Imaging of macrophages in soft-tissue infection in rats: relationship between ultrasmall superparamagnetic iron oxide dose and MR signal characteristics

PURPOSE: To describe dose-dependent signal intensity (SI) characteristics of experimentally induced soft-tissue abscesses on 1.5-T T1- and T2*-weighted magnetic resonance (MR) images obtained 24 hours after administration of ultrasmall superparamagnetic iron oxide (USPIO) and to describe the relationship between SI and amount of USPIO uptake and macrophage iron content. MATERIALS AND METHODS: Local institutional review committee on animal care approved the experiments, which were performed according to the guidelines of the National Institutes of Health and the committee on animal research at our institution. Unilateral calf muscle abscesses were induced in 21 rats with an injection of a Staphylococcus aureus suspension. The rats were divided into three groups of seven animals each: low USPIO dose (50 micromol of iron per kilogram of body weight), high USPIO dose (150 micromol Fe/kg), and control (saline solution). All rats were imaged before and 24 hours after USPIO administration at 1.5 T (transverse T1-weighted spin-echo, T2*-weighted fast gradient-echo, and short inversion time inversion-recovery sequences). Images were analyzed quantitatively and qualitatively with regard to SI and signal pattern. Temporal variation of calculated contrast-to-noise ratios was analyzed with the Wilcoxon signed rank test. MR findings were correlated with histopathologic findings, including those of electron microscopy. RESULTS: Twenty-four hours after USPIO administration in the high-dose group, susceptibility effects were present in abscess periphery on postcontrast T2*-weighted images (P=.04), and SI enhancement was noted on postcontrast T1-weighted images within both abscess wall and abscess center (P=.04 for both). In the low-dose group, SI enhancement was noted in entire abscess on T1-weighted postcontrast images (P=.03). Neither significant SI loss (P=.09) nor susceptibility effects were detected in periphery or center of any abscess on postcontrast T2*-weighted images. There was no obvious difference in total amount of macrophages among the groups, but there was a clear difference with regard to individual iron content of iron-positive macrophages between the USPIO dose groups. CONCLUSION: At 1.5 T, SI characteristics of abscesses on T1- and T2*-weighted images obtained 24 hours after USPIO injection strongly depend on administered dose of the contrast agent. At low doses, T1 effects were stronger than T2* effects.     

Characteristics of ultrasmall superparamagnetic iron oxides in patients with brain tumors

OBJECTIVE: The aim of this study was to evaluate the characteristics of an ultrasmall superparamagnetic iron oxides (USPIO) agent in patients with brain tumors and to correlate changes on MRI with histopathologic data collected systematically in all patients. SUBJECTS AND METHODS: Nine patients with brain tumors were imaged before and 24 hr after administration of a USPIO at a dose of 2.6 mg Fe/kg. Analysis of MR images included qualitative and quantitative comparison of the USPIO and gadolinium enhancement of brain tumors. Brain surgery was performed 25-112 hr after administration of the USPIO. The histopathologic workup included iron histochemistry with diaminobenzidine (DAB)-enhanced Perls stain. RESULTS: In seven of nine patients, USPIO-related changes of signal intensity were observed in gadolinium-enhancing brain tumors on T1- and T2*-weighted sequences. The difference in signal intensity on T1-weighted USPIO series was 40.1% +/- 26.7% (mean +/- SD). On T2*-weighted USPIO series, the difference in signal intensity was -33.1% +/- 18.4% in solid tumor parts. Areas of suspected radiation necrosis did not enhance in three patients with prior radiation therapy. Iron histochemistry revealed the presence of iron deposits in macrophages in two patients. CONCLUSION: USPIO agents will not replace gadolinium in the workup of patients with brain tumors. Our findings suggest that USPIO agents seem to offer complementary information and may help to differentiate between brain tumors and areas of radiation necrosis. Signal intensity changes on T2*-weighted images might be related to the blood pool properties of the agent, possibly reflecting steady-state susceptibility effects.     

<Superscript>99m</Superscript>Tc-EDDA/HYNIC-TOC and <Superscript>18</Superscript>F-FDG in thyroid cancer patients with negative <Superscript>131</Superscript>I whole-body scans

Several studies have reported on the expression of somatostatin receptors in patients with differentiated thyroid cancer (DTC). The aim of this study was to evaluate the imaging abilities of a recently developed technetium-99m labelled somatostatin analogue, ^99mTc-EDDA/HYNIC-TOC (^99mTc-TOC), in terms of precise localisation of disease. The study population comprised 54 patients (24 men, 30 women; age range 22–90 years) with histologically confirmed DTC who presented with recurrent or persistent disease as indicated by elevated Tg levels after initial treatment. All patients were negative on the iodine-131 post-therapy whole-body scans. Fluorine-18 fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) was performed in a subgroup of 36 patients. The study population consisted of two groups: Group A (n=22) comprised patients with disease recurrence as shown by elevated Tg levels but without detectable pathology. In group B (n=32), pre-existing lesions were known. Among the 54 cases, SSTR scintigraphy was true positive in 33 (61.1%), true negative in 4 (7.4%) and false negative in 17 (31.5%) cases, which resulted in a sensitivity of 66%. A total of 138 tumour foci were localised in 33 patients. The fraction of true positive ^99mTc-TOC findings was positively correlated (P<0.01) with elevated Tg levels (higher than 30 ng/ml). Despite two false positive findings, analysis on a lesion basis demonstrated better diagnostic efficacy with ¹⁸F-FDG PET (P<0.001); however, it also revealed substantial agreement between the imaging techniques [Cohens kappa of 0.62 (0.47–0.78)]. In conclusion, scintigraphy with ^99mTc-TOC might be a promising tool for treatment planning; it is easy to perform and showed sufficient accuracy for localisation diagnostics in thyroid cancer patients with recurrent or metastatic disease.     

Permeation enhancement of a highly lipophilic drug using supersaturated systems

The potential of supersaturation as a method for enhancing the membrane permeation of highly lipophilic compounds has been investigated using, as a model system, the transport of a lavendustin derivative (LAP, log K(o/w) = 5) through silicone membrane. Propylene glycol-water mixtures, which permitted the formulation of LAP at different levels of saturation, were prepared and tested for stability prior to conducting membrane permeation studies. The transport of LAP across silicone membrane from donor solutions containing the drug at different degrees of saturation (DS = 1-5) was evaluated by two independent experimental methods: (i) using attenuated total-reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and (ii) using standard vertical diffusion cells followed by quantification with high-performance liquid chromatography (HPLC). Both methods demonstrated a linear relationship between the DS of the applied solution and the flux through the membrane, yielding similar values for the diffusion coefficients of LAP [diffusion cells, D = 1.75 ( +/- 0.16) x 10(-7) cm(2) s(-1) and ATR-FTIR, D = 1.42 ( +/- 0.26) x 10(-7) cm(2) s(-1)). In addition to the characterization of LAP permeation, ATR-FTIR spectroscopy enabled an examination of solvent transport across the membrane.     

Ethical dilemmas related to counseling clients living with HIV/AIDS

This study tested an eight-factor model of client actions/decisions in terms of the extent to which professionals counseling persons with HIV/AIDS believed that those actions/decisions presented ethical dilemmas, and the frequency with which they encountered such actions. A confirmatory factor analysis lent initial support for the hypothetical eight-factor ethical-dilemma model for the ratings regarding the extent to which the participants believed those items constituted ethical dilemmas. Similar results were obtained for the frequency ratings, but in this case a second, competing model was equally plausible. Several significant predictors of participant ratings were found and are discussed.     

Interobserver variation in the interpretation of abdominal radiographs

A total of 140 sets of abdominal radiographs were reviewed independently by four qualified diagnostic radiologists. The degree of interobserver agreement was determined by calculating kappa values for 19 commonly used radiographic signs and diagnoses. There was fair to excellent interobserver agreement for 11 signs and diagnoses and poor agreement for the remaining eight. The signs and diagnoses for which agreement is poor cannot be considered reliable and include particularly large bowel obstruction and nonspecific gas pattern.     

Effect of intersection spacing on MR image contrast and study time

The effects of section separation on image contrast and calculated T1 relaxation times were investigated in healthy volunteers and a phantom using an early commercial version magnetic resonance imaging system. The effects are explained qualitatively on the basis of side lobes of excitation occurring outside the selected section resulting in reduction of the time permitted for T1 relaxation. The options for dealing with imperfect section selection, including separation of the sections (i.e., leaving gaps) and nonsequential excitation, are illustrated and the trade-offs involved in each explained.