© 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 Superior vena cava Aortic arch R pulmonary veins L pulmonary veins Chordae tendineae LA RA Aortic valve RV LV 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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