What is the difference between mra and cta

The capability for near-isotropic imaging is responsible for the superior spatial resolution of CT over MR imaging. MDCT has faster acquisitions, covers a larger area, and significantly reduces the amount of injected iodinated contrast necessary as compared with single-detector CT. The prime indications for imaging the intracranial vasculature are for the detection and treatment planning of aneurysms and the evaluation of specific clinical situations related to steno-occlusive disease.

A thin-section 1. With this technique, imaging is not significantly affected by the presence of hemorrhage. The high signal from the stationary tissue due to T1 contamination artifact of blood is eliminated by subtraction of the pre-enhancement volume from the contrast-enhanced time frame. MRA is better suited for their evaluation. In addition to general advantages, CE-MRA on a 3T magnet with fast gradient techniques provides an especially accurate depiction of cerebral aneurysms.

MRA has a tendency to overestimate the extent of stenosis; however, calcification in the arterial wall can eventuate in a nondiagnostic study by CTA. A limitation of MRA is that it cannot be performed in claustrophobic patients or in patients with pacemakers, certain implants, or aneurysm clips. Sixteen-channel MDCT has the potential to reduce artifacts due to surgical clips and calcification this requires further verification. Atherosclerosis is the most frequent indication to image the extracranial carotid arteries.

In the same study the sensitivity and specificity of CTA were quoted to be It has been suggested that plaque characterization by MRA may be used in treatment planning of atherosclerotic disease 31,32 Figure 4.

One must be aware of pitfalls of each technique. In the year , 1. Spiral scanning using 8 or 16 slices is performed with a digital electrocardiography EKG and oversampling of scan projections.

A mm slab with overlapping 20 slices of 3-mm thickness is obtained. The process takes only 10 to 12 minutes per 3D acquisition. CE-MRA could be used primarily to detect vascular anomalies and to evaluate cases deemed equivocal by other modalities Figure 5. The use of 2D spin-echo and gradient-echo techniques allows the visualization of flow in 2 successive slices to correlate with patency, while flow in 1 slice is equivocal, and no flow indicates occlusion.

A calcium score can be obtained. A low calcium score has a high negative predictive value for coronary artery disease CAD. With the latest improvement in spatial resolution coupled with better techniques to suppress motion and the potentially confounding influence of epicardial fat, MRA can serve as a "one-stop" examination in the detection of CAD.

Coronary artery disease is a major health problem causing significant morbidity in the expanding elderly population.

A test to detect CAD should be noninvasive, reliable, safe does not involve ionizing radiation , and inexpensive. Coronary MRA has some of these virtues. A meta-analysis was performed to investigate the efficacy of MRA compared with catheter angiography in the detection of significant coronary artery stenosis.

A Medline search was performed with the key words "coronary MR angiography. After excluding 2D MR techniques, 20 studies were identified. Strict inclusion criteria based on recommendations of Oxman et al 47 were applied Table 1. Nine studies Table 2 , met the criteria, and 11 studies were excluded Table 3. Based on the number of coronary segments evaluated, overall sensitivity and specificity of coronary MRA for the detection of significant stenosis were calculated. The meta-analysis was limited, as only two variables sensitivity and specificity were evaluated.

Due to the small number of studies that met the inclusion criteria, other variables, such as the effect of sample size on sensitivity and specificity, could not be evaluated. The study by Kim et al 40 had the maximum number of coronary segments evaluated, more than all other studies combined. There was a high level of interobserver variability for the determination of sensitivity of coronary MRA for significant stenosis. The specificity was near constant. MRA holds promise to be a safe, noninvasive, and an efficient test in evaluating the coronary arteries.

Technical advancements, such as faster imaging sequences, and prospective double-blinded studies are needed to evaluate the full extent of its clinical usefulness. The most frequent indication to image the pulmonary arteries is pulmonary embolism PE.

For good-quality images, breath-holding for at least 10 to 15 seconds for each lung acquisition is necessary, 69 which may not be possible in patients with dyspnea. Haage et al 74 report a detection rate of emboli of Gadolinium, an I.

An MRA can evaluate for intracranial or extracranial atherosclerosis, arteriovenous malformation, intact aneurysms, or other cerebrovascular disease. Explain that generally, the only uncomfortable part of the procedure is when vascular access is established for contrast injection. Tell the patient about the importance of being still during the scan; motion reduces the clarity of the images produced.

Because MRI produces an extremely loud noise, like a jackhammer, patients will most likely be offered ear protection such as earplugs. Screen your patient for any contraindications to MRI. Many institutions have a screening form to assess for metal in the body; you'll need to carefully question your patient and document the responses. Also screen your patient for claustrophobia; if necessary, obtain an order for an anxiolytic. If sedation is used, you'll need to use MRI-compatible monitoring equipment.

Many patients can be comforted by knowing healthcare personnel are just outside the room, and the patient can communicate with them if necessary. Be alert that most magnetic resonance scanners have a weight limit. Finally, carefully assess women of childbearing age for possible pregnancy. Although MRA doesn't use radiation, and no adverse effect to the fetus from magnetic resonance or gadolinium have been documented, this doesn't mean adverse effects don't exist.

The need for the MRA needs to be weighed against the safety of the fetus in the case of pregnancy. If your patient is breastfeeding, you may want to check with your lactation consultant about the patient's ability to nurse after contrast injection. Generally, it's considered safe. After the scan, monitor the patient's renal function. Although gadolinium is less nephrotoxic than conventional contrast, it can affect renal function.

Encourage patients to drink fluids for 24 to 48 hours after MRA, unless contraindicated. The multidetector lets the CT quickly take high-quality pictures of the brain. The healthcare provider can see an aneurysm, even if it's ruptured. Establish vascular access for the contrast injection and explain the need to lie still to assure good-quality images. The scanner also produces noise, but it's not as loud as magnetic resonance.

Patients undergoing CTA also can communicate with healthcare personnel if need be. It does not contain iodine, and it is less likely to cause an allergic reaction than CT and X-ray iodine based contrast.

Tell the radiologist and technologist about any serious health problems and what surgeries you have had. Some patients with severe kidney or liver disease may not be able to receive contrast material during an MRI exam. Women should always tell their doctor and technologist if they are pregnant. MRI has been used since the s with no reports of any ill effects on pregnant women or their unborn babies.

However, the baby will be in a strong magnetic field. Therefore, pregnant women should not have an MRI in the first trimester unless the benefit of the exam clearly outweighs any potential risks.

Pregnant women should not receive gadolinium contrast unless absolutely necessary. If you are breastfeeding at the time of the exam, ask your doctor how to proceed. It may help to pump breast milk ahead of time. Keep it on hand for use until all contrast material has cleared from your body about 24 hours after the test.

However, the most recent American College of Radiology ACR Manual on Contrast Media reports that studies show the amount of contrast absorbed by the infant during breastfeeding is extremely low. If you have claustrophobia fear of enclosed spaces or anxiety, ask your doctor to prescribe a mild sedative prior to the date of your exam. Infants and young children often require sedation or anesthesia to complete an MRI exam without moving. This depends on the child's age, intellectual development, and the type of exam.

Sedation can be provided at many facilities. A specialist in pediatric sedation or anesthesia should be available during the exam for your child's safety. You will be told how to prepare your child. Some facilities may have personnel who work with children to help avoid the need for sedation or anesthesia. They may prepare children by showing them a model MRI scanner and playing the noises they might hear during the exam. They also answer any questions and explain the procedure to relieve anxiety.

Some facilities also provide goggles or headsets so the child can watch a movie during the exam. This helps the child stay still and allows for good quality images.

Leave all jewelry and other accessories at home or remove them prior to the MRI scan. Metal and electronic items are not allowed in the exam room. They can interfere with the magnetic field of the MRI unit, cause burns, or become harmful projectiles. These items include:. In most cases, an MRI exam is safe for patients with metal implants, except for a few types. People with the following implants may not be scanned and should not enter the MRI scanning area without first being evaluated for safety:.

Tell the technologist if you have medical or electronic devices in your body. These devices may interfere with the exam or pose a risk. Many implanted devices will have a pamphlet explaining the MRI risks for that device. If you have the pamphlet, bring it to the attention of the scheduler before the exam. MRI cannot be performed without confirmation and documentation of the type of implant and MRI compatibility.

You should also bring any pamphlet to your exam in case the radiologist or technologist has any questions. If there is any question, an x-ray can detect and identify any metal objects. Metal objects used in orthopedic surgery generally pose no risk during MRI. However, a recently placed artificial joint may require the use of a different imaging exam.

Tell the technologist or radiologist about any shrapnel, bullets, or other metal that may be in your body. Foreign bodies near and especially lodged in the eyes are very important because they may move or heat up during the scan and cause blindness. Dyes used in tattoos may contain iron and could heat up during an MRI scan. This is rare. The magnetic field will usually not affect tooth fillings, braces, eyeshadows, and other cosmetics. However, these items may distort images of the facial area or brain.

Tell the radiologist about them. The traditional MRI unit is a large cylinder-shaped tube surrounded by a circular magnet. You will lie on a table that slides into a tunnel towards the center of the magnet. Some MRI units, called short-bore systems , are designed so that the magnet does not completely surround you. Some newer MRI machines have a larger diameter bore, which can be more comfortable for larger patients or those with claustrophobia.

They are especially helpful for examining larger patients or those with claustrophobia. Open MRI units can provide high quality images for many types of exams. Open MRI may not be used for certain exams. For more information, consult your radiologist. 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. Procedures use contrast material to clearly define the blood vessels being examined by making them appear bright white. The technologist will position you on the moveable exam table. They may use straps and bolsters to help you stay still and maintain your position. The technologist may place devices that contain coils capable of sending and receiving radio waves around or next to the area of the body under examination.

MRI exams generally include multiple runs sequences , some of which may last several minutes. Each run will create a different set of noises. If your exam uses a contrast material, a doctor, nurse, or technologist will insert an intravenous catheter IV line into a vein in your hand or arm. They will use this IV to inject the contrast material.

You will be placed into the magnet of the MRI unit. The technologist will perform the exam while working at a computer outside of the room.

You will be able to talk to the technologist via an intercom. If your exam uses a contrast material, the technologist will inject it into the intravenous line IV after an initial series of scans.