Quatech Audio/Video Capture USB 2.0 Spécifications télécharger pdf (Page 254)

9-52 z.one ultra and z.one ultra sp OPERATOR MANUAL

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The above accuracy statements are consistent with 2D measurement tests

performed using a Gammex 403GS phantom with 0.5 dB/cm-MHz attenuation

and a sound speed of 1540 m/s.

Elapsed Time

or Rate

Measurement

Accuracy

In M-Mode and PW Doppler, strip records of tissue motion or blood velocities over

time are produced.

■

The user may use the calipers to analyze these records to measure the

elapsed time between events, or, conversely, to determine the frequency of

such events (as in heart rate determinations).

■

The fundamental accuracy of these measurements depends on the accuracy

of the caliper placement in measuring elapsed time on the time record.

Since the smallest possible error in placing each caliper is ±1 pixel, the average

minimum error in estimating the elapsed time between two events is

approximately ±1.5 pixels. The error in estimating the elapsed time between two

events occurring 1.0 second apart depends upon the sweep speed (number of

pixels per second). In general, for a sweep speed that is n pixels/sec, the

fractional measurement error for an elapsed time of 1.0 sec is given by 1.5/n. The

relationship between sweep speed and the full strip sweep time depends on how

many pixels are allocated for a given strip mode display, which in turn depends on

the pixel density of the LCD.

For the example of the 640-by-480-pixel z.one Scan Engine display, the M-mode

strip is 492 pixels wide, and the corresponding error estimates are summarized in

the tables below.

NOTE: Notice among the different LCDs, the SmartCart/SmartCart sp display has

the best measurement accuracy due to its higher pixel density.

Accuracy of Caliper Measurements of Elapsed Time or Rate

Table 9-5. M-Mode Strip: Scan Engine Display

Sweep Speed

(pixels/sec)

Sweep Time

(sec)

Error in

Measurement (1.0

sec)

180 2.7 0.8%

90 5.4 1.7%

60 8.1 2.5%

Table 9-6. M-Mode Strip: SmartCart/SmartCart sp

Display

Sweep Speed

(pixels/sec)

Sweep Speed

(sec)

Error in

Measurement (1.0

sec)

240 2.8 0.6%

120 5.6 1.3%

60 11.2 2.5%

1 2 ... 249 250 251 252 253 254 255 256 257 258 259 ... 403 404

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