© 1998 Philips Medical Systems Nederland B.V Philips Medical Systems CARDIAC ANATOMY TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems The position of the heart Great vessels Lungs Sternum Diaphragm TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems The position of the heart Base Left atrium Right atrium Left ventricle Apex Right ventricle cm TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems The orientation of the heart Left lateral view Transverse section TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Wall structure of the heart Fibrous pericardium Serous pericardium } Pericardium Myocardium Endocardium Parietal layer Fluid Viceral layer TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Structure of the heart Aortic arch Superior vena cava R pulmonary veins L pulmonary veins LA RA Aortic valve LV Chordae tendineae RV Septum Papillary muscle Inferior vena cava Aorta TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Anatomy of the heart TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Branches of the aorta R com carotic art R subclavian art R subclavian v Brachiocephalic art L common carotic art L subclavian art R brachioceph v Aortic arch L brachioceph v L pulmonary art Sup vena cava Ascending aorta TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems The coronary arteries L coronary art L circumflex art LAD R coronary art TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Spatial Orientation of the Heart Pericardial fat Septum RV LV DA TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Mobile transducers • The first true 2D scanner was developed in the University of Colorado in 1957 • The “Pan Scanner” had a single element transducer that rotated in an arc around the patient inside a water tank • Only static images could be obtained TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Articulated arm transducers • Transducer was mounted on a muliple jointed flexible arm • The joints had position sensors, which indicated the current position of the transducer • Could only give static images TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Earliest published B scans Case study of an ovarian cyst published by Prof Xi-Fang Wang at Wuhan Universty in 1960 TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Mechanical transducers • Transducer was mounted on a rapidly oscillating arm, or rotating drum • No of scan lines = No of times the transducer fired during a single oscillation • Frame rate = No of oscillations made by the transducer in second • Enabled real-time imaging of moving objects TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Phased Array Transducers • 64 or more crystals in fixed position (elements) • Crystals are fired by an electronic system (beamformer) to produce a “beam” of ultrasound of desired width and focussing • Analog beamformers are being replaced by digital computer systems for tighter beam control and more accurate focussing • The imaging computers on the Philips Sonos systems have the power of more than 40 Pentium processors TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Beam steering • Ability of phased arrays to change beam direction independent from the transducer angle • Uses the Huygens principle • Requires computed timed firing of the elements TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Transducer construction • Elements are fixed on a damping layer which eliminates resonance • Wavefront travels through the matching medium • After passing the membrane, the wave propagates through gel / tissue TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Focussing • Focussing is achieved by creating or more angled wavefronts simultaneously • Focal Zone is the point where the wavefronts converge • Newer powerful beamformers can create multiple focal zones TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Transducer aperture • • • The aperture depends on the number of elements that can be fired simultaneously Larger aperture gives better lateral resolution, but requires a large amount of processing power to manage the data New transducers have digital multiplexing with up to 1024 channels to increase the aperture TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Near Field and Far Field • Multiple wave elements interact with each other, creating diffraction patterns • The diffraction zones dictate the length of near field and far field • The length of the near field is dictated by the Fresnel equation (Fresnel Zone) Fresnel diffraction is used by digital transducers for focussing by changing phase of the waves • The far field diffraction is determined by the Fraunhoffer equation (Fraunhoffer zone) The beam diverges rapidly and loses resolution in this zone TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Length of Near Field • The length of near field is calculated by the equation: L = r2/ (remember: = v/f, and v = 154000 cm/s) so, for a transducer with an aperture of 2cm, operating at MHz, the length of near field is calculated by: = 154000/2000000 = 0.077cm L=22/ 0.077 = 52cm TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Attenuation • Energy is absorbed by tissues, resulting in progressive weakening of the beam • Rate of attenuation in human tissues is approximately 1dB/MHz/cm • Remember, the wave gets attenuated on the return trip as well 2MHz Example 5cm Att=2x10=20dB TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Resolution • Spatial resolution - ability of the transducer to distinguish separation between closely situated points – Axial resolution - parallel to the beam, a function of wavelength – Lateral resolution - perpendicular to the beam, depends on wavelength and aperture TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Resolution • Contrast resolution - the distribution of the gray scale of the reflected signal and is often referred to as Dynamic Range • Images on systems with low dynamic range appear almost black & white, while high dynamic range images appear softer, with the subtle changes in tissue densities becoming evident • On Philips systems, the Compression control allows the compression or expansion of the dynamic range TRAD © 1998 Philips Medical Systems Nederland B.V Philips Medical Systems Questions? 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