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Copy of MRI of the Knee

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Grace Luo

on 24 October 2014

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Transcript of Copy of MRI of the Knee

Before a patient enters the room they must complete an MRI questionnaire. This is a general screening procedure for many safety issues that commonly arise during a scan.

General MRI Safety
Risk for radiofrequency heating:
Pregnancy - there is little data showing detrimental biological effects on the foetus and generally MRI will still be performed on a pregnant patient if all alternatives involve ionizing radiation.
Note: the amount of RF energy deposited into patient should not exceed maximum dose standards and no tissue should be affected by a temperature increase > 1˚C.
Figure 18. Incorrect patient positioning. Retrieved from: http://www.pmda.go.jp/english/service/pdf/safety/No25.pdf
Figure 19. Correct patient positioning. Retrieved from: http://www.pmda.go.jp/english/service/pdf/safety/No25.pdf
Incorrect Positioning
Correct Positioning
Knee Anatomy
The articular surface of the knee is composed of cartilage that acts as shock absorbers.
Medial meniscus (medial tibia attachment) and lateral meniscus (lateral tibia attachments).
The articular surface are subjected to wear and is common to undergo degeneration with age, resulting in arthritis.
What is MRI?
Magnetic Resonance Imaging:
KNEE

Sequences
Pathology
Magnetic Resonance Imaging (MRI) gives detailed information about internal structures and serves as a clinical tool for the assessment and diagnosis of pathology.
A strong magnetic field (1.5T) aligns the hydrogen protons in the body. Coils then send specific radiofrequencies to allow radio signals to be emitted from the targeted regions.
These signals are then detected and processed by a computer to produce comprehensive images of internal structures.
Figure 1. Cutaway diagram of MRI Scanner. Retrieved from: http://mritechniciansite.com/wp-content/uploads/2012/06/mri-scanner-cutaway.jpg
Group D: Benedict Cheng, Victoria Fang, Tracey Luu, Grace Luo, Benjamin Teo, Catherine Zhang
Provide main structural support in the knee.
Femur, Tibia, Fibula and Patella.
Figure 3. The bony components of the knee. Retrieved from:
http://www.kidport.com/reflib/science/humanbody/skeletalsystem/images/KneeJoint.jpg

Figure 4. Tendons in the knee: quadriceps and patellar. Retrieved from: http://www.eorthopod.com/images/ContentImages/knee/knee_quadriceps_tendonitis/knee_tendonitis_quadriceps_anatomy02.jpg
Ligaments join knee bones to other knee bones.
Anterior and posterior cruciate ligaments prevent tibia and femur sliding forwards and backwards.
Medial and lateral collateral ligaments prevents femur from sliding side-to-side.
These knee ligaments are prone to tears under excessive magnitude and directional forces.
The knee is a complex joint that is made up of 4 major components...
Figure 5. Ligaments of the Knee. Retrieved from: http://i50.photobucket.com/albums/f301/MDD4/knee_joint.jpg
Figure 6. Labeled MRI image of Knee. Retrieved from: http://mrimaster.com/anatomy/KNEE/knee%20cor/mri%20knee%20cross%20sectional%20anatomy%20coronal%20%208.jpg
Safety Issues
Meniscus Tears
A common knee injury and diagnosed through clinical history, patient presentation and MRI.
Patient Presentation: sharp pain then dull pain, unable to extend + joint effusion (common).

Posterior Cruciate Tears (PCL)
PCL is the strongest ligament in the knee, hence these injuries tend to be associated with serious trauma
E.g. Hyperextension, high impact on flexed knee --> 'dashboard injury'.
Patient presentation: swelling and instability

Other Pathology Includes:
Osteochondritis Dissecans: joint disorder in which cracks appear in articular cartilage and subchondral bone. X-rays can detect this however MRI is used to establish stability.
Abnormal bone marrow: e.g. Avascular Necrosis (AVN) is most common bone marrow abnormality.
Patellar dislocation: is common condition but not clinically recognised as patella goes back into normal position afterwards.
Tendon tears: quadriceps tendon tear and patellar tendonopathy
Cysts (e.g. popliteal cyst, bakers cyst, meniscal, subchondral), bursae (e.g. communicating, non-communicating) and recesses.
General X-ray
2D images acquired by exposing the knee to low dose radiation
Osseous pathology is best demonstrated while secondary indications of cysts and other soft tissue abnormalities may also be shown.
Typically used as initial modality but significantly less detail in comparison to MRI and therefore cannot provide a conclusive diagnosis of the ACL.
Computed Tomography
Arthroscopy
A surgical procedure where a small camera is inserted through a small incision in the knee.
Diagnosis of torn cartilage, joint alignment, ligament tears and patella damage can be made from direct contact with the knee structure.
An interventional study where surgeons can begin repair procedures if necessary, making it superior to MRI, which is used solely for diagnosis.
Invasive nature of the procedure increases the infection risks at incision sites and additional trauma may impact recovery of the joint.
Ultrasound
Transmission of high frequency sound waves and recording of the resultant echoes which are converted to images
Best used to visualise the popliteal vasculature, cysts, and can provide substantial diagnosis of muscles and tendons.
A quick and cheap imaging process
Provides insufficient detail when assessing the knee.
MRI must be performed to further evaluate the full extent of pathology if the ACL is suspected to be compromised
Nuclear Medicine
Alternative
Imaging
Modalities

The injection of a radionuclide into the knee, the radiation emitted is detected by a camera and reconstructed into diagnostic images.
Often used for post-operative knee replacements to check for possible infections or aseptic loosening.
This procedure can be performed even with metallic hardware present, which is a contraindication for MRI.
However, high radiation dose is administered to the patient and presence of residue radioactivity for a period of time after the procedure.
Arthrography
A fluoroscopic procedure where radiopaque contrast is injected either directly into the joint or into the bloodstream to be absorbed by the joint.
Best suited to assess the meniscus, cysts and ligament damage.
Usually performed as a post-operative procedure or to determine the need for arthroscopy.
Excels MRI where it allows for a dynamic evaluation of the knee.
However, it poses a higher risk to the patient due to the invasive nature and dose of radiation.
Cross-sectional images produced from a longer exposure of the x-rays from an unfixed source.
A secondary modality that demonstrates the anatomy of the knee in more detail than general x-ray.
Fractures, arthritis, tumours and ligaments can be better assessed.
Requires the use of ionising radiation, which may cause adverse biological effects.
The level of anatomical detail is inferior to that of MRI when diagnosing ACL pathology.
Figure 2. How MRI Scans Work. Retrieved from: http://www.bitterrootimaging.com/images/mri-diagram.png
Figure 26. X-ray of the knee. Retrieved from: http://www.wikiradiography.com/page/Knee+(non+trauma)+Radiographic+Anatomy
Figure 27. CT axial image of a knee. Retrieved from: http://www.imaios.com/var/ezwebin_site/storage/images/media/images/e-anatomy/knee-mri/en/knee-human-body-anatomy/4902-1-eng-GB/knee-human-body-anatomy_imagelarge.jpg
Figure 28. Ultrasound image of the superior aspect of the knee. Retrieved from: http://bpain.com/kneeultrasound.html
Figure 29. Radioactive hot spots of the knee. Retrieved from: http://jnm.snmjournals.org/content/50/4/534/F4.large.jpg
Figure 30. Arthrograph of the knee. Retrieved from: http://www.safehost.com.au/qdi/examplefilms/CT3D10.jpg
Figure 31. Knee Arthrocopy image. Retrieved from: https://stemcelldoc.wordpress.com/tag/knee-arthroscopy/
Artefacts
A major cause of noise is arterial flow in the popliteal artery due to flowing and pulsating movement.
This results in low signal intensity from the fast blood flow and/or due to displacement effect during image acquisition.

Must be considered to ensure a smooth and efficient examination.
They also serve to minimise errors and harm to patients.
Prior to any examination it is important to:
Ensure MRI machine is cleaned and pre-setting protocols
Check request form and patient identification
Explain examination procedure clearly and check patient consent forms which also serves to reduce the chance of movement artefacts
Remove metallic artefacts from patient

Pre-examination Preparation
Motion artefact degrades the image quality, physiologic and patient motion (voluntary or involuntary), ghosting and blurring occurs.
Aliasing is an artefact caused by using a field of view that is too small. For knee MRI, this will be less than 14-16cm.
Skin contact burns
can be avoided by:
Immobilisation by ensuring patient's legs are comfortable
Keeping knees away from bore and ensuring no part of lower legs/feet are touching
Peripheral nerve stimulation
can occur due to the gradient magnetic field (near bony prominences e.g. femoral condyles)
Level of exposure and rapid gradient switching used in knee MRI can result in tingling sensation in the muscle
Although not dangerous, can cause pain if exposure increases 50%-100% but should not occur under standard protocol
Modification of pulse sequences and gradient hardware
Note: Orthopedic implants including KNEE REPLACEMENTS are MRI safe as they are embedded in the bone and made from Titanium (non-ferromagnetic).
Normal variants can also cause artefacts and should not be misdiagnosed as meniscal tears.
E.g. the posterior lateral meniscus may appear torn due to the position of the popliteus tendon and its sheath posteriorly.
Figure 22. Sagittal proton density image showing pulsatile motion artefact. Retrieved from: MRI of the Musculoskeletal System (2013)
Figure 23. (a) Sagittal proton density image showing motion artefact. (b) repeat image demonstrates no meniscal abnormality. Retrieved from Motion Artifact … MRI of the Knee (1994)
(a)
(b)
Patient is positioned supine with knee immobilised in a high resolution extremity coil ensuring the apex of the patella is aligned with middle of the coil.
Leg should be slightly externally rotated and be extended if viewing cruciate ligaments or slightly flexed if viewing patella tendons.
Knee is placed close to iso-centre of magnetic field to promote more accurate tuning and imaging.
Patient Positioning
Figure 11: Position of a knee coil. Retrieved from:
http://weill.cornell.edu/mri/MRI/Extremity/Knee/knee1.htm
Figure 12. MRI Scan of Knee. Retrieved from https://www.healthcare.siemens.com/magnetic-resonance-imaging/options-and-upgrades/coils/tx-rx-15-channel-knee-coil
Scanning Planes
Knee MRI may last anywhere between 30-60 minutes due to varying protocols.
The minimal protocol requirements of ACL imaging include T2-weighted sequences (or proton-weighted fat-suppressed) in 2-3 orthogonal planes.
Figure 24. (a) The undersampling has caused abnormal bilateral soft tissue signal on either side of the tibia. Image (b) results from selecting a larger field of view.
Retrieved from http://www.konez.com/Vaka003_e.htm
(a)
Coronal/frontal:
Best demonstrates collateral ligaments, lateral and posterior meniscus, tibial plateau and condyles.

Axial/transverse
: Shows patella femoral joint, condyles, cruciate and all ligaments in cross section. This plane is invaluable in evaluation of the proximal ACL as it is free of partial volume artefact caused by the intercondylar roof.

Sagittal
: Highlights the horns of the meniscus, condyles, cartilage, cruciate and patella.
(b)
Figure 25. Sagittal T1 image showing artefact caused by normal anatomical variation [normal anterior horn of medial meniscus (m) and transverse ligament (tl)]. Retrieved from: MRI of the Musculoskeletal System (2013)
Most centres also routinely perform a sagittal or coronal T1-weighted scan to assess the menisci, bones, articular cartilage, and other ligamentous structures of the knee.
Additional imaging can also be done if needed and include:
Oblique and flexion views
: helpful in determining the presence, severity and location of ACL tears
Small coil images:
helpful for assessing delineating peripheral pathology around the knee
Figure 13. Scanning planes. Retrieved from http://1.bp.blogspot.com/-SOPU9H45Cys/TuWdfNzHhjI/AAAAAAAAAA0/4YOYB13HCXc/s1600/Planes7.jpg
Scanning Sequences
When imaging the knee, common MRI sequences are combined with different planes.
Fat saturation is also often used as part of knee imaging protocols. It produces detailed images of internal structures by increasing the systems sensitivity to fluid and suppressing fat signals.
References
Clinical Questions
& Relevance

Allen, A. M. (2013). MRI for Anterior Cruciate Ligament Injury. Retrieved from: http://emedicine.medscape.com/article/400547-overview#aw2aab6b7
American Academy of Orthopaedic Surgeons. (2014). Anterior Cruciate Ligament Injuries. Retrieved September 10, 2014, from: http://orthoinfo.aaos.org/topic.cfm?topic=a00549
Baikoussis, N. G., Apostolakis, E., Papakonstantinou, N. A., Sarantitis, I., & Dougenis, D. (2011). Safety of magnetic resonance imaging in patients with implanted cardiac prostheses and metallic cardiovascular electronic devices.
The Society of Thoracic Surgeons,
91
(6)
, 2006-2011. doi: 10.1016/j.athoracsur.2011.02.068
Berquist, T. H. (2013) MRI of the Musculoskeletal System (6th ed). Philadelphia, PA: Wolters Kluwer Health. (pp. 319-400)
Better Health Channel. (2014). X-ray Examinations. Retrieved September 11, 2014, from http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/X-ray_examinations?open
Bitar R, Leung G & Perng R. (2006). MR pulse sequences: what every radiologist wants to know but is afraid to ask.
Radiographics
;26 (2): 513-37.
Fitzgerald SW, Remer EM, Friedman H, Rogers LF, Hendrix RW, Schafer MF. (1993). MR evaluation of the anterior cruciate ligament: value of supplementing sagittal images with coronal and axial images. AJR Am J Roentgenol;160(6):1233-7.
Freiberger, R. & Pavlov. H.(1988). Knee Arthography.
Radiology
, 166, 489-492
Hoa, D. (2014). MRI safety and precautions. Retrieved September 12, 2014, from http://imaios.com/en/e-Courses/e-MRI/MRI-instrumentation-and-MRI-safety/MR-safety
Ivy Sports Medicine. (2014). Knee ultrasound examination. Retrieved September 11, 2014, from http://www.ivysportsmed.com/en/knee-pain/knee-pain-diagnosis/knee-ultrasound-examination-0
Koplas, M. & Schils, J.(2008). The painful knee: Choosing the right imaging test.
Cleavland Clinic Journal of Medicine
,75
(5)
, 377-384
Love, C., Tomas, M.B., Marwin S. E., Pugliease, P.V. & Palestro, C.J. (2001) Role of nuclear medicine in diagnosis of the infected joint replacement.
Radiographics
, 21
(5)
, 1229-1238
Olson, R.W (1967). Knee Arthrography.
American Roentgenoloy
,101
(4)
,897-914
Orthosports.(2009). Knee Arthroscopy. Retrieved September 10, 2014, from http://www.orthosports.com.au/content_common/pg-knee-arthroscopy.seo
Palestro, C.J. (2003). Nuclear Medicine, the Painful Prosthetic Joint, and Orthopedic Infection.
The Journal of Nuclear Medicine
, 44
(6)
, 927-929
Pavlov, H. , Dalinka, M.K, Alazraki, N., Berquist T.H., Daffner, R.H., DeSmet, A.A,…McCabe. J.B. (2000a). Acute trauma to the knee. American College of Radiology. ACR Appropriateness Criteria. Radiology, 215, 365-373.
Pavlov, H. , Dalinka, M.K, Alazraki, N., Berquist T.H., Daffner, R.H., DeSmet, A.A,…Sartoris. D. (2000b). Nontraumatic knee pain. American College of Radiology. ACR appropriateness criteria. Radiology, 215, 311-320.
Porter, N. (2014). MRTY3118 MR theory applications, lecture 4, week 4: MRI applications MSK & MRI safety [lecture PowerPoint slides]. Retrieved from https://elearning.sydney.edu.au/webapps/portal/frameset.jsp
Radiology, A. C. o. (2014). ACR-SSR practice parameter for the performance and interpretation of magnetic resonsance (MRI) of the knee.
Radiology, A. C. o., & America, R. S. o. N. (2013). Magentic Resonance Imaging - Knee. In RadiologyInfo (Ed.).
Remer, E. M., Fitzgerald, S. W., Friedman, H., Rogers, L. F., Hendrix, R. W., & Schafer, M. F. (1992). Anterior cruciate ligament injury: MR imaging diagnosis and patterns of injury. Radiographics, 12(5) 901-915.
Rubin, D. & Smithius, R. (2005) Knee - Non-meniscal Pathology. Retrieved from: http://www.radiologyassistant.nl/en/p42764e8fe927e/knee-non-meniscal-pathology.html
Schmider, C. (2010). Knee joint anatomy, function and problems. Retrieved 09/09, 2014, from http://www.healthpages.org/anatomy-function/knee-joint-structure-function-problems/#structures-of-the-knee
Shellock, F. D. (2014).
Bioeffects of gradient magnetic fields
. Retrieved October 9, 2014, from http://www.mrisafety.com/SafetyInfov.asp?SafetyInfoID=250
Skinner, S. (2012). MRI of the knee.
Australian Family Physician
, 41(11), 867-869.
Sundic, P. (n.d.). MRTY3118 MR theory applications: Chapter 6 – The knee [supplementary study notes]. Retrieved from https://elearning.sydney.edu.au/webapps/portal/frameset.jsp
Vohra, S., Anrnold, G., Doshi, S. & Marcantonio, D. (2011). Normal MR Imaging Anatomy of the Knee.
Magnetic Resonance Imaging Clinics of North America
, 19
(3)
, 637-653. doi :10.1016/j.mric.2011.05.012
Yoshioka, H., Schlechtweg, P. M., & Kose, K. (2009).
Magnetic Resonance Imaging.
doi: 10.1016/B978-0-323-04177-5.00003-3

THE END
THANK YOU
Clinical Indications
Bones
Ligaments
Tendons
Cartilage
Knee/kneecap pain, weakness, swelling or bleeding in the tissues and around the joint.
Damaged cartilage, meniscus, ligaments or tendons (such as tears).
Decreased range of motion of the knee joint.
Subtle bone fractures (can be missed on x-rays).
Degenerative joint disorders (e.g. arthritis).
Knee effusion: fluid accumulation.
Infections (e.g. Osteomyelitis).
Tumours (primary tumours/metastases) involving bones and joints.
Complications related to implanted surgical device.
Are these clinical indications relevant or significant for diagnosis?
These signs and symptoms often signify the existence of diverse knee pathologies
Clinical questions and patient history is crucial in assessing the need for a knee MRI, as well as assisting with the differential diagnosis.

When MRI is not relevant:
MRI is not usually indicated for patients with acute knee pain, or where physical examination shows no signs of cruciate or collateral ligament or meniscal injury.
Degenerative joint disease sufficiently seen on x-ray.
Figure 14. Image A: Knee without flexion.
Image B: Flexed knee.
Retrieved from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3302044/
Figure 15. Example MRI knee protocol. (Vohra et al, 2011)
Proton Density Fast Spin Echo (PD FSE)
Long TR and short TE permits short imaging time with high signal and resolution.
It the most useful in showing meniscal tears.
T1 Spin Echo (T1 SE)
Short TE and TR produces images with high signal, smaller field of views and higher resolution which allows use of lower field strengths.
Aids in the diagnosis of fractures or loose bodies in the knee as it best demonstrates disruptions of the cortex and cartilage.
T2 Fast Spin Echo (T2 FSE)
Allows optimal visualisation of fluid contrast in the knee whilst permitting short imaging time and a high signal and resolution.
Most important in diagnosing acute ACL injuries as it shows ligaments.
In the coronal plane with fat saturation micro fractures, fluid and trauma to the collateral ligaments and meniscus are easily seen.
Inversion Recovery (IR)
Most sensitive sequence for showing bone oedema and patella cartilage in the axial plane.
Figure 16. MRI Images of the knee using alternative sequence. Retrieved from: http://www.raddaily.com/whitepaperarticle.php?articleTitle=Knee+MRI+Basics
Knee MRI Safety (Musculoskeletal)
[1]
[1] Better Health Channel. (2014),
MRI Scan
. Retrieved from: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/MRI_scan
[2]
[2] Radiology, A. C. o., & America, R. S. o. N. (2013). Magentic Resonance Imaging - Knee. In RadiologyInfo (Ed.).
[3] Skinner, S. (2012).
MRI of the knee
. Australian Family Physician, 41(11), 867-869.
[3]
ACL Tears
[4]
[4] Radiology, A. C. o. (2014). ACR-SSR practice parameter for the performance and interpretation of magnetic resonsance (MRI) of the knee.
Anterior cruciate ligament (ACL) tears are the most common injuries of the major knee ligaments, affecting athletes and non athletes. ACL tears often occur from physical trauma such as:
Hit to side of knee, over extension and rapid stops and directional changes

Patient presentation: unable to weight bear, swelling at site of injury with limited range of motion.

Up to 90% of ACL tears can be diagnosed based on clinical history and
physical assessment. However, about half of these occur in addition to
damage of other structures in the knee.
Thus extensive imaging such as MRI is required to allow comprehensive
diagnosis and to prevent future osteoarthritis and secondary meniscus
tears.


Tears are often graded:
Grade 1:
ACL slightly damaged and stretched but still holds
joint stable.
Grade 2:
ACL becomes loose, often known as a partial tear. It is also
hard to diagnose without imaging.
Grade 3:
ACL is completely torn making the knee unstable. Most common injury with 70%
of tears occurring at the middle of the ACL.
MRI and ACL Tears
[4] Radiology, A. C. o. (2014). ACR-SSR practice parameter for the performance and interpretation of magnetic resonance (MRI) of the knee.
MRI has 78-100% sensitivity and 68-100% specificity in diagnosing ACL tears.
Primary signs of ACL tears on MRI include:
Non-visualisation of ACL and replacement by ill-defined cloud of focal oedema and haemorrhage which causes an increased signal intensity (Figure 8)
Abrupt angulation or wavy appearance in ACL (Figure 9)
Flattened axis of the distal ACL (Figure 10)
[4]
[4]
[5]
[20], [21]
[20] Pavlov, H. , Dalinka, M.K, Alazraki, N., Berquist T.H., Daffner, R.H., DeSmet, A.A,…McCabe. J.B. (2000a). Acute trauma to the knee. American College of Radiology. ACR Appropriateness Criteria. Radiology, 215, 365-373.
[21] Pavlov, H. , Dalinka, M.K, Alazraki, N., Berquist T.H., Daffner, R.H., DeSmet, A.A,…Sartoris. D. (2000b). Nontraumatic knee pain. American College of Radiology. ACR appropriateness criteria. Radiology, 215, 311-320.
[22] Koplas, M. & Schils, J.(2008). The painful knee: Choosing the right imaging test. Cleavland Clinic Journal of Medicine, 75(5), 377-384
[22]
Figure 8. MRI showing non-visualisation of ACL as it is replaced by high signal intensities from oedema.
[23] Ivy Sports Medicine. (2014).
Knee ultrasound examination
. Retrieved September 11, 2014, from http://www.ivysportsmed.com/en/knee-pain/knee-pain-diagnosis/knee-ultrasound-examination-0
[4] Radiology, A. C. o. (2014). ACR-SSR practice parameter for the performance and interpretation of magnetic resonsance (MRI) of the knee.
Figure 9: MRI showing abrupt angulation in ACL
Figure 10: MRI showing flattened axis in distal ACL
[8] Allen, A. M. (2013). MRI for Anterior Cruciate Ligament Injury. Retrieved from: http://emedicine.medscape.com/article/400547-overview#aw2aab6b7
[23]
[24] Love, C., Tomas, M.B., Marwin S. E., Pugliease, P.V. & Palestro, C.J. (2001) Role of nuclear medicine in diagnosis of the infected joint replacement. Radiographics, 21(5), 1229-1238
[25] Palestro, C.J. (2003). Nuclear Medicine, the Painful Prosthetic Joint, and Orthopedic Infection. The Journal of Nuclear Medicine, 44(6), 927-929
Figure 20. Total knee replacement. Retrieved from http://sharonsblog.wordpress.com/2008/07/08/total-knee-replacement-surgery/
Figure 21. MRI skin burns. Retrieved from: http://www.fda.gov/downloads/MedicalDevices/NewsEvents/WorkshopsConferences/UCM283552.pdf
Tendons connect bones to muscles.
Quadriceps (connect quadricep muscles to kneecap) and patellar (connects kneecap to tibia): resembling ligaments.
[24], [25]
[26], [27]
[26] Olson, R. W. (1967). Knee Arthrography. American Roentgenoloy,101(4),897-914
[27] Freiberger, R. & Pavlov. H.(1988). Knee Arthography. Radiology, 166, 489-492
[5] Schmider, C. (2010). Knee joint anatomy, function and problems. Retrieved 09/09, 2014, from http://www.healthpages.org/anatomy-function/knee-joint-structure-function-problems/#structures-of-the-knee
[6]
[6] Rubin, D. & Smithius, R. (2005)
Knee - Non-meniscal Pathology
. Retrieved from: http://www.radiologyassistant.nl/en/p42764e8fe927e/knee-non-meniscal-pathology.html
Figure 7. Complete tear of the ACL. Retrieved from: http://orthoinfo.aaos.org/topic.cfm?topic=a00549
[7] American Academy of Orthopaedic Surgeons. (2014).
Anterior Cruciate Ligament Injuries
. Retrieved September 10, 2014, from: http://orthoinfo.aaos.org/topic.cfm?topic=a00549
[8] Allen, A. M. (2013). MRI for Anterior Cruciate Ligament Injury. Retrieved from: http://emedicine.medscape.com/article/400547-overview#aw2aab6b7
[7]
[8]
[8]
[13] Fitzgerald, S.W., Remer, E.M., Friedman, H., Rogers, L.F., Hendrix, R.W., & Schafer, M.F. (1993). MR evaluation of the anterior cruciate ligament: value of supplementing sagittal images with coronal and axial images. AJR Am J Roentgenol;160(6):1233-7.
[13]
When the knee is extended, sagittal image shows features suspicious of an anterior cruciate ligament (ACL) tear, however when the knee is flexed, a gap (black arrow) is clearly present and confirms an ACL tear.
[10] Vohra, S., Anrnold, G., Doshi, S. & Marcantonio, D. (2011). Normal MR Imaging Anatomy of the Knee. Magnetic Resonance Imaging Clinics of North America, 19(3), 637-653. Doi :10.1016/j.mric.2011.05.012
[10]
[14] Porter, N. (2014). MRTY3118 MR theory applications, lecture 4, week 4: MRI applications MSK & MRI safety [lecture PowerPoint slides]. Retrieved from https://elearning.sydney.edu.au/webapps/portal/frameset.jsp 653. Doi :10.1016/j.mric.2011.05.012
[15] Yoshioka, H., Schlechtweg, P. M., & Kose, K. (2009). Magnetic Resonance Imaging. doi: 10.1016/B978-0-323-04177-5.00003-3
[16] Baikoussis, N. G., Apostolakis, E., Papakonstantinou, N. A., Sarantitis, I., & Dougenis, D. (2011). Safety of magnetic resonance imaging in patients with implanted cardiac prostheses and metallic cardiovascular electronic devices. The Society of Thoracic Surgeons, 91(6), 2006-2011. doi: 10.1016/j.athoracsur.2011.02.068
[17] Hoa, D. (2014). MRI safety and precautions. Retrieved September 12, 2014, from http://imaios.com/en/e-Courses/e-MRI/MRI-instrumentation-and-MRI-safety/MR-safety
[14]
Static magnetic field:
Can cause translation and rotation of ferromagnetic implants or objects outside body.
To avoid risk of injury, aneurysm clips, pacemakers/artificial heart valves, wheelchairs, oxygen tanks etc should not be brought into MRI room.
Orthopaedic implants that are non-ferromagnetic material (e.g. Titanium), are safe.
No risk of movement/displacement since they are lodged securely inside the bone.
Check model by referring to Shellock's Reference Manual or the manufacturer's website.
Oscillating magnetic field:
Stimulates conductive loop that concentrates radiofrequency (RF) energy which creates a current, heating up ferromagnetic objects. Heating of implants can cause malfunction or tissue burns.
Correct patient positioning and use of sponges for separation
[14]
[15]
[16]
[14]
[16]
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and insulation.
Flow Artefact
Motion Artefact
Aliasing
Anatomical Variation
Conclusion
MRI is currently the Gold Standard in NON-INVASIVE investigation of the knee allowing visualisation of the ACL and surrounding soft tissue.

Some benefits include:
Non-ionising
Non-invasive
High diagnostic value

Suitable for the majority of patients.
MRI sequences describe the pattern of the electromagnetic field during a scan
Various sequences exist to manipulate the electromagnetic field and alter the overall appearance of tissues.

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