MRI Scans

Introduction

Magnetic Resonance Imaging (MRI) is a map of the hydrogen atoms in the body. Hydrogen atoms are ideal for MRI because they have one proton and a large magnetic moment.

• Simply put, an MRI scanner is a large, powerful magnet in which the patient lies.
• The magnetic field created by the magnets produces a resonance from each proton in the hydrogen atom and the device can obtain the position of the proton.
• Since approximately 75% of our bodies are composed of water molecules MR imaging is capable of capturing accurate and detailed images of the examined body part.
• The signals produced by each cell are unique allowing the identification of tissues including skeletal joint tissue and cartilage. Images of any part of the body can be obtained on any plane[1]
• The MRI takes detailed pictures of all the hydrogen molecules in the body and is calculated to create an accurate representation of that part of the body.

There are several types of MRI depending on whether the image is captured in a distinct signal decay. T1 weighted MRI captures early signal decay that accelerates after the protons are fixed. T2 weighted MRI captures signal decay later or after minimal proton migration the original sound.[2]

Why Use

MRI scans have many applications in medical research.[3]

Uses include:

1. Neuroimaging: MRI is the screening tool of choice for lymph node cancer because it is more sensitive than CT for smaller tumors and provides better visualization of the posterior nerve. The contrast provided between gray and white makes it an excellent choice for many interior settings nervous system including demyelinating diseases (eg MS) schizophrenia infectious cerebrovascular disease and epilepsy[4].

2. Functional magnetic resonance imaging (fMRI): fMRI is based on the same technology as magnetic resonance imaging (MRI) is a non-invasive test that uses a strong magnetic field and radio waves to create a body a detailed view of the. But instead of an MRI fMRI image of organs and tissues monitor cerebral blood flow to identify active sites. These electronically captured changes in blood pressure help doctors understand more about how the brain works and pinpoint which parts of the brain are most active. fMRI can detect brain problems such as those caused by seizures or it can be used to image the brain if you need brain surgery for a seizure or seizure.[5]

3. Cardiovascular Image 3: Cardiac MRI Flow Visualization

• Cardiac MRI complements other imaging techniques such as echocardiography, cardiac CT, and nuclear medicine. Its applications include the assessment of myocardial ischemia and viable cardiomyopathy, myocarditis, iron overload, vascular disease, and congenital heart disease [6].
• Magnetic resonance angiography: (often shortened to MR angiography or MRA) is an alternative to conventional angiography and CT angiography that does not require ionizing radiation, iodinated contrast agents, and sometimes no contrast agent at all. It has evolved into multiple techniques Different advantages and applications:
  • contrast enhanced MR angiography (MRA)
  • Non-contrast-enhanced MR angiography (MRA) [7]

4. Musculoskeletal: Applications in the musculoskeletal system include spine imaging assessment of joint diseases and soft tissue tumors [8]

5. Oncology: MRI is the examination of choice in the preoperative management of colorectal and prostate cancer and plays a role in the diagnosis and follow-up of other tumors.[9] Cancerous tissue contains more fluid than healthy tissue. Excess fluid takes longer in an MRI machine it distinguishes the tumor from surrounding tissue in the imaging.[10]

6. MRI of liver and abdomen: Hepatobiliary MRI is used to detect and characterize hepatic pancreatic and vascular lesions. Extracellular contrast agents are widely used in liver MRI and new hepatobiliary contrast agents also offer the opportunity for functional biliary formation photography.[11]

Key Points

• MRI is a high-quality imaging modality for evaluating soft tissue.
• T1 and T2 weighted images (see below) represent the main MR images.
• T1 and T2 images can be modified: fat-filled gadolinium and inversion recovery.
• The sequence shows you what is in the tumor and how it is behaving. Using these features on the location of the lesion and the clinical history we can make an assessment[12].

Advantages and Disadvantages of MRI

Advantages of MRI

• the ability to imaging without the use of ionizing x-rays as opposed to CT scanning
• images can be obtained in multiple planes (axial sagittal coronal or oblique) without repositioning the patient. It has only recently been possible to reconstruct CT images in multiple planes with the same spatial resolution (i.e. isotropic voxels) .
• MRI images exhibit superior soft tissue contrast compared to CT scans and plain radiographs making it an excellent examination of the cerebral spinal cord joints and other soft tissue anatomies
• some angiographic images can be obtained without the use of contrast agents unlike conventional CT or angiography
• advanced techniques such as diffusion spectroscopy and perfusion allow more accurate characterization of tissues than simply ‘macroscopic’ imaging
• functional MRI makes it possible to see which parts of the brain are active during certain activities and also to understand the underlying connections

Disadvantages of MRI

• MRI scans are more expensive than CT scans
• MRI scans take much longer to acquire than CT, and patient comfort can be an issue, possibly exacerbated by:
• MR image acquisition is noisier compared to CT
• MRI scanner bores tend to be more closed than CT and can be claustrophobic. The NB Open MRI machine was created to make the experience more enjoyable for children and people suffering from symptoms of claustrophobia. [10]
• MR images are subject to unique artifacts that must be identified and mitigated (see MRI Artifacts)
• MRI scans are not safe for patients with some metal implants and foreign objects. Careful attention must be paid to safety measures to avoid serious injury to patients and staff, which requires special MRI-compatible equipment and strict adherence to safety protocols (see MRI Safety). [9]

Common Abbreviations Used for MRI

T1 and T2 images show different tissues depending on the timing of the RF pulses. Between the two, the main differences you need to be aware of are:

• T1 – ONE tissue is bright: fat
• T2 – two tissues are bright: fat and water (WW2 – water in T2 is white)
• T1 is the most “anatomical” image (Figure 1). In contrast, cerebrospinal fluid (CSF) is bright in T2 due to its water content.
• T2 is generally more commonly used, but T1 can be used as a reference for anatomy or to differentiate fat from watery signals.

Additional features for T1/T2 weighted images

• Fat Suppression (FS): Fat signal can be suppressed for better visualization of pathology in and around anatomical structures – especially edema. This is useful in adrenal tumors or bone marrow pathologies where the image will appear homogenous to the surrounding tissue due to the fat content.
• Gadolinium enhancement (Gad): Gadolinium enhances vasculature (ie, arteries) or pathological vascular tissue (eg, intracranial metastatic meningioma). The procedure involves injecting 5-15 ml of contrast medium intravenously, and images are taken shortly thereafter. Gadolinium appears bright in the signal Allows detection of detailed abnormalities (eg intracranial lesions).

Inversion recovery (IR) sequences

These types of images are T1 and T2 processed. They disable certain tissue types based on inversion time, preventing tissues such as fat and cerebrospinal fluid from showing up as bright signals. This helps to identify signs of pathology. Two main types are discussed below.

• Short tau Inversion Recovery (STIR): Based on T2 images, but the images are processed in such a way that fat (and any other material with a similar signal) is invalid. However, unlike fat-suppressed images, STIR cannot be used with gadolinium contrast agents. 4 As mentioned earlier, fat can make Interpretation of edematous areas and bone marrow is difficult.
• Fluid Attenuated Inversion Recovery (FLAIR): Similar to T2, but with no CSF signal. This is particularly useful for assessing structures in the central nervous system (CNS), including the periventricular sulci and gyri. For example, FLAIR can be used to identify a variety of plaques Cerebrospinal fluid may interfere with interpretation of other cases of stroke and pathological sclerosing minor edema [12]

Hybrid MRI sequences occur when radio frequency types and frequencies are manipulated and cause echoes. Gradient echo increases sensitivity or iron complexes such as articular cartilage defects and muscle hemorrhages, but conversely degrades metallic hardware such as needles or screw) from surgery. Spin echo has the added benefit of increasing tissue contrast and better visualization of meniscus tears. Stimulated echo reduces signal interference and thus can be used to observe specific molecular motions within tissue. [5]

Proton density images

1. Simple Proton Density Image
2. Areas of more dense protons will appear white (cortical marrow)
3. Less dense areas appear darker (fluid soft tissue)

Contraindications for MRI

• Pacemaker aneurysm clip cochlear implant and orbital foreign body
• Projectiles in the room (including oxygen cylinders, IV poles, stethoscopes, hair clips, etc.)

Historical Note

Nikola Tesla first discovered the rotating magnetic field in Budapest, Hungary in 1882, a phenomenon that made magnetic resonance imaging possible. Seventy-four years later, scientists honor his discovery by naming the Tesla unit as the official measure of magnetic field strength. [10] ]

Image: Nikola Tesla’s Columbus Egg The inventor used this setup to demonstrate the rotating magnetic field that drives his new AC induction motor by spinning a copper egg with the field.

Neurophysiology Fact

Charles Lim, an audiologist at Johns Hopkins University and a faculty member at the Peabody Institute of Music, wondered how some musicians were able to create concert-length pieces of music that were completely improvised from beginning to end. So he had jazz pianists and rappers get them in MRIs fulfill. The resulting images show that the most prolific improvisers somehow manage to switch off the parts of their brains that process self-monitoring, leading the limbs to the conclusion many musicians might intuitively: If you make a mistake,do not worry. [13]

Difference between MRI and CT

Like CT, MRI traditionally creates two-dimensional images of thin sections of the body and is therefore considered a tomographic imaging technique. Modern MRI instruments are capable of producing images in the form of 3D blocks, which can be considered a generalization of single-slice tomography concept. Unlike CT, MRI scans do not use X-rays, so possible problems with X-ray pictures and CT scans (which use X-rays) have nothing to do with MRI scans. [14] For example, since MRI has only been used since the early 1980s, there are no known effects of long-term exposure to intense radiation Static field (this is the subject of some debate; see “Safety” in MRI), so there is no limit to the number of scans an individual can receive compared to X-ray and CT. However, there are definite health risks associated with exposed tissue heating Presence of radio frequency fields and implanted devices in the body such as pacemakers. These risks are tightly controlled as part of the instrument design and the scanning protocol used.

Because CT and MRI are sensitive to different tissue properties, the appearance of images obtained using the two techniques differs significantly. In CT, X-rays must be blocked by some form of dense tissue to create an image, so image quality can be poor when looking at soft tissue. in MRI Any nucleus with a net nuclear spin can use the proton of the hydrogen atom and remains the most widely used, especially in clinical settings, because it is ubiquitous and returns a large signal. The nuclei present in the water molecules enable excellent soft tissue contrast.