Ultrasonic Physics in Musculoskeletal System Yio-wha Shau ( ), PhD Institute of Applied Mechanics, NTU Ultrasonography provides a less expensive and d

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1 Ultrasonic Physics in Musculoskeletal System Yio-wha Shau ( ), PhD Institute of Applied Mechanics, NTU Ultrasonography provides a less expensive and dynamic imaging of various disorders of musculoskeletal system. Disorders of tendons, musculature, bone cortex and soft tissues can often be accurately interpreted using clinical ultrasound. In terms of ultrasonography, the understanding of the physical principles of ultrasound is as important as the knowledge of anatomy. 2 MHz - 30 MHz c =1540 m/s c = λ f (Echo) (2-10µm) (mm) (Scattering) 1

2 ρ) ρ Non-biological Materials Speed of Sound (m/s) Biological Materials Speed of Sound (m/s) Air 330 Lung 600 Water 1480 Fat 1460 Lead 2400 Liver 1555 Aluminum 6400 Blood 1560 Kidney 1565 Muscle 1600 Lens of Eye 1620 Skull Bone

3 (attenuation) db/mhz cm (DGC) Continuous Wave (Pulse Wave) CW US PW US 3

4 CW vs. PW Doppler Ultrasound Measurements Continuous Wave (CW) Doppler Pulse Wave (PW) Doppler + Sensitivity + Spatial resolution + Inexpensive + Visibility and Focusing + High S/N ratio + Angle correction + Low power - High power - No spatial information - Low S/N ratio Color Duplex (1) - (Morphology) (2) - * * (Frame Rate) (Spatial resolution) 4

A ; B A (Pulse Repetition Frequency) Ultrasound Doppler) The Doppler effects was first observed and formulated in 1842 by Austrian physicist Johann Christian Doppler

If the sound source is moving toward the receiver, the receiver will obtain a sound wave at a higher frequency than the emitted wave.

5 A ; B A (Pulse Repetition Frequency) Ultrasound Doppler) The Doppler effects was first observed and formulated in 1842 by Austrian physicist Johann Christian Doppler ( ). This phenomenon occurs when the source and the receiver are mowing relative to each other. If the sound source is moving toward the receiver, the receiver will obtain a sound wave at a higher frequency than the emitted wave. The frequency-increment is proportional to the magnitude of approaching velocity. Doppler ultrasound provides a non-invasive measurement of blood flow in human body, the first attempt has been done by Satomura (1956) in the investigation of flow in the heart. (Pulse-Echo cycles) (T PRF ) 70 5

6 f 2 V cosα = C d f o Scattering of Red Blood Cells ( ) f d < 0.5 f PRF 15 cm f PRF 5.13kHz ( ) 2.6kHz f PRF /2 (aliasing) (CD) Mean averaged velocity Intensity-weighted average velocity (Variation) Three-Dimensional display of Doppler Spectra 6

7 RBC volume Brightness Color Doppler Color Coding Color Doppler Parameter s Doppler Gain Baseline Steering angle Angle Correction Doppler gate (SV) Wall Filter Pulse Repetition Rate Velocity Scale 7

8 Color Doppler for finding Blood Vessel Location of Blood Vessels? Color Encoding? Doppler (Velocity) Spectrum Blood flow in artery (Laminar Flow) Inverted 8

9 Clinical Applications of M-Mode Ultrasound Clinical Ultrasound KYOWA PS-2KB Portable Amplifier Non-invasive Assessment of Arterial Elasticity Pressure (mmhg) Diameter Distension (mm) Distension (mm) Pressure (mmhg) TH090d TH095d TH100d TH105d TH110d TH120d TH125d TH130d TH135d Pressure 9

Clinical Applications of Color Doppler Ultrasound Arterial Stenosis

Doppler spectrum) Vascularity of Renal/Liver Transplants (predicting

Stroke (ICA stenosis) Exploring Doppler Spectrum Flow Dwave Arterial

10 Clinical Applications of Color Doppler Ultrasound Arterial Stenosis (turbulent jet) Arterial Resistance Tumor Vascularity (feeding artery Doppler spectrum) Vascularity of Renal/Liver Transplants (predicting rejection) Tumor Vascularity (angiogenesis, malignancy and metastases) Stroke (ICA stenosis) Exploring Doppler Spectrum Flow Dwave Arterial Impedance Z= P / Q Non-invasive Assessment of Arterial Impedance (Vascular After-Load) 10

11 Malignancy of Tumor? Doppler Spectrum Kidney Tumor Vascularity PSV; PI; RI Organ Transplantation Vascularity of Graft Noninvasive Assessment of Vocal Folds Biomechanics (Vibratory Motion Color Artifact) 11

12 Power Doppler Ultrasound Power Doppler is a new method of ultrasound flow imaging that based on the integrated power of the Doppler spectrum rather than the mean Doppler spectrum. Power Doppler imaging is more sensitive in terms of blood flow detection than conventional color Doppler, thus it has the potential of displaying tissue perfusion. Since the strength of power Doppler is proportional to the number of scatterers (RBCs) flowing through the region-of-interest (ROI). Its relation to the flow volume is quite complex. Nevertheless, it is inherently unaffected by aliasing (i.e., low PRF) and relatively insensitive to the insonating angle or scanning depth. Power Doppler measures the number of scatterers (RBC) in the sampling volume (Dymling et al 1991) Amplitude: number of RBCs moving at such a velocity Clinical Applications of Power Doppler Ultrasound Since the power Doppler (PD) can quantify the fractional of moving blood volume through the ROI, attempts have been made to investigate the soft tissue perfusion in various hypervascular microvessel beds. The power Doppler imaging are often normalized and optimized to enhance the signals of moving scatters at low velocities (0.8 6 cm/sec), its magnitude does not proportional linearly to blood velocity. However, due to high sensitivity of tissue perfusion, the potential applications of PD are: vascularity in normal and transplanted renal tissues for rejection prediction, tumor vascularity for malignancy and metastases placental vascularity for possible previa accreta, 12

13 Color Doppler Imaging Power Doppler Imaging Tumor Vascularity Area of Colored pixels within tumor section PDVI: Area of tumor section Suprapatellar bursa Steroid injection 13

14 Heterogeneity of Soft Tissue Tumor 0.85 Harmonics of Normalized Waveform m mean =0.66 Power Doppler Imaging for Pulsatile Vascular Perfusion 14

15 C=1540m/s Dependence of depth and angle of incidence Effect of Doppler Sampling Volume (gate) Small SV Large SV 15

16 Effect of Scale Doppler Gain too high Saturation Increase scale Effect of Doppler Gain Doppler Gain too High Mirror Doppler Gain too high Reduce Doppler Gain Effect of Pulse Repetition Frequency (PRF) Spectral Aliasing Increase PRF Change baseline 16

Low PRF Higher PRF Low PRF results in higher sensitivity of flow detection (venous flow) Concluding Remarks The quality of diagnostic ultrasound relies on a proper selection of US scanhead pulse

17 Low PRF Higher PRF Low PRF results in higher sensitivity of flow detection (venous flow) Concluding Remarks The quality of diagnostic ultrasound relies on a proper selection of US scanhead pulse frequency2d gaindoppler gainscale and insonating angle Doppler Ultrasound provide a way of measuring blood flow non-invasively in vessels of order of a few hundred microns High frequency fluctuating movements cause CDI artifacts which can be used to quantify the dynamic behavior of soft tissues Color Doppler and Power Doppler look into different physics of flow in human body Power Doppler Imaging for microvessel perfusion (higher sensitivity and resolution) 17

357 P <. 5. TCD findings revealed that the contralateral vertebral artery systolic blood flow velocities in patients with phase Ⅰ Ⅱ and Ⅲ steal groups

357 P <. 5. TCD findings revealed that the contralateral vertebral artery systolic blood flow velocities in patients with phase Ⅰ Ⅱ and Ⅲ steal groups 356 TCD 212 3 215 4 TCD 45 TCD 8 Ⅰ 21 Ⅱ 11 Ⅲ 5 4 45 6 2 Ⅰ 12 9 Ⅱ 3 7 1 Ⅲ 3 2 r =. 78 P