MSK Chapter 1 Introduction Orthopedics MRI / MRS
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1.01 Introduction
It is impossible to cover everything in orthopedics MRI/MSK. Therefore I have selected several subjects and examples that form the crucial core. I have deep knowledge of these topics from visits to MRI sites and studying a great number of publications as the field has evolved over 35 years. This guide is therefore a thorough review of the MSK state of the art.
Here you will find out what is happening in the MRI/MRS world concerning MSK right now. I treat both theory and technique: a contemporary overview which will bring you up to date. Clinical tips and hints are included, that I have picked up and evaluated during years of training radiographers and radiologists in over 1,000 hospitals worldwide.
Both the MRI basics and advanced techniques should be familiar to the reader before starting this e-module.
Some chapters may overlap. For example, there are many knee MR images, but these techniques are applicable in all different MSK areas.
These modules cover MSK (MusculoSKeletal) MRI and MRS techniques to visualise joints, muscles/tendons, cartilages, infections, tumors and arthro-pathies. There are also spinal images, regarding pre- and post HNP, radiculopathy, myelopathy, MS, infections and tumors.
1.02 MSK disorders
The term ‘muscular-skeletal (MSK) disorder’ refers to conditions, diseases, and injuries of bones, joints and muscles. MSK disorders can be caused by neurological diseases (e.g. a stroke or cerebral palsy) and orthopedic disorders (e.g. anterior cruciate ligament injuries, osteoarthritis), that change the human MSK system and damage its functions. MSK disorders are numerous, and they are the cause of >20% of the total years lived with disability (ranked second after behavioral and mental health problems). Nowadays, standard static MRI RF sequences are made to deliver a clinical diagnosis and an understanding of bone and tissue pathology. However, it could be imagined and hypothesized, from a functional view, that abnormal or different MSK mechanics cause MSK disorders. Research has shown that MRI of static joint positions do not show a complete evaluation of the dynamic MSK system. Understanding normal and reduced MSK function during motion is a high radiological, bio-mechanical and clinical priority to:
- understand normal joint mechanics in asymptomatic individuals;
- foresee, detect or diagnose MSK disorders (e.g. scapho-lunate sub-luxation);
- regulate appropriate treatments for disorders using evidence-based analysis.
1.03 What is important in MSK?
- Coil / patient positioning
- The coil positioning is mostly rather well described in the application manuals of the different manufacturers. Indeed, it is difficult to give a general overview as many different surface coils are available. Therefore, this will not be covered in this e-module. Do note, however, that during the local basic training that I have given over the years I would typically spend at least one whole day on patient positioning (just to demonstrate how important it is and how creative you have to be, now and then).
- Anatomy: bone (fractures)-ligaments-menisci-discs-soft tissue-cartilage-synovia-fluid, muscles, bursae, capsular and tendinous structures
- Concerning the anatomy and pathology: there are many internet sites and books available on this subject and therefore this subject will not be covered, although it is often referred to in MRI images.
- Websites for MSK anatomy:
- www.freitasrad.net for basic MRI: knee, shoulder, ankle, elbow, wrist and hip
- E-radiologe.info for the anatomy of joints;
- www.essr.org/education/msk-apps MSK apps can be downloaded.
- Contrasts in orthopedics: T1-T2(*)-PD-mixed-diffusion
- Although the contrast behavior in MSK is very important, often a mixed contrast is used alongside the T1-T2-Pd and diffusion contrast, to differentiate ligaments, tendons, tears, menisci, bone, fractures, cartilage, fluid, cysts, muscles and soft tissues in and around the joints. The contrast-generation is covered in the RF sequence e-module.
- (Fat) Suppression methods
- There are considerable improvements in fat suppression techniques nowadays and, because it is important in MSK, I am dedicating a whole chapter to this subject;
- Water suppression;
- MT (Magnetisation Transfer Contrast technique) will be discussed;
- Some shimming methods.
- Additional RF sequences, Supporting techniques and IQ
- The routine RF sequences are described in the e-module of the RF sequences
- The following are specific and rather new RF sequences which are – or can be – used on a regular basis in MSK:-
- dGEMRIC: (Delayed Gadolinium-Enhanced MRI of Cartilage) is an imaging technique to estimate joint cartilage glycosaminoglycan content by T1-relaxation time measurements;
- UTE (Ultrashort TE) RF sequences will be explained and discussed: a RF sequence, which promises to “make invisible tissues visible”;
- Synthetic MRI/ SSI / MAGIC is a method in MRI for generating contrast weighted images based on measurement of tissue properties. The synthetic images are generated post scan from parametric maps of tissue properties. It is possible to generate several contrast weightings from the same acquisition. Apart from the different contrast weightings, modern MRI image processing methods have generated quantitative, morphometric, functional, and structural assessments of e.g. the human brain. The parametric maps can be computed from a particular MRI acquisition, designed for quantifying the tissue parameters. These settings can be TE and TR for an SE-based RF sequence or TE, TR and TI for an IR based (IR, FLAIR, STIR, PSIR, FSE-IR, TIRM) RF sequence. Calculating the images based on maps and system settings is called synthesising the images. I discussed it shortly in the e-module of RF sequences and we were already discussing it in the 1980’s;
Top row: conventional examination at 1.5T: 14:54min
Bottom row: with SyMRI: 5:48min
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- Although already discussed in the RF sequence e-module, Metal Artefact Reduction Techniques are also important in MSK imaging and will be discussed briefly: MARS, VAT and SEMAC as the RF sequence: MultiVane / BLADE / PROPELLER / Turbo-Prop / JET / RADAR. This chapter will also cover how synovitis/ tendo-synovitis and arthritis inflammations can be visualised;
- IQ, several parameter settings, including (advanced) Parallel Imaging, Compressed Sensing (or Hyper SENSE) and Multi Band: Compressed SENSE is a break-through acceleration technique speeding up not only sequences but the entire exam. This new paradigm in productivity requires a unique implementation, enabling 2D and 3D scans to be up to 50% faster with virtually equal IQ. Compressed SENSE can be used in all anatomical contrasts and all anatomies. Multi Band (Hyper Band) or SMS (Simultaneous multi slice) enables generalized Multi Band slice accelerated imaging for any type of MR RF pulse sequence. This was discussed in further detail in the RF sequence e-module.
- The T1- T2 mapping and Quantification
- This will be discussed in a separate chapter, because Quantification is becoming a must in MSK.
- T2 mapping
This pre-contrast Image of T2-map shows the pseudo-colour T2 values distribution within MACT (Matrix-associated Autologous Chondrocyte Transplantation). Corresponding T2 values are shown in the colour-bar. Transplant cartilage shows higher T2 values, compared to the hyaline cartilage reference. The MR measurement was conducted five months after the surgery. The borders of the cartilage transplant are visible.
○ T1 mapping
This post-contrast image shows color coded cartilage transplant post-contrast T1-map. This shows contrast enhancement of cartilage transplant after i.v. administration of contrast agent.
Computer-aided quantification in cartilage Imaging will be discussed in several chapters, as the quantification in muscles.
- Weight-bearing / Standing Up / Positional MRI / axial loaded MRI
- A very interesting field and I suspect it will be linked to functional MRI in the future;
- In this subchapter I will also discuss contrast agents: intra-articular (arthrography) and intra-venously injected.
MR arthrography
a: wrist arthrogram and concurrent MR arthrogram on coronal b: fat-suppressed T1-weighted image and c: water excitation 3D T1w image. MR arthrogram demonstrates small articular disc perforation
- Kinematics, functional and dynamic / Extension / flexion and Arthrograms
- Kinematic devices / imaging and arthrography;
- 3D Functional HR MRI (even in real-time) is getting possible and is a great feature in e.g. spine imaging, including quantification.
- Microscopic Imaging
- As mentioned before, bone imaging in MRI is in development. With the new UTE RF sequences, invisible tissues can be made visible.
From a normal visible wrist (1) to a conventional MRI (2), then to micro MRI (3), to the structure model of micro MRI (4) and then to an exclusive acquisition (5) to 3D post-processing and analysis (last image)
MRI of triangular fibro-cartilage:
S/N Ratio, spatial resolution, and contrast resolution: (a) Low and (b) high spatial resolution coronal PDw images of the wrist at 1.5T (Philips Healthcare), respectively obtained using 120 mm FOV with a flexible coil and a 50 mm FOV with a microscopic coil, . (c) Low and (d) high S/N Ratio coronal T2* GRE images of the wrist with an imaging matrix of 224 × 512 at 1.5T (Philips Healthcare), correspondingly obtained an 80-mm surface coil and a 47-mm microscopic coil, . (e) Low contrast without intra-articular contrast injection and (f) high contrast resolution with intra-articular contrast injection images with 3D coronal fat-suppressed T1w GRE images of the wrist at 3T (Siemens).
3T MRI of the wrist. Coronal (a) PDw and (b) fat-suppressed PD-weighted images at 3T
Due to their small size and complex structure, diagnosing injury of the proximal wrist ligamentous structures can be challenging. The TFCC (Triangular Fibro-Cartilage Complex) is an example of such a structure. Lesions as such structures may be missed, unless HR MRI attained via a standard matrix with a FOV or HR acquisition matrix is utilised. Although there have been recent advances in increasing MRI spatial resolution, efforts to improve visualisation by isolated increase in the spatial resolution, will be ineffective if S/N Ratio of the images gained is low. Also, high contrast resolution is important to enable a more detailed visualisation of these structures and their pathology. This means that a balance of the three important imaging factor qualifications of high spatial resolution, high S/N ratio and C/N Ratio, must be obtained for optimised TFCC and wrist imaging
- Cartilage Imaging
- I will discuss this in different chapters, for instance in “RF sequences” and “T1-T2 mapping and Quantification” ditto.
- Bone imaging, soft tissue etc.
- This will come back in the different chapters. Bone Imaging is getting exiting, thanks to MICRO-Imaging.
- Spectroscopy in MSK
- The basics will be reviewed too: repetition is always good in MSK and it is not only about Proton Spectroscopy.
- Optimised patient and examination workflow
- this is also an important subject, because the number of patients being examined is increasing. Costs need to be reduced, so shorter examination times need to be acquired. However, Patient Management is discussed in the MRI Safety e-module. So it will not be discussed in this e-module;
- 2nd Patient Handling System or possible table top disconnection (un-dock);
- minimising preparation- and examination-times.
- Sports medical MRI
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- Sports medicine physicians and orthopedic surgeons are raising IQ and precise and detailed diagnosis. Unfortunately, this is not always possible, because MR sites do not always have dedicated MSK radiologists and appropriate MSK protocols. The spatial resolution, the contrast and the selected RF sequences are not always optimally chosen, which results in a repetition of the MRI scan on another site to answer the clinical question correctly.
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Fortunately, the ESSR (European Society of Musculo-Skeletal Radiology) has published protocol guidelines for MRI in sports injuries which can also be used on older MRI systems (those systems do not always have state of the art protocols), showing an adequate IQ (see protocols Ara Kassarjian, MD, Madrid Spain). These guidelines show that it is not always necessary to scan with an ultra-high resolution. However, it is necessary to have the correct RF sequence, contrast and resolution.
- Oncology
- This is discussed in different chapters: how to visualise the different tumors, tips and hints for specific RF sequences and the growth of a total body MRI for screening metastasis, myelomas and other frequently appearing tumors.
- Diffusion and Perfusion in MSK
- How to characterise, qualify and quantify tumors? This is often related to oncology. Although the basics have been discussed in the RF sequences e-module, some of the diffusion and DTI in MSK will also be discussed.
1.04 Conclusion and future items
New MRI techniques include T2, and T1 mapping, DWI and DTI, Sodium imaging, MR spectroscopy and UTE RF sequences, which enable quantitative and non-invasive monitoring of the development of repaired tissue, following micro-fracture surgery and evaluation of earlier stages of pathology in MSK tissue. However, the newest and more advanced RF pulse sequences should be used, modified and optimised to achieve their full clinical potential, as should advances in both hardware and software technology, such as Compressed Sensing and Multi Band techniques.
1.05 Disclaimer
This document should not be construed to represent a definitive interpretation of the regulatory statutes regarding MRI and MRS, and the reader should be aware that regulations might change and render possible out-of-date information specified herein.
Although every attempt has been made to verify the information contained in this e-module, the author cannot guarantee its 100% accuracy. Each effort is made by the editorial board to see that no inaccurate or misleading data, opinion or statements occur. EMRIC sarl cannot accept responsibility for the completeness. This document may not be distributed or re-posted without the express written permission of EMRIC sarl.
I know not everything can be covered, but at least I would like to give an overview of MR knowledge, trying to stay updated, and also putting together what I picked up in the last 35 years. I still like to encourage everybody to do the same!
If you find an aspect of MRI and MRS that I have not covered, do let me know and I will resolve it.
1.06 Evaluation and skills
At the end of this e-module you should :
- Have an in-depth knowledge of the MSK MRI and MRS and what is happening in this field;
- Understand the principles, the basic and advanced RF sequences used in MSK and the acronyms and abbreviations used;
- Understand the importance and the different applications in MSK MRI and MRS;
- Apply techniques to reduce the acquisition time using several techniques;
- Describe various clinical applications for MSK RF sequences.
- At the end of this module have the skills and be creative in MRI and MRS, choosing the best methods, contrast and IQ in general, with the help of clinical tips and hints
I really hope you enjoy this course and pick out useful items: I advise against just scanning it quickly.
I hope it swallows you up, heart and soul!
This introductory chapter is freely available for potential students to get an idea about the content and set up of the e-module, Orthopedics MR-MRS / MSK Imaging.
1.07 Orthopedics: MRI-MRS / MSK Imaging E-module Chapters
- Weightbearing / Standing up-Positional / axial loaded MRI
- Kinematic and arthrograms
- Additional RF sequences – supporting techniques and IQ (parameters) in MSK
- DWI, DTI and DCE in MSK
- T1 and T2 mapping and quantification in MSK
- Fat and tissue suppression techniques
- MRS in MSK
- Microscopic imaging
- MR MSK in Sports Medicine
Conclusions, Reviews, Publications, Future views, Questions (false-true and multiple choice) and statements are built in at the end of each chapter.