Brain Tumor Enhancement in Magnetic Resonance Imaging: Dependency on the Level of Protein Binding of Applied Contrast Agents

Advocating the Development of Next-Generation High-Relaxivity Gadolinium Chelates for Clinical Magnetic Resonance

The question of improved relaxivity, and potential efficacy therein, for a next-generation of magnetic resonance gadolinium chelates with extracellular distribution and renal excretion, which could also be viewed from the perspective of dose, is addressed on the basis of historical development, animal experimentation, and human trials. There was no systematic evaluation that preceded the choice of 0.1 mmol/kg as the standard dose for human imaging with the gadolinium chelates. In part, this dose was chosen owing to bloodwork abnormalities seen in phase I and phase II studies. Animal investigations and early clinical trials demonstrated improved lesion detectability at higher doses in the brain, liver, and heart. By designing an agent with substantially improved relaxivity, higher enhancement equivalent to that provided with the conventional gadolinium agents at high dose could be achieved, translating to improved diagnosis and, thus, clinical care. Implicit in the development of such high-relaxivity agents would be stability equivalent to or exceeding that of the currently approved macrocyclic agents, given current concern regarding dechelation and gadolinium deposition in the brain, skin, and bone with the linear agents that were initially approved. Development of such next-generation agents with a substantial improvement in relaxivity, in comparison with the current group of approved agents, with a 2-fold increase likely achievable, could lead to improved lesion enhancement, characterization, diagnosis, and, thus, clinical efficacy.

Post-Surgery Glioma Growth Modeling from Magnetic Resonance Images for Patients with Treatment

Reaction diffusion is the most common growth modelling methodology due to its simplicity and consistency with the biological tumor growth process. However, current extensions of the reaction diffusion model lack one or more of the following: efficient inclusion of treatments' effects, taking into account the viscoelasticity of brain tissues, and guaranteed stability of the numerical solution. We propose a new model to overcome the aforementioned drawbacks. Guided by directional information derived from diffusion tensor imaging, our model relates tissue heterogeneity with the absorption of the chemotherapy, adopts the linear-quadratic term to simulate the radiotherapy effect, employs Maxwell-Weichert model to incorporate brain viscoelasticity, and ensures the stability of the numerical solution. The performance is verified through experiments on synthetic and real MR images. Experiments on 9 MR datasets of patients with low grade gliomas undergoing surgery with different treatment regimens are carried out and validated using Jaccard score and Dice coefficient. The growth simulation accuracies of the proposed model are in ranges of [0.673 0.822] and [0.805 0.902] for Jaccard scores and Dice coefficients, respectively. The accuracies decrease up to 4% and 2.4% when ignoring treatment effects and the tensor information, while brain viscoelasticity has no significant impact on the accuracies.

Advances in diagnostic radiology

Recent advances in diagnostic radiology are discussed on the basis of current publications in Investigative Radiology. Publications in the journal during 2009 and 2010 are reviewed, evaluating developments by modality and anatomic region. Technological advances continue to play a major role in the evolution and clinical practice of diagnostic radiology, and as such constitute a major publication focus. In the past 2 years, this includes advances in both magnetic resonance and computed tomography (in particular, the advent of dual energy computed tomography). An additional major focus of publications concerns contrast media, and in particular continuing research involving nephrogenic systemic fibrosis, its etiology, and differentiation of the gadolinium chelates on the basis of in vivo stability.

Evaluation of a fibrin-binding gadolinium chelate peptide tetramer in a brain glioma model

PURPOSE

To compare a fibrin-targeted, high relaxivity gadolinium tetramer, EP-2104R, in terms of magnitude of contrast enhancement (CE) and temporal time course, to a conventional extracellular gadolinium chelate, in a brain glioma model at 1.5-T magnetic resonance imaging.

METHODS

Six rats were evaluated, with each animal receiving (for separate studies) 0.05 mmol/kg gadopentetate dimeglumine (Gd DTPA or Magnevist) and 0.0125 mmol/kg of EP-2104R, with the 2 magnetic resonance examinations separated in each animal by 24 hours. The compound (EP-2104R) was synthesized using published methodology, being comprised of an 11 amino acid peptide derivatized at both the C- and N-termini with Gd-DOTA-like (Dotarem-like) moieties. T1-weighted scans were acquired precontrast and for 5 consecutive 2-minute intervals postcontrast, and subsequently at 15 and 20 minutes postcontrast.

RESULTS

Maximum tumor contrast-to-noise and CE both occurred at 1 minute versus at 5 minutes following administration of Gd DTPA versus EP-2104R, respectively. Utilizing an equivalent dose on a Gd ion per body weight basis, signal-to-noise, contrast-to-noise, and CE were greater for EP-2104R at all time points postcontrast, yielding overall statistically significantly greater levels of all 3 parameters with the latter. With EP-2104R, improvements in CE ranged between 87% and 391%, increasing at each measured time postcontrast with the exception of a slight decrease from 15 to 20 minutes postadministration. Histopathology confirmed, using immunofluorescence technique, abnormally increased fibrin within the tumor.

CONCLUSIONS

Statistically significantly greater brain tumor enhancement was noted with greater lesion enhancement at all observed time points postcontrast for EP-2104R utilizing an equivalent concentration to Gd DTPA on a per gadolinium ion basis. These findings together with the prolonged time course of enhancement suggest possible fibrin-binding and altered distribution kinetics.

MRI of experimental gliomas

Malignant gliomas are the most frequent primary brain tumours and they are associated with a grim prognosis. In order to elucidate the biological properties of these tumours and to assess treatment responses, valid animal models are needed. We have developed a model where human glioma specimens are operated into the brains of immunodeficient animals. Tumour development is followed by MR imaging and proton spectroscopy. In this chapter, operating procedures and the MR techniques are presented.