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DRAMIŃSKI ANIMALprofi is a portable ultrasound scanner for detecting pregnancy in small and large animals.
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Question: Sonography and Statistics Accuracy

Answer: Ultrasonography accuracy is relative. Most sonograms result “normal” in spite of pathology. You can prove a condition exists but, you cannot prove it does not exist. It is very difficult to get accurate statistics if you cannot do any biopsy or autopsy to verify your results. There are not ultimate proves either.

The current technology would let us surpass operator dependence up to some important level but most manufacturers prefer to stick to known and proven technology rather than creating new things. The first is more profitable while the second involves expensive risks.

IMHO, the only way we can honestly protect our patients is by doing our best at all times while being conscious of the technology limitations and ours as well.

Question: I am interested in finding out more information about the pros and cons of using US to diagnose solitary thyroid nodules, what other diagnostic modalities are available and why US may or may not be the modality of choice. Please forward to me your opinion or any other information you might have available.

Answer: Here are the pros of using ultrasonography to diagnose solitary thyroid nodules:

1. It is safe (there is no risk at all) and you can scan the patients repeatedly and have proper follow-ups
2. US can tell the difference between cysts and solid masses
3. US can easily tell how close the masses are form important vessels
4. US can detect changes consistent with malignancy
5. US can easily measure dimensions and volume
6. US is less expensive

Disadvantages: US cannot tell when a mass is hypo or hyperactive
Other diagnostic modalities you can use beside lab tests, cytology and biopsy are CT, Thermography, MRI and Gammagram.

Next 7 questions came from Fiona Soon Chin Fhong; Msc.in Medical Electronics University Technology of Malaysia.

Question: As a medical electronic student, i would like to seek for your stand point of view regarding the phenomenon called speckle noise. Does it has an effect during a scanning especially in early detection of pathologies? And, what do you think of the speckle effect during a scanning of obese person? Does the ultrasound machine offers a solution on that or can the sensitivity and contrast control reduce the problem?

Answer: Speckle noise is an undesirable artifact that masks pathology. It could be reduced using a phase insensitive technique, or a way to cancel the undesirable linear-phase representation. You could use a system sampling more images (more channels and memory needed). You could also consider adding a fuzzy logic algorithm. Be aware that if you do that, you are changing the image to meet your needs. That is the way ultrasound post-processing and pre-processing work though (changing the image to meet your needs).

The hardware requirements are difficult to meet now but if you use fuzzy logic algorithms, you could get outstanding results.

Speckle phenomena are common when scanning fat patients. Many scanners offer ways to somehow overcome this effect in a limited approach. One of my scanners - a digital one- uses special algorithms to cancel the speckle effect, but results are limited. Of course, digital imaging is a lot better. Gain and contrast controls offer poor improvement and pre and post-processing are better solutions (IMHO). The best practical solution now is scanning from different positions and angles and/or creating artificial acoustic windows.

Question: Through my recent reading in a paper by Dr. Aly A Farag ( IEEE Transaction in Medical imaging) , I was informed that the accuracy of using ultrasound diagnosis is about 78%. What about the other 28%? Do you agree with this statement?

Answer: I have not heard about it. It depends of the factors included in the survey. Sonography is a highly operator dependable procedure and results can vary much. If the statistics you mention consider different scanners, transducers, different operators, like sonologists, radiologists, sonographers, general physicians, care of the persons involved in the procedure (Private practice and research sonograms are more accurate), etc., the 78% would be accurate. No system is perfect.

In my personal experience, I have found ultrasonography being more accurate than CT and X-rays when dealing with abdominal and muscle pathology. Also found breast sonograms being a lot better than X-ray mammography and diagnostic laparoscopy. But I repeat: This is my experience. I have also seen absolutely wrong and useless sonograms. It is very relative.

Question: Why are there exist minor cases of radiologist misdiagnosed or made inaccurate interpretation?

Answer: Minor - and mayor- cases of radiologists’ misdiagnosis and inaccurate interpretations depend mainly on:

1- Insufficient knowledge.

2- Insufficient scanning time. Many services must scan a high number of patients a day to be profitable. I know of sites which pay for a pelvic sonogram less than USA $8.50. In the USA the same sonogram costs about USA $265.

3- Bad technique

4- Old and unreliable machines

Question: What are the difficulties found with the images by radiologist during an interpretation?

Answer: The most you talk with your patients, the better diagnosis you do. You could even get the diagnosis just by talking with the patient and practicing a limited physical examination. That is what I usually try to do, confirming my clinical diagnosis with my scanner but …

Moved by technology, I set up a telesonography service over the Internet: I receive sonogram pictures images, some data relating patient symptoms and give back my diagnosis. I also set up a secondary and inexpensive ultrasound service, helped by a sonographer. I must be honest though: Both services are relatively cheap for the users because I cannot get as good results as doing the sonograms by my self. I will keep trying to get best and more economical results though, but also will keep my private practice scanning my patients.

Question: Is there something wrong with the machine resolving power or due to other reasons? I’m very curious about that.

Answer: Most of the time scanners work perfectly. Let me tell you something I saw years ago:

I was attending an ultrasound meeting. Manufactures came from many countries with their best machines. Important professors came from all over the world. They set up a live demonstration and presented a pregnant woman to be scanned in front of the audience. She told she was in her 18th week. A famous professor scanned the woman using a well known French machine. He -and us- saw nothing. Several slave monitors showed no pregnancy at all. The professor, using the microphone told: “This machine is not working well. It is useless. Please, could any one give a good machine?”. A big “OOOOOOOOOOH” was heard coming from the astonished audience. The professor immediately got another equipment. Neither worked. He got another equipment, and other, and other, etc. None worked for the professor.

I realized the woman’s bladder was overfilled and displacing the pregnant uterus upwards out of the pelvis. I left my seat and went behind the scenes, and told them what was happening. Incidentally, the woman was the wife of a friend of mine and I could verify that she really was in her 18 week.. The professors also verified it …. behind the scenes . . .

Note a single word was told to the audience.

Question: During my last visit to Batu Pahat General Hospital in Malaysia, I was told by the radiologist that what is to be solved is to resolve the parenchymal changes on tissue and if possible find a solution in early detection of Hepatitis B. Do you agree with him?

Answer: You can resolve parenchymal changes that could be consistent with hepatitis, but you cannot assure it is hepatitis…. yet

Question: Last question, how much does a radiologist depend on the clinical test report during the scanning?

Answer: A lot. Non only on the scan report, but on the questions and answers the radiologist and patients exchange and on the limited physical examination the radiologist should perform before scanning

Question: How accurate are obstetric sonograms?

Answer: It depends mainly on these factors:

1. Gestational age: Individual differences increase as pregnancy progresses so, measurements taken early in pregnancy are most accurate
2. Used measurement: CRL measurement is more accurate than gestational sac volume, gestational sac volume is more accurate than measure just one GS diameter, etc.
3. Operator skill and experience: To get precise measurements, you must place the calipers according to proper anatomic landmarks
4. Scanning time: Faster examinations are less accurate that dedicated examinations
5. Hardware: Intracavitary probes provide higher frequency, so their resolution is better. Digital machines also do it better than analog machines
6. Software: Its precision depends of statistics accuracy and on the software algorithm. Dedicated external software is more accurate that the software the ultrasound scanners provide

Next statistics come from my own experience, when doing my own sonograms, considering that I have 19+ year sonography experience, dedicate necessary time for each examination (just private practice), use a very good digital machine with probes from 2.5 MHZ up to 8.5 MHz , and dedicated and updated software developed by myself, out of statistics obtained with appropriate feedback. Although they are very accurate, keep in mind that the decimal factor result from calculations and they does not mean accuracy. For example, 4.1 days, does not mean that accuracy goes as high as 0.1 day (2 hours. 24 minutes). They are displayed because they are used for calculations precision.

Dr. Karl Dussik, a psychiatrist, at the hospital in Bad Ischl, Austria was the first person publishing a medical use of diagnostic ultrasound.

He was trying to locate brain tumors with a new method consisting of an ultrasound emitter at one end and an ultrasound receiver at the other. The patient stayed between the two devices. He measured the ultrasound beam transmission through the patient’s head. The outbound ultrasound beam power was known and he calculated the receiving power, defining ultrasound attenuation and reinforcement. He also tried to visualize the cerebral ventricles by measuring the ultrasound beam modification through the head. Dr. Dussik published his technique in 1942 with the name of “Hyperphonography of the Brain.”

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Aliasing is an artifact that lowers the frequency components when the PRF is less than 2 times the highest frequency of a Doppler signal
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Beat frequency, for CW Doppler, is the Doppler shift
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Doppler shift is the change in the perceived frequency relative to the transmitted frequency. Doppler shift frequency: fD = fr - f0 = 2f0v/c
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Doppler shift frequency with incident angle: fD = 2f0v/c cos q
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Ensemble length -packet size, shots per line- is the number of pulses per scan line. In color Doppler, each line of sight most be pulsed several times
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FFT. Fast Fourier Transform analyzer is a common device that performs spectral analysis in ultrasound instruments. In this case, it displays different quadrature Doppler frequencies, or reflector velocities when a sample volume cursor is used (Doppler frequency is proportional to reflector velocity) along time
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High pass filter is the wall filter
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Nyquist Frequency is the maximum frequency that can be sampled without aliasing. NF = PRF/2 (PRF stands for Pulse Repetition Frequency)
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Quadrature detection is a signal processing method for directional Doppler in which the signal reference frequency for two channels differ in phase by 1/4 period. The output Doppler signal phase for both channels also depends on the Doppler shift, whether positive or negative
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Spectral analysis is the quantitative analysis to display the distribution of frequencies
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Variance is the variation of Doppler frequencies within each pixel during a pulse packet, efective to detect turbulence with color Doppler

This section provides some useful definitions or information in regard to important terms not easily found on the Internet:

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Absorption is the transfer of energy from the ultrasound beam to the tissue. It is proportional to frequency
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Apodization is a method for reducing side lobes in some arrays. It gradually decreases the vibration of the transducer surface with distance from its center. It is usually accomplished by using more power to excite the innermost elements.
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Axial resolution is the minimum separation between two interfaces located in a direction parallel to the beam so that they can be imaged as two different interfaces
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Decibel is a way to express the ratio of two sound intensities: dB=10log10I1/I2 being I1 the reference. For instance: +3 dB = I multiplied by 2 and -3 db = I divided by 2
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Diffraction is the change in the directions and intensities of a group of waves after passing by an obstacle or through an aperture
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Duty factor is the lapse of time the transducer is actively transmitting sound
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Echo ranging is the relationship between transit time and reflector depth expressed as t = 2d/c
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Grating lobes as side lobes are secondary ultrasound beams projecting off-axis at predictable angles to the main beam. Side lobes are too small to produce important artifacts.
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Half Value Layer (HVL) is the distance the sound beam penetrates into a tissue when its intensity has been reduced to one half of its initial value
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Huygens’ principle states that an expanding sphere of waves behaves as if each point on the wave front were a new source of radiation of the same frequency and phase
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Impedance is the product of the density of a material and the speed of sound in that material
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Pulse average intensity I(PA) is the average intensity during the pulse
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Lateral resolution is the minimum separation of two interfaces aligned along a direction perpendicular to the ultrasound beam. It depends on the beam width
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Partial Volume Artifact (slice thickness or volume averaging artifact), that occurs when the slice thickness is wider than the scanned structure
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Q-value means the degree that a transducer is finely tuned to specific narrow frequency range. For instance: Low Q means wide bandwitdh and High Q means narrow bandwidth
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Range resolution is the ability to determine the depth of reflectors
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Rayleigh scatterers are objects whose dimensions are much less than the ultrasound wavelength. Scattering increases with frequency raised to the 4th power and provides much of the diagnostic information from ultrasound
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Refraction is the bending of a wave beam when it crosses at an oblique angle the interface of two materials, through which the waves propagate at different velocities
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Snell’s law governs the direction of the transmitted beam when refraction occurs:
sin qt = (c2/c1) x sin qi (qt and qi are transmit and incident angles respectively)
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Spatial Average Intensity (SA) is the acoustic power within the beam, divided by the beam area
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Spatial Peak Intensity (SP) is the point in the sound field with maximum intensity
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Side lobes are energy in the sound beam falling outside the main beam
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Spatial resolution means how closely two reflectors -or scattering regions, can be to one another while they can be identified as different reflectors
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Subdicing is a technique used to overcome grating lobes: each major transducer element is devided into smaller parts, each one being a half wave lenght
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Temporal (instantaneous) Peak Intensity I(TP) or I(IP) is the maximum intensity during the pulse
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Time Average Intensity I(TA): average intensity calculated over the time between pulses:
ITA= I(PA) x Duty factor
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Wavelength is l=c/f (c = propagation speed; f = frequency)

First, it is important to understand the definition of sound. Let’s see two definitions of sound:

1. Simple definition: Sound is the perception of vibrations stimulating the ear
2. Scientific definition of sound: sound is a periodic disturbance in fluids density, or in the elastic strain of a solid, generated by a vibrating object. These waves (vibrations) propagate in two basic ways: longitudinal waves and transverse waves.