MRI artifacts can occur due to hardware issues, software issues, patient motion, tissue properties, or image processing. Hardware issues like an imperfect Faraday cage can cause zipper artifacts from external radiofrequency signals contaminating the scanner environment. Patient motion, such as from swallowing, can produce phase-encoded motion artifacts appearing as ghosting in the phase-encoding direction. During image processing, truncation artifacts appear as alternating light and dark bands near regions of abrupt intensity change due to the Fourier transformation. Susceptibility artifacts can also occur near metallic implants due to inhomogeneous magnetic fields. Recognition of artifacts can prevent confusion with pathology.
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
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
New Drug Discovery and Development .....NEHA GUPTA
The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
These simplified slides by Dr. Sidra Arshad present an overview of the non-respiratory functions of the respiratory tract.
Learning objectives:
1. Enlist the non-respiratory functions of the respiratory tract
2. Briefly explain how these functions are carried out
3. Discuss the significance of dead space
4. Differentiate between minute ventilation and alveolar ventilation
5. Describe the cough and sneeze reflexes
Study Resources:
1. Chapter 39, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 34, Ganong’s Review of Medical Physiology, 26th edition
3. Chapter 17, Human Physiology by Lauralee Sherwood, 9th edition
4. Non-respiratory functions of the lungs https://academic.oup.com/bjaed/article/13/3/98/278874
The prostate is an exocrine gland of the male mammalian reproductive system
It is a walnut-sized gland that forms part of the male reproductive system and is located in front of the rectum and just below the urinary bladder
Function is to store and secrete a clear, slightly alkaline fluid that constitutes 10-30% of the volume of the seminal fluid that along with the spermatozoa, constitutes semen
A healthy human prostate measures (4cm-vertical, by 3cm-horizontal, 2cm ant-post ).
It surrounds the urethra just below the urinary bladder. It has anterior, median, posterior and two lateral lobes
It’s work is regulated by androgens which are responsible for male sex characteristics
Generalised disease of the prostate due to hormonal derangement which leads to non malignant enlargement of the gland (increase in the number of epithelial cells and stromal tissue)to cause compression of the urethra leading to symptoms (LUTS
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.
NVBDCP.pptx Nation vector borne disease control programSapna Thakur
NVBDCP was launched in 2003-2004 . Vector-Borne Disease: Disease that results from an infection transmitted to humans and other animals by blood-feeding arthropods, such as mosquitoes, ticks, and fleas. Examples of vector-borne diseases include Dengue fever, West Nile Virus, Lyme disease, and malaria.
Acute scrotum is a general term referring to an emergency condition affecting the contents or the wall of the scrotum.
There are a number of conditions that present acutely, predominantly with pain and/or swelling
A careful and detailed history and examination, and in some cases, investigations allow differentiation between these diagnoses. A prompt diagnosis is essential as the patient may require urgent surgical intervention
Testicular torsion refers to twisting of the spermatic cord, causing ischaemia of the testicle.
Testicular torsion results from inadequate fixation of the testis to the tunica vaginalis producing ischemia from reduced arterial inflow and venous outflow obstruction.
The prevalence of testicular torsion in adult patients hospitalized with acute scrotal pain is approximately 25 to 50 percent
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Ve...kevinkariuki227
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
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
263778731218 Abortion Clinic /Pills In Harare ,sisternakatoto
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Knee anatomy and clinical tests 2024.pdfvimalpl1234
This includes all relevant anatomy and clinical tests compiled from standard textbooks, Campbell,netter etc..It is comprehensive and best suited for orthopaedicians and orthopaedic residents.
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
8. Gradient coils generate secondary
magnetic fields over the primary field.
The arrangement of these coils gives
mri the capability to image directionally
along the 3 axis.
Z gradient- long axis-axial
Y gradient – vertical axis –coronal
X gradient – horizontal axis - saggital
9. RF coils are
used for
transmitting
the RF pulse
and receiving
signals.
10.
11.
12.
13.
14.
15. The digital signal representing the
imaged body part is stored in the
temporary image space called K-
space.
The digital signal is then sent to an
image processor where a
mathematical formula called
fourier transformation is applied
and the image of the mri scan is
dispayed on a monitor
16. 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
22. • Cause: This type of artifact results from the
contamination of the MR scanner environment
(shielded MR suite) by spurious Radio Frequency
signals.
Zipper
artifact
23. 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.
24. • 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 )
25. Appearance- A dense broken line of alternatively dark
and bright pixels running across the image perpendicular
to the frequency encoding direction.
26.
27. 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
28. 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
29. 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 .
30. 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 occurs resultsing 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.
32. 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
33. 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
34. 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
37. 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.
.
38. 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
39. 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..)
40. 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
10% gap demonstrating impairedcontrast.
41. 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.
42. In this case, the scouts were
acquired in the following
order: axial, sagittal and
finally coronal. The sagittal
FOV involved the medial
gallbladder.
The protons in the medial half
of GB are already saturated.
Therefore, the immediate
subsequent RF pulse of the
coronal acquisition will result
in a low signal in the medial
gallbladder and can mimic
sludge.
43. 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.
44. 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.
45. 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.
46. 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.
47. 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
48. 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.
49. 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.
50. 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.
52. -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
53. 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.
-
54.
55.
56. 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.
57. 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.
58.
59.
60. 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.
61.
62.
63.
64.
65.
66. 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
67. 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
68. 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
72. 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
73. 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
74. 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
75. 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.
76. 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
77. a black band is seen on the left side of each kidney and a
white band on the right.
78. 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
79. axial T1 image also
demonstrates a chemical
shift artifact at the edges
between the mass and
the orbital fat.
ORBITAL HEMANGIOMA
80. 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.
82. Gibbs artifact /
truncationartifact
• It refers to a series of bright or dark lines, parallel & next to
borders of abrupt intensity change
This artefact occurs at areas of abrupt intensity change such as
-the CSF-Spinal Cord Interface.
-the Skull-Brain Interface.
83. Bright and dark bands are
seen parallel and adjacent
to the outer convexity of
calvaria
85. . 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”),
86. Truncation artifacts are reduced by
the use of a smaller field of view
(FOV) or a larger matrix size.
87. 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
88. -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.
89.
90. 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
91. 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.
92. Slice thickness 10mm
Unable to depict finer
structures due to partial
volume artefact
Slice thickness 3mm
Depicts cranial nerves