99mTc-red blood cells SPECT and planar scintigraphy in the diagnosis of hepatic hemangiomas

Compartmentalized agents: A powerful strategy for enhancing the detection sensitivity of chemical exchange saturation transfer contrast

Since the very beginnings of the chemical exchange saturation transfer (CEST) technique, poor overall sensitivity has appeared to be one of its strongest limitations for future applications. Research has therefore focused on designing systems, such as supramolecular and nanosized agents, that contain a high number of magnetically equivalent mobile spins. However, the number of mobile spins offered by these systems is still limited by their composition and surface/volume ratio. The design of compartmentalized agents, that is, systems where an aqueous inner core is separated from the MRI-detected bulk pool via a semipermeable barrier/membrane, is very much a step forward for the technique. These vesicular systems can (i) act as biocompatible and versatile carriers for dia-, para-, and hetero-nuclear CEST probes, thus offering new application options; and (ii) act as CEST probes themselves via the encapsulation of a suitable agent (e.g., a paramagnetic shift reagent) that can change the resonance frequency of the spin pool in the inner compartment only. LipoCEST agents were the pioneers in the latter category, as they are able to grant picomolar sensitivity (in terms of nanoparticle concentration), and paved the way for new applications for CEST agents, especially in the theranostic research area. The use of larger, natural vesicular systems, such as yeasts and cells, in which the huge number of intravesicular spins lowers the detection threshold to a femtomolar limit, is a further step forward in the development of compartmentalized CEST agents. Finally, interesting combinations of nanovesicular and cellular compartmentalized systems have been proposed, thus highlighting how the approach has the potential to drive CEST agents towards completing their journey to mature clinical translation.

To what extent can diverse types of liver lesions mimic hemangiomas? A retrospective quantitative analysis of masses found to be positive in SPECT/CT with labeled blood cells - a preliminary report

Background

Although specificity of SPECT/CT examination using technetium-99m radiolabeled red blood cells (Tc-99m-RBC) for detection of liver hemangiomas is very high, it is still not perfect. It is possible to overlook a malignancy. Moreover, the difference in accumulation of RBCs between a hemangioma and uninvolved liver remains unknown.

The aim of the study is to determine the quotients of accumulation of Tc-99m-RBC in hemangiomas and in normal liver parenchyma (HEM/liv), and to verify, whether the quotient could be potentially helpful in distinguishing hemangiomas from other RBC-accumulating liver masses.

Material/Methods

34 liver lesions larger than 1.5 cm classified scintigraphically (qualitatively) in our Department as either typical or suspicious of hemangioma 1.5–4 years earlier were enrolled in this retrospective study. Their SPECT/CT images were acquired 1 hour after in vivo labeling of RBCs with Tc-99m. In reconstructed images, ellipsoidal regions of interest (ROIs) with diameters of about 1.5 cm were created in the assessed lesions (HEM) and in the uninvolved liver parenchyma (liv). The HEM/liv quotients were calculated for each mass. The results were compared with radiological data.

Results

31 lesions were found to be clinically and radiologically typical for hemangiomas, their HEM/liv ratios were at least 1.6 (smaller masses) or 1.8 (larger masses). One lesion with HEM/liv ratio equal to 1.21 was classified as metastasis. Two lesions with HEM/liv 1.42 and 1.46 were classified as benign foci other than hemangioma.

Conclusions

The quantitative analysis can be preliminarily proposed as a helpful tool in the assessment of possible liver hemangiomas.