Slice & Dice: What The Heck Does An Mri Machine Do
The MRI machine has the capability to re-create your lumbar spine, slice by slice, in three planes: a view from the side , front , and bottom-up . Typically, the coronal series is not performed.
Unlike an x-ray machine which creates a compressed one-slice picture of the entire lumbar spine , MRI creates a sequential multi-slice series of images, which are typically taken from left to right, at intervals of 3-5mm. By employing this strategy, every nook and cranny of the lumbar spine is captured on at least one slice, which allows for the viewing of even the smallest of pathologies.
The figure above is a T1-weighted MRI film of 12 sequential slices through the lumbar spine. This series of images could have easily been put into disk format.
In order to help you understand this slicing concept of MRI technology, consider this analogy.
Upon your request, a deli worker will grab a log of salami , turned on the slicing machine , and, from one of the ends, begin slicing off thin pieces of salami, which you can then use for your sandwich.
Such slices of salami are analogous to the axial MRI images.
I suppose you could put the salami log in the deli slicer lengthwise , which would give you sagittal slices of salami for a very long sandwich! These long slices of salami would be analogous to the MRI sagittal images.
What Do Different Knee Injury Images Look Like
With knee MRI images of injuries, your provider is looking for a few telltale signs of concern. Common issues that are evaluated with a knee MRI include:
Dislocation The different parts of the knee get out of place. This can be the result of trauma or an abnormal knee structure.
Fluid Buildup Whether behind the knee or inside the knee joint, fluid buildup can indicate a number of underlying conditions.
Fracture A fall, sports injury, automobile accident or other trauma can break the bones in and around the knee joint.
Ligament Injury Sports trauma or auto accidents tear or otherwise injure the anterior or posterior cruciate ligament .
Meniscal Tear Arthritis, aging and sudden twisting or pivoting movements tear one or both of the menisci .
Pain In cases when knee pain comes and wont go away without a known source, knee MRI images help get to the root of the problem.
So What Does The Meniscus Do
The Meniscus a shock absorber and a spacer. So basically, its the shock absorber and the spacer inside your knee.
But before we start, its very important that you understand that there is no evidence that in middle aged to elderly patients a Meniscus tear causes symptoms. Now, you might be very surprised to hear about that, but theres very good research that shows that Meniscus tears in that age group are just as common as grey hair. So we cant look at a Meniscus tear on a MRI and say, Aha, thats causing your pain in middle-aged or elderly patients, so be very careful about someone who just looks at your image and says, Thats whats causing your pain because there is no science to support that.
In addition, theres no evidence that operating on a Meniscus tear with or without arthritis is effective. Again, you might be very surprised to hear that, but multiple high-quality studies have now shown that operating on a Meniscus tear isnt effective, doesnt help. So again, just to be absolutely clear on that point, were going to talk today about Meniscus tears, but the concept of operating on them has not been supported in the science.
The easiest way to find the Meniscus is on the Sagittal or Coronal images. This is what the Coronal will look like. This is what the Sagittal will look like.
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How A Knee Mri Is Performed
Before the scan, youll change into a hospital gown and remove all jewelry and body piercings. If youre using a contrast dye, an intravenous line will be inserted into your arm to inject the dye into your bloodstream.
An MRI machine looks like a giant wheel. The center is open so a flat table can slide in and out of the machine. The rounded, wheel-like part sends out the magnetic and radio waves used to produce images of your body.
Youll lie on your back or side on a padded table. The technician may use pillows or straps to make your knee more comfortable during the test. This will also help keep your leg still so the machine can take the clearest images.
The technician will then slide you into the machine feet first. Theyll tell you when to hold still and hold your breath. These instructions will be given over a microphone, since the technician will be in a separate room, watching the monitors as they collect images.
You wont feel the machine working, but there may be some loud noises, such as clacks or thuds, and possibly a whirring noise. The technician may give you earplugs or provide music.
The test typically takes between 30 minutes to an hour. Once the technician has recorded the images they need, youll be free to change back into your clothes and go about your day.
Citation Doi And Article Data
- Knee MRI reporting template
Knee MRI is one of the more frequent examinations faced in daily radiological practice. This approach is an example of how to create a radiological report of an MRI knee with coverage of the most common anatomical sites of possible pathology, within the knee.
A systematic review in the MRI of the knee is essential since knee anatomy itself is rather complex, pathologies, and injury patterns and are manifold and only rarely lead to an abnormality of a single structure but rather show diverse findings which might need to be addressed in further patient management 1.
and many more…
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What Is A Knee Mri
MRI of the knee provides detailed images of structures within the knee joint, including bones, cartilage, tendons, ligaments, muscles and blood vessels, from many angles.
Magnetic resonance imaging is a noninvasive test doctors use to diagnose medical conditions.
MRI uses a powerful magnetic field, radiofrequency pulses, and a computer to produce detailed pictures of internal body structures. MRI does not use radiation .
Detailed MR images allow doctors to examine the body and detect disease.
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How To Read A Normal Knee Mri
The MRI has many advantages over other imaging techniques, one of them being its superior ability to discriminate soft tissue structures. Without going into too much detail, the MRI scanner does this by triggering the protons in the tissues to produce a signal that is measured by receivers in the MRI machine and transformed into an image. Since different tissues have different density of protons, the signal can vary in intensity, which allows the MRI scanner to discriminate one tissue from another. For example, the bones have a higher density in protons and therefore emit a high signal, appearing hyperintense , while fluid has a low density and emits a low signal, appearing hypointense on an MRI.
To complicate matters a bit more, the intensity of tissue on a final MRI image also depends on the sequence technique being used. The most commonly used are T1 and T2- weighted sequences. In addition, proton density images are also used as a contrast enhancement technique. We can switch between these modalities depending on the tissue we want to observe:
As an example, shown here is an overview of the knee on an axial PD image on a slice through the femoral condyles. In this modality, fat and hyaline cartilage show as white, bones as white to gray, muscles as gray, and tendons and ligaments as black.
If this is still a bit confusing to you, have a look at our article to learn more about the fundamentals of the MRI.
How Do These Images Compare To A Healthy Knee
A healthy knee MRI shows none of these issues. Instead, all bones, ligaments, cartilage and tendons are in place. There are no tears or breaks. Healthy knees bend as they ought to, without pain.
A knee MRI of someone with a condition or injury will produce very different results. Talk with your doctor if you suspect a knee MRI could reveal an issue.
Are you tired of living with knee pain? Get an estimate of how much your knee MRI would cost by using American Health Imagings cost calculator
; ; ;;;American Health Imaging centers are accredited and voluntarily participate in programs that ensure safety and quality standards.
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How Does The Procedure Work
Unlike x-ray and computed tomography exams, MRI does not use radiation. Instead, radio waves re-align hydrogen atoms that naturally exist within the body. This does not cause any chemical changes in the tissues. As the hydrogen atoms return to their usual alignment, they emit different amounts of energy depending on the type of tissue they are in. The scanner captures this energy and creates a picture using this information.
In most MRI units, the magnetic field is produced by passing an electric current through wire coils. Other coils are inside the machine and, in some cases, are placed around the part of the body being imaged. These coils send and receive radio waves, producing signals that are detected by the machine. The electric current does not come into contact with the patient.
A computer processes the signals and creates a series of images, each of which shows a thin slice of the body. The radiologist can study these images from different angles.
MRI is often able to tell the difference between diseased tissue and normal tissue better than x-ray, CT, and ultrasound.
Knee Mri With Or Without Contrast
Knee MRI scans can be performed with or without contrast. In a knee MRI with contrast, a contrast agent is injected into the patient to highlight the joint structure in more detail. The contrast agent is injected into a vein in the arm and quickly circulates throughout the body, enhancing the scanned area in the MRI images.
Though very rare, patients can be allergic to the contrast liquid so it should only be administered if absolutely necessary. Adding contrast to an MRI scan significantly increases the cost so we always suggest checking with your doctor if it is absolutely necessary.
At First Look MRI we only perform knee MRI scans without contrast. If you require a scan with contrast feel free to get in touch and wed be happy to recommend a trusted facility that can provide this service.
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Chief Medical Editor Douglas W Jackson Md Speaks With Radiologist William Bradley Md About The Finer Points Of Mri Films And Terms
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More orthopedists are reading the actual MRI films obtained on theirpatients. They compare their reading to the radiologists reading. It isimportant to look at the actual studies and not just the report to make sure itis an adequate study, to confirm the pathology and to be certain you agree withthe written report.
To read the MRI, it is important to understand the imaging ofspecific tissues to be certain that the study demonstrates all of the possibleinformation contributing to an accurate diagnosis. To speak with colleagues andour patients, it is helpful if we understand the appropriate terminology.
This interview gave me the opportunity to talk to a veryknowledgeable friend and professor of radiology, William Bradley, MD.
Bill and I have spent many early morning conferences reviewing MRIson my patients, looking at interesting findings from his files and working onresearch projects. I asked him to give us his usual succinct answers addressedto orthopedists to the following four questions. It is a pleasure to share themwith our readers.
Douglas W. Jackson, MD
|University of California at San Diego Medical Center|
Douglas W. Jackson, MD: What is a T1-weighted imageand what does it show?
William Bradley, MD: All tissues can be described bythree fundamental MR parameters: T1, T2 and proton density. MR scans that bringout T1 contrast are defined as T1-weighted.
How To Prepare For The Test
You may be asked not to eat or drink anything for 4 to 6 hours before the scan.
Tell your health care provider if you are afraid of closed spaces . You may be given a medicine to help you feel sleepy and less anxious. Your provider may suggest an “open” MRI, in which the machine is not as close to the body.
Before the test, tell your provider if you have:
- Brain aneurysm clips
- Certain types of artificial heart valves
- Heart defibrillator or pacemaker
- Kidney disease or dialysis
- Recently placed artificial joints
- Certain types of vascular stents
- Worked with sheet metal in the past
Because the MRI contains strong magnets, metal objects are not allowed into the room with the MRI scanner:
- Pens, pocketknives, and eyeglasses may fly across the room.
- Items such as jewelry, watches, credit cards, and hearing aids can be damaged.
- Pins, hairpins, metal zippers, and similar metallic items can distort the images.
- Removable dental work should be taken out just before the scan.
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What Happens During An Mri
A typical MRI machine looks like large, hollow tube. Wearing a hospital gown or loose-fitting clothes, youâll lie on an exam table that slides into the tube. For a knee MRI, youâll go in feet first, and only your lower body will be in the tube. Expect to hold still for around 15 to 45 minutes, sometimes longer, while the machine makes images of your knee.
In some cases, youâll get a special dye injected into your arm before the exam. Itâs called a contrast agent, and it helps make the images of your knee even clearer. You may feel a cool sensation after you get the injection.
During the exam, youâre usually alone in the room. An MRI technologist will be outside, performing the exam from a computer. They can see you the whole time and will talk to you via a two-way intercom.
You wonât feel anything during the scan. But if itâs your first MRI, you may be surprised by how loud it is. The machine makes thumping, knocking, and humming sounds. The technologist will probably offer you headphones or earplugs. If they don’t, you can ask for them.
After the exam, the technician will send images to a radiologist, who will send a report to your doctor. Youâll be able to drive yourself home and continue your day as you normally would.
What Are The Limitations Of A Knee Mri
High-quality images are assured only if you are able to remain perfectly still while the images are being recorded. If you are anxious, confused or in severe pain, you may find it difficult to lie still during imaging. Constant coughing and shaking might also interfere with the scan. A bent knee that cannot be extended is also difficult to image.
A person who is very large may not fit into the opening of a conventional MRI machine.
The presence of an implant or other metallic object sometimes makes it difficult to obtain clear images and patient movement can have the same effect. In some cases, metal artifact reduction imaging is performed in patients who have metallic surgical implants at the knee and require MR imaging.
Present data show no convincing evidence that non contrast MRI harms the fetus of a pregnant woman. However, if the need for the exam is not time sensitive your doctor may delay the exam until after delivery. MRI gadolinium contrast agents are generally avoided during pregnancy except in very specific circumstances. Your doctor will discuss the benefits and risks of any MRI procedure with you. Doctors may perform MRI after the first trimester to assess the fetus for findings that are not fully evaluated by ultrasound.
An MRI exam typically costs more and may take more time than other imaging exams. Talk to your insurance provider if you have concerns about the cost of MRI.
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