One-dimensional Fourier transformation of M-mode sonograms for frequency analysis of moving structures with application to spinal cord motion.

BACKGROUND

Movements of the spinal cord are induced by arterial pulsation and breathing.

OBJECTIVE

The aim of this study was to analyse these oscillations in more detail and to classify them using one-dimensional fast Fourier transformation (1D-FFT).

MATERIALS AND

METHODS

A total of 153 M-mode studies in 53 patients (age 1 month to 14 years) were undertaken using a 5-MHz linear transducer (B- and M-mode). 1D-FFT was applied to the M-mode areas of digitized images.

RESULTS

1D-FFT shows characteristic patterns of spectra for groups of normal, reduced and missing cord motility. For normal cord motility, 1D-FFT peak frequency corresponded to the heart rate, and additional four to five harmonic maxima up to 11 Hz could be found. Reduced cord motility was characterised by one to three harmonic maxima; an immobile cord showed only zero to one maximum. The maximum speed of transverse motion of the neural structures in the lumbar region reached 25 mm/s.

CONCLUSIONS

Using 1D-FFT, characteristic frequency patterns of spinal cord motions can be analysed. In patients with meningomyelocoele individual classification of cord motility is possible. This method of analysis may assist with recognising those at risk of developing secondary tethered cord syndrome.