MRI Scans vs CT Scans

By Kathryn Dawson

There a few different methods of obtaining medical diagnostic images. Each method or type is known as a modality. In particular, MRI scans and CT scans bring a great deal to the field of medicine. Doctors use both modalities to help them provide accurate information about their patient in order to accurately diagnose what is wrong with them. There are differences between the two, with each providing its own advantages and disadvantages. This article acts as a guide to explaining the main differences between these two important and effective types of scan. Read on to find out more. 

The acronym CT, used with in the term CT scan, is an abbreviation of computed tomography. This modality uses x-rays which is a type of ionizing radiation to produce images of the body's interior. This makes it particularly good at investigating tissue that is more dense than the tissue that surrounds it. A good example of this is bone compared to muscle and the soft tissue and cells encasing it. In order to gain more clarity when using a CT scan, the medical personnel may administer what is known as a contrast agent. To get the most from this, the substance used may be more dense than the part of the body being investigated. This makes iodine or barium good substances to use. For example, for those of us who have had x-rays, the term barium meal may be familiar. 

The acronym MRI is an abbreviation of the term magnetic resonance imaging. Unlike CT and x-ray systems, MRI does not use ionizing radiation. Instead it uses radio waves sent through a magnetic field to acquire its images. This makes it ideal for investigating non-calcified tissue, i.e. other than bones and teeth. That is not to say it cannot be used for this purpose, it is just better suited for looking at softer tissue, organs and cells in the body. A contrast agent can also be used when carrying out an MRI scan: gadolinium or manganese are the most appropriate types as they have paramagnetic properties, and of course MRI makes use of magnetic fields. 

Although both CT and MRI scans produce two dimensional images of tissue and three dimensional reconstructions are created from this, MRI scans have greater image contrast capabilities. By varying an array of scanning parameters, different features of the body can be detected more easily. An MRI is generally considered to be more accurate when it comes to detecting tumors or problems in the brain, although a CT scan is better at detecting solid tumors in the abdomen or chest. 

A CT scan is cheaper than carrying out an MRI scan and is also more widely available so is usually the preferred route to take by doctors. An MRI scan tends to be used only when they have exhausted the other options and need further information still. A CT scan is also much quicker than an MRI scan. 

Both MRI scans and CT scans are important tools used by a doctor to facilitate accurate diagnoses of serious illnesses such as heart disease and cancer. When used in imaging in oncology, these modalities are particularly vital. By combining scanned images over time they allow information to be obtained such as how much the cancerous cells have spread and at what rate they are growing. This means patients can receive updates on whether their treatment is working and whether the cancer shrinking rather than growing in size. PET CT software in particular is vital for providing valuable oncological information such as this. Very different but equally as important as one another, CT scans, and MRI scans as well, play an important role in modern medicine.

Everything You Always Wanted to Know About Mammograms but Were Afraid to Ask

Mammography is a specific type of imaging that uses a low dose x-ray system to examine the breast; a mammogram -- a mammography exam -- is an x-ray photograph of the breast. It's a safe and highly accurate technique that has been around for the past 30 years. It is used both as a screening tool to detect early breast cancer, abnormal growths or changes in the breast tissue in women experiencing no symptoms, and to diagnose breast disease in women experiencing symptoms such as pain, lumps, or discharge from the nipple. In a screening mammogram, the breast is x-rayed from top to bottom and from side to side while in a diagnostic mammogram a particular lump or area of abnormal tissue is focused on.

A mammogram is carried out during a regular physical exam or to investigate any physical changes in the breast. As well as being useful to look for lumps that are too small to be felt during a physical exam, a mammogram can help a physician decide if any lump or growth needs further investigation. Mammography is therefore extremely important in detecting the early stages of breast cancer because it can identify an abnormal growth before it can be felt during a breast examination. There is no doubt that mammography can play a huge part in breast cancer survival -- and research has clearly shown this to be the case.

Mammography is performed on an outpatient basis. Any woman undergoing a mammogram should inform her doctor if she is pregnant or believes she might be pregnant. No changes to diet are required in preparation for a mammogram, and any medication should be taken as usual. Products such as body cream, deodorant, lotion, or powder should not be worn under the arms or on the chest on the day of the mammogram as this might interfere with the x-ray. All clothing should be removed (a gown will be provided for the patient to wear), as should all jewelry. The technologist should be advised of any breast problems and any previous mammogram results should be handed to the radiologist at the time of the current mammogram.

Registered mammography technologists perform the test, most of whom are women. The x-ray images are interpreted by a doctor specializing in this field.

During the test a patient will be asked to stand in front of an x-ray machine, and a technician will position the breast in a mammography unit. The breast will be placed on a platform and compressed with a clear plastic paddle. Compressing the breast is necessary to even out the breast thickness so that all the breast tissue can be visualized. Spreading out the tissue ensures that no small abnormalities are obscured by overlying breast tissue. It also allows for a lower dose of radiation to be used given that a thinner amount of breast tissue is being imaged. The patient must remain very still during the imaging and may be asked to refrain from breathing for a few seconds while the x-ray photo is being taken. The patient may feel a little discomfort during this process but it should only last a few seconds. Once the images have been taken, the technician will ask the patient to wait until she has determined that the images are of sufficient quality to enable the radiologist to make a reading. Compression on the breast will probably cause discomfort but this is necessary in order to get a clear picture with as small a dose of radiation as possible. However, any pain felt should be reported to the technician. One way a woman can minimize the discomfort is to schedule her mammogram seven to 10 days after the start of her last period when there is the least chance of her breasts being tender. The breast will be x-rayed from a number of positions to get an adequate visualization of the breast tissue. During a routine mammogram, two images of each breast are taken which takes about 30 minutes. Additional images of the breasts or an ultrasound may be required after the images have been interpreted to enable a more precise diagnosis to be carried out: this is a routine measure.

After the test, it’s quite normal for a patient to feel tenderness or aching where the breasts were compressed during the screening. There may also be some very slight bruising. A mild painkiller such as aspirin or ibuprofen will help alleviate any discomfort; and normal activities can be resumed immediately after the mammogram.

The results of the mammogram will be sent to the patient’s physician (the patient will also receive the results from the mammography facility). All results are now required to be sent within 30 days of screening and contact will be made with the patient within five days if there’s a problem. However, no one should assume that their results were normal if they don’t hear anything -- they should contact their physician to get confirmation. There are some centers performing mammograms that are able to produce the results while a patient waits.

According to the American Cancer Society, out of every 1000 mammograms only one or two lead to a diagnosis of cancer. Approximately 10 percent of women require additional mammography, and only eight to 10 percent of those women need a biopsy of which 80 percent will not be cancer.

The risk of breast cancer increases with age, so for a woman over 40 it’s important to have a yearly mammogram. Any woman believing that she needs one should contact her physician.

Breast self-examination is still very important, as not all breast cancers are detected by a mammogram. And self-examination is especially important for younger women who have denser breast tissue. All women should perform breast self-examination once a month from age 20. Women should also have their breasts examined by their physician or physician's nurse every three years from age 20 and every year from age 40.

In the US, breast cancer is the most common cancer among women accounting for nearly one of every three cancers diagnosed. In 2001, it was estimated that 192,200 American women were diagnosed with breast cancer for the first time and 40,200 women died from the disease. The National Cancer Institute, the American Cancer Society, and the American College of Radiology all now recommend that women over the age of 40 have annual mammograms.

While breast cancer in men is uncommon, it does happen. Both men and women have breast tissue, although men have much less of it than women; most of the breast tissue in men is located behind the nipple. Breast cancer in men accounts for less than one percent of all breast cancers

Regular mammograms can help reduce a woman’s chance of developing breast cancer, and the higher risk of breast cancer a woman has, then the more important it is to have regular screenings. Once a woman reaches 40 her chances of developing breast cancer increase. Any woman who has a family history of breast or ovarian cancer or has received radiation treatment to her chest in the past is advised to start having annual mammograms from the age of 30. The National Cancer Institute advises those women who have had breast cancer and those who are at increased risk due to a genetic history of breast cancer to seek expert medical advice about whether they should begin screening before age 40 and about the frequency of screening. And anyone who is concerned about the frequency of their mammograms should discuss the issue with their physician.

The bottom line is that mammograms save lives. However, there are a few drawbacks: mammograms don’t detect all types of breast cancer -- they can miss 15-20 percent of breast cancers that are just not visible using this technique. It's also important to remember that mammograms can sometimes produce incorrect readings and result in unnecessary surgery.

Nevertheless, while mammograms can’t guarantee to prevent breast cancer, they can save lives by detecting abnormalities in the breast at a very early stage. Mammograms have been shown to reduce the risk of dying from breast cancer by 35% in women over the age of 50; and for women between 40 and 50 studies suggest mammograms may reduce the risk of dying from breast cancer by 25–35%. Detecting breast cancer in its early stages through mammography also increases a woman's chance of being able to keep her breasts.

Magnetic resonance imaging (MRI) tests are also used to detect breast cancer. However, while MRI tests are more thorough than mammograms they also detect more growths that look suspicious but which in fact turn out to be benign. MRI tests are also much more expensive than mammograms and may not be covered by insurance. Mammography screening remains the best technique to detect breast cancer early.

The cost of a screening mammogram is between $100 and $150. Most states have laws stating that health insurance companies must reimburse individuals all or part of the cost of a screening mammogram. All women aged 40 and over with Medicare can get a screening mammogram each year. Medicare will also pay for one baseline (a woman’s first screening) mammogram for women between the ages of 35 and 39.

Coronary Computed Tomography Angiography: General Considerations

Coronary computed tomography (CCTA) is currently considered to be a technique for high-resolution computed tomography (CT) imaging of the heart. It has become generally accepted that patients with negative CT cardiac results will not need to undergo cardiac catheterization. The radiation dose for the CCTA with modern techniques is much lower than even a few years ago and in some cases, even lower than for cardiac catheterization.

The 64-Slice CT scanner is considered to be the high-end CT system and is preferable for CCTA. However, even earlier generation CT systems are suitable for this task.

In some research studies, there has been an attempt to determine the most beneficial use of cardiac CT scanners, and the consensus appears to be that the high negative predictive value of the multislice CT scanner, used to filter out those patients who do not require further investigatory tests for coronary disease, is where it is currently used most effectively.

CCTA is a non-invasive test, requiring only a contrast injection and for some patients, beta blockers. Therefore the CT scan can be performed as an outpatient examination. The disadvantage of CCTA is that there is a limitation with respect to the image quality for patients with irregular or high heart rates. In such cases, patients may be medicated by beta blockers.
CCTA is also limited where there is extensive calcification, as the high contrast of the calcium leads to "blooming" artifact.

The implementation of X- ray tube current modulation resulted in a dramatic decrease in radiation. In addition, the use of CT scans with ECG -triggering of the radiation resulted in average doses around 3 MSV.

The cost of premium-class, 64-slice CT scanning can be $1.2 - $1.5 million. A dual-source, 64-slice CT scan system costs $1.9 - $2.5 million.
The running costs including: a service contract, three full- time staff members and contrast media are $700 - $850k. In terms of potential revenue, the CCTA exam costs about 10% to 12% of the cost of cardiac catheterization.

Technical Considerations

CCTA requires an accurate imaging of coronary arteries, which move with the cardiac and respiratory cycles. Therefore, high spatial resolution and high temporal resolution are essential.

High contrast-to-noise ratio is of primary importance. To achieve a good enough ratio, it is possible to either increase the X-ray tube output and use thicker slices, or to increase the contrast. The spatial resolution will be impaired by increasing the slice width and filtering the signals.

To eliminate cardiac motion artifact, high-rotation speed system is necessary. Current cardiac CT scanners have 3-3.3 R.P.M speed.

For higher temporal resolution, half the gantry rotation time is used for the reconstruction. To assure the best temporal resolution, it is important to acquire the image in the most stationary phase of the cardiac cycle. Therefore, ECG signal is used to enable the reconstruction of the CCTA image in the cardiac phase of least motion.

The typical scan length of a CCTA examination is about 14 CM. It is essential that the CT scan is completed well within a patient's breathhold, so as to avoid respiratory motion artifacts.

Imaging of the coronary arteries can be achieved on a CT scanner in a variety of different ways. Where the complete heart cycle is scanned, greatest flexibility is available in selecting the optimal phase for coronary artery image reconstruction. This approach enables the best functional analysis. However, the dose to the patient is high. Where only a selected part of the cardiac cycle is CT scanned, the radiation is only during a short interval. In this situation, the radiation is low. There is also the merging of the two approaches: all phases of the heart are CT scanned with reduced radiation, and only the stationary phase window is fully illuminated. Full image quality is obtained for the coronary artery image required phase, whereas the images for functional analysis have lower quality.

In general, the CCTA systems can be classified in 4 groups:

1. Axial scan, Prospective ECG Triggered: this is the most commonly used mode, due to the resultant lower dose. Modern systems typically require 3-4 rotations. It is suitable for patients with heart rates below 70 BMP.

2. Axial scan, Retrospective ECG Gated: in this mode, the axial scan is performed over the full cardiac cycle, over a number of gantry rotations (depending on the detector coverage) so the patient is exposed to high-dose rates.

3. Helical Scan, Retrospective ECG Gated: in this mode the radiation is continuous, while the heart is covered with a low-pitch helical scan. The involved radiation dose is high. This is the mode of choice for patients with high or unstable heart rates.

4. Helical scan, Prospective ECG Triggered: in this mode, the radiation is triggered by ECG, as it is with the axial triggered systems. Systems with dual source (two x-rays tubes and detectors which are positioned at 90 degrees each to other) can be operated at high pitch. A full scan can be performed in less than 0.5 seconds.

Low-pitch prospective systems are rare nowadays.

Performance of CCTA
CT scanning results in a plain-scan resolution of approximately 0.5 mm. With a typical reconstruction field of view of 25 cm, and a reconstruction matrix of 512×512, the pixel size is approximately 0.5 mm, which is a good match for the resolution.

The longitudinal axis resolution of modern, quality CT scanner systems approaches 0.5 mm.

Radiology - Certified vs Registered vs Licensed - What is the Difference

If you're thinking of getting a radiological education, you may be wondering, "Radiology-certified vs. registered vs. licensed-what is the difference?" It is actually all connected, with slight differences depending on your specific specialization. You must be certified to get into the career, and licensed and registered to continue working in the field. These are all topics you should become more familiar with as you complete your education in radiography, nuclear medicine or ultrasound technology.

If you are going to become a radiological technologist, also known as a Rad Tech or RT, you need to become certified. In order to get certified, you have get certified and registered through the American Registry of Radiological Technologists. If you are going to go into ultrasound technology or sonography you will need to be certified and licensed through the American Registry of Diagnostic Medical Sonography. Nuclear medicine technologists must get their certification through the Nuclear Medicine Technology Certification Board.

So you're probably still wondering what exactly the difference between certified, registered and licensed radiology professionals is. It's simpler than it seems. Basically, certification is just the first step that you take after finishing your educational program and passing the required examinations. Registration is what you do annually from there on to continue working in this professional field. And licensure is something that differs with each state. Every state grants its own licenses for medical professionals such as radiology technicians to work in that state. This should all become clearer as you complete an accredited degree program in radiology, prepare for your career and get hands on training in the field.

If you are planning on becoming a radiography technician you should become acquainted with the American Registry of Radiological Technologists (ARRT) and their membership. Likewise, ultrasound students should familiarize themselves with the American Registry for Diagnostic Medical Sonography (ARDMS) and those studying nuclear medicine should learn as much as possible about the Nuclear Medicine Technology Certification Board (NMTCB). Your certification, registry and licensure will be determined by these various organizations, and they can be valuable career resources.

Dubai-based radiography firm warned for poor safety regulations - GulfNews

Abu Dhabi: The Federal Authority for Nuclear Regulation (FANR) has warned a Dubai-based industrial radiography company for not complying with safety regulations.

"While allowing it to store or export radiological sources, FANR banned the company from using them," FANR said in a statement.

Exotherm Technical Testing Laboratory (Dubai) applied for a licence on 29 June 2010 to use radioactive sources for the purpose of industrial radiography, as mandated by the UAE's Federal Law by Decree No 6 of 2009.

"However, during the assessment of the application, FANR found substantial cause for concern that the company's radiation protection arrangements did not meet the authority's requirements. In particular, the arrangements for assessing the doses of workers were severely deficient and it could not be established that no worker has received dangerous doses of ionising radiation."

FANR said in these circumstances, it has issued a licence to the company that allows it only to store and export the radioactive sources, but prohibited it from conducting any other activity with them.

"Following several unannounced inspections to Exotherm during the past weeks, FANR radiation safety inspectors delivered last Thursday official correspondence from the regulatory authority in this regard. They also placed notices in multiple languages on Exotherm premises that severe legal penalties may be applied to any person using those radioactive sources. FANR inspectors were joined by officers from the Dubai Municipality who supported the action," it added.

FANR also informed the company that its initial licence application was still under investigation by the authority as there appears to be some irregularities with the documents submitted.

John Loy, FANR's Director of Radiation Safety, in the statement, said any entity that did not meet regulatory safety standards would face similar actions.

"Radiation sources are essential tools for many industrial applications," he added. "But we are here to protect the workers and the public from possible hazards of radioactivity and will exert all possible authority given to us by the Federal Laws."

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