Current Molecular Imaging (Discontinued) - Volume 4, Issue 2, 2015

As MRI has been used in biomedical research and medicine since the 1970s, Magnetic Resonance Spectroscopy (MRS) has been employed to study biochemical alterations in living animals and humans. By taking advantage of its noninvasive nature, 1H, 13C and 31P MRS are being actively utilized in clinical and biomedical studies to detect lipids, metabolites, and/or kinetic information, such as acetyl carnitine content and ATP synthesis rates in vivo. These data would be quite difficult to assess by other modalities. Furthermore, many studies have indicated that in vivo values obtained by MRS show a close correlation with important metabolic parameters (e.g., hepatic and intramyocellular lipid content by 1H-MRS correlated with insulin sensitivity), which adds value of MRS. Moreover, hepatic glycogen synthesis and breakdown can be directly detected by 13C-MRS, whereas in vivo ATP synthesis rates in mitochondria can be assessed by 31P-MRS as well. These in vivo data offer critical metabolic information in animals and humans, and often serve as useful biomarkers for the pathophysiology and state of a disease. Thus, in this review, important and frequently used modalities and applications of MRS in muscle, liver, and other organs are described.

Magnetic Resonance Imaging (MRI) is a mature methodology that has been widely used for the evaluation of brain gliomas. Conventional MR imaging can provide morphometric characterization of gliomas, whereas proton Magnetic Resonance Spectroscopy (MRS) provides metabolite information for gliomas non-invasively in vivo. In the application to brain gliomas, proton MRS plays an important role in diagnosis, differential diagnosis, classification, evaluation, treatment planning and prognostic evaluation, and monitoring response to therapy. Over the past more than three decades, both the MRS techniques and their applications in brain gliomas have experienced remarkable proliferation. The aim of this article is to introduce the technique, the metabolites and review its clinical applications in brain gliomas.

Proton Magnetic Resonance Spectroscopy (1H MRS) of the brain is a versatile technique for the study of brain metabolism and brain function and has found wide applications in biomedical research and clinical diagnosis. Proton MRS is capable of measuring concentrations of brain chemicals, probing cellular energetic mechanism, membrane metabolism, and mitochondrial function, thus allowing us to understand the neuro-pathophysiology of psychiatric disorders including autistic spectrum disorders. The aim of this article is to introduce the MRS techniques and review the recent advances of their applications in autistic disorders. Emphasis is given to the practical use of these techniques and the most important and challenging brain chemicals for autistic disorder including N-acetyleaspartate, glutamate and glutamine, gamma-Aminobutyric acid, and lactate.

As a sensitive MRI method, Chemical Exchange Saturation Transfer (CEST) MRI based on endogenous contrast has been increasingly utilized for molecular imaging of various metabolites. Among these applications, the authors have described CEST MRI for molecular imaging of brain metabolites in this review, including brain glutamate, the most abundant excitatory neurotransmitter; creatine, a key molecular of bioenergetics; and myo-inositol, a biomarker of glial cells. Those metabolites conventionally have been quantified with MR spectroscopy methods. Compared to MR spectroscopy, CEST methods typically provide a few hundred to a few thousand fold enhancement in sensitivity, enabling twodimensional imaging or mapping of metabolites at high resolution. In this review, the authors have also reviewed the preliminary applications of these molecular imaging methods. Finally, the challenges related to CEST MRI for molecular imaging in general are discussed.

PET/CT has had an evolutionary role in Oncology. Gynecological malignancies have been increasing in incidence in the last decades. Delay in diagnosis and management have led to worsening prognosis among the patients. Lowering the threshold in suspecting these tumors, may significantly improve the patients’ overall survival. In this review we will address the role of FDG-PET/CT in diagnosing, staging, assessing the response to therapy and predicting survival in gynecological malignancies, namely endometrial, ovarian and cervical cancer. We will briefly compare the diagnosing ability of PET/MRI to PET/CT. We will address the interesting fact about simultaneously utilizing the Apparent Diffusion Coefficient (ADC) with the Standardized Uptake Value (SUV) in hybrid MRI imaging and we will also discuss about the role of PET/MRI in diagnosing primary and recurrent gynecological malignancies.

Crohn's Disease (CD) is a chronic inflammatory bowel disorder which can lead to complications like fistulas, strictures and abscesses. It is difficult to differentiate between chronic fibrotic and acute inflammatory processes with current non-invasive and invasive methods. FDG-PET/CT might help to identify active inflammatory processes and morphological information via one examination. It is a case report of a 22 year old woman diagnosed with CD who experienced an abscess of the left psoas muscle after few years which had to be drained. In 2011, she again complained about left side abdominal pain. This case underlines the usefulness of a combined PET/CT study for identifying active inflammatory processes common on patients suffering from Crohn’s disease. Generally it would be optimal to combine the PET and a diagnostic quality CT-E into a single session.

Semantic Dementia (SD) is classified as a type of Frontotemporal Lobar Degeneration (FTLD) characterized by progressive impairment of conceptual knowledge, accounting for approximately 30% of cases of FTLD. Clinical symptoms and brain Magnetic Resonance (MR) imaging are helpful to reach the diagnosis in the advanced stage, but brain positron emission tomography with [18F] Fluoro-2-Deoxy-D-Glucose (FDG-PET) might be useful to evaluate and distinguish the early stage of SD. This review summarizes 9 studies using FDG-PET with either SPM or three-dimensional stereotactic surface projection statistical software to elucidate the features of SD. The main hypometabolic lesions associated with SD were located in the bilateral temporal lobes. The so-called core lesions were predominantly located in the left and anterior and lower parts of the temporal lobe. Hypometabolism on FDGPET was more extensive than atrophy detected on MR imaging in the temporal lobes and especially involved the bilateral orbitofrontal areas, right caudate nucleus, and insula. FDG-PET is very helpful to diagnose SD in the early to advanced stages.