MRI artifacts can occur due to hardware issues, software issues, patient motion, and other factors. Common artifacts include zipper artifacts from RF contamination entering the shielded room, herringbone artifacts from RF pulse discrepancies, moire fringes from lack of field homogeneity, slice overlap artifacts from multi-slice acquisitions, phase encoding motion artifacts from tissue movement, susceptibility artifacts near metallic objects, chemical shift artifacts at fat-water interfaces, truncation artifacts at organ boundaries, and aliasing artifacts when the field of view is too small. Understanding the causes and appearances of artifacts can help avoid confusing them with pathology.
3 tesla mri, its physics, advantages and disadvantages, its comparison with 1.5 tesla mri scanner, clinical applications of 3 tesla mri, various artifacts related to 3 tesla, physics of silent mri, advantages of silent mri
3 tesla mri, its physics, advantages and disadvantages, its comparison with 1.5 tesla mri scanner, clinical applications of 3 tesla mri, various artifacts related to 3 tesla, physics of silent mri, advantages of silent mri
In this Presentation we talk about :-
What is PACS (Picture Archiving and Communication System).
Functions carried out by PACS.
Storage Devices in PACS
RAID Techniques
Cloud Based PACS
This presentation is a starter for folks interested in the implementation and application of compressed sensing (CS) MRI. It includes a Matlab demo and list of well-known resources for CS MRI.
Mri spin echo pulse sequences its variations andYashawant Yadav
MRI spin echo pulse sequences its variation and applications , in this slide collection principle of spine echo pulse sequences is described with physic behind it ,, this slide also coves the inverse recovery pulse sequences and types ,,,, image weighting and parameters are explained .. hope it may be help ful.
MRI artifacts remains a big challenge to get a diagnostic image. This represents a practical comprehensive approach to understand MRI artifacts & how to get rid of.
Magnetic resonance imaging (MRI) is a medical imaging technique that uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body.
Most MRI machines are large, tube-shaped magnets. When you lie inside an MRI machine, the magnetic field temporarily realigns water molecules in your body. Radio waves cause these aligned atoms to produce faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread.
The MRI machine can also produce 3D images that can be viewed from different angles.
Products & Services
Sign up for Email: Get Your Free Resource – Coping with Cancer
Why it's done
MRI is a noninvasive way for your doctor to examine your organs, tissues and skeletal system. It produces high-resolution images of the inside of the body that help diagnose a variety of problems.
MRI of the brain and spinal cord
MRI is the most frequently used imaging test of the brain and spinal cord. It's often performed to help diagnose:
Aneurysms of cerebral vessels
Disorders of the eye and inner ear
Multiple sclerosis
Spinal cord disorders
Stroke
Tumors
Brain injury from trauma
A special type of MRI is the functional MRI of the brain (fMRI). It produces images of blood flow to certain areas of the brain. It can be used to examine the brain's anatomy and determine which parts of the brain are handling critical functions.
This helps identify important language and movement control areas in the brains of people being considered for brain surgery. Functional MRI can also be used to assess damage from a head injury or from disorders such as Alzheimer's disease.
MRI of the heart and blood vessels
MRI that focuses on the heart or blood vessels can assess:
Size and function of the heart's chambers
Thickness and movement of the walls of the heart
Extent of damage caused by heart attacks or heart disease
Structural problems in the aorta, such as aneurysms or dissections
Inflammation or blockages in the blood vessels
In this Presentation we talk about :-
What is PACS (Picture Archiving and Communication System).
Functions carried out by PACS.
Storage Devices in PACS
RAID Techniques
Cloud Based PACS
This presentation is a starter for folks interested in the implementation and application of compressed sensing (CS) MRI. It includes a Matlab demo and list of well-known resources for CS MRI.
Mri spin echo pulse sequences its variations andYashawant Yadav
MRI spin echo pulse sequences its variation and applications , in this slide collection principle of spine echo pulse sequences is described with physic behind it ,, this slide also coves the inverse recovery pulse sequences and types ,,,, image weighting and parameters are explained .. hope it may be help ful.
MRI artifacts remains a big challenge to get a diagnostic image. This represents a practical comprehensive approach to understand MRI artifacts & how to get rid of.
Magnetic resonance imaging (MRI) is a medical imaging technique that uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body.
Most MRI machines are large, tube-shaped magnets. When you lie inside an MRI machine, the magnetic field temporarily realigns water molecules in your body. Radio waves cause these aligned atoms to produce faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread.
The MRI machine can also produce 3D images that can be viewed from different angles.
Products & Services
Sign up for Email: Get Your Free Resource – Coping with Cancer
Why it's done
MRI is a noninvasive way for your doctor to examine your organs, tissues and skeletal system. It produces high-resolution images of the inside of the body that help diagnose a variety of problems.
MRI of the brain and spinal cord
MRI is the most frequently used imaging test of the brain and spinal cord. It's often performed to help diagnose:
Aneurysms of cerebral vessels
Disorders of the eye and inner ear
Multiple sclerosis
Spinal cord disorders
Stroke
Tumors
Brain injury from trauma
A special type of MRI is the functional MRI of the brain (fMRI). It produces images of blood flow to certain areas of the brain. It can be used to examine the brain's anatomy and determine which parts of the brain are handling critical functions.
This helps identify important language and movement control areas in the brains of people being considered for brain surgery. Functional MRI can also be used to assess damage from a head injury or from disorders such as Alzheimer's disease.
MRI of the heart and blood vessels
MRI that focuses on the heart or blood vessels can assess:
Size and function of the heart's chambers
Thickness and movement of the walls of the heart
Extent of damage caused by heart attacks or heart disease
Structural problems in the aorta, such as aneurysms or dissections
Inflammation or blockages in the blood vessels
Magnetic resonance imaging (MRI) is a medical imaging technique that uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body.
Most MRI machines are large, tube-shaped magnets. When you lie inside an MRI machine, the magnetic field temporarily realigns water molecules in your body. Radio waves cause these aligned atoms to produce faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread.
The MRI machine can also produce 3D images that can be viewed from different angles.
Products & Services
Sign up for Email: Get Your Free Resource – Coping with Cancer
Why it's done
MRI is a noninvasive way for your doctor to examine your organs, tissues and skeletal system. It produces high-resolution images of the inside of the body that help diagnose a variety of problems.
MRI of the brain and spinal cord
MRI is the most frequently used imaging test of the brain and spinal cord. It's often performed to help diagnose:
Aneurysms of cerebral vessels
Disorders of the eye and inner ear
Multiple sclerosis
Spinal cord disorders
Stroke
Tumors
Brain injury from trauma
A special type of MRI is the functional MRI of the brain (fMRI). It produces images of blood flow to certain areas of the brain. It can be used to examine the brain's anatomy and determine which parts of the brain are handling critical functions.
This helps identify important language and movement control areas in the brains of people being considered for brain surgery. Functional MRI can also be used to assess damage from a head injury or from disorders such as Alzheimer's disease.
MRI of the heart and blood vessels
MRI that focuses on the heart or blood vessels can assess:
Size and function of the heart's chambers
Thickness and movement of the walls of the heart
Extent of damage caused by heart attacks or heart disease
Structural problems in the aorta, such as aneurysms or dissections
Inflammation or blockages in the blood vessels
Usg transducer and basic principles of ultrasound Doppler, this slide describe the basic physics of ultrasound transducer and Doppler , must know thing is given in this presentaion. Good review for radiology resident. Thanks.
Similar to artifactsusgctmriradiologypk-190830131406.pptx (20)
Anti ulcer drugs and their Advance pharmacology ||
Anti-ulcer drugs are medications used to prevent and treat ulcers in the stomach and upper part of the small intestine (duodenal ulcers). These ulcers are often caused by an imbalance between stomach acid and the mucosal lining, which protects the stomach lining.
||Scope: Overview of various classes of anti-ulcer drugs, their mechanisms of action, indications, side effects, and clinical considerations.
Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
New Directions in Targeted Therapeutic Approaches for Older Adults With Mantl...i3 Health
i3 Health is pleased to make the speaker slides from this activity available for use as a non-accredited self-study or teaching resource.
This slide deck presented by Dr. Kami Maddocks, Professor-Clinical in the Division of Hematology and
Associate Division Director for Ambulatory Operations
The Ohio State University Comprehensive Cancer Center, will provide insight into new directions in targeted therapeutic approaches for older adults with mantle cell lymphoma.
STATEMENT OF NEED
Mantle cell lymphoma (MCL) is a rare, aggressive B-cell non-Hodgkin lymphoma (NHL) accounting for 5% to 7% of all lymphomas. Its prognosis ranges from indolent disease that does not require treatment for years to very aggressive disease, which is associated with poor survival (Silkenstedt et al, 2021). Typically, MCL is diagnosed at advanced stage and in older patients who cannot tolerate intensive therapy (NCCN, 2022). Although recent advances have slightly increased remission rates, recurrence and relapse remain very common, leading to a median overall survival between 3 and 6 years (LLS, 2021). Though there are several effective options, progress is still needed towards establishing an accepted frontline approach for MCL (Castellino et al, 2022). Treatment selection and management of MCL are complicated by the heterogeneity of prognosis, advanced age and comorbidities of patients, and lack of an established standard approach for treatment, making it vital that clinicians be familiar with the latest research and advances in this area. In this activity chaired by Michael Wang, MD, Professor in the Department of Lymphoma & Myeloma at MD Anderson Cancer Center, expert faculty will discuss prognostic factors informing treatment, the promising results of recent trials in new therapeutic approaches, and the implications of treatment resistance in therapeutic selection for MCL.
Target Audience
Hematology/oncology fellows, attending faculty, and other health care professionals involved in the treatment of patients with mantle cell lymphoma (MCL).
Learning Objectives
1.) Identify clinical and biological prognostic factors that can guide treatment decision making for older adults with MCL
2.) Evaluate emerging data on targeted therapeutic approaches for treatment-naive and relapsed/refractory MCL and their applicability to older adults
3.) Assess mechanisms of resistance to targeted therapies for MCL and their implications for treatment selection
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
neurochemical systems and has rewarding and addictive properties. It
is the oldest recreational drug and likely contributes to more morbidity,
mortality, and public health costs than all illicit drugs combined. The
5th edition of the Diagnostic and Statistical Manual of Mental Disorders
(DSM-5) integrates alcohol abuse and alcohol dependence into a single
disorder called alcohol use disorder (AUD), with mild, moderate,
and severe subclassifications (American Psychiatric Association, 2013).
In the DSM-5, all types of substance abuse and dependence have been
combined into a single substance use disorder (SUD) on a continuum
from mild to severe. A diagnosis of AUD requires that at least two of
the 11 DSM-5 behaviors be present within a 12-month period (mild
AUD: 2–3 criteria; moderate AUD: 4–5 criteria; severe AUD: 6–11 criteria).
The four main behavioral effects of AUD are impaired control over
drinking, negative social consequences, risky use, and altered physiological
effects (tolerance, withdrawal). This chapter presents an overview
of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
Pulmonary Thromboembolism - etilogy, types, medical- Surgical and nursing man...VarunMahajani
Disruption of blood supply to lung alveoli due to blockage of one or more pulmonary blood vessels is called as Pulmonary thromboembolism. In this presentation we will discuss its causes, types and its management in depth.
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Ozempic: Preoperative Management of Patients on GLP-1 Receptor Agonists Saeid Safari
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Lung Cancer: Artificial Intelligence, Synergetics, Complex System Analysis, S...Oleg Kshivets
RESULTS: Overall life span (LS) was 2252.1±1742.5 days and cumulative 5-year survival (5YS) reached 73.2%, 10 years – 64.8%, 20 years – 42.5%. 513 LCP lived more than 5 years (LS=3124.6±1525.6 days), 148 LCP – more than 10 years (LS=5054.4±1504.1 days).199 LCP died because of LC (LS=562.7±374.5 days). 5YS of LCP after bi/lobectomies was significantly superior in comparison with LCP after pneumonectomies (78.1% vs.63.7%, P=0.00001 by log-rank test). AT significantly improved 5YS (66.3% vs. 34.8%) (P=0.00000 by log-rank test) only for LCP with N1-2. Cox modeling displayed that 5YS of LCP significantly depended on: phase transition (PT) early-invasive LC in terms of synergetics, PT N0—N12, cell ratio factors (ratio between cancer cells- CC and blood cells subpopulations), G1-3, histology, glucose, AT, blood cell circuit, prothrombin index, heparin tolerance, recalcification time (P=0.000-0.038). Neural networks, genetic algorithm selection and bootstrap simulation revealed relationships between 5YS and PT early-invasive LC (rank=1), PT N0—N12 (rank=2), thrombocytes/CC (3), erythrocytes/CC (4), eosinophils/CC (5), healthy cells/CC (6), lymphocytes/CC (7), segmented neutrophils/CC (8), stick neutrophils/CC (9), monocytes/CC (10); leucocytes/CC (11). Correct prediction of 5YS was 100% by neural networks computing (area under ROC curve=1.0; error=0.0).
CONCLUSIONS: 5YS of LCP after radical procedures significantly depended on: 1) PT early-invasive cancer; 2) PT N0--N12; 3) cell ratio factors; 4) blood cell circuit; 5) biochemical factors; 6) hemostasis system; 7) AT; 8) LC characteristics; 9) LC cell dynamics; 10) surgery type: lobectomy/pneumonectomy; 11) anthropometric data. Optimal diagnosis and treatment strategies for LC are: 1) screening and early detection of LC; 2) availability of experienced thoracic surgeons because of complexity of radical procedures; 3) aggressive en block surgery and adequate lymph node dissection for completeness; 4) precise prediction; 5) adjuvant chemoimmunoradiotherapy for LCP with unfavorable prognosis.
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2. Introduction
• An Artifact is something observed in a scientific
investigation that is not naturally present but occurs as
a result of the investigative procedure.
• It is a structure not normally present, but visible as a
result of malfunction in the hardware or software of the
device, or a consequence of environmental influences
8. • Cause: This type of artifact results from the
contamination of the MR scanner environment
(shielded MR suite) by spurious Radio Frequency
signals.
Zipper
artifact
9. A Faraday cage is a
conductive enclosure
used to shield a
space from
electromagnetic
interference.
In MR imaging, this
type of structure
provides
radiofrequency
shielding to the
scanning room to
minimize occurrence
of imaging artifacts.
10. • The contamination can result dueto
1)BreechintheRadiofrequencycagei.e. RF entering the shielded
room from outside
2) Illumination devices & other medical equipment (e.g pulse
oximeter )
11. Appearance- A dense broken line of alternatively dark
and bright pixels running across the image perpendicular
to the frequency encoding direction.
12.
13. Solution:
1) Scan door should be closed
2) Breech in RF cage should be located and repaired
3) Equipments in the scan room should be serviced
14. Herringbone
artifact
• Herringbone artifact (also known as ascrisscross
artifact or corduroyartifact)
• Due to interferences which occur while filing‐in of
the k‐space
• These interferences are usually RF spikes which
lead to points in k‐space with high intensity
• Causes ;
• Fluctuating power supply
• RF pulse discripencies
15. Appearance- It appears as obliquely oriented stripes seen throughout the image. Artifact is
scattered all over the image in a single slice or multiple slices .
16. Moire
fringes
• Moire fringes are an interference pattern most commonly seen when
doing gradient echo images with the body coil.
• Because of lack of perfect homogeneity of the main magnetic field
from one side of the body to the other
, aliasing of one side of the
body to the other results in superimposition of signals of different
phases that alternatively add and cancel.
• This causes the banding appearance and is similar to the effect of
looking though two screenwindows.
18. Solutions:
1) Use of spin echo sequences
2) Use of anti Aliasing remedies
3) Plug on the receiver coil should be firmly put in the
socket
19. Slice-overlap
artifact
• Loss of signal in an image due to a multi‐slice, multi‐angle acquisition
or imperfect sliceprofile
• The mechanism behind this artifact is spinsaturation
20. Image depicts Two sets of spine images, at different angles, covering L4‐5 and L5‐S1 respectively. The
set acquired later(red) will have image spins that have already been excited and that are
saturated,leading to signal loss
If slices at different angles cross, then spins that have been previously
excited (saturated) can not be excited again, thus leading to a signal
drop in the crossing region
23. Cross excitation
artifact
• There is loss of signal within a slice due to pre-excitation from RF
pulse meant for an adjacent slice
• Appearance- ThisArtefact causes a reduction in SNR in adjacent
slices in a Slice stack.
.
24. Cause : Ideally the profile of a slice
should be square or rectangular
when viewed from the edge, but in
practice a radio frequency excitation
pulse is not able to achieve this.
The adjacent slices receive energy
from the RF excitation pulse of their
neighbors .
When the tissues in next slice receive
their own RF pulse they are unable to
produce a signal as they are already
saturated
25. Solution:-
• Cross excitation can be reduced by insuring that
there is at least at 30% gap between the slices
(Gap= 30% of the Slice thickness )
This reduces the likelihood of RF pulse exciting
adjacent slice.
• Interleaving between slices i.e.
FIrst acquiring the odd number slices(1,3,5,7..)
Then acquiring the even number slices( 2,4,6,8..)
26. Effect of cross-talk on image contrast. On left is
a SE image with 50% gap showing expected spin-
density contrast. On right the same sequence with 0%
gap demonstrating impairedcontrast.
27. On the coronal scout, the lumen of the gallbladder is sharply divided into low signal
medially and high signal laterally with a "level" appearance suggesting layering
sludge. However, the axial T2W shows no sludge in the gallbladder. This finding is
attributed to cross-excitation artifact.
28. Phase-encoded motion
artifact
• Phase-encoded motion artifact occurs as a result
of tissue/fluid moving during the scan. It manifests
as ghosting in the direction of phase-encoding.
• 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. Periodic
motion, such as respiratory or cardiac/vascular
pulsation, produces discrete, well-defined ghosts.
29. This is a typical example of
phase-encoded artifact secondary
to aortic pulsation. The ghost
images of the aorta are:
discrete, well defined, lining with
the aorta along the short axis of
the abdomen (AP axis) at regular
intervals and extending beyond
the field of view.
These features help recognize
them and not to confuse them
with any pathology.
30. Blood flow in the sagittal sinus and carotids causes Periodic ghosting which gives the
impression of an enhancing lesion in the occipital lobe as well as anterior to the right
temporal horn. Wide windowing demonstrates the ghosting extending beyond the confines
of the patient's anatomy.
Apparent enhancement in the
occipital lobe and right temporal
lobe in a patient with
malignancy.
windowed slice demonstrates
the phase mismapping artefact from
the superior sagittal sinus.
31. Swallowing artifact has
produced horizontal
band of noise along
phase-encoded
direction. Where it
passes over vertebral
body and spinal cord,
there are local intensity
and contrast changes,
rendering these portions
of scan suspect.
32. Solutions
cardiac/respiratory gating
spatial presaturation bands placed over moving tissues (e.g.
over the anterior neck in sagittal cervical spines)
spatial presaturation bands placed outside the FOV, especially
before the entry or after the exit slice for reducing ghosting
from vascular flow
scanning prone to reduce abdominal excursion
increasing the number of signal averages
shorten the scan time when motion is from patient movement
33. Cardiac Gating
This involves the acquistion of a series of MR images of a
single anatomic section during a specific point in the
cardiac cycle ,which is being monitored with ECG.
Data within the k-space is linked with specific time point
in cardiac cycle.
The acquired datasets are then sorted according to time
stamp to produce sequential images allowing a dynamic
evaluation of myocardial function.
34. Respiratory gating
respiration related motion is monitored, using bellows or
breathing belt, and image acquisition is timed to take
place at end expiration, when there is little or no motion.
however this is infrequently used in clinical imaging.
-Breath holding method most often used
-Sequences with short acquisition time may be used, or if
breath holding possible for limited time, exam may be
divided into several brief acquisitions.
35. Saturation pulses
Saturation pulses involve the application of RF energy to
suppress the MR signal from moving tissues outside the
imaged volume to reduce or eliminate motion artifacts.
37. -Most commonly used in abdominal imaging at the interface of lung and diaphragm
-Application of small, one dimensional spatial encoding gradient in a plane perpendicular to
diaphragm.
- Echo measured at this location allows correction of imaging dataset and ensures that only the
imaging data acquired when diaphragm is at its peak (end expiration), is used in image
reconstruction.
Navigator Echo
38. Entry slice
phenomenon
Entry slice phenomenon occurs when unsaturated spins in
blood first enter into a slice .
Unsaturated spins = protons without transverse magnetisation
When a large number of such protons encounter a RF pulse for
the first time(i.e. at the entry slice),they undergo transverse
magnetisation and emit a strong signal.
- It is characterized by the bright signal in a blood vessel
(artery or vein) at the first slice that the vessel enters.
-
39.
40.
41. This artefact can be confused with thrombosis
Solutions-
-The characteristic location and if necessary, the use of
gradient echo flow techniques can be used to
differentiate entry slice artefacts from occlusions.
-Spatial saturation bands place before the first slice and
after the last can also be used to eliminate this artefact.
42. Magic angle
artefact
• The magic angle effect is important in the clinical MR
imaging of certain tissues that are highly structured
and are oriented obliquely to the main magnetic field
(especially tendons, cartilage, and peripheral nerves).
• In tendons, the water molecules are aligned along the tendon sheath
and have strong dipolar interactions. Due to these dipolar
interactions, protons in the collagen rapidly dissipate their energy
after encountering a RF pulse i.e. tendons have a short intrinsic
T2 value (1-10 ms).
The signal of tendons is uniformly low on all conventional MR
sequences due to this rapid T2 decay.
43.
44.
45. however, when the tendons are aligned at an angle of 55degree to the
main magnetic field , these dipolar interactions go to zero, leading to
an increase in T2 relaxation time and consequent sudden increase in
signal.
46.
47.
48.
49.
50.
51. Common sites:
proximal part of the Posterior cruciate ligament
infrapatellar tendon at the tibial insertion
peroneal tendons as they hook around the lateral
malleolus
Supraspinatus tendon
52. High signal within a tendon can mimic tendinopathy so it
is important that radiologists are aware of the magic
angle phenomena.
Look for it in the outer portions of the rotator cuff,
supraspinatus tendon, the distil patellar tendon, tendons
of the ankle, extensor and flexor policis tendons of the
wrist or any part made of collagen that lies in a curve
53. Susceptibility
artifact
• Due to the presence of substances ( e.g.ferromagnetic materials) that
causes variation in the local magneticfield
• Results in increased magnetic field inhomogeneity ,leading to spin
dephasing and consequent signal drop
• Becomes worse for long echo times and GRE sequences( no RF 180
pulse)
• Less visible in fast spin echosequence
• Worse for higher fieldstrength
57. Remedies
• Use spin-echo sequences
A spin echo sequence uses a 180-degree RF
pulse .
The main purpose of this 180-degree pulse is
to correct local field inhomogeneities.
A gradient echo pulse sequence does not
utilize such a “refocusing” pulse.
As such, local field inhomogeneities are
much more readily apparent when gradient
echo sequences are utilized
58. Chemical Shift
-Chemical Shift is the difference between precessional
frequencies of water and fat.(3.5ppm)
-Artefact is the displacement of signal intensity due to this
difference
59. AT 1.5 T W>F by 220Hz
At 3T W>F by 440Hz
WATER FAT
Water molecules have low
electron shielding and their
nucleus is more susceptible to
external magnetic field.
As a result water molecules
precess at a higher frequency
at the same magnetic field.
Fat molecules have higher
electron shielding and their
nucleus is comparitively less
susceptible to external
magnetic field.
Fat molecules precess at a
lower frequency at the same
mag field
60. water and lipid
protons coexist at
the interface, the
signal emitted by
the lipid protons will
have a lower
frequency than that
of the water
protons,leading to
mismapping of fat.
61. CHEMICAL SHIFT TYPE 1: MISMAPPING ARTIFACT
-Most commonly seen around water containg structures
sorrounded bt Fat(Liver,Kidneys,Orbits)
-Artifact appears as a dark band on one side of the
water/fat interface and a bright band on the other side
62. a black band is seen on the left side of each kidney and a
white band on the right.
63. T2 weighted image demonstrates
chemical shift artefact around the
lipoma.
Note the signal loss anteriorly
(black arrows) and hyperintensity
posteriorly (white arrows).
This is the result of inaccurate
spatial encoding, resulting in the
lipoma being incorrectly placed
posterior to its actual location.
LIPOMA
64. axial T1 image also
demonstrates a chemical
shift artifact at the edges
between the mass and
the orbital fat.
ORBITAL HEMANGIOMA
65. Chemical Shift: 2nd Kind
The chemical shift artifact of the second kind is sometimes
known as the India Ink or black line artifact because it
looks like organs and muscle bundles have been outlined
with a black pen. The line does not correspond to a true
anatomic structure, but results from destructive
interference of signals at the boundary pixels that contain
both water and fat. For this reason it is sometimes often
called the phase cancellation artifact. Examples in the
spine, thigh, and abdomen.
67. Gibbs artifact /
truncationartifact
• It refers to a series of bright or dark lines, parallel & next to
borders of abrupt intensity change
Areas of abrupt intensity change such as
-the CSF-Spinal Cord Interface.
-the Skull-Brain Interface.
68. Bright and dark bands are
seen parallel and adjacent
to the outer convexity of
calvaria
70. . Figure illustrates a syrinx-like artifact
(red arrow) within the center of the cord, a
classic truncation artifact that appears as a
result of alternating dark and light signal
bands overlying the spinal cord.
This artifact can be easily mistaken for
hydromyelia (dilatation of the central canal,
more commonly referred to as a “syrinx”),
71. Truncation artifacts are reduced by
the use of a smaller field of view
(FOV) or a larger matrix size.
72. Aliasing / wrap
aroundartifact
• It occurs when the field of view (FOV) is smaller than
the body part being imaged. The part of the body that
lies beyond the edge of the FOV is projected onto the
other side of the image
• Caused by under‐sampling in the phase encoding direction
73. -phase shifts of between 0° and 360°
encompass the field-of-view.
The subject's left flank in the drawing
extends outside the field-of-view and
encompasses phase shifts from 361°
to 450°.
Since all meaningful frequencies
have been defined over the range of
0° to 360°, a phase shift of 361° will
be assigned to the spatial position of
1°, and a shift of 450° will be
assigned to 450°-360° = 90°.
Hence ,the left side of the patient's
body will therefore be "wrapped
around" and spatially mismapped to
the opposite (right) side of the image.
74.
75. Solution
-Enlarging the field of view (FOV)
-Using pre-saturation bands on areas outside the FOV
-Anti-aliasing software
-Use a surface coil to reduce the signal outside of the
area of interest
76. PARTIAL VOLUME ARTIFACT
-Partial volume artefact occurs if slice thickness >
thickness of the tissue of interest.
-Occurs when multiple tissue types are encompassed
within a single voxel
-If a small structure is entirely contained within the slice
thickness along with other tissue of differing signal
intensities, the resulting signal displayed on the image is a
combination of these two intensities.
This reduces contrast of the small structure.
77. Slice thickness 10mm
Unable to depict finer
structures due to partial
volume artefact
Slice thickness 3mm
Depicts cranial nerves