high frequency = high spatial resolution but limited depth of penetration

low frequency = greater depth of penetration but lower spatial resolution

is it correct?

The spatial resolution of ultrasound is actually quite good.  The limitation is that the field-of-view is usually smaller than other imaging techniques.  Ultrasound is also constrained by not being able to image through bone or gasses.

higher frequency = higher spatial resolution but less depth of penetration

lower frequency = greater depth of penetration but lower spatial resolution

Generally speaking these sentences are correct,

Resolution in ultrasound imaging defined in two orthogonal directions, in the direction of wave propagation (axial resolution) and in the direction perpendicular to this direction (lateral resolution){I am considering 2D imaging}

Axial resolution depends on frequency, pulse duration, sampling frequency.

Lateral resolution depends on frequency, transducer geometry and size, the used technique for beam_forming, line number of every frame.

The width of the beam determines the lateral resolution. The length of the pulse determines the axial resolution. Also, the successive partial reflexions on tissue layers should be considered. Another efects is 'the side lobes". The probe cannot produce a pulse that travels purely in one direction. Pulses also travel off at specific angles. 

Why does an ultrasound image has Low Contrast?

It's accounted for by minor differences in acoustic characteristics of organs. For e.g intra-abdominal organs like the pancreas, liver, spleen, and kidney, all listed in increasing hypoechogenicity, you rely on capsular outlines and peritoneal reflections which are hyperechoic for tissue differentiation. But a trained and experienced sonographer or sonologist need not have such problems. Also, consider the type of equipment you use.

Sound waves are not as good as electomagnetic waves.

In general the resolution of a image produced with irradiation is a function of the wave length (Bragg's equation).  

Lautebur employed magnetic field gradients over the sample to get spatial resolution much higher than wavelength (and received his Nobel for that realization).  So it isn't that electromagnetic waves are better it is that there is a perturbation available to allow applications like MRI.

Photo-acoustic imaging makes use of a perturbation added to Ultrasound to gain resolution (or sensitivity) depending on the implementation. 

Ultrasound has poor contrast (nonspecific) in soft tissue because the speed of sound varies by less than 10%.  So, it is difficult to separate fat and water-based tissue.  However, US spatial resolution is typically better than MRI and CT.

The resolution of ultrasound is actually quite good compared to CT and MRI.  The slice thickness is a function of the quality of the probe but can be a mm or two.  The resolution changes over the field of view do to focusing.  The highest resolution is at the location of the best focusing.

Axial resolution is good but too many artifacts in ultrasound makes the quality of ultrasound image lower

hello

1. very important is the frequency range of the US probe/system

that means with multifrequency probes you get good image quality in the near and far field

2. new matrix probes will improve US image

hope this helps

ferdinand

High frequencies give us short wavelength, good axial (range) resolution with decreased Spatial Pulse Length (SPL=cn/f; c=USG propagation speed, f= frequency, n= number of cycles in a pulse), longer near field (Fresnel zone; NZL = A2f/4c; A = transducer size, f = frequency (MHz), c = propagation speed of ultrasound (m/s) and less divergence in a far field. High frequencies also make better beam shape which improves lateral resolution as well. High frequencies lead to decreased depth of penetration as they attenuate and absorb faster than lower frequencies.

Penetration of lower frequencies is better but they give us worse spatial resolution of the image (shorter NZL, more divergence in a far field).

due to speckle noise its  resolution decreases.

Using the relation  ∂=0.5 (pulse cycle  x  wavelength). This relation is inversely proportional to resolution, hence the choice of wavelength (frequency) and contact time of probe to skin greatly affect resolution.

hi david

is correct

however new probe technologies overcome this problem 

double beam forming

matrix arrays

overall the resolution of us has increased significantly

we are testing probes with a frequency up to 50 mhz

will be a revolution

regards

ferdinand

thickness of the tissue sectioned will matter to the resolution i.e if tissue is very thick resolution will be affected negatively

As per I studied, it depends on the Frequency of sound wave given during the Ultrasound. If the frequency is lower it has greater wavelength and as a result it penetrates deep and cannot be absorbed or attenuated by the tissues. That is why the Resolution will be bad, because two adjacent tissues cannot be differentiate.

An ultrasound image has poor resolution because the speed of sound varies by less than 10% and the speckle noise but with the new technologies overcome this problem

regards

Spatial or detail resolution is the ability to distinguish between distinct image points (reflectors) lying close to each other. Lateral resolution describes the minimum separation of two reflectors aligned along a direction perpendicular to the ultrasound beam.

An ultrasound image has poor resolution because the speed of sound varies by less than 10% and the speckle noise but with the new technologies overcome this problem

Spatial or detail resolution is the ability to distinguish between distinct image points (reflectors) lying close to each other. Lateral resolution describes the minimum separation of two reflectors aligned along a direction perpendicular to the ultrasound beam.

An ultrasound image has poor resolution because the speed of sound varies by less than 10% and the speckle noise but with the new technologies overcome this problem

For more details, we have:

https://www.utmb.edu/pedi_ed/ADAPT/LOs/Regional%20Anesthesia%20Rotation-%20original/page_10.htm

Article Resolution in ultrasound imaging