Peripheral pulses have been recorded and analysed to determine the accuracy with which pulse transit times (PTTs) can be measured. Measurements of PTT between the ECG Q-wave and various peripheral sites were made in 10 normal subjects on 10 separate days. Mean values were determined for the ears (174 ms), fingers (245 ms), and toes (361 ms). The technique was sufficiently accurate to detect small changes in PTT due to changes in posture; sitting to lying, 5.2 ms. When comparing simultaneous measurements on bilateral sites only small differences in PTT were discovered, and these were not significant in the study group as a whole. However, these differences were significant in some individuals. When the subjects raised a single arm or leg, significant differences (38 ms and 49 ms respectively) were recorded between sides. The day-to-day repeatability sigma (expressed as the square root of the within-subject mean square variance) of individual PTT measurements on a subject (supine) was for ears, fingers and toes respectively 9.4, 9.2 and 12 ms. For right-left differences the repeatability was 7.2, 5.9 and 14 ms. Hence changes in PTTs, or differences between right and left sides, can be detected from single measurements with 95% confidence if they exceed approximately 20 ms in ears or fingers and 30 ms in toes.
The strength of agreement between two noninvasive methods of assessing lower limb arterial disease and their relationship to patient symptoms following exercise have been investigated. Color-duplex ultrasound (CDU) and ankle/brachial pressure index (ABPI) (before and afer exercise) measurements were obtained from 200 consecutive patients referred to a vascular investigations laboratory. From these patients, 290 limbs were available for study, comprising limbs without previous vascular surgery, from patients without diabetes and who could attempt a walking exercise test. The overall level of agreement between CDU and resting ABPI measurements was 83% (Kappa 0.66). The ABPI technique identified the more serious disease; a resting ABPI of less than 0.6 gave 100% agreement with CDU. With higher resting ABPIs the level of agreement became poorer: 83% (0.6 < or = ABPI <0.9) and 76% (normal ABPI > or = 0.9). The addition of postexercise ABPI measurements in determining significant arterial disease increased the strength of relationship between the two techniques by only 2% (85%, Kappa 0.69). The exercise test was generally limited by the most symptomatic limb in each patient, and the agreement between CDU and postexercise ABPI measurements in these limbs was higher at 93% (Kappa 0.81). In comparison, agreement for the least symptomatic group of limbs was found to be poor (69%, Kappa 0.37). Compared with symptoms after exercise, overall agreements with CDU and ABPI were both 67% (Kappa 0.27). The agreement was better (91%) when the resting ABPI was less than 0.6. The ABPI is biased toward the detection of more severe disease and is more consistent with CDU when the most symptomatic limbs are compared. The relationship between either test and symptoms after exercise is strong only for limbs with major disease.
The reconstruction of the speed-of-sound distribution within a target can be achieved by CT techniques from measurements on transmitted ultrasonic pulses. The mathematical relationship between speed-of-sound imaging and the conventional CT situation is explained. An experimental system, which has been developed to investigate speed-of-imaging and other forms of in-vivo ultrasound CT, is described, along with the techniques used for data acquisition and image reconstruction. These include measurement of pulse time-of-flight by the threshold or cross-correlation methods. Techniques for reducing artifacts in speed-of-sound images are also described, such as median filtering and modified Shepp-Logan filtering. These techniques have been used to obtain high quality speed-of-sound images of various phantoms. Images of tissue in-vitro have been less satisfactory, because of refraction and attenuation effects. Ways of overcoming these difficulties in an improved system are proposed.
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