K W Lam

Publications (2)2.29 Total impact

• Article: Noninvasive cerebrospinal fluid shunt flow measurement by Doppler ultrasound using ultrasonically excited bubbles: a feasibility study.

  K W Lam, J M Drake, R S Cobbold
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  ABSTRACT: Because normal cerebrospinal fluid (CSF) has almost no natural Doppler scatterers, patency testing of ventriculoperitoneal cerebrospinal fluid shunts (small silastic tubing with lumen diameter of approximately 1 mm draining excessive CSF from the brain) cannot be performed by Doppler ultrasound. We have developed a low-frequency bubble excitation system that generates microbubble scatterers in both distilled water and CSF. Doppler ultrasound can then be used for flow measurement in a ventriculoperitoneal shunt. By using low duty-cycle (approximately 10%), low-frequency (approximately 30 kHz), and low-amplitude (approximately 30 kPa) ultrasound, a population of microbubbles can be maintained for sufficiently long times (>10 min) for Doppler ultrasound measurement, although bubble initiation is inconsistent. The minimum pressure needed for bubble maintenance was found to decrease with increasing burst length and duty cycle. It has been possible to detect the presence of CSF shunt flow down to a mean flow rate of 3 mL/h (mean velocity approximately 0.6 mm/s). The bubble maintenance scheme developed satisfies the safety parameters specified by the American Institute of Ultrasound in Medicine (AIUM) and the US Food and Drug Administration (FDA). Results from both in vitro and in vivo (externalized shunts) experiments indicate the feasibility of this scheme for determining realistic CSF shunt flows, though some practical problems remain before the technique will be ready for clinical use.
  Ultrasound in Medicine & Biology 04/1999; 25(3):371-89. · 2.29 Impact Factor
• Conference Proceeding: Ultrasound bubble excitation for Doppler measurement of cerebrospinal fluid shunt flow

  K.W. Lam, P.A.J. Bascom, A.E. Karpelson, J.M. Drake, R.S.C. Cobbold
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  ABSTRACT: Normal cerebrospinal fluid (CSF) contains few natural scatterers making it difficult to measure the flow by Doppler ultrasound. A new technique is proposed whereby bubbles are generated in a shunt tube by low-frequency (LF) ultrasound (100-300 kHz) at peak pressures of only 0.1 MPa, and their velocity is measured by Doppler ultrasound. Preliminary experimental results using a simple in-vitro model are presented to demonstrate the feasibility of this non-invasive method for measuring flows in a 1.3 mm(ID) shunt
  Engineering in Medicine and Biology Society, 1996. Bridging Disciplines for Biomedicine. Proceedings of the 18th Annual International Conference of the IEEE; 12/1996