dr. masciotra speed of sound role in us studies

Antonio Pio MasciotraCampobasso – Molise – Italy

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How speed of sound adjustments change the informations of

Bidimensional US, Color/Powerdoppler and Shear Wave Elastography

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The local sound speed is the measure of how fast a sound pressure wave travels through a local volume of tissue.

A linear relationship exists between the sound speed and density for a range of soft tissues.

Breast glandular tissue has a higher sound speed than breast fat.

Patients with dense breasts tend to have a considerably higher overall breast sound speed.

Kossoff et al measured the overall average composite (fat and gland) breast sound speed.

The mean values reported were :

1.468 m/s in postmenopausal women

1.510 in premenopausal women

These differences are consistent with the higher fraction of glandular tissue in younger women.

This approach used a differential method to calculate the sound speed in a sample, where the path length between

transmitting and receiving transducers was computed using the known sound speed of water.

Other groups have used the same differential method in measuring the sound speed of a sample using both

transmission and reflection US.

Breast cancers have an even higher density and sound speed, likely due to changes in cancerous tissue mechanical

and elastic properties.

Mean values from published sound speed reports are as follows:

Fat 1.478 m/s

Glandular breast 1.510 m/s

Benign breast tumors 1.513 m/s

Malignant breast tumors 1.548 m/s

Then sound speed can be used to assess breast density

and potentially detect breast cancer.

Tissue Density( kg/m3 )

Speed(m/s)

Impedance(rayls)

AttenuationdB/(MHz x cm)

Lung 400 0,26

Fat 920 1.450 1,35 0,48

Breast 0,75

Water 1.000 1.484 1,52 0,0022

Brain 1.030 1,55-1,66 0,6

Kidney 1.040 1.560 1,62 1,0

Blood 1.060 1.570 1,62 0,20

Liver 1.060 1.570 1,64-1,68 0,50

Spleen 1.060 1.570 1,65-1,67 0,50

Soft tissue (average) 1.540 0.54

Muscle 1.070 1575-1590 1,65-1,74 1,09

Fibrous tissue 1,57

Tendon 4,7

Bone 1.380-1.810 4.080 3,75-7,38 6,9-9,9

In this table the key point

is that higher density

tissues show also higher

speed of sound,

impedance and

attenuation (with only a few exceptions).

TissueTuner™ allows you to adjust the receive parameters

associated with the assumed speed of sound of ultrasound in

the body.

Adjusting the speed of sound parameter to match the type

of tissue being interrogated results in increased spatial and

lateral resolution.

USCT provides three types of images:

• reflection images

• attenuation images

• speed of sound images.

Reflection images reveal changes in the echotexture and are

therefore able to image the surface of tissues.

This results in the visualization of the morphology.

Attenuation and speed of sound images are expected to

provide a tissue characterization.

As shown in the figure, a high speed of sound is expected to

be an indicator of cancerous tissue.

Additionally, the combination of speed of sound information

with attenuation information might further improve the

specificity.Relation between the ultrasonic properties speed of

sound and attenuation for different breast tissues.


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Breast cancer


Bidimensional US, Colord/Poweroppler and Shear Wave Elastography




C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s

B scan image

15-4 MHz Linear Probe

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s

Colordoppler15-4 MHz Linear Probe

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s

2D SW Elastography15-4 MHz Linear Probe

C = 1.420 m/s C = 1.600 m/s C = 1.660 m/s

C = 1.420 m/s C = 1.600 m/s C = 1.660 m/s

C = 1.420 m/s

C = 1.600 m/s

C = 1.420 m/s

C = 1.600 m/s

C = 1.420 m/s

C = 1.600 m/s

C = 1.420 m/s C = 1.660 m/s3D SW Elastography



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Thyroid cancer






• Woman 18 years old, since 3 years affected by Hashimoto thiroiditis, but without nodules until 8 moths before• Actually a solid nodule in right lobe with microcalcifications, intranodular vessels and stiff areas at SW elastography (>90 kPa)• Suspicious lymphnode in right middle laterocervical site

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s

15-4 MHz Linear ProbeB scan image

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s


Colordoppler

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s

Lin. 15-4 MHz 1.420 m/s 1.480 m/s 1.540 m/s 1.600 m/s 1.660 m/s

Mean stiff. 24.3 29.3 29.0 28.1 24.6

Min. stiff. 0.1 0.1 0.1 0.1 0.1

Max. stiff. 81.5 71.8 92.9 111.1 84.6

St. Dev. 19.9 17.6 16.7 21.8 18.4

Area 1.25 1.53 1.55 1.55 2.03

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s


B scan image

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s


Colordoppler


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Liver hemangioma






C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s

6-1 MHz Convex Probe

B scan image

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s


Powerdoppler

C = 1.660 m/sC = 1.600 m/s

C = 1.420 m/s C = 1.480 m/s C = 1.540 m/s


Shear wave elastography



Take Home messages

It doesn’t exist a common speed of sound preset bringing optimal informations both

qualitative (morphology, spatial and contrast resolution) and quantitative (depiction of

vessels and stiffness) in all the tissues , in all the applications and with all the probes

In general slower speeds of sound give more detailed qualitative informations while

faster speeds of sound seem to give a better shear wave map

Vascular map seems to be not influenced by the speed of sound selection

The above points are true in the US study of focal diseases

In my opinion the US study of diffuse disease does require detailed and large data

acquisition to well understand which is the best speed of sound choice to guarantee

the accuracy and the repeatibility of the stiffness quantification in conditions like the

evaluation and follow up of liver fibrosis.

I experienced sound speed was more influenced on Breast images than on abdomen.It may be because of high frequency (= short wave length) imaging, which is more sensitive to the wave shift.

And the optimum speed for breast is generally lower (1480) than liver (1540).Regarding SWE, since the sound speed of shear wave is much slower than ultrasound wave, speed of sound setting doesn’t effect on the shear wave propagation in the physically point of view.But the practical point of view, shear wave is always measured by the method same as Doppler measurement. So, if in the wrong sound speed, Doppler’s image quality in terms of spatial resolution becomes worse. I think this phenomena will effect on the precision of shear wave measurement.

Actually US imaging is based only on the assignment of speed of sound speed's value only to received parameters, while it's not used in changing the beamformer (speed of sound in transmitted parameters).And the process of back projection used in CT scan for the density map reconstruction of the body is not used in the image formation US based.So I believe that actually US is only at 20% of its potentiality.We always manage with time, velocities and paths!Compressional waves travel at a speed of 1.540 m/sShear waves travel at a speed of a few m/sd in arteries travels at around 1 m/s speedBlood in veins travels at a few cm/s.Both compressional and SW hasten in cancer and 'hard (or denser) tissues'.

Actually the system of US imaging is similar to a marathon race in which the judge has the chronometer and measures the time passed in the completion of the whole path.Then he knows only the mean velocity, being unknown the speed in the different segments of the path.


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dr. masciotra speed of sound role in us studies

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