Ultrasound
Ultrasound is an imaging technique using ultrasound. It is used routinely in medicine but can be used in research, exploration veterinary industry.
Terminology
The word "ultrasound" comes from two Greek roots: echo (echo) and graphy (writing). It is therefore defined as "written by the echo."
The term "ultrasound" refers to both the medical procedure that the image that results. It is abbreviated so common in "echo" (female, "she had a response).
The ultrasound apparatus is an "ultrasound".
The doctor who performed an ultrasound is a sonographer.
The devices all include a Doppler. That is why we speak of "echography-doppler" (abbreviated as "echo-doppler or echo-dop").
Equipment
The ultrasound system consists of:
* A probe, allowing the transmission and reception of ultrasound;
* A computer system, transforming the time between receipt and issuing of the ultrasound image;
* A command console, allowing the introduction of patient data and settings;
* A system of display: display;
* A system for recording data, either in an analog (video, print) or digitally (DICOM format);
The whole is mounted on a mobile cart, to carry out the bed of the patient.
The needs are different depending on the organ studied. The most challenging is the heart, mobile by nature, which requires a good definition of the image space but also time.
The probe
The first studies on ultrasound were not applied to medicine, but designed to detect submarines at the First World War. In 1951, two British, JJ Wild (doctor) and J. Reid (electronics), presented to the medical community a new device: the ultrasound. It was designed to search for brain tumors but will career in obstetrics. The use of obstetric early 1970 with equipment designed to capture the sounds of the fetal heart (see Doppler effect).
The basic ultrasound is a piezoelectric ceramic (PZT), located in the probe, which, subjected to electric pulses, generating ultrasonic vibrates. The echoes are picked up by the same ceramic, which then acts as a receiver: one speaks of ultrasonic transducer. An ultrasound is equipped with an ultrasound probe, ultrasound appointed bar, provided the source of 64, 96 or 128 ultrasonic transducers online. Of ultrasound probes now have modern up to 960 elements. Echocardiography in the number of elements is brought to 3 000 elements. Finally, the probes of future generations (in 2009) will be over 12 000 piezoelectric elements is 64 times more than that still used to date. The program is carried out successively on each transducer.
Ultrasound are sent within a delimited (often trapezoidal), and the echoes are recorded signatures of obstacles they have encountered. The echogenicity is greater or lesser ability of a fabric rear diffuser ultrasound.
The frequency ultrasound can be modulated: increasing frequency provides a more accurate signal (and therefore a more fine), but ultrasound is then depreciated rapidly in the body and considered no longer possible to examine the deep structures . In practice the sonographer has in place several probes with different frequencies:
* 1.5 to 4.5 MHz used for the deep (abdomen and pelvis), with a definition of a few millimeters;
* 5 MHz for the intermediate structures (heart of a child for example) with a resolution below the millimeter;
* 7 MHz for the exploration of small structures close to the skin (arteries or veins) with a resolution close to the tenth of a millimeter;
* 10 Mhz to 18 Mhz more example for the study, research, small animal, but also in the medical field for imaging superficial (close to the structures of the skin).
This resolution also depends on the structure considered: it is much better if it is perpendicular to the ultrasonic beam as if it is parallel to the latter.
The receive frequency also influences the image quality: the fundamental mode transducer detects signals in the same frequency as that of the show. Harmonic mode, it detects signals from a dual frequency (second harmonic) than the broadcast. The advantage of this system is that it essentially detects the echoes back to the same effect as the issuance, excluding de facto the echoes and making available much less noisy signal. Nonlinear detection has a particular response, it does not react to the first few centimeters after the probe, thereby facilitating imaging in overweight patients (including the layer of fat under the skin makes the passage of ultrasound).
Signal processing
The electronics of the ultrasound will amplify and process these signals to convert them into a video signal. The image is grayscale depending on the intensity of the echo back.
How are the different tissues of the body?
* The simple liquids, where there are no particles in suspension, are content to let through the sounds. They are therefore not reported by echoes. They will be black on the screen (hypoechogenes Structures)
* Liquids with particles, blood, mucus, small return echoes. They will appear in shades of gray, more or less homogeneous.
* The solid structures, eg bone, better return echoes. So we'll see a form with a white shadow behind. An exception, however, the skull, very fine and perpendicular to the echoes, in passes.
* The soft tissues are more or less echogenic: the placenta is whiter than the uterus, which is whiter than the ovaries.
* The gas and air, as the bones are very white.
Different settings
* The output power is adjustable, but does little in the quality of the image. It should theoretically use the minimum acceptable to avoid heating of the tissues examined. In practice this risk is negligible.
* The frequency can be modified within the specifications of the probe.
* The gain at the reception can be increased or decreased overall or in different ways, depending on the depth of the explored area (GCT for time gain compensation).
* Different filters can be set: compression ...
* The imaging can be changed in a fundamental mode of a second harmonic mode (abstract harmonic mode) to have a better definition.
* The ultrasonic beam can be focused (lens acoustic emission delay set electronically) to a greater or lesser depth (did very little about the quality of the image).
* The area of interest to explore the body may extend, or to shrink. In the latter case, the image has a better definition.
* The acquisition rate (frame rate in English) can be resolved. This parameter is very important in the case of fixed bodies but must be substantially increased to study the mobility of a structure (heart).
The command console is equipped with a keyboard for entering patient identifiers and comments. It provides access to various modes of ultrasound and Doppler, as well as processing and storing images. It can also make measurements (distance, surface ...) and various calculations.
Viewing images
It is done through a screen.
Different modes are available:
* The most common method is the BD (for two-dimensional) is a cross section of the organ studied, the plan of which is determined by the position given by the examiner to the probe.
* The mode Tm (time for motion in English) represents the evolution of a line of fire (ordered) according to time (abscissa). This mode allows you to accurately assess mobile structures (left ventricle to the heart, for example) and assess its size. The latter, however, depends heavily on the choice of the firing line and is therefore very examiner-dependent.
These grayscale images, can be associated data in color doppler.
Storage and distribution of images
Theoretically, the data to store the film to match the duration of the examination (a few minutes to half an hour), which still poses problems about the importance of memory needed. In practice, shall be kept as still images or short loops of images. The format is often the owner (with DICOM conversion tool) or in native DICOM. This format, widely used in medical imaging, to keep in a document identifying the patient, the image and characteristics of the acquisition of the latter.
So simple, the selected image is printed and attached to the report. It did in this case is for illustrative purpose, the quality of reproduction does not allow to re-evaluate, for example, a diagnosis.
The image can be stored in analog video, resulting in a deterioration of the definition, but to retain sufficient information to derive a posteriori information.
How recently the existence of DVD recorder in real time (simultaneously) the realization of the review can scan several hours of examinations.
The processing of the image
* By interpolation of a loop of images taken with a rapid acquisition rate, we can simulate a Tm curve.
* Recognition automated contour remains the cornerstone of the U.S. in 2005.
* Parametric imaging is to encode each pixel following parameters calculated on the image (changing in time, phase shift ...). This is a topic still under research.
* The three-dimensional imaging, the beginning of this millennium, was made by interpolation and superposition of several successive images, made using different cutaways (either freely or with a rotating probe). The process is relatively easy for fixed bodies but much more complex for moving (superposition of loops of images rather than single images). Currently, some ultrasound probes are equipped with sensors transmitters, rather than online, but arranged in a rectangular matrix, allowing a direct three-dimensional acquisition. The technical information and make that the standard image is significantly less well defined, both spatial and temporal, and the volume of the body directly viewable remains small in size.
The different types of devices
* The equipment standards, although arranged on wheeled carts, are not intended to be used in fixed. They can be connected to a network, an external printer. Their cost ranges between 50 000 and over 150 000 €.
* Some smaller devices are designed to be used at bedside. The flat screen is of lower quality and they do not always have all the features. They operate on the sector. Their price is less than 100 000 €.
* Ultrasound on the size and weight of a laptop have been developed. The imagery is of much lower quality and only the basic functions are available. They have the great advantage of being autonomous in their diet. The interest is mainly that of a "free preview" in the field to select patients who require further examination. Their cost ranges between 10 000 and 15 000 €.
Advantages and disadvantages of ultrasound
* Advantages:
o The use of ultrasound is virtually no danger: it is the only technique to have an image of the fetus with a good safety. There is no allergy or against-indication for this examination.
o It is painless for the patient. It does not require, with certain exceptions, no hospitalization or anesthesia. It can be repeated without problems.
o Ultrasound is a medical imaging technique relatively inexpensive: it requires only a camera and the price of consumables can be negligible. The examination is done with one person (doctor or manipulative in some countries like the United States).
o The ultrasound system is mobile, capable of reaching the same consideration to bed of a patient in an intensive care unit for example.
o If done by a doctor, the result is immediate.
o This is one of the few imaging techniques in real time, with which we can always complete the examination and clinical examination of the patient being examined. It allows highly accurate diagnostic expert hands and can use several means to identify an anomaly: 2D, 3D planar reconstructions, contrast echocardiography, pulsed Doppler or color, elastography, dynamic maneuvers.
o When the echogenicity and the distance to allow the organ, ultrasound has in some cases a higher spatial resolution scanner and MRI
* Cons:
o The image sometimes lacks sharpness, sometimes up to be unworkable: the problem of echogeneicite, low especially in cases of obesity.
o The review, and therefore its results, remains "examiner-dependent." Measurements and image quality depend very much on the position of the probe (cutting plane), and therefore the ability and skill of the examiner. The manual positioning of the probe varies from one examination to another and is not known a priori, which makes complex any reinterpretation of the examination and registration with another modality of medical imaging. In other words, in case of doubt or discussion, consideration must be repeated in full, ideally by another examiner.
o The main noise which disturbs the ultrasound images is the "speckle" or granularity (because the picture gives the impression of being composed of grains). This noise is due to the fact that ultrasound imaging is a coherent imaging technique, which allows interference between waves and therefore this aspect of the grainy image.
Read also Pregnancy
wikipedia
