BACKGROUND AND PURPOSE: CSF pulsation artifact is a pitfall of fast fluid-attenuated inversion-recovery (FLAIR) brain MR imaging. We studied ventricular CSF pulsation artifact (VCSFA) on axial FLAIR images and its relationship to age and ventricular size.
What is an artifact in an MRI?
Artifacts in magnetic resonance imaging (MRI) may be caused by the MR scanner hardware itself or by the interaction of the patient with the hardware [1]. Artifacts and foreign bodies within the patient’s body may be confused with a pathology or just reduce the quality of examinations.
What causes artifacts in magnetic resonance imaging?
Figure 1D is from a breast MR image in which the phase-encoding direction is oriented horizontally from right to left. Part 1: Motion and Pulsation Artifact Motion is a very common cause of artifacts in magnetic resonance imaging (MRI).
What is a presaturation pulse used for in imaging?
Presaturation pulses can be used to null fat if its signal is contributing to the motion artifact. It can also be used to saturate the protons in flowing blood before it enters the volume of tissue being imaged, and is a frequently used technique in time-of-flight (TOF) imaging (see Chapter 11).10
How is pulsation artifact diagnosed in cerebral aneurysm?
The diagnosis is clinched with recognition of pulsation artifact in the phase-encoding direction, which is due to pulsatile blood flow within the aneurysm. However, lack of artifact does not exclude an aneurysm, since completely thrombosed aneurysms will not produce pulsation artifact.
What causes motion artifacts in MRI?
Why does flowing blood cause motion artifacts?
How to reduce motion artifacts?
How does spatial gradient affect motion?
What is a T2 lesion?
What is a T2 bright lesion?
What are ghosting artifacts?
See 2 more
What is pulsation artefact?
These artifacts may be seen from arterial pulsations, swallowing, breathing, peristalsis, and physical movement of a patient. When projected over anatomy it can mimic pathology, and needs to be recognized. Motion that is random such as the patient moving produces a smear in the phase direction.
What does it mean when an MRI shows an artifact?
Artifacts in magnetic resonance imaging (MRI) may be caused by the MR scanner hardware itself or by the interaction of the patient with the hardware [1]. Artifacts and foreign bodies within the patient's body may be confused with a pathology or just reduce the quality of examinations.
What is CSF pulsation artifact?
Background and purpose: CSF pulsation artifact is a pitfall of fast fluid-attenuated inversion-recovery (FLAIR) brain MR imaging. We studied ventricular CSF pulsation artifact (VCSFA) on axial FLAIR images and its relationship to age and ventricular size.
What does movement artifact mean?
Motion artifact is a patient-based artifact that occurs with voluntary or involuntary patient movement during image acquisition. Misregistration artifacts, which appear as blurring, streaking, or shading, are caused by patient movement during a CT scan.
What is the most common cause of artifact when performing MRI?
Patient movement, the inherent aspects of MR imaging, and contamination are the most common sources of artifacts in MRI images.
What does artifact mean in medical terms?
Definition: artifact. artifact. In radiology, something artificial that appears on a medical image but is not a part of the living tissue being examined. The image distortion could be due to an obstruction, such as a surgical metal clip, or to a problem with the imaging equipment.
How does CSF appear on MRI?
Normal CSF has long T1 and long T2 times that manifest as dark signal on T1-weighted images and bright signal on T2-weighted images. FLAIR imaging results in nulling and dark CSF signal. The normal CSF signal is frequently altered by superimposed flow phenomena that can confound interpretation [1].
What are the symptoms of leaking spinal fluid?
The most common symptom of a spinal CSF leak is headache. These headaches usually: Cause pain in the back of the head....Other symptoms of spinal CSF leaks may include:Neck or shoulder pain.Ringing in the ears (tinnitus)Changes in hearing.Dizziness.Nausea or vomiting.Changes in vision.Changes in cognition or behavior.
What is CSF signal on MRI?
MRI of the brain or spine that evaluates the flow of cerebral spinal fluid (CSF) around the brain, brainstem or spinal cord.
What causes muscle artifacts?
These are typically caused by muscle activity near the head, such as swallowing or head movements, and are characterized by high-frequency activity (> 20 Hz) [1]. Because muscle activity arises from different type of muscle groups, muscle artifacts are harder to stereotype than eye artifacts (cf.
How do I get rid of motion artifacts?
An existing method to remove the motion artefact is to employ an accelerometer for measuring the body movement at the same time of ECG detection [5]. However, for non-contact electrode structure of ECG detection, an accelerometer directly attached to the human body is unacceptable.
What does muscle artifact mean?
Muscle artifacts are characterized by surges in high frequency activity and are readily identified because of their outlying high values relative to the local background activity.
What is an example of an artifact?
An artifact is an object made by a human being. Artifacts include art, tools, and clothing made by people of any time and place. The term can also be used to refer to the remains of an object, such as a shard of broken pottery or glassware. Artifacts are immensely useful to scholars who want to learn about a culture.
How many types of MRI artifacts are there?
three groupsMR artifacts are considered in three groups here based upon their origin from tissue properties, motion, or technical parameters.
What are the different sources of MRI artifact?
Artifacts are caused by a variety of factors that may be patient-related such as voluntary and physiologic motion, metallic implants or foreign bodies. Finite sampling, k-space encoding, and Fourier transformation may cause aliasing and Gibbs artifact.
What is artifact in radiology?
An artifact on an image is a feature that does not correlate with the physical properties of the subject being imaged and may confound or obscure interpretation of that image. In this article, examples of artifacts from flat-panel detector–based digital radiographic systems are presented.
MRI - Cerebro Spinal Fluid Pulsation Artifact - MR-TIP: Database
Pulsatile cerebro spinal fluid flow produces ghost artifacts that are superimposed in the image. Image Guidance Flow compensation should be used to reduce these artifacts. This applies an additional gradient to eliminate phase differences for both stationary and moving spins at the echo time.At TE no phase differences is measured. If flow compensation is applied and there are still flow ...
MRI - vascular pulsation artifact - MR-TIP: Database
Flow phenomena are intrinsic processes in the human body. Organs like the heart, the brain or the kidneys need large amounts of blood and the blood flow varies depending on their degree of activity. Magnetic resonance imaging has a high sensitivity to flow and offers accurate, reproducible, and noninvasive methods for the quantification of flow. MRI flow measurements yield information of blood ...
Ventricular CSF pulsation artifact | Radiology Case | Radiopaedia.org
Di Muzio, B. Ventricular CSF pulsation artifact. Case study, Radiopaedia.org. (accessed on 06 Oct 2022) https://doi.org/10.53347/rID-37774
What are artifacts in MRI?
A gallery of such images was presented in this manuscript. A truncation artifact in the spinal cord could be misinterpreted as a syrinx. Motion artifacts caused by breathing, cardiac movement, CSF pulsation/blood flow create a ghost artifact which can be reduced by patient immobilization, or cardiac/respiratory gating. Aliasing artifacts can be eliminated by increasing the field of view. An artificially hyperintense signal on FLAIR images can result from magnetic susceptibility artifacts, CSF/vascular pulsation, motion, but can also be found in patients undergoing MRI examinations while receiving supplemental oxygen. Metallic and other foreign bodies which may be found on and in patients’ bodies are the main group of artifacts and these are the focus of this study: e.g. make-up, tattoos, hairbands, clothes, endovascular embolization, prostheses, surgical clips, intraorbital and other medical implants, etc. Knowledge of different types of artifacts and their origin, and of possible foreign bodies is necessary to eliminate them or to reduce their negative influence on MR images by adjusting acquisition parameters. It is also necessary to take them into consideration when interpreting the images. Some proposals of reducing artifacts have been mentioned. Describing in detail the procedures to avoid or limit the artifacts would go beyond the scope of this paper but technical ways to reduce them can be found in the cited literature.
What causes a FLAIR image to be hyperintense?
An abnormally hyperintense signal on FLAIR images can result from CSF/vascular pulsation (Figure 9), magnetic susceptibility artifact (Figure 10), motion, but also in patients undergoing MRI examinations while receiving supplemental oxygen [6].
What is the FOV of an aliasing artifact?
Aliasing artifact (“wrap around”) on brain MRI with FOV=24×18 cm (A). The same patient, examination with FOV=24×24 cm (B).
What causes blurry images of the uterus?
Motion artifacts caused by the peristalsis produce a blurry image of the uterus in pelvic MRI (A). Reduction of the artifacts after intramuscular or intravenous administration of buscolysin (B).
What is a truncation artifact?
A truncation artifact in the spinal cord could be misinterpreted as a syrinx. Motion artifacts caused by breathing, cardiac movement, CSF pulsation/blood flow create a ghost artifact which can be reduced by patient immobilization, or cardiac/respiratory gating.
How to reduce ghost artifacts?
They can be reduced by patient immobilization, cardiac/respiratory gating, saturation bands, or drugs that slow down the intestinal peristalsis. One can also reduce motion artifacts by using echo-planar imaging (EPI), a very fast MR imaging technique [4].
Why is it important to know about artifacts?
The knowledge of the artifacts and their sources is extremely important in order to avoid false diagnoses and to learn how to eliminate them [2].
What are MRI artifacts?
MRI artifacts. MRI artifacts are numerous and give an insight into the physics behind each sequence. Some artifacts affect the quality of the MRI exam while others do not affect the diagnostic quality but may be confused with pathology. When encountering an unfamiliar artifact, it is useful to systematically examine general features ...
What causes a Gibbs artifact?
Artifacts are caused by a variety of factors that may be patient-related such as voluntary and physiologic motion, metallic implants or foreign bodies. Finite sampling, k-space encoding, and Fourier transformation may cause aliasing and Gibbs artifact.
Who wrote the book Planning and Positioning in MRI?
1. Anne B. Planning and Positioning in MRI. Churchill Livingstone. (2011) ISBN:0729539857. Read it at Google Books - Find it at Amazon
Is artifact bad?
Remember that artifacts are not all bad, and that occasionally they are intentionally exploited, e.g. susceptibility artifact.
What is an MRI artifact?
From Wikipedia, the free encyclopedia. Jump to navigation Jump to search. An MRI artifact is a visual artifact (an anomaly seen during visual representation) in magnetic resonance imaging (MRI). It is a feature appearing in an image that is not present in the original object.
How do partial volume artifacts occur?
Partial volume artifacts arise from the size of the voxel over which the signal is averaged. Objects smaller than the voxel dimensions lose their identity, and loss of detail and spatial resolution occurs. Reduction of these artifacts is accomplished by using a smaller pixel size and/or a smaller slice thickness.
How do metal artifacts affect the tissue?
This distortion changes the precession frequency in the tissue leading to spatial mismapping of information . The degree of distortion depends on the type of metal (stainless steel having a greater distorting effect than titanium alloy), the type of interface (most striking effect at soft tissue-metal interfaces), pulse sequence and imaging parameters. Metal artifacts are caused by external ferromagnetics such as cobalt containing make-up, internal ferromagnetics such as surgical clips, spinal hardware and other orthopaedic devices, and in some cases, metallic objects swallowed by people with pica. Manifestation of these artifacts is variable, including total signal loss, peripheral high signal and image distortion (Figs 3 and 4). Reduction of these artifacts can be attempted by orientating the long axis of an implant or device parallel to the long axis of the external magnetic field, possible with mobile extremity imaging and an open magnet. Further methods used are choosing the appropriate frequency encoding direction, since metal artifacts are most pronounced in this direction, using smaller voxel sizes, fast imaging sequences, increased readout bandwidth and avoiding gradient-echo imaging when metal is present. A technique called MARS (metal artifact reduction sequence) applies an additional gradient, along the slice select gradient at the time the frequency encoding gradient is applied. ==Signal processing dependent artifacts== The ways in which the data are sampled, processed and mapped out on the image matrix manifest these artifacts.
What is wrap around artifact?
A wrap-around artifact also known as an aliasing artifact, is a result of mismapping of anatomy that lies outside the field of view but within the slice volume. The selected field of view is smaller than the size of the imaged object. The anatomy is usually displaced to the opposite side of the image (Figs 6 and 7). It can be caused by non-linear gradients or by undersampling of the frequencies contained within the return signal. The sampling rate must be twice the maximal frequency that occurs in the object ( Nyquist sampling limit ). If not, the Fourier transform will assign very low values to the frequency signals greater than the Nyquist limit. These frequencies will then ‘wrap around’ to the opposite side of the image, masquerading as low-frequency signals. In the frequency encode direction a filter can be applied to the acquired signal to eliminate frequencies greater than the Nyquist frequency. In the phase encode direction, artifacts can be reduced by an increasing number of phase encode steps (increased image time). For correction, a larger field of view may be chosen.
How does flow affect the signal?
Flow can manifest as either an altered intravascular signal (flow enhancement or flow-related signal loss ), or as flow-related artifacts (ghost images or spatial misregistration). Flow enhancement, also known as inflow effect, is caused by fully magnetised protons entering the imaged slice while the stationary protons have not fully regained their magnetization. The fully magnetized protons yield a high signal in comparison with the rest of the surroundings. High velocity flow causes the protons entering the image to be removed from it by the time the 180-degree pulse is administered. The effect is that these protons do not contribute to the echo and are registered as a signal void or flow-related signal loss (Fig. 2). Spatial misregistration manifests as displacement of an intravascular signal owing to position encoding of a voxel in the phase direction preceding frequency encoding by time TE/2.The intensity of the artifact is dependent on the signal intensity from the vessel, and is less apparent with increased TE.
What causes Gibbs artifacts?
Gibbs artifacts or Gibbs ringing artifacts, also known as truncation artifacts are caused by the under-sampling of high spatial frequencies at sharp boundaries in the image. Lack of appropriate high-frequency components leads to an oscillation at a sharp transition known as a ringing artifact. It appears as multiple, regularly spaced parallel bands of alternating bright and dark signal that slowly fade with distance (Fig. 8). Ringing artifacts are more prominent in smaller digital matrix sizes. Methods employed to correct Gibbs artifact include filtering the k-space data prior to Fourier transform, increasing the matrix size for a given field of view, the Gegenbauer reconstruction and Bayesian approach. ==Machine/hardware-related artifacts== This is a wide and still expanding subject. Only a few common artifacts are recognised.
What causes ghost images in MR?
A motion artifact is one of the most common artifacts in MR imaging. Motion can cause either ghost images or diffuse image noise in the phase-encoding direction. The reason for mainly affecting data sampling in the phase-encoding direction is the significant difference in the time of acquisition in the frequency- and phase-encoding directions. Frequency-encoding sampling in all the rows of the matrix (128, 256 or 512) takes place during a single echo (milliseconds). Phase-encoded sampling takes several seconds, or even minutes, owing to the collection of all the k-space lines to enable Fourier analysis. Major physiological movements are of millisecond to seconds duration and thus too slow to affect frequency-encoded sampling, but they have a pronounced effect in the phase-encoding direction. Periodic movements such as cardiac movement and blood vessel or CSF pulsation cause ghost images, while non-periodic movement causes diffuse image noise (Fig. 1). Ghost image intensity increases with amplitude of movement and the signal intensity from the moving tissue. Several methods can be used to reduce motion artifacts, including patient immobilisation, cardiac and respiratory gating, signal suppression of the tissue causing the artifact, choosing the shorter dimension of the matrix as the phase-encoding direction, view-ordering or phase-reordering methods and swapping phase and frequency-encoding directions to move the artifact out of the field of interest.
What is TOF loss in MRI?
Signal formation in MRI depends on mobile protons experiencing the initial radiofrequency pulse and the subsequent refocusing mechanism. TOF loss typically occurs in spin-echo or fast spin-echo imaging when protons do not experience both the initial radiofrequency pulse and the subsequent radiofrequency refocusing pulse. TOF effects are more pronounced (darker signal) with faster proton velocity, thinner slices, longer TE, and an imaging plane perpendicular to flow (Figs. 1A, 1B, 1C, 1D and 2 ). In addition, TOF loss in single-shot fast spin-echo (SSFSE) techniques is related to whether the pulse sequence was acquired during systole with TOF loss or diastole without TOF loss (Fig. 3A, 3B ). Finally, gradient-recalled echo (GRE) techniques are resistant to TOF loss because of the short TE (Fig. 4A, 4B ).
What is the CSF flow artifact?
A commonly encountered CSF flow artifact is the signal void in the dorsal subarachnoid space on sagittal T2-weighted images of the thoracic spine ( Fig. 13 ). This artifact is due to a combination of the respiratory and cardiacrelated pulsatile CSF flow superimposed on cranially directed bulk CSF flow and turbulent flow from CSF moving from the ventral subarachnoid space to the dorsal subarachnoid space. This complex CSF motion results in phase incoherence leading to signal loss.
What is the signal of a N ormal CSF?
N ormal CSF has long T1 and long T2 times that manifest as dark signal on T1-weighted images and bright signal on T2-weighted images. FLAIR imaging results in nulling and dark CSF signal. The normal CSF signal is frequently altered by superimposed flow phenomena that can confound interpretation [ 1 ]. This article will review commonly encountered appearances and artifacts of CSF due to flow effects.
What is the result of turbulent flow?
Turbulent flow results in a broader spectrum of proton velocities and a wide range of flow directions that are not seen in typical laminar flow. The varied flow velocities and directions result in more rapid dephasing and signal loss termed “intravoxel dephasing.”
Is CSF normal on MRI?
CONCLUSION. Normal CSF has inherent MRI properties of low signal intensity on T1-weighted sequences and high signal intensity on T2-weighted sequences. However, the normal CSF signal is frequently altered by superimposed flow phenomena that can confound interpretation.
What causes motion artifacts in MRI?
Motion is a very common cause of artifacts in magnetic resonance imaging (MRI). Motion artifacts are the result of movement during the data acquisition period. More specifically, when motion is present, tissues excited at a specific location during the radiofrequency (RF) pulse are erroneously mapped to a different location (or often multiple different locations in cases of motion artifacts) during detection. Motion is often divided into two categories: gross body movement and physiologic motion , such as cardiac and respiratory cycles, or blood or cerebrospinal fluid (CSF) flow. In most conventional imaging methods, motion artifact is predominantly manifested in the phase-encoding direction.
Why does flowing blood cause motion artifacts?
Why does flowing blood cause motion artifacts? After application of the dephasing lobe of the slice selection and frequency-encoding gradients, blood moves to a different location and experiences a rephasing gradient of a different strength. The phase shift induced by the dephasing lobe cannot be reversed by a gradient of a different strength, and the phase difference persists as ghost artifacts.10
How to reduce motion artifacts?
Numerous methods can be used to reduce motion artifacts. Increasing the sampling bandwidth (recall the relationship bandwith = 1/time for echo) is a simple method to reduce motion artifact at the expense of the signal-to-noise ratio. While it is true that increasing the gradient strength or the time in which the gradient is applied will increase susceptibility to motion artifact, increasing the strength of the frequency encoding gradient is an exception. The sampling bandwidth increases with increasing (steeper) gradient strength. A steeper gradient means that rephasing of the protons happens more quickly and an echo forms faster, thereby decreasing sampling time.10
How does spatial gradient affect motion?
The extensive use of spatial gradients complicates and amplifies motion artifacts, as stronger gradients induce larger phase shifts from motion (see Understanding the Need for Gradients In Image Formation and Its Implication in Motion Artifacts). While some gradient combinations can compensate for motion (e.g., the flow-compensated gradients; see below for more details), many of the imaging gradient pulses cannot. As such, the inconsistent nature of motion can induce different phase shifts during the image readout period. When viewed from the phase-encoding direction in the final data space, these inconsistencies introduce local deviations that result in ghosting artifacts in the image space as the result of Fourier transformation. For example, a pulsatile effect in one of the data lines (along the frequency-encoding direction) would be viewed as a spike along the phase-encoding direction, which would then result in a streaking line artifact along the phase-encoding direction. More severely, several inconsistent data lines would result in more extensive ghosting artifacts.
What is a T2 lesion?
1. The differential diagnosis of a subtle, T2 bright lesion in the liver includes hemangioma, metastatic disease, and primary liver tumor. However, given its location, oriented vertically just above the aorta, a pseudo-lesion as a result of pulsation artifact from the aorta is also in the differential. 2. Round low-signal lesion in the right ...
What is a T2 bright lesion?
1. The differential diagnosis of a subtle, T2 bright lesion in the liver includes hemangioma, metastatic disease, and primary liver tumor. However, given its location, oriented vertically just above the aorta, a pseudo-lesion as a result of pulsation artifact from the aorta is also in the differential.
What are ghosting artifacts?
Ghosting artifacts appear in abnormal locations as replicas of the moving structure from which they result. They are observed only in the phase-encoding direction and can be the result of any periodic motion such as respiration, arterial pulsation, or cerebrospinal fluid pulsation. 4.
