Compressive sensing in electrical impedance tomography for breathing monitoring

OBJECTIVE

Electrical impedance tomography (EIT) is a functional imaging technique in which cross-sectional images of structures are reconstructed based on boundary trans-impedance measurements. Continuous functional thorax monitoring using EIT has been extensively researched. Increasing the number of electrodes, number of planes and frame rate may improve clinical decision making. Thus, a limiting factor in high temporal resolution, 3D and fast EIT is the handling of the volume of raw impedance data produced for transmission and its subsequent storage. Owing to the periodicity (i.e. sparsity in frequency domain) of breathing and other physiological variations that may be reflected in EIT boundary measurements, data dimensionality may be reduced efficiently at the time of sampling using compressed sensing techniques. This way, a fewer number of samples may be taken.

APPROACH

Measurements using a 32-electrode, 48-frames-per-second EIT system from 30 neonates were post-processed to simulate random demodulation acquisition method on 2000 frames (each consisting of 544 measurements) for compression ratios (CRs) ranging from 2 to 100. Sparse reconstruction was performed by solving the basis pursuit problem using SPGL1 package. The global impedance data (i.e. sum of all 544 measurements in each frame) was used in the subsequent studies. The signal to noise ratio (SNR) for the entire frequency band (0 Hz-24 Hz) and three local frequency bands were analysed. A breath detection algorithm was applied to traces and the subsequent error-rates were calculated while considering the outcome of the algorithm applied to a down-sampled and linearly interpolated version of the traces as the baseline.

MAIN RESULTS

SNR degradation was generally proportional with CR. The mean degradation for 0 Hz-8 Hz (of interest for the target physiological variations) was below ~15 dB for all CRs. The error-rates in the outcome of the breath detection algorithm in the case of decompressed traces were lower than those associated with the corresponding down-sampled traces for CR  ⩾  25, corresponding to sub-Nyquist rate for breathing frequency. For instance, the mean error-rate associated with CR  =  50 was ~60% lower than that of the corresponding down-sampled traces.

SIGNIFICANCE

To the best of our knowledge, no other study has evaluated the applicability of compressive sensing techniques on raw boundary impedance data in EIT. While further research should be directed at optimising the acquisition and decompression techniques for this application, this contribution serves as the baseline for future efforts.

Asthma knowledge and approach among Pakistani family physicians and the impact of an educational programme

OBJECTIVES

To assess asthma knowledge and approach among Pakistani family physicians and the impact of an educational programme.

DESIGN

A total of 89 family physicians attending a continuing medical education programme were evaluated using a 17-item questionnaire before and after a lecture and seminar-based educational programme. Three scores -- total score (TSc), knowledge subscore (KSc) and approach subscore (ASc) -- were calculated before and after the course.

RESULTS

A total of 82 (92%) family physicians completed the questionnaire. A minimum TSc of > or =9 was achieved by 57% physicians before the course; this increased to 78% after the course. Physicians with < or =10 years since graduation achieved a higher baseline TSc than those who had graduated > or =20 years previously. The latter group showed a larger post-course improvement. Analysis of individual questions disclosed that 79% of family physicians were unable to assess the empirical risk of asthma in an unborn child, 61% were unable to correctly classify/treat Stage 2 asthma and a similar number peak expiratory flow rate (PEFR) (l/min) based acute asthma exacerbation. Reassuringly, 97% correctly identified clinical signs and 87% life-threatening features of asthma.

CONCLUSION

Of all family physicians who responded to the questionnaire, 57% achieved acceptable baseline standards. Deficiencies regarding areas such as genetic counselling and disease severity assessment were observed. Strengths in identifying clinical signs and life-threatening features were evident. Continuing medical education resulted in a significant improvement in the post-course assessment, regardless of the years since graduation.