV) of the wave emanating from the sample/reflector surface interface to the corresponding amplitude of the wave emanating from the delay-line/sample interface was computed as amplitude ratio. To introduce a diffraction correction term, the pressure amplitude was assumed to be either inversely proportional or exponentially related to the normalized distance (distance divided by the near field). Expressions for pressure amplitude of echoes P1 and P2 were written as a function of the following independent variables: initial pressure amplitude, attenuation coefficient in the sample, sample height, impedance of transmitting medium and sample, wavelength in the sample, and transducer area divided by π. Where P1 and P2 are the pressures amplitudes at interfaces of delay-line/sample and sample/ reflector (stainless steel), respectively. Taking the ratio of P2/ P1, and eliminating some variables, Kumar and Kumar (1996) derived expressions for attenuation coefficient that accounted for diffraction loss. For this study, it was assumed for simplicity that pressure amplitude was inversely proportional to the normalized distance. Thus, Eq. (1), adapted from Kumar and Kumar (1996) for the experimental set-up in this study, was used. 8:686 P2 R1 1 kd Ld þ km Lm a¼ d ln d d : ð1Þ 2Lm P1 R2 TT V kd Ld R1 and R2 are reflection coefficients at the two interfaces; T and T′ are transmission coefficients at the interfaces of delayline/sample and the sample/reflector, respectively; λd and λm are wavelengths of ultrasound propagation in the delay-line and in the sample material, respectively; and Ld and Lm are lengths of delay-line and thickness of the chicken sample, respectively. Experimental values of reflection and transmission coefficients were obtained in a similar approach as given by McClements and Fairley (1991).
2.2.5. Testing of piston and cylinder apparatus Distilled water was used to test the piston and cylinder apparatus. Chicken breast thickness typically ranged from 10 mm to 24 mm. Hence, plexiglass pipe lengths ranging from 8 to 40 mm were used to cover the range. The ratios of delayline length (7.08 mm) to water column heights (8 mm to 40 mm) were of the same order of magnitude. Thus, the diffraction correction was included in the computation of attenuation coefficient. Distilled water temperature ranged from 23.1 °C to 24.4 °C, with a mean temperature of 24.1 (± 0.5) °C. Distilled water density, corresponding to sample temperature, was obtained from Kay and Laby (1986). 2.2.6. Data analyses Spreadsheets (Excel, Microsoft Office 2000, Microsoft Corp., Redmond, WA) were used for most of the computations. All statistical analyses were performed using SAS ® Propriety Software Release 8.2 (SAS Inst., Cary, NC) on a Sun OS 5.8. The SAS procedures CORR, GLM, and MEANS were employed. 3. Results and discussion 3.1. Distilled water The mean value of ultrasonic velocity data was 1492.85 ± 3.50 m/s. For the temperature range used, the corresponding mean value computed from the data of Del Grosso and Mader (1972) was 1494.19 ± 1.39 m/s. From Kay and Laby (1986) the computed ultrasonic velocity was 1493.32 m/s at 24.1 °C. Thus, ultrasonic velocity data obtained in the study matched published data. Mean and standard deviation of acoustic impedance values were 1.49E + 06 kg/(m2 s) and 3.19E + 03 kg/(m2 s), respectively. For fresh water at 20 °C, Ensminger (1973) documented an acoustic impedance of 1.48E + 06 kg/(m2 s), closer to the value obtained in this study. The mean value of amplitude ratio was 2.57 ± 0.25. Based on Eq. (1) computed attenuation coefficient values were negative. This impossible result may imply that attenuation is too small to be accurately determined for the distances (8 mm to 40 mm) used in this study. Using pulse–echo mode, McClements and Fairley (1991) reported an attenuation coefficient of 0.0078 dB/ mm for a 12 mm wide sample of distilled water at 2.1 MHz and ambient temperature. However, a widely accepted attenuation coefficient value of 0.000869 dB/mm for distilled water at 2.1 MHz and 24.1 °C was estimated from Kay and Laby (1986). Thus, the attenuation coefficient value obtained by McClements and Fairley (1991) is nine times higher than the corresponding value using the equation from Kay and Laby (1986). This underscores the difficulty in measuring low attenuation coefficient. 3.2. Chicken breast muscle samples There were 19 and 18 scanned data sets, to determine the effects of bone fragment sizes, and vertical location of bone fragment, respectively. For all properties of uncut samples, the
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probability of significant differences between the two data sets was higher than 0.05. Hence all (19 + 18 = 37) observations for uncut samples were combined. The following mean parameter values were obtained: temperature = 25.3 ± 0.7 °C, compression = 5.48 ± 4.02%, density = 1066 ± 44 kg/m3, velocity = 1567 ± 21 m/s, and impedance = 1.67E + 06 ± 6.40E + 04 kg/(m2 s). The coefficients of variation of sample temperature, density, velocity and impedance were less than 5%. Sample compression ranged from 0.04% to 16.4% and sample heights from 12 mm to 22 mm. As stated earlier, the length of the plexiglass pipe for each sample was carefully chosen to minimize uniaxial compression. However, compression was more sensitive for shorter samples than for longer samples. For example, a 2 mm difference between pipe and sample lengths yields higher compression for shorter samples. In this study, the mean value of sample density of 1067 ± 43 kg/m3 compared closely with 1070 kg/m3 reported by McFarlane et al. (2003), and with values of 1070 kg/m3 and 1100 kg/m3 obtained for poultry meat by Sanz, Alonso, and Mascheroni (1987). Thus, the volume displacement technique, used in this study was apparently as effective as the Archimedes principle based method used by McFarlane et al. (2003). The mean value of ultrasonic velocity of 1567 m/s at a mean sample temperature of 25.3 °C, in this study, was similar to the corresponding value of 1570 m/s at 25 °C for low fat chicken reported by Chanamai and McClements (1999). In this study, mean sample mass and sample height used were 8.72 ± 1.66 g and 17.14 ± 3.04 mm compared with corresponding values of 25 g and 16 mm, respectively, used by Chanamai and McClements (1999). Thus, both distilled water and chicken breast muscle sample velocities obtained using the P&C apparatus were comparable to corresponding published values. The mean value of impedance of 1.67E + 06 ± 6.40E + 04 kg/(m2 s), obtained in this study, was within the range of 1.65E + 06 to 1.74E + 06 kg/(m2 s) for muscle at 39 °C given by McClements (1997). Thus, both the experimentally determined values of velocity and density compared favorably to values from the literature. For low attenuation material such as water and chicken muscle, impedance is simply the product of velocity and density. The GLM procedure of SAS was used to test whether different breasts (block effect) influenced chicken breast muscle sample properties. Samples were taken from 14 different breasts. For most properties, there were no significant differences between breasts. However, for temperature and amplitude ratio, the probability of rejecting significant differences was N 0.0009. This implies i) that different breasts were tested at significantly different temperatures, and ii) that different breasts had significantly different amplitude ratios. These differences may presumably be attributed to muscle orientation and muscle strength in each breast. Genetics, age diet, exercise etc. of each bird may have contributed to these significant differences. The only significant correlation (Pearson correlation coefficient = 0.922, Prob. N |r| was b 0.0001) was between impedance and density. This result is expected since by definition impedance is directly proportional to density, as stated earlier.
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3.3. Detection of bone fragment based on size The GLM procedure of SAS was used (for unbalanced data) to analyze the effects of breast (block) and treatment. As discussed earlier there was a block effect on amplitude ratio of uncut chicken breast samples. The chicken breast was considered to be covariate to remove the variation due to block effect. Hence, treatment was the only specified class variable, although the model (velocity or amplitude ratio) was dependent on both breast and treatment effects. Duncan's multiple range test was performed to rank the means. There were total of (19 data sets × 5 treatments = ) 95 observations and samples were taken from seven breasts (A to G). Results are shown in Table 1. Velocity was not dependent on either breast or treatment. Thus, velocity could not be used to detect the presence of a bone fragment (treatment effect). The model for amplitude ratio was highly significant. Results of the Type III sums of squares revealed that both breast and treatment effects were highly significant sources of variation. There was a significant difference of mean amplitude ratio values i) between uncut samples and all other cut samples (with or without a bone fragment), and ii) between the cut (only) samples and the cut samples with a bone fragment. There were no significant differences between mean amplitude ratio values of cut samples with a bone fragment of any size. This suggests that amplitude ratio can be used to distinguish between uncut and cut samples, and between cut or uncut (only) samples and cut samples containing a bone fragment of any size used in this study. Zhao et al. (2003) demonstrated that amplitude ratio was successfully used to detect foreign bodies in glass bottles containing liquid. In this study, the transducer detected a cut surface presumably because of the following reasons: i) the upper and the lower surfaces of the cut sample were not completely in contact, and ii) the cut surfaces may not have been Table 1 Results of the detection of bone fragments based on size Dependent variable
Model Pr N F
Velocity m/s 0.419
Amplitude ratio
R2
Source
0.054 Breast
Pr N F
Treatment Mean
0.381
u c s Treatment 0.380 m l b 0.0001 0.584 Breast b 0.0001 u c s Treatment b 0.0001 m l
1563 a⁎ 1566 a 1573 a 1573 a 1568 a 0.85 (± 0.37) a⁎ 0.53 (± 0.39) b 0.20 (± 0.17) c 0.18 (± 0.17) c 0.17 (± 0.15) c
n = 19 data sets, u: uncut sample, c: cut sample, s: cut sample with small bone fragment, m: cut sample with medium bone fragment, l: cut sample with large bone fragment. ⁎ a to c : for each dependent variable, means in a column with similar letter are not statistically significant at 95% confidence level.
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perfectly horizontal resulting in reflection of ultrasonic waves away from the transducer. Introduction of a bone fragment in a cut sample presumably reflected ultrasound waves. Hence, the ultrasound system could detect the presence of a bone fragment compared to a cut (only) sample. The following factors apparently contributed to lack of significant differences between cut samples containing a bone fragment, irrespective of size: i) experimental error resulting from off-center placement of bone fragment, ii) curved surface of bone fragment reflecting away ultrasonic waves, and iii) possible differences in curvature on both surfaces of a bone fragment. The coefficient of variation for amplitude ratio for the uncut, cut (only), and cut samples with a bone fragment were 43%, 75%, and 88% (average value), respectively. This suggests that the process of cutting introduced additional variability in measuring amplitude ratio. Placement of a bone fragment independent of size further increased variability in measuring amplitude ratio for reasons previously discussed. Thus, experimental techniques and the P&C apparatus may have contributed to some variability in consistently measuring amplitude ratio. Notwithstanding the statistical analysis of the effect of bone fragment size, intuitively a larger projected area of a foreign body should result in a lower amplitude ratio. Fig. 5 shows a plot of the dimensionless ratio of amplitude ratios of cut samples with bone fragments to cut (only) samples as a function of the dimensionless ratio of projected areas of bone fragment to the transducer, essentially dimensionless plots of amplitude ratio versus projected area. As dimensionless projected area ratio increases, dimensionless amplitude ratio decreases. A larger bone fragment presumably reflected more ultrasonic waves in chicken breast muscle samples, compared to a smaller bone fragment. 3.4. Detection of bone fragment at different vertical locations There were total of (18 data sets × 4 treatments/data set = ) 72 observations, and samples were taken from seven breasts (H to N). Results are shown in Table 2. Velocity was dependent on breast (block effect) but was independent of treatment effect. Thus, velocity could not be used to detect the presence of cuts in the sample or presence of medium bone fragment located at the upper or lower cut.
Table 2 Results of the detection of medium bone fragment based on vertical location Dependent variable
Model Pr N F
Velocity m/s 0.344
R2
Source
0.064 Breast Treatment
Amplitude ratio
b 0.0001 0.579 Breast
Pr N F 0.047 0.927 0.748
Treatment Mean uc cc mu md uc cc
Treatment b 0.0001 mu md
1571 a⁎ 1573 a 1572 a 1575 a 0.89 (± 0.44) a⁎ 0.50 (± 0.30) b 0.14 (± 0.10) c 0.13 (± 0.08) c
n = 18 data sets, uc: uncut sample, cc: cut sample, mu: cut sample with medium bone fragment placed in upper cut, md: cut sample with medium bone fragment placed in lower cut. ⁎ a to c : for each dependent variable, means in a column with similar letter are not statistically significant at 95% confidence level.
The results of this section are similar to that of the previous section. Thus, amplitude ratio can be used to distinguish between uncut and twice cut samples, and between twice cut (only) samples and twice cut samples containing a medium bone fragment either at the upper or lower cut. From the data it appears that a lower location of a bone fragment reduces the amplitude ratio. However, intuitively, it appears that it would be more difficult to locate a smaller bone fragment at a higher vertical location. 4. Conclusions The piston and cylinder apparatus based on pulse–echo technique was developed to perform ultrasound scans for both liquids and solids of variable sample heights. For distilled water samples, velocity and acoustic impedance could be measured accurately, whereas attenuation values varied widely. For chicken breast muscle samples, density, velocity, and impedance were accurately measured, whereas amplitude ratio values varied widely. Amplitude ratio, not velocity, could successfully discriminate between uncut samples, cut samples, and cut samples with bone fragment with projected area from 6 mm2 to 16 mm2. The ratio of amplitude ratios of cut samples with bone fragment to that of cut samples decreased as ratio of projected areas of bone fragment to that of the transducer increased. Amplitude ratio, not velocity, could successfully discriminate between uncut samples, cut samples, and cut samples with bone fragment projected area of 10 mm2 irrespective of vertical location. Acknowledgements
Fig. 5. Plot of the ratio of amplitude ratios of cut samples with bone fragments to cut (only) samples versus ratio of projected areas of bone fragment to transducer (each point is the average from 19 independent observations).
The authors acknowledge the technical support of John Boldt and Ping Yang from the University of Waterloo, and Bill Verpagen and Dr. Jixian Zhang of the University of Guelph. The Natural Science and Engineering Research Council (NSERC) of Canada provided financial support for this project.
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McClements, D. J. (1997). Ultrasonic characterization of foods and drinks: Principles, methods, and applications. Critical Reviews in Food Science and Nutrition, 37, 1−46. McClements, D. J., & Fairley, P. (1991). Ultrasonic pulse echo reflectometer. Ultrasonics, 29, 58−62. McFarlane, N. J. B., Speller, R. D., Bull, C. R., & Tillett, R. D. (2003). Detection of bone fragments in chicken meat using X-ray backscatter. Biosystems Engineering, 85, 185−199. Sanz P.D, Alonso M.D., Mascheroni R.H., “Thermophysical properties of meat products: General bibliography and experimental values”, Transactions of the ASAE, Volume 30, (1987), pp. 283–289 and 296. Tao, Y., & Ibarra, J. G. (2000). Thickness-compensated X-ray imaging detection of bone fragments in deboned poultry — Model analysis. Transactions of the ASAE, 43, 453−459. Wallin, P., & Haycock, P. (1998). Future and emerging technologies. In P. Wallin & P. Haycock (Eds.), Foreign body prevention, detection and control (pp. 323−327). London, UK: Blackie Academic & Professional. Zhao, B., Basir, O. A., & Mittal, G. S. (2003). Foreign body detection in food by ultrasound pulse/echo method. Food Research International, 36, 513−521.
Innovative Food Science and Emerging Technologies 9 (2008) 109 – 115 www.elsevier.com/locate/ifset
Ultrasonic detection of bone fragment in mechanically deboned chicken breasts Lino R. Correia a , Gauri S. Mittal a,⁎, Otman A. Basir b a
b
School of Engineering, University of Guelph, Guelph, Ontario, Canada N1G 2W1 Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 Received 30 January 2007; accepted 14 June 2007
Abstract A piston and cylinder apparatus was designed and fabricated based on pulse–echo technique to perform ultrasound scans for both liquids and solid samples of variable heights. A short time fast Fourier transform program was used to reduce noise in the signal. This apparatus was tested with distilled water. Velocity was accurately measured, whereas values of amplitude ratio varied widely. Chicken breast muscles' density, velocity, impedance and amplitude ratio were determined. Amplitude ratio could successfully discriminate between uncut samples, cut samples, and cut samples with a bone fragment, regardless of bone fragment size from 6 mm2 to 16 mm2 projected area. The ratio of amplitude ratios of cut samples with bone fragment to that of cut (or uncut) samples decreased as the ratio of bone fragment projected area to transducer projected area increased. © 2007 Elsevier Ltd. All rights reserved. Keywords: Ultrasound; Foreign body detection; Bone fragment; Chicken breast; Food safety Industrial relevance: New hygiene regulations now require all food industries to implement a documented safety management system based on hazards analysis and critical control point (HACCP) principles. There is a need to detect and remove bone fragments from deboned poultry products before marketing. The technology developed in this research provides a non-invasive cost effective solution to a food safety concern that is causing production bottlenecks and hazardous situations in deboned poultry meat production.
1. Introduction Consumers expect food products to be free from biological, chemical, and physical contaminants. Mechanical deboning machines rapidly separate chicken breast muscles from the carcasses, sometimes breaking bones and leaving bone fragments in the fillets (Tao & Ibarra, 2000). In the Hazard Analysis and Critical Control Points (HACCP) for chicken breast fillets, the Canadian Food Inspection Agency (CFIA, 2004) identified, among others, knife chips, metal chips, pieces of equipment, bone and plastic particles as physical hazards. Hence, there is a need to detect and remove these physical hazards from deboned chicken products before marketing. Tao and Ibarra (2000) developed imaging algorithms to integrate thickness and X-ray images to produce a thickness⁎ Corresponding author. Tel.: +1 519 824 4120x52431; fax: +1 519 836 0227. E-mail address: [email protected] (G.S. Mittal). 1466-8564/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2007.06.004
compensated X-ray image for the detection of bone fragment signals in chicken products. Four types of plastic molds were used to simulate actual bone fragments. Experimental results from sample analyses demonstrated that the four types of frequent and hard-to-detect-bone fragments could be detected irrespective of location in the chicken meat of uneven thickness. McFarlane, Speller, Bull, and Tillett (2003) used X-ray backscatter to detect near-surface fragments of chicken clavicle, 2 cm long, and 20–60 mg in mass, in polystyrene phantoms and in samples of chicken breasts. Presently bone fragments in deboned poultry products are detected using conventional X-ray inspection systems. However, these machines are very costly and adequate precaution must be exercised to protect humans from the deleterious effects of X-rays. McClements (1997) conducted an extensive review of ultrasonic characterization of foods and drinks. Ultrasound systems are safe, non-destructive, low cost, hygienic (Wallin & Haycock, 1998) and can be operated in real time. Ultrasound
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technology is being increasingly used to detect and identify foreign bodies in food products (Hæggström & Luukkala, 2001). Cho and Irudayaraj (2003) used a non-contact air instability compensation ultrasound imaging technique to detect foreign objects in boneless chicken breast. The size of the glass and metal fragments used varied from 2 × 2 mm2 to 7 × 7 mm2. Results from image processing showed a good potential for non-destructive and rapid detection of foreign objects and defects in food material. However, they used different foreign bodies and sizes with regular shapes. Actual bone fragments were not used. Although a temperature compensation transducer reduced standard deviation of data, direct or watercoupled contact is preferable to air contact. Chanamai and McClements (1999) used a pulse–echo low-intensity ultrasonics to measure chicken composition. They used a sample holder with a fixed depth. However, they did not use the apparatus to detect foreign body in samples. Thus, not much work has been published on using a pulse–echo, direct or water-coupled, and low-intensity ultrasonic device to detect actual bone fragment in chicken breast fillet of variable heights. Thus, the objectives of this study were i) to design, fabricate and test a pulse–echo low-intensity ultrasonic apparatus for chicken breast fillet samples of variable thicknesses, ii) to measure ultrasonic properties of chicken breast muscle, iii) to evaluate the effect of various chicken bone fragment sizes on chicken breast ultrasonic properties, and iv) to study the effect of vertical location of a bone fragment size on chicken breast ultrasonic properties. 2. Materials and methods 2.1. Materials Boneless, skinless chicken breasts were purchased from a local grocery store at Guelph, ON, Canada. The breasts were equilibrated at ambient temperature (24 ± 0.5 °C) for at least 1 h prior to experimentation. A borer (or punch) of 25.4 mm (1″) inside diameter was used to obtain cylindrical samples from the thicker end of a chicken breast. Thus, the cross-sectional area of a bored chicken breast sample was 506.7 mm2. Bone fragments were produced by breaking a chicken bone into small pieces. The chicken breast with bones was cooked in boiling water for 20 min. After cooling the breast at room temperature, breast meat was manually removed from the pectoral bone system. The bones were heated in a convection oven at 93 ± 1 °C for 4 h. Any remnants of breast meat attached to the bone system were carefully removed. Bone fragments were produced from the rib by breaking this bone into small pieces (Tao & Ibarra, 2000). The “large” and “medium” sized bone fragments were approximately rectangular and square in shape, respectively, with major dimensions of 4.3 mm × 3.5 mm, and 3.0 mm × 3.0 mm, respectively. The “small” bone fragments were trapezoidal in shape with parallel dimensions of 2.6 mm and 3.9 mm, and perpendicular dimension of 1.9 mm. Thus, projected areas of the selected large, medium, and small bone fragments used were estimated to be 15.75, 9.92, and 6.18 mm2, respectively.
Fig. 1. Cross-sectional diagram of the piston and cylinder apparatus.
2.2. Methods 2.2.1. Piston and cylinder apparatus A Piston and cylinder (P&C) apparatus was developed to provide a chamber to perform pulse–echo based ultrasonic measurements for liquid or solid samples of variable heights (Fig. 1). This apparatus was an ultrasonic pulse–echo reflectometer based on the same principle of operation as provided by McClements and Fairley (1991). Essentially a cylinder of inside diameter of 32.75 mm (1.25″) and 3.175 mm (0.125″) thickness was attached to a plexiglass circular base plate. A stainless steel solid cylinder (density of 7927 kg/m3) was used to reflect ultrasonic pulses emitted and received by a piezoelectric transducer. If necessary, another stainless steel or plexiglass solid cylinder was placed below the reflecting stainless steel cylinder. A plexiglass pipe, 25.4 mm (1″) inside diameter, of a specified height, measured to the nearest 0.01 mm (Moore and Wright micrometer, Sheffield, UK) rested on the stainless steel reflector. The purpose of using a pipe of known height was to closely match sample height, thus limiting uniaxial sample compression. Plexiglass pipes of lengths ranging from 10 mm to 40 mm were cut for this study. A rexalite (cross-linked polystyrene) delay-line, cylindrical in shape (7.08 mm in length, 5.39 mm in diameter) (Technisonic Research, Fairfield, CT, USA) was housed in a plexiglass cylindrical piston 32.07 mm in diameter and 12.47 mm in height. The transducer could be screwed into a metal nut that was snugly fitted into the piston cavity, just above the delay-line. Prior to a scanning operation, the piston cavity was filled with distilled water. Then the transducer was screwed into the nut. A sample was placed between the bottom of the rexalitecentered plexiglass piston and the top of the stainless steel reflector cylinder at the bottom. To ensure adequate sample contact, a 1 kg mass was placed over the transducer (Fig. 2). After 30 s of stabilization, the sample was ultrasonically
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Fig. 3. Block diagram of the ultrasonic measurement system.
Fig. 2. Picture of the piston and cylinder apparatus during ultrasonic scanning of a chicken breast muscle sample.
scanned. Then the sample was again scanned twice in quick succession. An average of three scan readings were taken. Thus, the P&C apparatus provided a chamber wherein ultrasonic properties of liquid and solid samples of variable depths could be determined. 2.2.2. Sample preparations Appropriate sample preparations were required to investigate treatment effects. To ascertain effects of bone fragment sizes on ultrasonic characteristics, the cylindrical chicken breast samples were ultrasonically scanned several times as follows. Firstly, some breast samples were scanned. Secondly, the samples were horizontally cut approximately 80% of their circumferences at their mid-heights, and then ultrasonically scanned in the P&C apparatus. Thirdly, the samples were retrieved from the P&C apparatus, and a large, medium or small bone fragment was placed in the center of the bottom cut surface. A thin circular, gasket-type, rubber template with a center opening of 6.35 mm (0.25″) diameter was placed on the bottom cut surface to only guide placement of the bone fragment at the center of the bottom cut surface. A small chord segment of the template was cut-off near the circumference, to facilitate its placement near the uncut sample circumference. The samples inserted with large, medium or small bone fragments were sequentially scanned. Thus, the following five samples were ultrasonically scanned: uncut sample (u), horizontally cut sample (at its midheight) (c), cut sample with large bone fragment (l), cut sample with medium bone fragment (m), and cut sample with small bone fragment (s). There were 19 replications. To ascertain the effects of vertical location of bone fragment, the following sample preparations were conducted, before being ultrasonically scanned. Firstly, the samples were horizontally cut around approximately 80% of the circumference at two heights: a) one-third from the top surface, and b) two-thirds
from the top surface; then ultrasonically scanned in the P&C apparatus. Secondly, the samples were retrieved from the P&C apparatus, and the medium bone fragment was placed in the center of each uppercut sample. The circular template was used to only guide placement of the bone fragment at the center of the bottom surface. Thirdly, the medium bone fragment was removed from the upper cut bottom surface and placed at the center of the lower cut bottom surface. Thus, the following four samples were ultrasonically scanned: uncut sample (uc), horizontally cut (at two vertical locations) sample (cc), sample with the medium bone fragment placed at the center of the upper cut (mu), and the medium bone fragment placed at the center of the lower cut (md). There were 18 replications. 2.2.3. Ultrasound system The flat-focused ultrasonic transducer used (GRD-1502-HR, Technisonic Research, Fairfield, CT) had a nominal frequency of 15 MHz and 6.35 mm diameter. A pulse/receiver ultrasound card (SR 9000, Matec Instrument Co., Northborough, MA) was used to drive the transducer and to receive echo signals (Fig. 3). A pulse of 4 MHz peak frequency was produced by the SR9000 card at a repetition rate of 2 kHz (Zhao, Basir, & Mittal, 2003). The signal sampling frequency was 100 MHz. A typical raw signal plot of pressure amplitude (mV) versus time (μs) for a chicken breast sample is shown in Fig. 4a, wherein it is difficult to decipher peak amplitudes. Hence a Short Time Fourier Transform (STFT) algorithm (Jiang, Zhao, Basir, & Mittal, 2003) was implemented to enhance the signal-to-noise ratio. A Hamming window (Jiang et al., 2003) of 100-point
Fig. 4. Display of amplitude (mV) versus time: a) raw signal, b) processed signal.
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length was used to obtain a frequency of 4 MHz. A Labview 5.0 program (National Instruments, Cambridge, Ontario, Canada) was developed to control the SR-9000 card and to process the echo signals simultaneously. Fig. 4b shows a processed signal output of this program for a chicken breast sample clearly showing the two peak amplitudes. Digital values of amplitude and time data were also displayed in the output. 2.2.4. Property measurements A plexiglass pipe with an appropriate height equal to or slightly less than sample height was selected to ensure adequate sample contact with both the piston and with the stainless steel cylinder, yet minimizing uniaxial compression. Sample temperature was measured by inserting a digital thermocouple based thermometer (± 0.1 °C) into the sample after ultrasound scanning. Sample density was measured after ultrasonic scanning by determining a sample's mass and its volume. Ultrasonic velocity (m/s) was computed by dividing distance traveled in a sample by the corresponding travel time. Acoustic impedance (kg/(m2 s)) was computed as the product of ultrasonic velocity in the sample and corresponding sample density. For each scan, the ratio of the pressure amplitude (mV) of the wave emanating from the sample/reflector surface interface to the corresponding amplitude of the wave emanating from the delay-line/sample interface was computed as amplitude ratio. To introduce a diffraction correction term, the pressure amplitude was assumed to be either inversely proportional or exponentially related to the normalized distance (distance divided by the near field). Expressions for pressure amplitude of echoes P1 and P2 were written as a function of the following independent variables: initial pressure amplitude, attenuation coefficient in the sample, sample height, impedance of transmitting medium and sample, wavelength in the sample, and transducer area divided by π. Where P1 and P2 are the pressures amplitudes at interfaces of delay-line/sample and sample/ reflector (stainless steel), respectively. Taking the ratio of P2/ P1, and eliminating some variables, Kumar and Kumar (1996) derived expressions for attenuation coefficient that accounted for diffraction loss. For this study, it was assumed for simplicity that pressure amplitude was inversely proportional to the normalized distance. Thus, Eq. (1), adapted from Kumar and Kumar (1996) for the experimental set-up in this study, was used. 8:686 P2 R1 1 kd Ld þ km Lm a¼ d ln d d : ð1Þ 2Lm P1 R2 TT V kd Ld R1 and R2 are reflection coefficients at the two interfaces; T and T′ are transmission coefficients at the interfaces of delayline/sample and the sample/reflector, respectively; λd and λm are wavelengths of ultrasound propagation in the delay-line and in the sample material, respectively; and Ld and Lm are lengths of delay-line and thickness of the chicken sample, respectively. Experimental values of reflection and transmission coefficients were obtained in a similar approach as given by McClements and Fairley (1991).
2.2.5. Testing of piston and cylinder apparatus Distilled water was used to test the piston and cylinder apparatus. Chicken breast thickness typically ranged from 10 mm to 24 mm. Hence, plexiglass pipe lengths ranging from 8 to 40 mm were used to cover the range. The ratios of delayline length (7.08 mm) to water column heights (8 mm to 40 mm) were of the same order of magnitude. Thus, the diffraction correction was included in the computation of attenuation coefficient. Distilled water temperature ranged from 23.1 °C to 24.4 °C, with a mean temperature of 24.1 (± 0.5) °C. Distilled water density, corresponding to sample temperature, was obtained from Kay and Laby (1986). 2.2.6. Data analyses Spreadsheets (Excel, Microsoft Office 2000, Microsoft Corp., Redmond, WA) were used for most of the computations. All statistical analyses were performed using SAS ® Propriety Software Release 8.2 (SAS Inst., Cary, NC) on a Sun OS 5.8. The SAS procedures CORR, GLM, and MEANS were employed. 3. Results and discussion 3.1. Distilled water The mean value of ultrasonic velocity data was 1492.85 ± 3.50 m/s. For the temperature range used, the corresponding mean value computed from the data of Del Grosso and Mader (1972) was 1494.19 ± 1.39 m/s. From Kay and Laby (1986) the computed ultrasonic velocity was 1493.32 m/s at 24.1 °C. Thus, ultrasonic velocity data obtained in the study matched published data. Mean and standard deviation of acoustic impedance values were 1.49E + 06 kg/(m2 s) and 3.19E + 03 kg/(m2 s), respectively. For fresh water at 20 °C, Ensminger (1973) documented an acoustic impedance of 1.48E + 06 kg/(m2 s), closer to the value obtained in this study. The mean value of amplitude ratio was 2.57 ± 0.25. Based on Eq. (1) computed attenuation coefficient values were negative. This impossible result may imply that attenuation is too small to be accurately determined for the distances (8 mm to 40 mm) used in this study. Using pulse–echo mode, McClements and Fairley (1991) reported an attenuation coefficient of 0.0078 dB/ mm for a 12 mm wide sample of distilled water at 2.1 MHz and ambient temperature. However, a widely accepted attenuation coefficient value of 0.000869 dB/mm for distilled water at 2.1 MHz and 24.1 °C was estimated from Kay and Laby (1986). Thus, the attenuation coefficient value obtained by McClements and Fairley (1991) is nine times higher than the corresponding value using the equation from Kay and Laby (1986). This underscores the difficulty in measuring low attenuation coefficient. 3.2. Chicken breast muscle samples There were 19 and 18 scanned data sets, to determine the effects of bone fragment sizes, and vertical location of bone fragment, respectively. For all properties of uncut samples, the
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probability of significant differences between the two data sets was higher than 0.05. Hence all (19 + 18 = 37) observations for uncut samples were combined. The following mean parameter values were obtained: temperature = 25.3 ± 0.7 °C, compression = 5.48 ± 4.02%, density = 1066 ± 44 kg/m3, velocity = 1567 ± 21 m/s, and impedance = 1.67E + 06 ± 6.40E + 04 kg/(m2 s). The coefficients of variation of sample temperature, density, velocity and impedance were less than 5%. Sample compression ranged from 0.04% to 16.4% and sample heights from 12 mm to 22 mm. As stated earlier, the length of the plexiglass pipe for each sample was carefully chosen to minimize uniaxial compression. However, compression was more sensitive for shorter samples than for longer samples. For example, a 2 mm difference between pipe and sample lengths yields higher compression for shorter samples. In this study, the mean value of sample density of 1067 ± 43 kg/m3 compared closely with 1070 kg/m3 reported by McFarlane et al. (2003), and with values of 1070 kg/m3 and 1100 kg/m3 obtained for poultry meat by Sanz, Alonso, and Mascheroni (1987). Thus, the volume displacement technique, used in this study was apparently as effective as the Archimedes principle based method used by McFarlane et al. (2003). The mean value of ultrasonic velocity of 1567 m/s at a mean sample temperature of 25.3 °C, in this study, was similar to the corresponding value of 1570 m/s at 25 °C for low fat chicken reported by Chanamai and McClements (1999). In this study, mean sample mass and sample height used were 8.72 ± 1.66 g and 17.14 ± 3.04 mm compared with corresponding values of 25 g and 16 mm, respectively, used by Chanamai and McClements (1999). Thus, both distilled water and chicken breast muscle sample velocities obtained using the P&C apparatus were comparable to corresponding published values. The mean value of impedance of 1.67E + 06 ± 6.40E + 04 kg/(m2 s), obtained in this study, was within the range of 1.65E + 06 to 1.74E + 06 kg/(m2 s) for muscle at 39 °C given by McClements (1997). Thus, both the experimentally determined values of velocity and density compared favorably to values from the literature. For low attenuation material such as water and chicken muscle, impedance is simply the product of velocity and density. The GLM procedure of SAS was used to test whether different breasts (block effect) influenced chicken breast muscle sample properties. Samples were taken from 14 different breasts. For most properties, there were no significant differences between breasts. However, for temperature and amplitude ratio, the probability of rejecting significant differences was N 0.0009. This implies i) that different breasts were tested at significantly different temperatures, and ii) that different breasts had significantly different amplitude ratios. These differences may presumably be attributed to muscle orientation and muscle strength in each breast. Genetics, age diet, exercise etc. of each bird may have contributed to these significant differences. The only significant correlation (Pearson correlation coefficient = 0.922, Prob. N |r| was b 0.0001) was between impedance and density. This result is expected since by definition impedance is directly proportional to density, as stated earlier.
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3.3. Detection of bone fragment based on size The GLM procedure of SAS was used (for unbalanced data) to analyze the effects of breast (block) and treatment. As discussed earlier there was a block effect on amplitude ratio of uncut chicken breast samples. The chicken breast was considered to be covariate to remove the variation due to block effect. Hence, treatment was the only specified class variable, although the model (velocity or amplitude ratio) was dependent on both breast and treatment effects. Duncan's multiple range test was performed to rank the means. There were total of (19 data sets × 5 treatments = ) 95 observations and samples were taken from seven breasts (A to G). Results are shown in Table 1. Velocity was not dependent on either breast or treatment. Thus, velocity could not be used to detect the presence of a bone fragment (treatment effect). The model for amplitude ratio was highly significant. Results of the Type III sums of squares revealed that both breast and treatment effects were highly significant sources of variation. There was a significant difference of mean amplitude ratio values i) between uncut samples and all other cut samples (with or without a bone fragment), and ii) between the cut (only) samples and the cut samples with a bone fragment. There were no significant differences between mean amplitude ratio values of cut samples with a bone fragment of any size. This suggests that amplitude ratio can be used to distinguish between uncut and cut samples, and between cut or uncut (only) samples and cut samples containing a bone fragment of any size used in this study. Zhao et al. (2003) demonstrated that amplitude ratio was successfully used to detect foreign bodies in glass bottles containing liquid. In this study, the transducer detected a cut surface presumably because of the following reasons: i) the upper and the lower surfaces of the cut sample were not completely in contact, and ii) the cut surfaces may not have been Table 1 Results of the detection of bone fragments based on size Dependent variable
Model Pr N F
Velocity m/s 0.419
Amplitude ratio
R2
Source
0.054 Breast
Pr N F
Treatment Mean
0.381
u c s Treatment 0.380 m l b 0.0001 0.584 Breast b 0.0001 u c s Treatment b 0.0001 m l
1563 a⁎ 1566 a 1573 a 1573 a 1568 a 0.85 (± 0.37) a⁎ 0.53 (± 0.39) b 0.20 (± 0.17) c 0.18 (± 0.17) c 0.17 (± 0.15) c
n = 19 data sets, u: uncut sample, c: cut sample, s: cut sample with small bone fragment, m: cut sample with medium bone fragment, l: cut sample with large bone fragment. ⁎ a to c : for each dependent variable, means in a column with similar letter are not statistically significant at 95% confidence level.
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perfectly horizontal resulting in reflection of ultrasonic waves away from the transducer. Introduction of a bone fragment in a cut sample presumably reflected ultrasound waves. Hence, the ultrasound system could detect the presence of a bone fragment compared to a cut (only) sample. The following factors apparently contributed to lack of significant differences between cut samples containing a bone fragment, irrespective of size: i) experimental error resulting from off-center placement of bone fragment, ii) curved surface of bone fragment reflecting away ultrasonic waves, and iii) possible differences in curvature on both surfaces of a bone fragment. The coefficient of variation for amplitude ratio for the uncut, cut (only), and cut samples with a bone fragment were 43%, 75%, and 88% (average value), respectively. This suggests that the process of cutting introduced additional variability in measuring amplitude ratio. Placement of a bone fragment independent of size further increased variability in measuring amplitude ratio for reasons previously discussed. Thus, experimental techniques and the P&C apparatus may have contributed to some variability in consistently measuring amplitude ratio. Notwithstanding the statistical analysis of the effect of bone fragment size, intuitively a larger projected area of a foreign body should result in a lower amplitude ratio. Fig. 5 shows a plot of the dimensionless ratio of amplitude ratios of cut samples with bone fragments to cut (only) samples as a function of the dimensionless ratio of projected areas of bone fragment to the transducer, essentially dimensionless plots of amplitude ratio versus projected area. As dimensionless projected area ratio increases, dimensionless amplitude ratio decreases. A larger bone fragment presumably reflected more ultrasonic waves in chicken breast muscle samples, compared to a smaller bone fragment. 3.4. Detection of bone fragment at different vertical locations There were total of (18 data sets × 4 treatments/data set = ) 72 observations, and samples were taken from seven breasts (H to N). Results are shown in Table 2. Velocity was dependent on breast (block effect) but was independent of treatment effect. Thus, velocity could not be used to detect the presence of cuts in the sample or presence of medium bone fragment located at the upper or lower cut.
Table 2 Results of the detection of medium bone fragment based on vertical location Dependent variable
Model Pr N F
Velocity m/s 0.344
R2
Source
0.064 Breast Treatment
Amplitude ratio
b 0.0001 0.579 Breast
Pr N F 0.047 0.927 0.748
Treatment Mean uc cc mu md uc cc
Treatment b 0.0001 mu md
1571 a⁎ 1573 a 1572 a 1575 a 0.89 (± 0.44) a⁎ 0.50 (± 0.30) b 0.14 (± 0.10) c 0.13 (± 0.08) c
n = 18 data sets, uc: uncut sample, cc: cut sample, mu: cut sample with medium bone fragment placed in upper cut, md: cut sample with medium bone fragment placed in lower cut. ⁎ a to c : for each dependent variable, means in a column with similar letter are not statistically significant at 95% confidence level.
The results of this section are similar to that of the previous section. Thus, amplitude ratio can be used to distinguish between uncut and twice cut samples, and between twice cut (only) samples and twice cut samples containing a medium bone fragment either at the upper or lower cut. From the data it appears that a lower location of a bone fragment reduces the amplitude ratio. However, intuitively, it appears that it would be more difficult to locate a smaller bone fragment at a higher vertical location. 4. Conclusions The piston and cylinder apparatus based on pulse–echo technique was developed to perform ultrasound scans for both liquids and solids of variable sample heights. For distilled water samples, velocity and acoustic impedance could be measured accurately, whereas attenuation values varied widely. For chicken breast muscle samples, density, velocity, and impedance were accurately measured, whereas amplitude ratio values varied widely. Amplitude ratio, not velocity, could successfully discriminate between uncut samples, cut samples, and cut samples with bone fragment with projected area from 6 mm2 to 16 mm2. The ratio of amplitude ratios of cut samples with bone fragment to that of cut samples decreased as ratio of projected areas of bone fragment to that of the transducer increased. Amplitude ratio, not velocity, could successfully discriminate between uncut samples, cut samples, and cut samples with bone fragment projected area of 10 mm2 irrespective of vertical location. Acknowledgements
Fig. 5. Plot of the ratio of amplitude ratios of cut samples with bone fragments to cut (only) samples versus ratio of projected areas of bone fragment to transducer (each point is the average from 19 independent observations).
The authors acknowledge the technical support of John Boldt and Ping Yang from the University of Waterloo, and Bill Verpagen and Dr. Jixian Zhang of the University of Guelph. The Natural Science and Engineering Research Council (NSERC) of Canada provided financial support for this project.
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