Ny teknologi: Fagdagene ved St. Olavs Hospital Lasse Løvstakken Dept. Circulation and Medical Imaging

Transcription

1 1 Ny teknologi: Ultralyd måler m blodstrøm Fagdagene ved St. Olavs Hospital Lasse Løvstakken Dept. Circulation and Medical Imaging

2 2 Conventional imaging methods of blood flow using ultrasound

3 3 CW- / PW-Doppler Measures the full spectrum of velocities within a region of interest Allows for in-depth analysis of blood flow characteristics Velocity LV blood flow Carotid artery velocity spectrum Aortic blood flow Time

4 4 Color-Doppler imaging Measures the mean velocity and direction along the beam in a 2 or 3-dimensional region of interest Allows for easier detection of abnormalities manifested in blood flow patterns 2-D CDI of a carotid bifurcation 3-D CDI of a mitral regurgitation jet

5 5 Clinical examples Mitral valve regurgitation jet Atrial septum defect shunt flow

6 6 More clinical examples Carotid artery stenosis Thyroid nodule vascularization

7 7 Other modalities Contrast-enhanced ultrasound Injection of gas bubbles with a radius of 1-5 μm, that stay in the blood pool Superior tissue signal separation Also suitable for perfusion imaging B-Flow imaging A power-doppler variant, no directional information B-mode and flow image from same data, no color blooming artifacts Carotid bifurcation with contrast B-Flow: Carotid ulceration Carotid bifurcation without contrast B-Flow: Dialysis Graft Pseudoaneurysms Videos: N. de Jong & GE Healthcare

8 8 A brief history lesson 1 Technology and research progressed from single-range gate to multi-range gated Doppler, and further to 2-D Doppler imaging Single-range gate Multi-range gate 2-D Doppler s 1980s timeline Image source: J. Woo, A short History of the development of Ultrasound in Obstetrics and Gynecology,

9 9 Doppler imaging at NTNU Successful Doppler imaging instruments and its clinical use was developed in Trondheim in the late-seventies Liv Hatle and others at St. Olavs hospital were pioneers in the use of Doppler ultrasound in cardiology 1976: PEDOF Doppler instrument Bjørn Angelsen and Kjell Kristoffersen

10 10 Doppler imaging at NTNU The company formed based on this research, now called GE Vingmed Ultrasound, is currently one of the world s leading manufacturers of cardiovascular ultrasound imaging systems 1986: Vingmed CFM : GE Vingmed Vivid E9

11 11 Limitations of current methods for blood flow imaging

12 12 Aliasing and angle-dependency Aliasing is a sampling phenomenon that occurs when the velocity exceeds the maximum value: Angle-dependency v max = cprf 4f 0 Aliasing Angle-dependencies occur as only the axial velocity component is measured Applies to all Doppler-based methods

13 13 Flashing artifacts Flashing artifacts are false coloring of tissue regions Due to insufficient separation (filtering) of the blood In general a problem when the velocity of tissue and flow become comparable Physiological movements Probe movement during imaging Flashing artifact Example: Thyroid imaging

14 14 Other limitations and trade-offs (mainly for CDI) Sensitivity vs. spatial resolution Seperate acquisition needed for flow imaging Leads to color blooming artifacts where color covers the tissue Frame rate vs. image quality Frame rate requirements reduce the image quality in flow, leads to more smoothed images Accuracy of velocity measurements A relatively high variance and velocity dependent bias CDI is mainly used qualitatively at the moment

15 15 Improved flow imaging methods under investigation (at NTNU)

16 16 High acquisition rates Plane-wave imaging (PWI) Parallel beam formation A sufficient frame rate is often only achieved at the expence of reduced image quality and / or reduced image width Using recent technology, multiple image lines can be generated in parallel per ultrasound pulse transmitted Unfocused Focused ultrasound pulse Plane (unfocused) ultrasound beams allows for a high number of parallel beams without introducing image artifacts depth

17 17 PWI: What is the difference? An illustration of the frame rate difference for the same amount of image lines. Playback is at 20% of real-time. Example: Neonate heart with an atrioventricular septum defect (AVSD). Parasternal image crosssection using a linear array transducer Roughly equivalent to current high-end acquisition Plane wave imaging, 16x parallel beams (both B-mode and CFI)

18 18 Aliasing-free and angle-independent Doppler imaging why? General improvements In general less interpretation of color images, i.e. increased diagnostic certainty No need for angle-correction, i.e. more accurate quantitative measurements New clinical information? Improved volume flow quantification Improved detection of shunt flow Detection of circulatory / oscillatory flow, flow vorticity Wall shear rate / shear stress estimation

19 19 Blood Flow Imaging (BFI) Angle independent flow visualization An angle-independent blood pattern visualization has been developed at NTNU, compatible with existing methods Regular Color Flow Imaging Speckle + Color Flow Imaging

20 20 2-D velocity vector imaging Speckle tracking RA LV LVOT Quantifying the blood speckle movement using image pattern matching Utilizing plane wave image acquisition, the accuracy can be substantially increased LA Example: Vector velocity imaging of cardiac flow (systole) in a newborn No speckle tracking With speckle tracking

21 21 Extended velocity range in CDI Healthy thyroid PRF = 4 khz Packet size = 12 Healthy thyroid PRF = 0.8 khz Packet size = 12 Insufficient signal No aliasing No flashing Sufficient signal Aliasing Flashing Healthy thyroid PRF = 4 khz Packet size = 60 Sufficient signal No aliasing Less flashing Healthy thyroid PRF = 4 khz Packet size = 60 High gain Sufficient signal No aliasing Less flashing

22 22 High-frequency imaging Commercial systems and transducer technology are now available which allow for imaging at very high frequencies and at a high frame rate 1cm Examples: Imaging of venous flow in a healthy volunteer using a 16 MHz linear array transducer prototype. At high frequencies blood scattering may be visible in the B-mode images.

23 23 Real-time 3-D flow imaging with 2-D matrix arrays From 1D Array array elements to 2D Array array elements Example: Mitral valve insufficiency. Real-time 3-D CDI without ECG triggering and volume stitching.

24 24 Estimation of Valvular regurgitation Area by 3D HPRF Doppler Valvular regurgitant jet area can be quantified by isolating the Dopper signal power from the jet over the whole leakage area relative to a known reference signal from the center of the jet (vena contracta) Mitral valve insufficiency Mitral valve 3-D beam pattern T. Hergum, T. Skaug

25 25 In vivo - compared to MRI Vena contracta position determined with PW Doppler. Jet power isolated with high pulse repetition frequency (HPRF). Acquire 3D HPRF data. Obtains jet geometry, cross sectional area, and regurgitant volume. Small leakages overestimated when compared to MRI. This is expected due to the finite beam width. Look for the narrow bandwidth of vena contracta Regurgitant volume (RV) = area * velocity-time-integral T. Hergum, T. Skaug

26 26 Thank you for your attention