Purpose: Mammography is used to diagnose breast diseases in women breast, usually breast cancer. This test can’t determine if the tumor is benign or malignant, so if a tumor found usually more tests are recommended, like biopsy.
Description of instrument: there is an x-ray tube in a rectangular box, this x-ray devise used only for mammography. There is shielding to protect the body from the radiation. There is a device that holds and compress the breast, so the thickness of the breast will be equal in all is area (as much as possible).
Film- digital or conventional is exposed to the x-ray that passed through the breast and give as the image.
The scientific principle: the same as all the x-ray diagnostic tests, photon that pass through matter, like breast, are attenuated, the more the Z number of the matter they pass is bigger the less number of photon will pass. The Z number of tumor is greater then the Z of the normal fat that is in the breast, so if there is a tumor we will see in the film a white spot.
Operation: the test is done by a radiologist technologist; the breast is placed on a special platform witch stable and compresses the breast.
While the patient gets the exposure the technologist will be behind a glass. And he will ask the patient to move between each image, this done for each breast separately.
The test is taking 15 minutes.
The dose the patient gets is very low 0.3 mSv.
Safety features: the test is considered to be very safe because it used a very low x-ray beam, and a very low dose. But like every exposure to radiation cell are damaged. If the woman is pregnant she must notify the doctor.
Most expert thinking that the risk is very low in comparison to the benefit.
The x-rays are monitored to assure that the smallest amount of radiation is given.
References:
1. http://www.radiologyinfo.org/content/mammogram.htm#top
2. http://www.nlm.nih.gov/medlineplus/ency/article/003337.htm
Tuesday, June 17, 2008
SPECT Scan | Summary
Purpose:
SPECT (Single photon emission computed tomography) is a noninvasive diagnostic technique for many heart problems or diseases. By this test we can determine if the patient have a high risk for heart attack.
In contrast to CT or MRI witch gives us only anatomical image, SPECT in addition gives to the doctor the function of the organ.
It is used also to determine rate and volume of blood flow, size and location of blockage or narrowing coronary blood vessels.
SPECT is very good for heart disease in women, because the other tests are not accurate enough (particularly in women who have big breast). It is also used to finding tumors in beast and other organs like the brain.
Description of instrument:
Gamma cameras- there are two types rotating, few detectors that rotating around the patient, or circular, that do not rotate but it has lot of detectors in all the angles.
Each detector is connected to photomultiplier tubes that convert every photon to light that converted to electrical signal. The signal process in a computer know from witch angle this photon came, the computer get many signals so it can calculate the location of the tracer in that two dimensional slice. Then the table is moved to get another slice, so the computer from all the slices can get a there dimensional image.
Radiopharmaceuticals or tracers- they are proteins or organic molecules that attached to a radionuclide mostly thalium-201 or technetium-99m. Usually the radionuclide has a short half live, so it must be deliver routinely.
Chemical stress test- the test is done first when the heart is relax, and secondly after exercise, some people can not do it safely, like people who have pacemaker, so they get drugs that make the heart react as it was exercising. The names are persantine, dobutamine, adenosine.
Scientific principle:
Radioactivity- the radionuclide is decaying and emitting a photon.
Tracer- the radio tracer is bonded to a molecules or proteins that used mostly by the organ that we want to check, like the heart muscles. And staying there emitting the photons.
Places that have high level of tracer the picture will be bright(hot spot) and vise versa to the dark spots. By this the doctor can tell if it is normal or not.
Operation:
You should not eat or drink 12 hours before the exam.
The tracer is injected to the blood.
Waiting few minutes until it gets to the organ we check (brain, heart).
The patient lies in the bed and the gamma camera start to absorb the photon and after awhile we get the image of the organ.
Usually the will be to tests one in rest and another one after running in a treadmill for few minutes.
The test will take 15-30 minutes.
After the exam the patient can go back to normal activity.
The dose amount is a few mCi.
Safety features:
The tracer is going out from the body after 48 hours.
The dose amount is very low.
Pregnant or breast-feeding women must council their doctor before the test.
Breast-feeding women should not feed her baby for 36 hours after the examination.
The patient has to drink a lot after the exam so the radionuclide will go by the urine outside the body.
Web sites
http://www.asnc.org/patientinfo/information.cfm
http://www.heartcenteronline.com/
http://www.howstuffworks.com/
http://www.brighamandwomens.org/nuclearmedicine/patient/myocardial.asp
SPECT (Single photon emission computed tomography) is a noninvasive diagnostic technique for many heart problems or diseases. By this test we can determine if the patient have a high risk for heart attack.
In contrast to CT or MRI witch gives us only anatomical image, SPECT in addition gives to the doctor the function of the organ.
It is used also to determine rate and volume of blood flow, size and location of blockage or narrowing coronary blood vessels.
SPECT is very good for heart disease in women, because the other tests are not accurate enough (particularly in women who have big breast). It is also used to finding tumors in beast and other organs like the brain.
Description of instrument:
Gamma cameras- there are two types rotating, few detectors that rotating around the patient, or circular, that do not rotate but it has lot of detectors in all the angles.
Each detector is connected to photomultiplier tubes that convert every photon to light that converted to electrical signal. The signal process in a computer know from witch angle this photon came, the computer get many signals so it can calculate the location of the tracer in that two dimensional slice. Then the table is moved to get another slice, so the computer from all the slices can get a there dimensional image.
Radiopharmaceuticals or tracers- they are proteins or organic molecules that attached to a radionuclide mostly thalium-201 or technetium-99m. Usually the radionuclide has a short half live, so it must be deliver routinely.
Chemical stress test- the test is done first when the heart is relax, and secondly after exercise, some people can not do it safely, like people who have pacemaker, so they get drugs that make the heart react as it was exercising. The names are persantine, dobutamine, adenosine.
Scientific principle:
Radioactivity- the radionuclide is decaying and emitting a photon.
Tracer- the radio tracer is bonded to a molecules or proteins that used mostly by the organ that we want to check, like the heart muscles. And staying there emitting the photons.
Places that have high level of tracer the picture will be bright(hot spot) and vise versa to the dark spots. By this the doctor can tell if it is normal or not.
Operation:
You should not eat or drink 12 hours before the exam.
The tracer is injected to the blood.
Waiting few minutes until it gets to the organ we check (brain, heart).
The patient lies in the bed and the gamma camera start to absorb the photon and after awhile we get the image of the organ.
Usually the will be to tests one in rest and another one after running in a treadmill for few minutes.
The test will take 15-30 minutes.
After the exam the patient can go back to normal activity.
The dose amount is a few mCi.
Safety features:
The tracer is going out from the body after 48 hours.
The dose amount is very low.
Pregnant or breast-feeding women must council their doctor before the test.
Breast-feeding women should not feed her baby for 36 hours after the examination.
The patient has to drink a lot after the exam so the radionuclide will go by the urine outside the body.
Web sites
http://www.asnc.org/patientinfo/information.cfm
http://www.heartcenteronline.com/
http://www.howstuffworks.com/
http://www.brighamandwomens.org/nuclearmedicine/patient/myocardial.asp
PET Scan | Summary
PET (Positron Emission Tomography) scan is used to detect cancer and cardiovascular or neurological abnormalities.
Show whether a tumor is benign or malignant.
Help doctors determine the stage of disease.
See if the cancer is metastasizing.
Help doctors evaluate the effectiveness of chemotherapy.
Help do differentiate Alzheimer’s from other forms of dementia such as Pick’s disease.
Test blood flow and cardiovascular disease.
Description of instrument:
Tracer: a radioisotope with short half live is connected with glucose; there is a list of some of them:
Labeling agent
Half-life
carbon-11
20.3 minutes
oxygen-15
2.03 minutes
fluorine-18
109.8 minutes
bromine-75
98.0 minutes
Gantry: compose of several rings of radiation detectors. When a photon get inside the detector a pulse of light is emitted, it gets to the photocathode and amplified by the photomultiplier and from there to the computer.
The computer: reconstructs the exact places where each pulse of radiation came from. It also counts the number of pulses per second coming from each point of the image.
Reconstruction of the image: The number of radiation pulses counted by the computer during a fixed interval of time is displayed in the screen as a dot, with its intensity shown in shades of gray. Black means no activity, and pure white the highest count level. The same image can be displayed in false color, which is able to show in a better contrast the "hot" regions. The false color scale converts each level of gray into a shade of color, like in a rainbow.
The computer shows an image which is like a cross section.
Taking several adjacent slices at a time, a special computer program can be used to make a three-dimensional reconstruction of the brain.
Scientific principle:
A positron emitter is connected to glucose and injected to the body after few minutes of circulation in the blood it gets into the organ that is examined, if there is cancer there, it will be lots of metabolism in the area and lots of sugar will accumulate there, and more photons will be emitted from there.
When a positron meets an electron, the collision produces two gamma rays having the same energy, but going in opposite directions (1800). The gamma rays leave the patient’s body and are detected by the PET scanner.
Only photons that were detected by two detectors that are 1800 (±30) in location from each other and in the same time are computed.
Operation:
The patient will be injected with an appropriate dose of radiotracer. After few minutes the technologist will position you on a "bed" (also called a "couch") that is attached to the PET scanner. The scanner itself looks like a large box with a central, round opening. Gamma ray detectors are located all around the opening. The bed will slide into the opening, and the detectors will record the gamma rays being released from the body from your head to your feet depending on the type of the examination. The test is taken about 45 minutes, the patient must not move so the picture will not be ruined.
After the scan is complete, the patient is able to resume normal daily activities. There will be no restrictions on eating or drinking.
Safety features:
· Because the radioactivity is very short-lived, your radiation exposure is extremely low. The substance amount is so small that it does not affect the normal processes of the body.
· The test may not be appropriate for pregnant women or those who are breastfeeding.
· If you are breastfeeding, you should not nurse your baby for approximately 36 hours after the radiotracer injection, since radiation can be passed through the breast milk.
· The radiation injected during a nuclear medicine study is eliminated from you body through the kidneys. For that reason, the patient should drink plenty of fluids and urinate frequently after the examination.
http://www.brighamandwomens.org/nuclearmedicine/Patient/PETScan.asp
http://www.triumf.ca/welcome/petscan.html
http://www.radiologyinfo.org/content/petomography.htm
http://www.epub.org.br/cm/n01/pet/petworks.htm
Show whether a tumor is benign or malignant.
Help doctors determine the stage of disease.
See if the cancer is metastasizing.
Help doctors evaluate the effectiveness of chemotherapy.
Help do differentiate Alzheimer’s from other forms of dementia such as Pick’s disease.
Test blood flow and cardiovascular disease.
Description of instrument:
Tracer: a radioisotope with short half live is connected with glucose; there is a list of some of them:
Labeling agent
Half-life
carbon-11
20.3 minutes
oxygen-15
2.03 minutes
fluorine-18
109.8 minutes
bromine-75
98.0 minutes
Gantry: compose of several rings of radiation detectors. When a photon get inside the detector a pulse of light is emitted, it gets to the photocathode and amplified by the photomultiplier and from there to the computer.
The computer: reconstructs the exact places where each pulse of radiation came from. It also counts the number of pulses per second coming from each point of the image.
Reconstruction of the image: The number of radiation pulses counted by the computer during a fixed interval of time is displayed in the screen as a dot, with its intensity shown in shades of gray. Black means no activity, and pure white the highest count level. The same image can be displayed in false color, which is able to show in a better contrast the "hot" regions. The false color scale converts each level of gray into a shade of color, like in a rainbow.
The computer shows an image which is like a cross section.
Taking several adjacent slices at a time, a special computer program can be used to make a three-dimensional reconstruction of the brain.
Scientific principle:
A positron emitter is connected to glucose and injected to the body after few minutes of circulation in the blood it gets into the organ that is examined, if there is cancer there, it will be lots of metabolism in the area and lots of sugar will accumulate there, and more photons will be emitted from there.
When a positron meets an electron, the collision produces two gamma rays having the same energy, but going in opposite directions (1800). The gamma rays leave the patient’s body and are detected by the PET scanner.
Only photons that were detected by two detectors that are 1800 (±30) in location from each other and in the same time are computed.
Operation:
The patient will be injected with an appropriate dose of radiotracer. After few minutes the technologist will position you on a "bed" (also called a "couch") that is attached to the PET scanner. The scanner itself looks like a large box with a central, round opening. Gamma ray detectors are located all around the opening. The bed will slide into the opening, and the detectors will record the gamma rays being released from the body from your head to your feet depending on the type of the examination. The test is taken about 45 minutes, the patient must not move so the picture will not be ruined.
After the scan is complete, the patient is able to resume normal daily activities. There will be no restrictions on eating or drinking.
Safety features:
· Because the radioactivity is very short-lived, your radiation exposure is extremely low. The substance amount is so small that it does not affect the normal processes of the body.
· The test may not be appropriate for pregnant women or those who are breastfeeding.
· If you are breastfeeding, you should not nurse your baby for approximately 36 hours after the radiotracer injection, since radiation can be passed through the breast milk.
· The radiation injected during a nuclear medicine study is eliminated from you body through the kidneys. For that reason, the patient should drink plenty of fluids and urinate frequently after the examination.
http://www.brighamandwomens.org/nuclearmedicine/Patient/PETScan.asp
http://www.triumf.ca/welcome/petscan.html
http://www.radiologyinfo.org/content/petomography.htm
http://www.epub.org.br/cm/n01/pet/petworks.htm
The History of Nuclear Medicine
The nuclear medicine began with most notably discover of the x-rays in 1895 by Wilhelm Rentgen, and the second important discovery of the "artificial radioactivity" in 1934.
Marie and Pierie Curie were working with the radium element, they notice that diseased cell in the blood of laboratory animals was killed by the radiation that emitted from the radium; they immediately understood the medical potential of the discovery.
The first time that cancer was treated successfully was in 1946, it was a thyroid cancer that treated with radioactive iodine.
A few years later in the early 1950 the clinical use of the cancer treatment became wide-spread.
The iodine was at the beginning the most used isotope, it used for diagnosing thyroid cancer, and still use today.
Use of radioactive tracer, Georg von Hevesey studied in 1923 the biological system of plants by following the tracers from the root of the plants to the live.
In 1929, Ernest O.Lawrence, invented the cyclotron, it used to create radioisotopes, he accelerate atoms in order to make a collision with other atom, the result was new particles. For doing it he needed high energy voltage supply that was not possible to achieve. He thought about using a magnetic field, in order to bend the particle course and make it become spiral that way in each circle the particle will get more energy.
Using an advanced cyclotron, some scientists produced iron-59, with this isotope it was possible to learn about the hemoglobin in the human blood.
In 1938, Seaborg and Emilio serge discovered the isotope technetium 99m. This is one of the most common use radioisotopes these days.
At 1953 the first positron detector was built, it was based on the pair production principle, that two photons eject in opposite direction.
The technological developments brought that in the 1970 it was possible to visualize and scan the most of the body organs like liver, spleen, brain.
In the 1970s the use of computers brought new imaging techniques to the nuclear physician, it allowed for a better analysis of images and lead to the development of topographic or three dimensional imaging.
references:
http://www.snm.org/nuclear/history.html
http://www.chm.bris.ac.uk/webprojects2002/wrigglesworth/background.htmhttp://www.atomicmuseum.com/tour
Marie and Pierie Curie were working with the radium element, they notice that diseased cell in the blood of laboratory animals was killed by the radiation that emitted from the radium; they immediately understood the medical potential of the discovery.
The first time that cancer was treated successfully was in 1946, it was a thyroid cancer that treated with radioactive iodine.
A few years later in the early 1950 the clinical use of the cancer treatment became wide-spread.
The iodine was at the beginning the most used isotope, it used for diagnosing thyroid cancer, and still use today.
Use of radioactive tracer, Georg von Hevesey studied in 1923 the biological system of plants by following the tracers from the root of the plants to the live.
In 1929, Ernest O.Lawrence, invented the cyclotron, it used to create radioisotopes, he accelerate atoms in order to make a collision with other atom, the result was new particles. For doing it he needed high energy voltage supply that was not possible to achieve. He thought about using a magnetic field, in order to bend the particle course and make it become spiral that way in each circle the particle will get more energy.
Using an advanced cyclotron, some scientists produced iron-59, with this isotope it was possible to learn about the hemoglobin in the human blood.
In 1938, Seaborg and Emilio serge discovered the isotope technetium 99m. This is one of the most common use radioisotopes these days.
At 1953 the first positron detector was built, it was based on the pair production principle, that two photons eject in opposite direction.
The technological developments brought that in the 1970 it was possible to visualize and scan the most of the body organs like liver, spleen, brain.
In the 1970s the use of computers brought new imaging techniques to the nuclear physician, it allowed for a better analysis of images and lead to the development of topographic or three dimensional imaging.
references:
http://www.snm.org/nuclear/history.html
http://www.chm.bris.ac.uk/webprojects2002/wrigglesworth/background.htmhttp://www.atomicmuseum.com/tour
Ultrasound | Summary
Purpose: the ultrasound machine mostly used to check the developing of fetuses in pregnant woman. They can see the size of the fetus, the position, sex, number of fetuses; check the amount of amniotic fluid around the fetus. In the 3-dimensional ultrasound you actually see the baby and check if every thing is ok.
It is also used to see tumors in the ovary and breast, check the heart, prostate, and detect kidney stones. There is also a Doppler ultrasound that used for measuring blood flow through the heart, kidneys and major vessels.
The scientific principle: when sound waves move in medium it always move forward, but if it hit another medium some of the waves get reflected back and some continue forward. The ratio between the two waves is influenced by the difference between the densities of the two mediums.
In the ultrasound machine there is a transducer that transmits pulses of high frequency sound wave to the body. The wave moves in the body and every time it hits a different tissue it reflects some of the waves, the more the different between the tissues is higher more waves reflected. The probe is also collecting the reflected sound and transfers them to the CPU of the machine. The CPU knows when the sound wave was sent, it also the speed of the wave in the tissue, so when it receive the reflected wave the distance of the organ can be calculated. At the end we get a two dimensional picture of the distance and the intensities of the reflected waves.
The Doppler ultrasound base on the Doppler effect, when a sound wave hit an object some of it reflects back, if the object is moving the frequency of the wave will change a bit, if the object is moving toward the wave the frequency will increase and vice versa.
The size of the change of the frequency is depends on the velocity of the object.
The piezoelectric effect- in the probe there is a piezoelectric crystal that when it gets an electric current it starts to vibrate, the frequency is depends on the intensity of the current. And conversely when a sound waves hit the crystal it producing a current that’s depends on the frequency of the wave.
Description of instrument:
Transducer probe: it transmit a sound wave by using a crystal, the wave is transmitted in pulses so after the pulse is in the body the crystal inside the probe is in receiving mode and wait the reflected sound wave to produce a current that depends on the frequency.
There are some kinds of probes smalls for narrow view, big for wide view. There are some that have some crystals. And some that designed to insert body through its openings as vagina, rectum, and esophagus to see the body from the inside.
Central processing unit (CPU): the brain of the machine, its control the probe, control the timing of the transmitting wave and also get the current from the probe, and making all the calculations of the data.
Transducer pulse controls: it let the operator to control the frequency and duration of the sound wave pulses. The frequency determines the deep of the entrance to the body.
Display: the monitor, it shows the data that processed in the CPU, it can show a two dimensional picture or 3 dimensional depends on the model.
Keyboard/curser: the operator uses it to add notes and to take measurement from the data.
Disk storage: it can be any storage device that used in computer to save the data of the examination.
Operation: the operator put jelly on the skin to avoid air between the probe and the body, the probe is covered by plastic cover, and then the operator moves the probe on the skin and an image is obtained in the monitor. Usually the test is on the belly but the position could change. If the exam is internal so the position is different.
Safety features: the ultrasound consider a very safe test, in the past people were afraid of the heat that produce by the energy that absorbed in the body, and the bubbles that could be. But after lots of studies no reason to concern is found.
Sources of Data:
http://electronics.howstuffworks.com/ultrasound4.htm
It is also used to see tumors in the ovary and breast, check the heart, prostate, and detect kidney stones. There is also a Doppler ultrasound that used for measuring blood flow through the heart, kidneys and major vessels.
The scientific principle: when sound waves move in medium it always move forward, but if it hit another medium some of the waves get reflected back and some continue forward. The ratio between the two waves is influenced by the difference between the densities of the two mediums.
In the ultrasound machine there is a transducer that transmits pulses of high frequency sound wave to the body. The wave moves in the body and every time it hits a different tissue it reflects some of the waves, the more the different between the tissues is higher more waves reflected. The probe is also collecting the reflected sound and transfers them to the CPU of the machine. The CPU knows when the sound wave was sent, it also the speed of the wave in the tissue, so when it receive the reflected wave the distance of the organ can be calculated. At the end we get a two dimensional picture of the distance and the intensities of the reflected waves.
The Doppler ultrasound base on the Doppler effect, when a sound wave hit an object some of it reflects back, if the object is moving the frequency of the wave will change a bit, if the object is moving toward the wave the frequency will increase and vice versa.
The size of the change of the frequency is depends on the velocity of the object.
The piezoelectric effect- in the probe there is a piezoelectric crystal that when it gets an electric current it starts to vibrate, the frequency is depends on the intensity of the current. And conversely when a sound waves hit the crystal it producing a current that’s depends on the frequency of the wave.
Description of instrument:
Transducer probe: it transmit a sound wave by using a crystal, the wave is transmitted in pulses so after the pulse is in the body the crystal inside the probe is in receiving mode and wait the reflected sound wave to produce a current that depends on the frequency.
There are some kinds of probes smalls for narrow view, big for wide view. There are some that have some crystals. And some that designed to insert body through its openings as vagina, rectum, and esophagus to see the body from the inside.
Central processing unit (CPU): the brain of the machine, its control the probe, control the timing of the transmitting wave and also get the current from the probe, and making all the calculations of the data.
Transducer pulse controls: it let the operator to control the frequency and duration of the sound wave pulses. The frequency determines the deep of the entrance to the body.
Display: the monitor, it shows the data that processed in the CPU, it can show a two dimensional picture or 3 dimensional depends on the model.
Keyboard/curser: the operator uses it to add notes and to take measurement from the data.
Disk storage: it can be any storage device that used in computer to save the data of the examination.
Operation: the operator put jelly on the skin to avoid air between the probe and the body, the probe is covered by plastic cover, and then the operator moves the probe on the skin and an image is obtained in the monitor. Usually the test is on the belly but the position could change. If the exam is internal so the position is different.
Safety features: the ultrasound consider a very safe test, in the past people were afraid of the heat that produce by the energy that absorbed in the body, and the bubbles that could be. But after lots of studies no reason to concern is found.
Sources of Data:
http://electronics.howstuffworks.com/ultrasound4.htm
MRI | Summary
Purpose:
The MRI is a very accurate diagnostic instrument it is usually used for the following diagnostic tests:
Diagnosing multiple sclerosis.
Diagnosing tumors of the pituitary gland and brain.
Diagnosing infections in the brain, spine or joints.
Visualizing torn ligaments in the wrist, knee and ankle.
Visualizing shoulder injuries.
Diagnosing tendonitis.
Evaluating masses in the soft tissues of the body.
Evaluating bone tumors, cysts and bulging or herniated discs in the spine.
Diagnosing strokes in their earliest stages.
Description of the instrument:
The biggest and most important component in an MRI system is the magnet.
There are three basic types of magnets used in MRI systems:
Resistive magnets: consist of many windings or coils of wire wrapped around a cylinder or bore through which an electric current is passed. This causes a magnetic field to be generated. It is the cheapest magnet to buy but because the resistance of the wires it requires a huge amount of electricity to operate it. And its have a low magnetic field about 0.3 tesla, more then that will take too much electricity.
A permanent magnet: Its magnetic field is always there and always on full strength, so it costs nothing to maintain the field. The major drawback is that these magnets are extremely heavy: They weigh many, many tons so it is complicated and expensive to build them. Its also have a low magnetic field about 0.4 tesla more then that it will be to big and heavy.
Superconducting magnets: the most commonly used. It is similar to the resistive magnet, but the difference is that the wire is cooled by liquid helium, that brings to a huge reduce in the resistance of the wire, so we don’t need so much electricity. It is expensive but we can reach 2 tesla with it.
RF transmitter: RF pulses are usually applied through a coil. MRI machines come with many different coils designed for different parts of the body: knees, shoulders, wrists, heads, necks and so on. They also collect the energy release of the hydrogen atoms and send it to the computer.
Computer system: receives a mathematical data that is converted, through the use of a Fourier transform, into a picture that we can put on film. That is the "imaging" part of MRI.
Scientific principle
Usually the atoms are randomly spinning in every direction. When a magnetic field is applied all of the hydrogen protons will align with the magnetic field in one direction or the other. The vast majority cancels each other out, but few from millions of the atoms will not cancel each other. We concern only about the hydrogen atoms because they have a large magnetic momentum so they have a strong tendency to line up with the direction of the magnetic field.
The machine applies an RF pulse toward the examined area in the body, the few hydrogen atoms (that do not had another atom that will cancel them) absorb the energy and begins to spin in another direction and in a specific frequency.
When the RF pulse is turned off, the hydrogen protons begin to slowly (relatively speaking) return to their natural alignment within the magnetic field and release their excess stored energy. When they do this, they give off a signal that the coil now picks up and sends to the computer system.
Operation:
There is a horizontal tube running through the magnet from front to back. This tube is known as the bore of the magnet. The patient, lying on his back, slides into the bore on a special table. Whether or not the patient goes in head first or feet first, as well as how far in the magnet they will go, is determined by the type of exam to be performed. Once the body part to be scanned is in the exact center of the magnetic field, the scan can begin. The test can take more then 20 minutes.
Safety features:
An MRI scan is a painless radiology technique, which has the advantage of avoiding x-ray radiation exposure. There are no known side effects of an MRI scan.
Patients who have any metallic materials within the body must notify to their doctor before the examination. Metallic chips, materials, surgical clips, or foreign material (artificial joints, metallic bone plates, or prosthetic devices, etc.) can significantly distort the images obtained by the MRI scanner. Patients who have heart pacemakers, metal implants, or metal chips or clips in or around the eyeballs cannot be scanned with an MRI because of the risk that the magnet may move the metal in these areas. Similarly, patients with artificial heart valves, metallic ear implants, bullet fragments, and chemotherapy or insulin pumps should not have MRI scanning.
Some people can experience a claustrophobic sensation during the procedure. Therefore, patients with any history of claustrophobia should notify the MRI stuff.
1. http://www.medicinenet.com/MRI_Scan/
2. http://electronics.howstuffworks.com/mri.htm
The MRI is a very accurate diagnostic instrument it is usually used for the following diagnostic tests:
Diagnosing multiple sclerosis.
Diagnosing tumors of the pituitary gland and brain.
Diagnosing infections in the brain, spine or joints.
Visualizing torn ligaments in the wrist, knee and ankle.
Visualizing shoulder injuries.
Diagnosing tendonitis.
Evaluating masses in the soft tissues of the body.
Evaluating bone tumors, cysts and bulging or herniated discs in the spine.
Diagnosing strokes in their earliest stages.
Description of the instrument:
The biggest and most important component in an MRI system is the magnet.
There are three basic types of magnets used in MRI systems:
Resistive magnets: consist of many windings or coils of wire wrapped around a cylinder or bore through which an electric current is passed. This causes a magnetic field to be generated. It is the cheapest magnet to buy but because the resistance of the wires it requires a huge amount of electricity to operate it. And its have a low magnetic field about 0.3 tesla, more then that will take too much electricity.
A permanent magnet: Its magnetic field is always there and always on full strength, so it costs nothing to maintain the field. The major drawback is that these magnets are extremely heavy: They weigh many, many tons so it is complicated and expensive to build them. Its also have a low magnetic field about 0.4 tesla more then that it will be to big and heavy.
Superconducting magnets: the most commonly used. It is similar to the resistive magnet, but the difference is that the wire is cooled by liquid helium, that brings to a huge reduce in the resistance of the wire, so we don’t need so much electricity. It is expensive but we can reach 2 tesla with it.
RF transmitter: RF pulses are usually applied through a coil. MRI machines come with many different coils designed for different parts of the body: knees, shoulders, wrists, heads, necks and so on. They also collect the energy release of the hydrogen atoms and send it to the computer.
Computer system: receives a mathematical data that is converted, through the use of a Fourier transform, into a picture that we can put on film. That is the "imaging" part of MRI.
Scientific principle
Usually the atoms are randomly spinning in every direction. When a magnetic field is applied all of the hydrogen protons will align with the magnetic field in one direction or the other. The vast majority cancels each other out, but few from millions of the atoms will not cancel each other. We concern only about the hydrogen atoms because they have a large magnetic momentum so they have a strong tendency to line up with the direction of the magnetic field.
The machine applies an RF pulse toward the examined area in the body, the few hydrogen atoms (that do not had another atom that will cancel them) absorb the energy and begins to spin in another direction and in a specific frequency.
When the RF pulse is turned off, the hydrogen protons begin to slowly (relatively speaking) return to their natural alignment within the magnetic field and release their excess stored energy. When they do this, they give off a signal that the coil now picks up and sends to the computer system.
Operation:
There is a horizontal tube running through the magnet from front to back. This tube is known as the bore of the magnet. The patient, lying on his back, slides into the bore on a special table. Whether or not the patient goes in head first or feet first, as well as how far in the magnet they will go, is determined by the type of exam to be performed. Once the body part to be scanned is in the exact center of the magnetic field, the scan can begin. The test can take more then 20 minutes.
Safety features:
An MRI scan is a painless radiology technique, which has the advantage of avoiding x-ray radiation exposure. There are no known side effects of an MRI scan.
Patients who have any metallic materials within the body must notify to their doctor before the examination. Metallic chips, materials, surgical clips, or foreign material (artificial joints, metallic bone plates, or prosthetic devices, etc.) can significantly distort the images obtained by the MRI scanner. Patients who have heart pacemakers, metal implants, or metal chips or clips in or around the eyeballs cannot be scanned with an MRI because of the risk that the magnet may move the metal in these areas. Similarly, patients with artificial heart valves, metallic ear implants, bullet fragments, and chemotherapy or insulin pumps should not have MRI scanning.
Some people can experience a claustrophobic sensation during the procedure. Therefore, patients with any history of claustrophobia should notify the MRI stuff.
1. http://www.medicinenet.com/MRI_Scan/
2. http://electronics.howstuffworks.com/mri.htm
CT Scan | Summary
Purpose:
CT scan(Computed Tomography) is a diagnostic machine that provides us a detailed cross sectional view of all type of tissues; the doctor can see slices of the organ or even three dimensional views. Usually it is used to diagnosing of cancer; we can see the precise location and size of the tumor. It is also used for helping to plan radiation treatments or to guide biopsies or other invasive procedures.
Description of instrument:
The most used CT is the one known us the third generation.
Fan shaped x-ray beam is made to pass through body, it rotate by the gantry.
After its passes the body it detected by ionic gas chamber like xenon or solid state like cesium iodide, the detectors are collimated. Multiple projections are taken to reconstruct a single image.
Each unit of tissue called voxel is represented on a computer display matrix called pixel. Each pixel is assigned a CT number. And then an image is accepted.The gantry uses a strong engine 60kw.
X-ray tube- require high anode hear capacity, that why it is rotating.
The beam is collimated as it exits the tube and again before it strikes the detector.
Collimation defines the beam thickness and reduces scattering.
Scientific principle:
CT number: Number used to represent the mean x-ray attenuation associated with each vocal. Numbers are normally expressed in terms of Hounsfield units (HU). Measured values of attenuation are transformed into CT numbers using the international Hounsfield scale:
CT Number= (µ(Material)-µ(Water))/(µ(water)) *1000
Where µ is the effective linear attenuation coefficient for the x-ray beam.The CT number scale is defined so that water has a value of 0 HU and air a value of -1000 HU.
Image quality: it is characterized in terms of contrast, noise, and spatial resolution.
Usually the quality of the image is a tradeoff between these 3 factors and radiation dose.
Contrast: is the difference it the HU values between tissues. Its increases as kVp decrease and not affected by mA or scan time.
It can be increased artificially by adding a contrast medium such as iodine.
Noise: is determined by the number of photons used to make the image, because the STDV is the root of the number of the photons.
It is increased us increasing the kPv, mA, scan time, or voxel size by decreasing matrix size.
Resolution: is the ability to discriminate between adjacent cells and is a function of pixel size.
Operation:
The patient lies down on a platform that moves slowly through the hall, while the x-ray tube is rotating. Each round scans a narrow slice. In this spiral motion the computer varies the intensity of the beam to the optimum of the tissue that is examined.
Later, the computer processes all the information to give us an image of the organ.
Safety features:
The exposure is about 10mSv.
The dose is increased with number of slices, slice thickness, scan time, kVp, mA.
The patient is protected by shielding in the areas that is not examined to decrease the exposure.
Pregnant women most inform the doctor.
Nursing mothers should wait for 24 hours after contrast injection before resuming breast feeding.
Some people get allergic reaction to iodine that is used sometimes as a contrast material. But it is rare.
Internet sites:
http://www.vrundavan.com/ctscan.htm
http://www.medicinenet.com/CAT_Scan/article.htm
http://www.radiologyinfo.org/content/ct_of_the_body.htm
http://www.drs.dk/guidelines/ct/quality/Page043.htm
http://science.howstuffworks.com/cat-scan2.htm
CT scan(Computed Tomography) is a diagnostic machine that provides us a detailed cross sectional view of all type of tissues; the doctor can see slices of the organ or even three dimensional views. Usually it is used to diagnosing of cancer; we can see the precise location and size of the tumor. It is also used for helping to plan radiation treatments or to guide biopsies or other invasive procedures.
Description of instrument:
The most used CT is the one known us the third generation.
Fan shaped x-ray beam is made to pass through body, it rotate by the gantry.
After its passes the body it detected by ionic gas chamber like xenon or solid state like cesium iodide, the detectors are collimated. Multiple projections are taken to reconstruct a single image.
Each unit of tissue called voxel is represented on a computer display matrix called pixel. Each pixel is assigned a CT number. And then an image is accepted.The gantry uses a strong engine 60kw.
X-ray tube- require high anode hear capacity, that why it is rotating.
The beam is collimated as it exits the tube and again before it strikes the detector.
Collimation defines the beam thickness and reduces scattering.
Scientific principle:
CT number: Number used to represent the mean x-ray attenuation associated with each vocal. Numbers are normally expressed in terms of Hounsfield units (HU). Measured values of attenuation are transformed into CT numbers using the international Hounsfield scale:
CT Number= (µ(Material)-µ(Water))/(µ(water)) *1000
Where µ is the effective linear attenuation coefficient for the x-ray beam.The CT number scale is defined so that water has a value of 0 HU and air a value of -1000 HU.
Image quality: it is characterized in terms of contrast, noise, and spatial resolution.
Usually the quality of the image is a tradeoff between these 3 factors and radiation dose.
Contrast: is the difference it the HU values between tissues. Its increases as kVp decrease and not affected by mA or scan time.
It can be increased artificially by adding a contrast medium such as iodine.
Noise: is determined by the number of photons used to make the image, because the STDV is the root of the number of the photons.
It is increased us increasing the kPv, mA, scan time, or voxel size by decreasing matrix size.
Resolution: is the ability to discriminate between adjacent cells and is a function of pixel size.
Operation:
The patient lies down on a platform that moves slowly through the hall, while the x-ray tube is rotating. Each round scans a narrow slice. In this spiral motion the computer varies the intensity of the beam to the optimum of the tissue that is examined.
Later, the computer processes all the information to give us an image of the organ.
Safety features:
The exposure is about 10mSv.
The dose is increased with number of slices, slice thickness, scan time, kVp, mA.
The patient is protected by shielding in the areas that is not examined to decrease the exposure.
Pregnant women most inform the doctor.
Nursing mothers should wait for 24 hours after contrast injection before resuming breast feeding.
Some people get allergic reaction to iodine that is used sometimes as a contrast material. But it is rare.
Internet sites:
http://www.vrundavan.com/ctscan.htm
http://www.medicinenet.com/CAT_Scan/article.htm
http://www.radiologyinfo.org/content/ct_of_the_body.htm
http://www.drs.dk/guidelines/ct/quality/Page043.htm
http://science.howstuffworks.com/cat-scan2.htm
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