Doppler imaging of blood flow and tissue movement
One of the strengths of ultrasound imaging is its ability to measure blood and tissue velocities with high precision and at a high frame rate. Information of blood velocities can in the diagnostic setting be used to identify abnormal blood flow related to pathology, such as the jet flow pattern resulting from a heart valve leakage. Further, information about tissue velocities can be used to quantify the function of the heart, through the identification of areas of the heart muscle with reduced contractibility.You can read more about Tissue Velocity Imaging here.
Traditional velocity measurements with ultrasound are based on the Doppler principle, which states that sound emitted from a moving source or sound reflected from a moving target will lead to a shift in the frequency of the sound. This so-called Doppler shift can be measured directly from the received signal through a continuous wave ultrasound emission (CW-Doppler), or sampled through the emission of several ultrasound pulses (PW-Doppler).
Today, Doppler ultrasound measurement is an integral part of commercial scanner systems. Conventional blood flow imaging modalities include spectral Doppler, in which the complete spectrum of velocities within one specific region is displayed. Another modality estimates the mean velocity and direction of blood in many points in a distributed region, which is encoded as a parametric color image, displayed overlaid an image of the anatomy. This latter color flow imaging (CFI) modality has proven very useful for the detection of areas of abnormal blood flow, which can be investigated further using spectral Doppler techniques. In Figure 1, the operation of both CFI and spectral Doppler techniques are shown.
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| Figure 1: PW Doppler and Color Flow Imaging are established methods for blod flow imaging. |
Blood Flow Imaging – a new ultrasound modality to visualise blood flow in congenital heart defects
Background:
A new real time ultrasound flow imaging modality called blood flow imaging (BFI) is able to visualise blood flow in any direction of the image and is not limited by velocity aliasing.
An opening between the left and right atrium (atrial septal defect = ASD) constitutes 7-12 % of congenital heart defects. Pulmonary venous anomalies may be encountered either as isolated lesions or as a component of a more complex lesion in infants with congenital heart disease.
Purpose:
Our aim is to study if ultrasound BFI improves the visualisation of ASD and pulmonary veins in children.
Projects:
1) Pilot study: Ultrasound BFI to visualise ASD flow in children
CDI and BFI were used in the same examination to study ASD flow in 13 children (1 month to 9 years old). This study indicated that BFI improves the visualisation of interatrial blood flow in children. (Echocardiography. 2007;24(9):975-981)
2) Ultrasound BFI to visualise the pulmonary veins in newborns
Twenty six neonates with suspected congenital heart disease were prospectively examined with echocardiography and BFI of the pulmonary veins. You can read more about this study here.
3) Ultrasound BFI for guiding transcatheter device closure of ASD
This project is a co-operation with Rikshospitalet. Transthoracal echocardiography is essential to select patients for transcatheter device closure of ASD, and transesophageal echocardiography is important to guide the device deployment procedure. In this study we plan to compare BFI with the established reference BSD (balloon stretched diameter) to measure ASD size. In addition, we will compare BFI and X-ray angiography, which is regarded as the"gold standard" in the visualisation of the pulmonary veins. (Inclusion completed, analysis and writing remains)
Contact Siri Ann Nyrnes, Lasse Løvstakken or Hans Torp for further information.
Plane wave imaging for high frame rate flow visualisation in neonates with congenital heart disease
There is a trade off between frame rate and image quality in Colour Doppler Imaging, for instance in neonates due to their high heart rates. With the aim to improve echocardiography imaging in neonatal echocardiography, we have started this study using plane wave imaging.
We plan to include 30 neonates with different types of congenital heart defects. We will use used linear array transducers where plane unfocused beams can be emitted in order to avoid image artefacts and increase the frame rate, receiving 16 image lines in parallel for every plane transmit pulse. To visualise flow, we utilize conventional Colour Doppler Imaging and also Blood Flow Imaging, a new flow visualisation technique based on Colour Doppler Imaging and an additional angle independent display of blood speckle movement.
Preliminary data show that by using plane wave imaging, the frame rate increases substantially while preserving good flow image quality.
Plane Wave Imaging in a neonate with atrioventricular septal defect to the left and hypoplastic left ventricle to the right.The bottom plot shows a velocity trace from the region of interest. Each dot represents a new color frame for PWI, while each circle represents colour frames using conventional imaging.
Contact Siri Ann Nyrnes, Lasse Løvstakken or Hans Torp for further information.
Checking leaking heart valves using 3D Doppler
There are four valves in the heart to make sure that the blood flows the correct way through the heart. If these valves are leaking, some of the blood will flow backwards through the hole instead of out into the body. To make sure that the body gets enough blood the heart compensates for this leakage by pumping faster and harder. If this condition is not detected and treated in time, the heart will eventually get weaker from being constantly overworked - and stop.
We have developed a new method for diagnosis based on
Contact Thomas Skaug, Tonje Fredriksen or Hans Torp for further information.
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