**1. Introduction**

Mechanisms responsible for the course of the rheumatic diseases have not been fully explained till today. Molecular imaging sits among the available tools that may help in studies of these mechanisms, particularly techniques emphasized by nuclear medicine.

In contrast to such imaging modalities as CT, US or MRI, that reveal only structural pathologies, radionuclide methods enable imaging of functional changes that occur in the course of the disease and more importantly are usually featured by a very high specificity. Radionuclide studies also make it possible to determine the changes in the molar concentration of specific chemical compounds up to 10−11 or even 10−3–10−4 if an MRI is used. It means that radionuclide studies enable the performance of diagnosis of disorders in the molar concentration of the

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

specific chemical compounds that take place in the course of the disease. It is important to note that the functional character of disorders should be the basis for the choice of treatment.

that allow for an early and accurate prognosis as well as monitoring of therapy [5]. Beyond any doubts, another important feature of these methods is the capability of making the diagnosis at the subclinical phase of the disease, thanks to which a proper treatment can be started

Molecular Imaging

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http://dx.doi.org/10.5772/intechopen.77200

Procedures offered by nuclear medicine meet the number of important expectations associ-

**a.** The capability of putting a considerably early diagnosis of pathological changes as well as the determination of their character, which is crucial to make an appropriate diagnosis

**c.** The ability to predict the course of the disease and the subsequent introduction of person-

**d.** The reduction of constantly increasing the costs of medical procedures by use of such evaluation tools that provide a good assessment of the effectiveness of the applied treatment.

**e.** The need of the determination of remission of the pathological changes as well as an early

Taking these facts into account, it is clear that radionuclide studies and MRI have proven to be useful in solving all of the clinical issues. Moreover, it is important to note that it meets

The most commonly used radiopharmaceutical used in PET-CT studies is fluorodeoxyglucose (18F-FDG), which is a structural glucose analog. Areas of increased tracer uptake indicate the intensification of metabolic processes associated with increased glucose demand. This feature can be found both in a tumor and inflammatory setting. Increased uptake of 18F-FDG is associated with increased activity of the GLUT1 and GLUT3 transport mechanisms as well as the activity of hexokinase—these phenomena are typical for cells that undergo fast proliferation as well as other types of cells such as macrophages, neutrophils and young

Choline is another tracer that features high sensitivity for proliferative processes that occur in the course of the disease. This tracer is uptaken by quickly dividing cells where it undergoes phosphorylation by choline kinase into phosphorylcholine. Choline is essential for phospholipids synthesis, especially phosphatidylcholine (also known as lecithin) which serves as the building block of the cell membranes. Increased uptake of choline depends on the

**b.** The ability of accurate determination of the degree of pathological changes.

long before irreversible morphological changes occur.

before irreversible structural changes occur.

alized therapy.

diagnosis of their relapse.

**2. Radiopharmaceuticals**

granulation tissue [6–8].

**2.2. 11C-choline**

**2.1. 18F-FDG**

ated with the development of modern medical sciences, such as:

economic and pharmacological criteria for cost-effectiveness.

Over the last several decades, the introduction of new biological agents has greatly improved the effectiveness of treatment. Those agents influence the activity of specific receptor and metabolic pathways [1]. Along with the application of new agents, it has become necessary to introduce new diagnostic methods, which allow evaluation of the activity of those biological processes. Unfortunately, neither clinical examination nor laboratory tests nor conventional X-ray does not provide such findings. A clinical evaluation can be highly subjective; laboratory tests are frequently non-specific and inconsistent, while conventional X-ray shows structural changes only at the advanced stage of the disease.

It seems that the introduction of molecular imaging techniques may lift those limitations. The fundamental methods of molecular imaging are radionuclide studies. Recent advances in nuclear medicine allowed to develop target-specific agents making it possible to reveal molecular level disturbances that take place on the course of the ongoing disease [2]. The fundamental radionuclide studies include a PET, SPECT, and classic scintigraphy. Moreover, hybrid devices are used more frequently in diagnostics these days—these consist of gamma camera and CR/MRI. Thanks to hybrid techniques, it is possible to perform CT/MRI combined with scintigraphy (for example PET-CT, PET-MRI, and SPECT-CT). It is also important to mention that the combination of those techniques allows applying attenuation correction of the absorbed radiation that is being emitted by radioisotope, as well as making it possible to determine the exact location of the abnormal uptake of the radiopharmaceutical. Finally, the images obtained are of very high quality.

Technological advances allow obtaining images of much better resolution and allow combining both structural and functional data. Vogel et al. noted in his study that hybrid imaging technique 18F-FDG PET-CT, apart from providing the capability of assessing the degree of inflammation localized in the tarsus of a rheumatoid arthritis (RA) patient, also allows precise localization of the disease activity in particular joints [3]. Neither physical examination nor X-ray can provide such relevant data. Furthermore, 18F-FDG PET/CT allows to visualize and diagnose metabolically active subcutaneous nodules, activated lymph nodes or other affected joints in the course of the disease (such as those of the knee or atlantoaxial joints). This method allows better discrimination between juxtaarticular disease and articular processes as well as delineation of tendon sheath and bursal inflammation. Furthermore, this method makes it possible to delineate inflammation of the tendon sheaths and bursae. Miese et al. [4] also assessed the high suitability of PET/MRI apparatus in his work about the diagnosis of RA, in which he showed increased uptake of 18F-FDG in the corresponding metacarpophalangeal joints that were affected by synovitis and tenovaginitis as identified on contrast-enhanced MRI.

MRI is second modern imaging modality that is very useful in the diagnosis of rheumatic diseases. This method features a very high resolution and similarly good contrast between the soft tissues. Thanks to the new sequences and specific contrast agents, and modern MRI allows imaging of vast amounts of pathologies.

Both of these methods provide the information about molecular pathological mechanisms that accompany the disease; thus allowing a better understanding of the pathophysiology of rheumatic diseases. Moreover, they allow a search of the new forms of molecular treatment that allow for an early and accurate prognosis as well as monitoring of therapy [5]. Beyond any doubts, another important feature of these methods is the capability of making the diagnosis at the subclinical phase of the disease, thanks to which a proper treatment can be started long before irreversible morphological changes occur.

Procedures offered by nuclear medicine meet the number of important expectations associated with the development of modern medical sciences, such as:


Taking these facts into account, it is clear that radionuclide studies and MRI have proven to be useful in solving all of the clinical issues. Moreover, it is important to note that it meets economic and pharmacological criteria for cost-effectiveness.
