Magnetic resonance imaging (MRI)

Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body. In many cases MRI gives different information about structures in the body than can be seen with an X-ray, ultrasound, or computed tomography (CT) scan. MRI also may show problems that cannot be seen with other imaging methods.

For an MRI test, the area of the body being studied is placed inside a special machine that contains a strong magnet. Pictures from an MRI scan are digital images that can be saved and stored on a computer for more study. The images also can be reviewed remotely, such as in a clinic or an operating room. In some cases, contrast material may be used during the MRI scan to show certain structures more clearly.

Magnetic resonance imaging (MRI) is done for many reasons. It is used to find problems such as tumors, bleeding, injury, blood vessel diseases, or infection. MRI also may be done to provide more information about a problem seen on an X-ray, ultrasound scan, or CT scan. Contrast material may be used during MRI to show abnormal tissue more clearly. An MRI scan can be done for the:

• Head. MRI can look at the brain for tumors, an aneurysm, bleeding in the brain, nerve injury, and other problems, such as damage caused by a stroke. MRI can also find problems of the eyes and optic nerves, and the ears and auditory nerves.

• Chest. MRI of the chest can look at the heart, the valves, and coronary blood vessels. It can show if the heart or lungs are damaged. MRI of the chest may also be used to look for breast or lung cancer.

• Blood vessels. Using MRI to look at blood vessels and the flow of blood through them is called magnetic resonance angiography (MRA). It can find problems of the arteries and veins, such as an aneurysm, a blocked blood vessel, or the torn lining of a blood vessel (dissection). Sometimes contrast material is used to see the blood vessels more clearly.

• Abdomen and pelvis. MRI can find problems in the organs and structures in the belly, such as the liver, gallbladder, pancreas, kidneys, and bladder. It is used to find tumors, bleeding, infection, and blockage. In women, it can look at the uterus and ovaries. In men, it looks at the prostate.

• Bones and joints. MRI can check for problems of the bones and joints, such asarthritis, problems with the temporomandibular joint, bone marrow problems,bone tumors, cartilage problems, torn ligaments or tendons, or infection. MRI may also be used to tell if a bone is broken when X-ray results are not clear. MRI is done more commonly than other tests to check for some bone and joint problems.

• Spine. MRI can check the discs and nerves of the spine for conditions such asspinal stenosis, disc bulges, and spinal tumors.

Computed Tomography

A CT scan stands for Computed Tomography scan. It is also known as a CAT (Computer Axial Tomography) scan. It is a medical imaging method that employs tomography. Tomography is the process of generating a two-dimensional image of a slice or section through a 3-dimensional object (a tomogram).

The medical device (the machine) is called a CTG scanner; it is a large machine and uses X-rays. It used to be called an EMI scan, because it was developed by the company EMI. Undergoing a CT scan is a painless procedure.

The CT scanner uses digital geometry processing to generate a 3-dimensional (3-D) image of the inside of an object. The 3-D image is made after many 2-dimensional (2-D) X-ray images are taken around a single axis of rotation - in other words, many pictures of the same area are taken from many angles and then placed together to produce a 3-D image.

The Greek word tomos means "slice and the Greek word graphein means "write".

How does a CT scan work?

A CT scanner emits a series of narrow beams through the human body as it moves through an arc, unlike an X-ray machine which sends just one radiation beam. The final picture is far more detailed than an X-ray one.

Inside the CT scanner there is an X-ray detector which can see hundreds of different levels of density. It can see tissues inside a solid organ. This data is transmitted to a computer, which builds up a 3-D cross-sectional picture of the part of the body and displays it on the screen.

Sometimes a contrast dye is used because it shows up much more clearly on the screen. If a 3-D image of the abdomen is required the patient may have to drink a barium meal. The barium appears white on the scan as it travels through the digestive system. If images lower down the body are required, such as the rectum, the patient may be given a barium enema. If blood vessels are the target images the barium will be injected.

The accuracy and speed of CT scans may be improved with the application of spiral CT. The X-ray beam takes a spiral path during the scanning - it gathers continuous data with no gaps between images. For a spiral scan of the chest, for example, the patient will be asked to hold his/her breath for a few seconds.

What Is Coronary Angiography?

Coronary angiography (an-jee-OG-rah-fee) is a test that uses dye and special x rays to show the insides of your coronary arteries. The coronary arteries supply oxygen-rich blood to your heart.

A waxy substance called plaque (plak) can build up inside the coronary arteries. The buildup of plaque in the coronary arteries is called coronary heart disease(CHD).

Over time, plaque can harden or rupture (break open). Hardened plaque narrows the coronary arteries and reduces the flow of oxygen-rich blood to the heart. This can cause chest pain or discomfort called angina (an-JI-nuh or AN-juh-nuh).

If the plaque ruptures, a blood clot can form on its surface. A large blood clot can mostly or completely block blood flow through a coronary artery. This is the most common cause of a heart attack. Over time, ruptured plaque also hardens and narrows the coronary arteries.

Overview

During coronary angiography, special dye is released into the bloodstream. The dye makes the coronary arteries visible on x-ray pictures. This helps doctors see blockages in the arteries.  

A procedure called cardiac catheterization (KATH-eh-ter-ih-ZA-shun) is used to get the dye into the coronary arteries.

For this procedure, a thin, flexible tube called a catheter is put into a blood vessel in your arm, groin (upper thigh), or neck. The tube is threaded into your coronary arteries, and the dye is released into your bloodstream. X-ray pictures are taken while the dye is flowing through the coronary arteries.

Cardiologists (heart specialists) usually do cardiac catheterization in a hospital. You're awake during the procedure, and it causes little or no pain. However, you may feel some soreness in the blood vessel where the catheter was inserted.

Cardiac catheterization rarely causes serious complications.

X-Ray Radiography

X-Ray Radiography is a nondestructive semiconductor failure analysis technique used to examine the interior details of the package. It operates on the principle of dissimilar transmission of X-Rays through different materials.  The ability of a material to block X-Rays increases with its density. It is this dissimilar transmission of X-rays through different materials that is utilized to create an image of various contrasts.  X-Ray imaging may be accomplished on film, by fluoroscopy, or by using image intensifying video systems.

  

A typical modern X-Ray inspection equipment has a filament that produces an electron beam used to excite a target into producing X-Rays. The X-Ray emissions are then directed to and transmitted through the specimen. The transmitted X-Rays are collected by a detector, translated into electric signals, amplified, and transformed into an X-Ray image.

           

The varying densities of the various materials comprising the specimen allow different amounts of X-Rays to pass through, resulting in varying grayscale levels on the X-Ray image.  The quality of the X-Ray image formed therefore depends not only on the proper operation of the X-Ray equipment used, but on the composition of the specimen as well. Some materials used in semiconductor assembly, such as aluminum wires, are transparent to X-Ray, and are therefore invisible in X-Ray images.           

                              

X-Ray radiography is commonly used to inspect for wiresweeping and other wirebond problems, die attach voids, package voids and cracks. It is excellent for determining leadframe outlines as well. Traditional x-ray systems use photosensitive films to record the x-ray image. Since X-Rays are not easy to focus, this method produces low-resolution images, which greatly limits its usefulness. 

                            

Today, X-Ray systems use a microspot source, real-time detection and automated manipulation of the sample to achieve higher resolution and throughput. These systems are capable of detecting much finer package details and defects.

Digital Radiography & Fluoroscopy

Digital radiology may represent the greatest technological advancement in medical imaging over the last decade. The use of radiographic films in x ray imaging might become obsolete in a few years. An appropriate analogy that is easy to understand is the replacement of typical film cameras with digital cameras. Images can be immediately acquired, deleted, modified, and subsequently sent to a network of computers.

The benefits from digital radiology are enormous. It can make a radiological facility or department filmless. The referring physician can view the requested image on a desktop or a personal computer and often report in just a few minutes after the examination was performed. The images are no longer held in a single location; but can be seen simultaneously by physicians who are kilometres apart. In addition, the patient can have the x ray images on a compact disk to take to another physician or hospital.

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