95bone integrity after successful ENK cell therapy in myelomatous mice (Fig. 6.4).
Although MRI is a useful imaging technique, but this technology has some
disadvantages such as low sensitivity for detection of very early disease activity
compared to functional imaging modalities, longer acquisition time and high costs.
Also, presence of indwelling metal devices such as identification microchips in the
body limits its utility for preclinical studies [ 32 – 34 ]. In addition, the detection of
lesions in the bone implants can be challenging because of the respiratory movements
in small animals.
Use of MRI contrast agents and higher magnetic fields has improved the sensitiv-
ity of MRI [ 29 ]. Recently, MRI has been used with drug-containing liposomes,
either labelled with gadolinium or other paramagnetic substances, to facilitate
image-supervised therapeutic delivery and subsequent monitoring of efficacy [ 35 , 36 ].
Advancements in technology have now led to more sensitive quantitative MRI tech-
niques, such as high-field MRI and dynamic contrast-enhanced MRI (DCE- MRI),
which are even more valuable for research into tumor vasculature and the effects of
drugs [ 23 ].
6.2.5 18 F–FDG-PET Imaging
(^18) F–Fluorodeoxyglucose (FDG), a radiolabeled analogue of glucose, is introduced
into the animals and its uptake and metabolism is monitored. The cells with high
metabolic rate take up F^18 -FDG in proportion to their metabolic activity. The^18 F-
FDG gets trapped within the cell after phosphorylation. The^18 F decays via emission
of positrons. Immediately after its decay annihilation reaction occurs and the
positron combines with an electron to generate two 511 KeV photons. These are
detected using the coincidence detection circuitry within a PET scanner. A three-
dimensional image is created of the functional processes corresponding to the
biological activity and uptake of the radiotracer. It presents crucial insight into the
biology of the system [ 37 ]. High uptake indicates high glucose metabolism and
intensified glycolysis that is associated with malignancy which helps in differentiation
between malignant and non-malignant tissue [ 38 , 39 ].
One advantage of FDG-PET is the whole body can be imaged in a single proce-
dure, in approximately ~45 min [ 32 , 40 ]. FDG-PET has been sensitive in detecting
the areas which could not be imaged by MRI. Further, PET can detect bone marrow
involvement with high sensitivity and specificity. In addition, it can differentiate
between extramedullary and intramedullary lesions [ 40 ]. A major advantage of
FDG-PET is probably its ability to detect disease function, which can discriminate
between inactive and active state of the disease [ 41 ].
6 MRI & PET for Evaluation of Myeloma in SCID-hu Mice