Metal–Drug–Protein Assemblies: Gd3+ Self-Enhanced Magnetic Resonance Imaging,High-Sensitive Tumor-Targeting Imaging and Efficient Chemo-Phototherapy

Magnetic resonance imaging (MRI) contrast agents are broadly employed for better clinical trials in MR imaging. Magnevist solution (Gd-DTPA), a clinical MRI contrast agent, possesses inherent shortcomings like poor r₁ relaxation, short half-time, nephrotoxicity, etc. To overcome these problems, Gd-DTPA-grafted protein assemblies (Gd-P-ABs) loading with anticancer drug cisplatin and photosentizer IR-780 are constructed via chelation of Gd³⁺. Gd-P-ABs exhibit dual MR/fluorescence (FL) imaging–guided chemo/photothermal therapy. Interestingly, Gd-P-ABs behave as aggregation-enhanced magnetic resonance imaging with an extremely high r₁ value of 26.391 s⁻¹ mm ⁻¹, which is about 5.5-fold larger than Gd-DTPA (≈4.8 s⁻¹ mm ⁻¹). Consequently, better MRI performance is presented with the same concentration of Gd ions. When exposed to acidic tumor microenvironment and light irradiation, Gd-P-ABs show significant drug release capacity. Good cell killing ability in vitro is also determined due to effective folate-targeting ability and high photo–heat conversion. In vivo MR/FL imaging results reveal that Gd-P-ABs possess high-sensitivity tumor-targeting imaging and long tumor retention, which are attributed to the folate-targeting ability and small size effect. Combined chemo/photothermal therapy in vivo demonstrates that the tumor can be eventually ablated. Altogether, the Gd-P-ABs possess great potential for clinical imaging-guided tumor therapy.     

SIMS depth profiling of polymer blends with protein based drugs

We report the results of the surface and in-depth characterization of two component blend films of poly(l-lactic acid) (PLLA) and Pluronic surfactant [poly(ethylene oxide) (A) poly(propylene oxide) (B) ABA block copolymer]. These blend systems are of particular importance for protein drug delivery, where it is expected that the Pluronic surfactant will retain the activity of the protein drug and enhance the biocompatibility of the device. Angle dependant X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) employing an SF₅⁺ polyatomic primary ion source were both used for monitoring the surfactant's concentration as a function of depth. The results show an increased concentration of surfactant at the surface, where the surface segregation initially increases with increasing bulk concentration and then remains constant above 5% (w/w) Pluronic. This surface segregated region is immediately followed by a depletion region with a homogeneous mixture in the bulk of the film. These results suggest the selection of the surfactant bulk concentration of the thin film matrices for drugs/proteins delivery should achieve a relatively homogeneous distribution of stabilizer/protein in the PLLA matrix. Analysis of three component blends of PLLA, Pluronic and insulin are also investigated. In the three component blends, ToF-SIMS imaging shows the spatial distribution of surfactant/protein mixtures. These data are reported also as depth profiles.     

Fast chemical-shiftT 1 imaging in toroid cavities for the structural analysis of gels and emulsions

Fast chemical-shiftT ₁ imaging in toroid cavity cells (TCCs) is introduced and applications to diagnostic ultrasound gel and skin-care ointment are presented. TCCs are an advancement over previously used toroid cavity detectors because they combine resonator and sample container into one part. Additionally, they are removable from the top of the probe and facilitate convenient probe and sample handling. Radially resolvedT ₁ relaxation times in TCCs are obtained through combination of SR (saturation recovery) experiments with the RIPT (rapid imaging with a pulse train) technique. Because of the strong radialB ₁ gradient in TCCs, only pulse-burst saturation was found satisfactory to generate the most even starting condition for SR experiments. Because RIPT does not resolve chemical-shift information, magnetization andT ₁ profiles of individual components in mixed samples are monitored by double-transient experiments with selective on-resonance saturation, which is achieved by converging trains of sinc pulses. The new techniques were applied to cellulose hydrogel and oil-in-water emulsion both exposed to significant shear stress deformation during the charging of the TCC. In both cases,T ₁ profiles as a function of time reveal structural recovery (thixotropy) that slowly progresses from one or more sample interfaces into the bulk.     

Amphiphilic Core–Shell Nanocomposite Particles for Enhanced Magnetic Resonance Imaging

A scalable synthesis of magnetic core–shell nanocomposite particles, acting as a novel class of magnetic resonance (MR) contrast agents, has been developed. Each nanocomposite particle consists of a biocompatible chitosan shell and a poly(methyl methacrylate) (PMMA) core where multiple aggregated γ‐Fe₂O₃ nanoparticles are confined within the hydrophobic core. Properties of the nanocomposite particles including their chemical structure, particle size, size distribution, and morphology, as well as crystallinity of the magnetic nanoparticles and magnetic properties were systematically characterized. Their potential application as an MR contrast agent has been evaluated. Results show that the nanocomposite particles have good stability in biological media and very low cytotoxicity in both L929 mouse fibroblasts (normal cells) and HeLa cells (cervical cancer cells). They also exhibited excellent MR imaging performance with a T₂ relaxivity of up to 364 mM_Fe^?1 s^?1. An in vivo MR test performed on a naked mouse bearing breast tumor indicates that the nanocomposite particles can localize in both normal liver and tumor tissues. These results suggest that the magnetic core–shell nanocomposite particles are an efficient, inexpensive and safe T₂‐weighted MR contrast agent for both liver and tumor MR imaging in cancer therapy.     

A statistical fMRI model for differential T2* contrast incorporating T1 and T2* of gray matter

Relaxation parameter estimation and brain activation detection are two main areas of study in magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI). Relaxation parameters can be used to distinguish voxels containing different types of tissue whereas activation determines voxels that are associated with neuronal activity. In fMRI, the standard practice has been to discard the first scans to avoid magnetic saturation effects. However, these first images have important information on the MR relaxivities for the type of tissue contained in voxels, which could provide pathological tissue discrimination. It is also well-known that the voxels located in gray matter (GM) contain neurons that are to be active while the subject is performing a task. As such, GM MR relaxivities can be incorporated into a statistical model in order to better detect brain activation. Moreover, although the MR magnetization physically depends on tissue and imaging parameters in a nonlinear fashion, a linear model is what is conventionally used in fMRI activation studies. In this study, we develop a statistical fMRI model for Differential T₂^? ConTrast Incorporating T₁ and T₂^? of GM, so-called DeTeCT-ING Model, that considers the physical magnetization equation to model MR magnetization; uses complex-valued time courses to estimate T₁ and T₂^? for each voxel; then incorporates gray matter MR relaxivities into the statistical model in order to better detect brain activation, all from a single pulse sequence by utilizing the first scans.     

Temperature and magnetic field responsive hyaluronic acid particles with tunable physical and chemical properties

We report the preparation and characterization of thiolated-temperature-responsive hyaluronic acid-cysteamine-N-isopropyl acrylamide (HA-CYs-NIPAm) particles and thiolated-magnetic-responsive hyaluronic acid (HA-Fe-CYs) particles. Linear hyaluronic acid (HA) crosslinked with divinyl sulfone as HA particles was prepared using a water-in-oil micro emulsion system which were then oxidized HA-O with NaIO₄ to develop aldehyde groups on the particle surface_. HA-O hydrogel particles were then reacted with cysteamine (CYs) which interacted with aldehydes on the HA surface to form HA particles with cysteamine (HA-CYs) functionality on the surface. HA-CYs particles were further exposed to radical polymerization with NIPAm to obtain temperature responsive HA-CYs-NIPAm hydrogel particles. To acquire magnetic field responsive HA composites, magnetic iron particles were included in HA to form HA-Fe during HA particle preparation. HA-Fe hydrogel particles were also chemically modified. The prepared HA-CYs-NIPAm demonstrated temperature dependent size variations and phase transition temperature. HA-CYs-NIPAm and HA-Fe-CYs particles can be used as drug delivery vehicles. Sulfamethoxazole (SMZ), an antibacterial drug, was used as a model drug for temperature-induced release studies from these particles.     

Mesoporous Silica Promoted Deposition of Bioinspired Polydopamine onto Contrast Agent: A Universal Strategy to Achieve Both Biocompatibility and Multiple Scale Molecular Imaging

Polydopamine (PDA) preserves universal coating and metal‐binding ability, and is suitable for application in synthesizing multifunctional agents. Herein, utilizing mesoporous silica assisted deposition to enhance both heterogeneous nucleation and loading amounts of PDA, the magnetic resonance (MR) T₁ component (PDA‐Fe³⁺) and MR T₂/computed tomography (CT)/multiphoton luminescence (MPL) component (FePt) have been successfully integrated in aqueous solution. This four‐in‐one (T₁, T₂, CT, MPL) imaging nanocomposite, FePt@mSiO₂ @PDA‐polyethylene glycol (PEG), demonstrated its multi‐imaging power both in vitro/in vivo. According to our in vitro/in vivo results, FePt@mSiO₂@PDA‐PEG reveals water‐content‐dependent property in T₁ MR imaging, which suggests the necessity of having dual‐modal MR ability in a single particle for the precision diagnosis. Most importantly, this dual (T₁,T₂)‐MRI/CT contrast agent is demonstrated complementary to each other in the in vivo testing. PDA coated mesoporous silica also offers an advantage of delayed degradation that prevents adverse effects caused by silica fragments before excretion. The potential of this nanocomposites in both drug carrier and photothermal agent was further evaluated by using doxorubicin and monitoring solution temperature after irradiating 808 nm continuous‐wave, respectively The merits of controlled polymerization, enhanced PDA loading, and biofavorable degradation make this methodology promising to other nanoparticle@mSiO₂ for a wide range of bioapplications.     

Synthesis and characterization of noscapine loaded magnetic polymeric nanoparticles

The delivery of noscapine therapies directly to the site of the tumor would ultimately allow higher concentrations of the drug to be delivered, and prolong circulation time in vivo to enhance the therapeutic outcome of this drug. Therefore, we sought to design magnetic based polymeric nanoparticles for the site directed delivery of noscapine to invasive tumors. We synthesized Fe₃O₄ nanoparticles with an average size of 10±2.5 nm. These Fe₃O₄ NPs were used to prepare noscapine loaded magnetic polymeric nanoparticles (NMNP) with an average size of 252±6.3 nm. Fourier transform infrared (FT-IR) spectroscopy showed the encapsulation of noscapine on the surface of the polymer matrix. The encapsulation of the Fe₃O₄ NPs on the surface of the polymer was confirmed by elemental analysis. We studied the drug loading efficiency of polylactide acid (PLLA) and poly (l-lactide acid-co-gylocolide) (PLGA) polymeric systems of various molecular weights. Our findings revealed that the molecular weight of the polymer plays a crucial role in the capacity of the drug loading on the polymer surface. Using a constant amount of polymer and Fe₃O₄ NPs, both PLLA and PLGA at lower molecule weights showed higher loading efficiencies for the drug on their surfaces.     

B(1)(+)/actual flip angle and reception sensitivity mapping methods: simulation and comparison

Knowledge of the spatial distribution of transmission field B₁⁺ and reception sensitivity maps is important in high-field (≥3 T) human magnetic resonance (MR) imaging for several reasons: these include post-acquisition correction of intensity inhomogeneities, which may affect the quality of images; modeling and design of radiofrequency (RF) coils and pulses; validating theoretical models for electromagnetic field calculations; testing the compatibility with MR environment of biomedical implants. Moreover, inhomogeneities in the RF field are an essential source of error for quantitative MR spectroscopy. Recent studies have also shown that B₁⁺ and reception sensitivity maps can be used for direct calculation of tissue electrical parameters and for estimating the local specific absorption rate (SAR) in vivo.Several B₁⁺ mapping techniques have been introduced in the past few years based on actual flip angle (FA) mapping, but, to date, none has emerged as a standard. For reception sensitivity calculation, the signal intensity equation can be used where the nominal FA distribution must be replaced with the actual FA distribution calculated by one of the B₁⁺ mapping techniques.This study introduces a quantitative comparison between two known methods for B₁⁺/actual FA and reception sensitivity mapping: the double-angle method (DAM) and the fitting (FIT) method. Experimental data obtained using DAM and FIT methods are also compared with numerical simulation results.     

Quantifying phosphoric acid in high‐temperature polymer electrolyte fuel cell components by X‐ray tomographic microscopy

Synchrotron‐based X‐ray tomographic microscopy is investigated for imaging the local distribution and concentration of phosphoric acid in high‐temperature polymer electrolyte fuel cells. Phosphoric acid fills the pores of the macro‐ and microporous fuel cell components. Its concentration in the fuel cell varies over a wide range (40–100 wt% H₃PO₄). This renders the quantification and concentration determination challenging. The problem is solved by using propagation‐based phase contrast imaging and a referencing method. Fuel cell components with known acid concentrations were used to correlate greyscale values and acid concentrations. Thus calibration curves were established for the gas diffusion layer, catalyst layer and membrane in a non‐operating fuel cell. The non‐destructive imaging methodology was verified by comparing image‐based values for acid content and concentration in the gas diffusion layer with those from chemical analysis.     

Facile Synthesis of Single‐Phase Mesoporous Gd2O3:Eu Nanorods and Their Application for Drug Delivery and Multimodal Imaging

In this work, a new and facile strategy is developed to synthesize a single‐phase Eu³⁺‐doped mesoporous gadolinium oxide nanorods (MS‐Gd₂O₃:Eu@PEG) by incorporating a facile wet‐chemical route, which includes an induced silica layer being coated onto the nanorods, and evolution of pores and formation of channels, as well as a surface‐modified process for multimodal imaging and anti‐cancer drug delivery. The properties of these as‐prepared Gd₂O₃:Eu nanorods are characterized by transmission electron microscopy (TEM), X‐ray diffraction (XRD), N₂ adsorption/desorption, and photoluminescence (PL). The in vitro cytotoxicity test, drug loading, and drug release experiments reveal that the MS‐Gd₂O₃:Eu@PEG nanorods have good biocompatibility, efficient loading capacity, and pH‐sensitive releasing behavior, suggesting the nanorods could be an ideal candidate as drug delivery vehicles for cancer therapy. Furthermore, the MS‐Gd₂O₃:Eu@PEG nanorods show clearly dose‐dependent contrast enhancement in T₁‐weighted magnetic resonance images and can potentially be used as a T₁‐positive contrast agent. These results indicate our prepared multifunctional mesoporous gadolinium oxide nanorods can serve as a promising platform for simultaneous anti‐cancer drug delivery and multimodal imaging.     

Deriving new soft tissue contrasts from conventional MR images using deep learning

Versatile soft tissue contrast in magnetic resonance imaging is a unique advantage of the imaging modality. However, the versatility is not fully exploited. In this study, we propose a deep learning-based strategy to derive more soft tissue contrasts from conventional MR images obtained in standard clinical MRI. Two types of experiments are performed. First, MR images corresponding to different pulse sequences are predicted from one or more images already acquired. As an example, we predict T_1ρ weighted knee image from T₂ weighted image and/or T₁ weighted image. Furthermore, we estimate images corresponding to alternative imaging parameter values. In a representative case, variable flip angle images are predicted from a single T₁ weighted image, whose accuracy is further validated in quantitative T₁ map subsequently derived. To accomplish these tasks, images are retrospectively collected from 56 subjects, and self-attention convolutional neural network models are trained using 1104 knee images from 46 subjects and tested using 240 images from 10 other subjects. High accuracy has been achieved in resultant qualitative images as well as quantitative T₁ maps. The proposed deep learning method can be broadly applied to obtain more versatile soft tissue contrasts without additional scans or used to normalize MR data that were inconsistently acquired for quantitative analysis.     

Facile Synthesis of Lactobionic Acid‐Targeted Iron Oxide Nanoparticles with Ultrahigh Relaxivity for Targeted MR Imaging of an Orthotopic Model of Human Hepatocellular Carcinoma

Development of multifunctional nanoprobes for tumor diagnosis is extremely important in the field of molecular imaging. In this study, the facile synthesis of lactobionic acid (LA)‐targeted superparamagnetic iron oxide (Fe₃O₄) nanoparticles (NPs) with ultrahigh relaxivity for targeted magnetic resonance (MR) imaging of an orthotopic hepatocellular carcinoma (HCC) is reported. Polyethyleneimine (PEI)‐stabilized Fe₃O₄ NPs prepared via a mild reduction route are sequentially coupled with fluorescein isothiocyanate and polyethylene glycol‐LA (LA‐PEG‐COOH) segment, followed by acetylation of the remaining PEI surface amines. The formed LA‐targeted Fe₃O₄ NPs are thoroughly characterized. It is shown that the developed multifunctional LA‐targeted Fe₃O₄ NPs are colloidally stable and water‐dispersible, display an ultrahigh r ₂ relaxivity (579.89 × 10^?3 m ^?1 s^?1) and excellent hemocompatibility and cytocompatibility in the given concentration range, and can target HepG2 cells overexpressing asialoglycoprotein receptors as confirmed by in vitro cellular uptake assay, flow cytometry, and confocal microscopy. Most strikingly, the developed multifunctional LA‐targeted Fe₃O₄ NPs can be used as a nanoprobe for targeted MR imaging of HepG2 cells in vitro and an orthotopic tumor model of HCC in vivo. With the ultrahigh r ₂ relaxivity and the versatile PEI amine‐mediated conjugation chemistry, a range of different Fe₃O₄ NP‐based nanoprobes may be developed for theranostics of different types of cancer.     

Enhanced direct sunlight photocatalytic oxidation of methanol using nanocrystalline TiO2 calcined at different temperature

The pharmacokinetics (PK) of carrier-mediated agents (CMA) is dependent upon the carrier system. As a result, CMA PK differs greatly from the PK of small molecule (SM) drugs. Advantages of CMAs over SMs include prolonged circulation time in plasma, increased delivery to tumors, increased antitumor response, and decreased toxicity. In theory, CMAs provide greater tumor drug delivery than SMs due to their prolonged plasma circulation time. We sought to create a novel PK metric to evaluate the efficiency of tumor and tissue delivery of CMAs and SMs. We conducted a study evaluating the plasma, tumor, liver, and spleen PK of CMAs and SMs in mice bearing subcutaneous flank tumors using standard PK parameters and a novel PK metric entitled relative distribution over time (RDI-OT), which measures efficiency of delivery. RDI-OT is defined as the ratio of tissue drug concentration to plasma drug concentration at each time point. The standard concentration versus time area under the curve values (AUC) of CMAs were higher in all tissues and plasma compared with SMs. However, 8 of 17 SMs had greater tumor RDI-OT AUC_0–last values than their CMA comparators and all SMs had greater tumor RDI-OT AUC_0–6 h values than their CMA comparators. Our results indicate that in mice bearing flank tumor xenografts, SMs distribute into tumor more efficiently than CMAs. Further research in additional tumor models that may more closely resemble tumors seen in patients is needed to determine if our results are consistent in different model systems.     

Multi-components of T2 relaxation in ex vivo cartilage and tendon

The multi-components of T₂ relaxation in cartilage and tendon were investigated by microscopic MRI (μMRI) at 13 and 26 μm transverse resolutions. Two imaging protocols were used to quantify T₂ relaxation in the specimens, a 5-point sampling and a 60-point sampling. Both multi-exponential and non-negative-least-square (NNLS) fitting methods were used to analyze the μMRI signal. When the imaging voxel size was 6.76 × 10⁻⁴ mm³ and within the limit of practical signal-to-noise ratio (SNR) in microscopic imaging experiments, we found that (1) canine tendon has multiple T₂ components; (2) bovine nasal cartilage has a single T₂ component; and (3) canine articular cartilage has a single T₂ component. The T₂ profiles from both 5-point and 60-point methods were found to be consistent in articular cartilage. In addition, the depletion of the glycosaminoglycan component in cartilage by the trypsin digestion method was found to result in a 9.81–20.52% increase in T₂ relaxation in articular cartilage, depending upon the angle at which the tissue specimen was oriented in the magnetic field.     

Simultaneous quantification of SPIO and gadolinium contrast agents using MR fingerprinting

PurposeDevelop a magnetic resonance fingerprinting (MRF) methodology with R₂¹ quantification, intended for use with simultaneous contrast agent concentration mapping, particularly gadolinium (Gd) and iron labelled CD8+ T cells.MethodsVariable-density spiral SSFP MRF was used, modified to allow variable TE, and with an exp.(−TE·R₂¹) dictionary modulation. In vitro phantoms containing SPIO labelled cells and/or gadolinium were used to validate parameter maps, probe undersampling capacity, and verify dual quantification capabilities. A C57BL/6 mouse was imaged using MRF to demonstrate acceptable in vivo resolution and signal at 8× undersampling necessary for a 25-min scan.ResultsStrong agreement was found between conventional and MRF-derived values for R₁, R₂, and R₂¹. Expanded MRF allowed quantification of iron-loaded CD8+ T cells. Results were robust to 8× undersampling and enabled recreation of relaxation profiles for both a Gd agent and iron labelled cells simultaneously. In vivo data demonstrated sufficient SNR in undersampled data for parameter mapping to visualise key features.ConclusionMRF can be expanded to include R₁, R₂, and R₂¹ mapping required for simultaneous quantification of gadolinium and SPIO in vitro, allowing for potential implementation of a variety of future in vivo studies using dual MR contrast agents, including molecular imaging of labelled cells.     

X-ray electron probe microanalysis of the reaction zone of thermally stimulated heterovalent anion substitution in the Ga 2III Se 3VI -GaAs solid-phase system

X-ray electron probe microanalysis (EPMA) was used to study the concentration profiles of the main reaction components in the Ga₂Se₃-GaAs heterojunction obtained as a result of thermally stimulated heterovalent anion substitution. It has been found that the quasi-equilibrium and quasi-steady diffusion modes for delivery of chalcogen to the reaction zone are different with respect to the kinetics of the A₂^IIIC₃^VI layer growth. Independent of this, the concentration profiles of the reaction elements are self-organized with time, which allows heterostuctures with a sharp interphase boundary to be reproduced.     

A Multifunctional Magnetic Composite Material as a Drug Delivery System and a Magnetic Resonance Contrast Agent

Magnetic iron oxide coated in hydrogenation silica (Fe₃O₄@HSiO₂) is constructed as both a tumor drug carrier and a magnetic resonance (MR) contrast agent. Colchicine (COLC) is loaded in Fe₃O₄@HSiO₂ with the highest amount of 28.3 wt% at pH 9. The release performance of COLC can be controlled by pH, as the porous HSiO₂ shell can partially shed at pH below 3.0 to facilitate the release of COLC. MR imaging (MRI) tests prove that Fe₃O₄@HSiO₂ at pH 3.0 (H⁺‐Fe₃O₄@HSiO₂) shows a stronger MR contrast enhancement than Fe₃O₄. Cytotoxicity experiment indicates that Fe₃O₄@HSiO₂ has excellent biocompatibility and magnetic targeting performance. Additionally, COLC‐loaded Fe₃O₄@HSiO₂ (Fe₃O₄@HSiO₂–COLC) displays a higher inhibition effect on tumor cells under a magnetic field than free COLC. The visibility upon MRI, high targeting, and pH‐controlled release characteristics of Fe₃O₄@HSiO₂–COLC are favorable to achieve the aim of reducing side effects to normal tissues, making Fe₃O₄@HSiO₂–COLC an attractive drug delivery system for nanomedicine.     

Spectral Line HeII 6560 Å as a Sensor of the Electron Concentration in a Dense Plasma of a Current Sheet

Stark broadening of the spectral line HeII 6560 Å by plasma was studied. The profiles of the line HeII 6560 Å were calculated for different values of the electron concentration N_e. We used the quasi‐static approximation to account for the perturbing ions and the impact approximation to describe the perturbing electrons. The electron concentration N_e in the central region of a current sheet plasma was deduced by comparing the experimentally obtained profiles of the line HeII 6560 Å with the set of the theoretically calculated profiles of this line.     

Determination of T1ρ values for head and neck tissues at 0.1 T: a comparison to T1 and T2 relaxation times

In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T₁ρ relaxation times for normal tissues were determined. Furthermore, T₁ρ was compared to T₁ and T₂ relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T₁ρ values were determined by first measuring the tissue signal intensities with different locking pulse durations (TL), and then by fitting the signal intensity values to the equation with the least-squares method. The T₁ρ relaxation times were shortest for the muscle and tongue, intermediate for lymphatic and parotid gland tissue and longest for fat. T₁ρ demonstrated statistically significant differences (p < 0.05) between all tissues, except between muscle and tongue. T₁ρ values measured at locking field strength (B1L) of 35 μT were close to T₂ values, the only exception being fat tissue, which showed T₁ρ values much longer than T₂ values. Determination of tissue relaxation times may be utilized to optimize image contrast, and also to achieve better tissue discrimination potential, by choosing appropriate imaging parameters for the head and neck spin-lock sequences.