PSF What is PSF 1way/2way PSFs PSFs for continious & discrete apertures

Grating Lobes Linear array: – 32 element array – 3 MHz –‘ pitch ’ l = 0.4 mm – = 0.51 mm – L= N l = 13 mm How to avoid: – design for horizon-to- horizon safety How many elements? What Spacing? Main Lobe Grating Lobe

Array design Linear array: – 32 element array – 3 MHz – pitch l = 0.4 mm – = 0.51 mm – L array = N l = 13 mm How to avoid: – design for horizon-to- horizon safety How many elements? What Spacing?

5 Point Spread Function (PSF)  Defined as the response of an imaging system to a point reflector in space  Totally charecterizes the imaging ability of the system  The degree of spreading in the image of this point object is a measure for the quality of an imaging system  The real image of an imaging medium can be found by the convolution of PSF and the reflectivity function of imaging space

6 Imaging Performance Metrics Axial (Range) Resolution  Refers to the ability of the system to separate objects located along the propagation axis of the ultrasound beam  Determined by the shape and length of the transmitted pulse and which is inversely proportional to the pulse bandwidth BW Lateral Resolution  Used to measure the ability of an imaging system to separate objects located perpendicular to the beam axis  Determined by the beam width of the transducer Contrast Resolution  Defined as the smallest difference in tissue acoustic impedance which can be resolved and displayed as two different gray levels in the image  Primary factors influencing contrast resolution are spatial resolution, systems dynamic range, side lobe level, and image noise

7 Effective Aperture (Coarray) 2-way Point Spread Function Effective Aperture (Coarray)Function

Spatial frequency

SNR Calculation Sqrt(Nt times Nr*Nr) CPA Sqrt(Nt times Nr) CSA

Number of beams in medium?