SPI PRACTICE EXAM.docx

The typical frame rate of an Ultrasound system is? - correct answer Between 30 Hz and 100 Hz Temporal resolution is synonymous with frame rate. Typical frame rates in imaging systems are 30-100 Hz. - correct answer The temporal resolution or frame rate = 1/(time to scan 1 frame). Frame rate can drop down to 5 Hz. Pulse duration is related to bandwidth how? - correct answer Pulse Duration = 1 / Bandwidth Specular reflectors have physical dimensions that are what size in relation to the wavelength? - correct answer Greater Two identical systems produce a pulse. One pulse is 0.8 usec in duration while the other is 1.4 usec. The best radial resolution will be created by which system? - correct answer 0.8 Pulse duration (length of pulse) With a short pulse duration we have a small pulse length. The shorter the SPL the better the longitudinal resolution. To achieve better depth (axial) resolution. You must have what? - correct answer FEWER CYCLES PER PULSE -Axial resolution = SPL / 2 or # cycles in the pulse x wavelength / 2 - correct answer Ultrasound wave attenuation is denoted by which units? - correct answer dB (DECIBELS) If it takes 1/20 of a second to construct a single frame, what is the current frame rate? - correct answer 20 hz--Hz = cycles per second. The rate is 1/20th of a second. So 20 cycles per second = 20 Hz With a focused ultrasound beam, bioeffects...? - correct answer Are less likely to occur The smaller the beam the less likelihood of cavitation. Exam duration has the greatest effect on patient exposure. - correct answer Bioeffects intensity limit: SPTA 100 mW/cm2 Unfocused 1 W/cm2 or 1000 mW/cm2 Focused HIGHEST output intensities used with pulsed doppler. - correct answer Lowest output intensities are with gray-scale imaging. With which type of array are grating lobes most common? - correct answer Linear array Which equation is used to find the doppler shift? - correct answer Fd = 2 Fi v / c In standard diagnostic imaging instrumentation, which has the higher numerical value? - correct answer Lateral Resolution-LATA= higher numerical value LARD = smaller value Reflectors that are closer together than the width of the beam create what artifact? - correct answer Pulse Width artifact-Also known as lateral resolution artifact and beam width artifact. Basically they are shown as a single point because the resolution of the image - correct answer is only as good as the minimal thickness of the beam at that depth. As a wave propagates, the period will? - correct answer Not Change As the operator increases the maximum imaging depth the Pulse Repetition Period (PRP)...? - correct answer Increases--As you image deeper you have to wait longer for the signal to come back so you send less pulses per second. So as you increase the depth you increase the time, you increase the PRP. Brightness of the display is affected by? - correct answer Receiver Amplification Comet tail artifact is produced by? - correct answer Strong reflectors and high propagation speeds. If the propagation speed of a medium is less than soft tissue, where will the resulting echo be placed? - correct answer Deeper than it actually is. The following characteristic is true of all waves. - correct answer They carry energy from one site to another. If the thickness of the 2 substances forming the interface is increased then the amount of beam reflected is...? - correct answer Unchanged-Reflection = (Z2 - Z1)/(Z2 + Z1) Thickness of the medium isn't involved in this equation. Mirror image artifact manifests the associated anatomic structure how? - correct answer Always deeper on the produced image than physically in the body. The period of the wave is proportional to the wavelength how? - correct answer Reciprocal--The longer the wave length, the longer it takes to complete a wave. So if the wavelength goes up the period goes up. - correct answer If the wavelength goes up the frequency goes down, because it just can't make as many. At the focus the ultrasound beam is ______ ? - correct answer where the optimal transverse resolution is located. The beam is narrowest at the focus. Therefore it will have the best ______. - correct answer lateral resolution and the highest intensity.