The machines typically range in length from 5 to 8 feet. The patient is positioned with most or all of his body within the length of the device.
MRI machines come in two varieties, closed and open, both of which use essentially the same technology. In a closed contraption, the patient lies inside a tube that is centrally located within the device.
Generally, the tube of a closed MRI is about 2 feet wide. Open machines tend to be less powerful than their closed counterparts, but they are the preferred option for patients who have difficulty with tight quarters or suffer from full claustrophobia.
As the name implies, open designs do not enclose the patient fully. Some models allow the patient to undergo a scan while sitting or standing.
Inside the structure of an MRI device are powerful magnetic coils that create an intense magnetic field where the patient is situated. This magnetic field causes the protons of some atoms in the patient's body---notably hydrogen atoms---to line up along the magnetic field.
Hydrogen atoms are ideal for medical imaging because the human body is predominately made up of water, which is composed of two hydrogen atoms and one oxygen atom. The contraption then sends a series of bursts of radio frequency (RF) that causes only the hydrogen atoms to become excited.
These excited hydrogen atoms move out of alignment with the magnetic field the machine has produced. As the hydrogen atoms then attempt to return to alignment with the magnetic field, they shed the excess energy they picked up from the RF.
The device detects and records that energy. In some cases, the patient may swallow or receive an injection of a contrast agent (typically gadolidium) before undergoing a scan.
A contrast agent helps to create an MRI image with better resolution by making portions of the body where the contrast agent collects appear brighter in the image. On popular medical shows you will sometimes see images displayed on a computer screen.
These types of images are not produced directly from the information a machine records. What the device is actually detecting is the energy being shed as a function of time.
The images on the computer screen are a translation of those readings from a function of time to a function of frequency. In simplest terms, the machine is taking a lot of mathematical data about what the atoms are doing and processing that data through a complicated set of mathematical processes called a Fourier transformation.
The Fourier transformation creates information that the system can read or display on a computer screen as a visual representation of the entire body or part of the body. An MRI contraption uses a powerful magnetic field to align the nuclear magnetization of protons in water in the body.
Your body is mostly comprised of water molecules which contain two hydrogen nuclei or protons. The machine makes the protons align with the direction of the field.
MRI machines emit radio wave energy which causes the hydrogen nuclei to make a rotating magnetic field. The machines pick up on this field and make pictures of structures and organs inside the body.
During the scan, a second radio frequency (RF) electromagnetic field is turned on to cause the protons in your body to absorb some of its energy. When the RF is turned off, the protons release energy which is detected in an MRI.
Additional magnetic fields are added during the scan to locate other protons, so the image can be built up. The technician does this by turning gradients coils on and off.
This creates the knocking sounds you hear during an MRI. The MRI machine picks up the location of diseased tissue, such as tumors, because the protons vary from other tissues.
When the technician changes the parameters on the scanner, there is contrast between different types of tissue. To enhance the appearance of tumors, blood vessels, inflammation or other abnormalities, contrast agents can be injected into the patient's body through an IV.
Author Resource:-
Tom Selwick has worked and researched in the engineering industry for the last 14 years. He has written many articles on his findings, especially on the topic of theborescope.
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