Instruct: Given a question, retrieve relevant documents that answer the question.
Query: Are MRI's for soft tissue scans?
Applications in the musculoskeletal system include spinal imaging, assessment of joint disease, and soft tissue tumors.[23]
In the 1950s, Herman Carr reported [19] creating a one-dimensional MR image. Prompted by Damadian's report on the potential medical uses of NMR, Paul Lauterbur expanded on Carr's technique and developed a way to generate the first MRI images, in 2D and 3D, using gradients. Peter Mansfield from the University of Nottingham then developed a mathematical technique that would allow scans to take seconds rather than hours and produce clearer images than Lauterbur had. While Lauterbur and Mansfield focused on animals and human limbs, Damadian built the first full-body MRI machine[15] and produced the first full magnetic resonance imaging ("MRI") scan of the human body, albeit using a “focused field” technique that differs considerably from modern imaging. In recording the history of MRI, Mattson and Simon (1996) credit Damadian with describing the concept of whole-body NMR scanning, as well as discovering the NMR tissue relaxation differences that made this feasible.
The most important component for CAS is the development of an accurate model of the patient. This can be conducted through a number of medical imaging technologies including CT, MRI, x-rays, ultrasound plus many more. For the generation of this model, the anatomical region to be operated has to be scanned and uploaded into the computer system. It is possible to employ a number of scanning methods, with the datasets combined through data fusion techniques. The final objective is the creation of a 3D dataset that reproduces the exact geometrical situation of the normal and pathological tissues and structures of that region. Of the available scanning methods, the CT is preferred, because MRI data sets are known to have volumetric deformations that may lead to inaccuracies. An example data set can include the collection of data compiled with 180 CT slices, that are 1 mm apart, each having 512 by 512 pixels. The contrasts of the 3D dataset (with its tens of millions of pixels) provide the detail of soft vs hard tissue structures, and thus allow a computer to differentiate, and visually separate for a human, the different tissues and structures. The image data taken from a patient will often include intentional landmark features, in order to be able to later realign the virtual dataset against the actual patient during surgery. See patient registration.
Patient with orthopaedic implants sometimes need to be put under magnetic resonance imaging (MRI) machine for detailed musculoskeletal study. Therefore, concerns have been raised regarding the loosening and migration of implant, heating of the implant metal which could cause thermal damage to surrounding tissues, and distortion of the MRI scan that affects the imaging results. A study of orthopaedic implants in 2005 has shown that majority of the orthopaedic implants does not react with magnetic fields under the 1.0 Tesla MRI scanning machine with the exception of external fixator clamps. However, at 7.0 Tesla, several orthopaedic implants would show significant interaction with the MRI magnetic fields, such as heel and fibular implant.
Because CT and MRI are sensitive to different tissue properties, the appearances of the images obtained with the two techniques differ markedly. In CT, X-rays must be blocked by some form of dense tissue to create an image, so the image quality when looking at soft tissues will be poor. In MRI, while any nucleus with a net nuclear spin can be used, the proton of the hydrogen atom remains the most widely used, especially in the clinical setting, because it is so ubiquitous and returns a large signal. This nucleus, present in water molecules, allows the excellent soft-tissue contrast achievable with MRI.
Electromyographic (EMG) nerve-conduction studies may be required. X-rays may be needed to exclude bone abnormalities that might put pressure on the nerve; likewise CT or MRI scans to exclude soft tissue causes such as a tumor.
It is recommended that magnetic resonance imaging (MRI) scan of the pituitary gland is performed if the diagnosis is suspected; this has a sensitivity of over 90% for detecting pituitary apoplexy; it may demonstrate infarction (tissue damage due to a decreased blood supply) or hemorrhage. Different MRI sequences can be used to establish when the apoplexy occurred, and the predominant form of damage (hemorrhage or infarction). If MRI is not suitable (e.g. due to claustrophobia or the presence of metal-containing implants), a computed tomography (CT) scan may demonstrate abnormalities in the pituitary gland, although it is less reliable. Many pituitary tumors (25%) are found to have areas of hemorrhagic infarction on MRI scans, but apoplexy is not said to exist unless it is accompanied by symptoms.
According to a Wall Street Journal article,[14] Damadian's initial methods were flawed for practical use,[15] relying on a point-by-point scan of the entire body and using relaxation rates, which turned out to not be an effective indicator of cancerous tissue. However, the same article pointed out, “Nevertheless, his observation of T1 and T2 differences in cancerous tissue was a Eureka moment for Paul Lauterbur.” Furthermore, Damadian's seminal paper[13] documented in its Table 2 that T1 relaxation times were different, beyond experimental uncertainty, across all his samples over different healthy tissues: rectus muscle, liver, stomach, small intestine, kidney, and brain. This showed the way to accurate imaging of the body's soft tissues for the first time; X-ray imaging was severely deficient for soft tissue analysis because the difference in absorption was so small (<4%). So when in the court case Fonar v. General Electric, GE's attorneys made the same claim that relaxations times were also prolonged in non-cancerous tissue, so were not a good diagnostic, Fonar's attorneys responded that it was unfair to punish Damadian because his methods detected even more features than he had intended. Indeed, even today, 90% of MRI scans on patients produce images that are relaxation dependent, either T1- or T2-dependent images.
Imaging has a limited role in the diagnosis of necrotizing fasciitis. The time delay in performing imaging is a major concern. Plain radiography may show subcutaneous emphysema (gas in the subcutaneous tissue), which is strongly suggestive of necrotizing changes, but it is not sensitive enough to detect all the cases, because necrotizing skin infections caused by bacteria other than clostridial infections usually do not show subcutaneous emphysema. If the diagnosis is still in doubt, computed tomography (CT) scans and magnetic resonance imaging (MRI) are more sensitive modalities than plain radiography. However, both the CT scan and MRI are not sensitive enough to rule out necrotizing changes completely. CT scan may show fascial thickening, edema, subcutaneous gas, and abscess formation. In MRI, when fluid collection with deep fascia involvement occurs, thickening or enhancement with contrast injection, necrotizing fasciitis should be strongly suspected. Meanwhile, ultrasonography can show superficial abscess formation, but is not sensitive enough to diagnose necrotizing fasciitis. CT scan is able to detect about 80% of cases, while MRI may pick up slightly more.
A white blood cell count less than 15,000 cells/mm and serum sodium level greater than 135 mmol/l have a sensitivity of 90% in detecting the necrotizing soft tissue infection. It also has a 99% chance of ruling out necrotizing changes if the values have shown otherwise. Various scoring systems are being developed to determine the likelihood of getting necrotizing fasciitis, but a scoring system developed by Wong and colleagues in 2004 is the most commonly used. It is the laboratory risk indicator for necrotizing fasciitis (LRINEC) score, which can be used to stratify by risk those people having signs of severe cellulitis or abscess to determine the likelihood of necrotizing fasciitis being present. It uses six laboratory values: C-reactive protein, total white blood cell count, hemoglobin, sodium, creatinine, and blood glucose. A score of 6 or more indicates that necrotizing fasciitis should be seriously considered. The scoring criteria are:
Magnetic Resonance Imaging (MRI) scans provide an image of the soft tissues in the body using radio waves and strong magnets. MRI can be used instead of CT if the patient exhibits an allergy to the contrast media administered for the test. Sometimes prior to the MRI scan, an intravenous injection of a contrasting material called gadolinium is given to allow for a more detailed image. Patients on dialysis or those who have renal insufficiency should avoid this contrasting material as it may induce a rare, yet severe, side effect known as nephrogenic systemic fibrosis. A bone scan or brain imaging is not routinely performed unless signs or symptoms suggest potential metastatic involvement of these areas.
MRI scans should also be considered to evaluate tumour extension which has grown in major blood vessels, including the vena cava, in the abdomen. MRI can be used to observe the possible spread of cancer to the brain or spinal cord should the patient present symptoms that suggest this might be the case.
The contrast agents used for DCE-MRI are often gadolinium-based. Interaction with the gadolinium (Gd) contrast agent (commonly a gadolinium ion chelate) causes the relaxation time of water protons to decrease, and therefore images acquired after gadolinium injection display higher signal in T1-weighted images indicating the present of the agent. It is important to note that, unlike some techniques such as PET imaging, the contrast agent is not imaged directly, but by an indirect effect on water protons. Common procedure for a DCE-MRI exam is to acquire a regular T1-weighted MRI scan (with no gadolinium), then gadolinium is injected (usually as an intravenous bolus at a dose of 0.05-0.1 mmol/kg) before further T1-weighted scanning. DCE-MRI may be acquired with or without a pause for contrast injection, and may have varying time resolution depending on preference - faster imaging (less than 10s per imaging volume) allows pharmacokinetic (PK) modelling of contrast agent, but can limit possible image resolution. Slower time resolution allows more detailed images, but may limit interpretation to only looking at signal intensity curve shape. In general, persistent increased signal intensity (corresponding to decreased T1 and thus increased Gd interaction) in a DCE-MRI image voxel indicates permeable blood vessels characteristic of tumour tissue, where Gd has leaked into the extravascular extracellular space. In tissues with healthy cells or a high cell density, gadolinium re-enters the vessels faster since it cannot pass the cell membranes. In damaged tissues or tissues with a lower cell density, the gadolinium stays in the extracellular space longer.
Magnetic Resonance Imaging (MRI) produces a 3-dimensional image that allows for exceptional evaluation of soft tissue structures, as well as the detection of boney change and the presence of excessive fluid accumulation associated with inflammation. Like CT, an MRI image may be viewed in various planes of orientation, improving visualization of anatomic structures and any associated pathologic change. MRI is considered the gold standard for diagnosing soft tissue injury within the foot. While it can provide a definitive diagnosis in cases where other imaging modalities have failed, it does have several limitations. Available magnet size restricts imaging to the level of the stifle or elbow, or below. MRI takes a significant amount of time acquire an image, which translates to long anesthesia times and therefore reduces the size of the area that may be imaged in a single session. The area thought to be associated with lameness must be placed in the MRI. MRI is therefore inappropriate for any lameness that can not be localized to a specific region of the limb. Additionally, MRI has limited availability and high cost compared to the other imaging modalities.
Cranial ultrasound is usually only used in babies, whose open fontanelles provide acoustic windows allowing ultrasound imaging of the brain. Advantages include the absence of ionising radiation and the possibility of bedside scanning, but the lack of soft-tissue detail means MRI is preferred for some conditions.
MRI uses strong magnetic fields to align atomic nuclei (usually hydrogen protons) within body tissues, then uses a radio signal to disturb the axis of rotation of these nuclei and observes the radio frequency signal generated as the nuclei return to their baseline states. The radio signals are collected by small antennae, called coils, placed near the area of interest. An advantage of MRI is its ability to produce images in axial, coronal, sagittal and multiple oblique planes with equal ease. MRI scans give the best soft tissue contrast of all the imaging modalities. With advances in scanning speed and spatial resolution, and improvements in computer 3D algorithms and hardware, MRI has become an important tool in musculoskeletal radiology and neuroradiology.
In symptomatic cases the diagnosis should be confirmed by an MRI scan. However, in cases with slight symptoms, a faster and cheaper CT scan (although it is inferior to MRI scan) may be recommended. While a CT scan can show the bony structures in more detail, an MRI scan can better portray soft tissue.
Early in the 1980s, Dean argued that without a functional bases to tests the increase in scanning technology would have decreased the efficacy of neuropsychological assessment. His concerns were realized with both the sophistication and geometric growth of radiological scanning techniques over the past 30 years. These computer driven scanning devices such as the CT scan, and more recently the less invasive MRI,and fMRI have begun offered microscopic views of the soft tissue of the central nervous system that was not possible prior to the early 1970s when skull x-rays were the state of the art.
CT is well suited to show foreign objects, bone and air or gas distribution throughout the body, whereas MRI sequences are strong in detailing organ and soft tissue findings. A comprehensive analysis of both surface and deep tissue findings may require fusion of CT, MRI and 3D surface data.
Typically, in soft tissues "T" is around one second while "T" and "T" are a few tens of milliseconds. However, these values can vary widely between different tissues, as well as between different external magnetic fields. This behavior is one factor giving MRI its tremendous soft tissue contrast.
Ultimately, the best method of imaging soft tissue is magnetic resonance imaging (MRI), though it is cost-prohibitive and carries a high false positive rate.
Magnetic resonance elastography works by using an additional gradient waveform in the pulse sequence to sensitize the MRI scan to shear waves in the tissue. The shear waves are generated by an electro-mechanical transducer on the surface of the skin. Both the mechanical excitation and the motion sensitizing gradient are at the same frequency. This encodes the amplitude of the shear wave in the tissue in the phase of the MRI image. An algorithm can be used to extract a quantitative measure of tissue stiffness from the MRI in an elastogram.
Subdural and epidural hematomas are serious conditions and should be immediately diagnosed and treated by a physician. Hematomas may not show the full extent of the problem initially after the head injury, but it may be revealed after comprehensive medical evaluation and diagnostic test. Diagnostic test may include: blood test, x-ray, computed tomography scan (CT/CAT scan), electroencephalogram (EEG), and magnetic resonance imaging (MRI). The two most important diagnostic tests are the CT scan and the MRI. The CT scan reveals evidence of blood within the skull, fractures, and signs of compression on the brain from the hematoma. The MRI is a more thorough evaluation of injuries to the brain tissue. Yet, a MRI cannot take place if the injured victim is in a confused state. Small hematomas may not require surgery if there is no pressure on the brain and minimal symptoms. Small hematomas may be monitored closely to ensure the hematoma is not enlarging and resolved properly. A large hematoma larger than 1 cm at its thickest point produces severe headaches and brain function deterioration requires immediate surgery by a neurosurgeon. Surgery reduces the pressure within the brain and stops the bleeding.
Requiring no injections, OCE is an non-invasive imaging method can gives more details than ultrasound or MRI. Using light source to image biological tissue, OCE is considered generally safe compared to CT scan and other radiographic imaging modalities which involve with ionizing radiation. And it is also more affordable and time efficient compared to MRI. However, OCE can also cause tissue damage in some handling. For example, surface acoustic wave OCE can cause to a tissue is primarily concentrated on temperature effects. In the focus point, the temperature of the tissue will rise locally. Therefore, it is necessary to take this into account in certain circumstances.
Orthopedics established early the MRI as the tool of choice for joint- and soft tissue-imaging, because its non-invasiveness, the lack of radiation exposure, multi planar slicing possibilities and the high soft tissue contrast.
"Magnetic resonance imaging" (originally called nuclear magnetic resonance imaging), an imaging methodology based on aligning the spin axis of nuclei within molecules of the object being visualized using both powerful superconducting magnets and radio frequency and detectors. Cardiology uses are growing, especially since MRI differentiates soft tissues better than CT and allows for comprehensive exams including the quantitative assessment of size, morphology, function, and tissue characteristics in one single session. Current implementations for Cardiology uses are sometimes limited by lengthy protocols, claustrophobia and contraindications based on some complex metallic implants (pacemakers, defibrillators, insulin pumps), while artificial valves and coronary stents are generally not problematic. Image quality can be reduced by the continuous movement of heart structures. There is a promising future in cardiac MRI by more efficient scans, increasing availability of scanners and more widespread knowledge about its clinical application.
The US National Science Foundation notes "The patent included the idea of using NMR to 'scan' the human body to locate cancerous tissue." However, it did not describe a method for generating pictures from such a scan or precisely how such a scan might be done. Meanwhile, Paul Lauterbur at Stony Brook University expanded on Carr's technique and developed a way to generate the first MRI images, in 2D and 3D, using gradients. In 1973, Lauterbur published the first nuclear magnetic resonance image and the first cross-sectional image of a living mouse in January 1974. In the late 1970s, Peter Mansfield, a physicist and professor at the University of Nottingham, England, developed the echo-planar imaging (EPI) technique that would lead to scans taking seconds rather than hours and produce clearer images than Lauterbur had. Damadian, along with Larry Minkoff and Michael Goldsmith, obtained an image of a tumor in the thorax of a mouse in 1976. They also performed the first MRI body scan of a human being on July 3, 1977, studies they published in 1977. In 1979, Richard S. Likes filed a patent on k-space .
During the 1970s a team led by John Mallard built the first full-body MRI scanner at the University of Aberdeen. On 28 August 1980 they used this machine to obtain the first clinically useful image of a patient's internal tissues using MRI, which identified a primary tumour in the patient's chest, an abnormal liver, and secondary cancer in his bones. This machine was later used at St Bartholomew's Hospital, in London, from 1983 to 1993. Mallard and his team are credited for technological advances that led to the widespread introduction of MRI.