Magnetic resonance imaging of renal abscess in an experimental animal model

The value of magnetic resonance imaging (MRI) in the diagnosis of renal abscess was investigated in an experimental animal model. MRI is capable of depicting the location and extent of the inflammatory process using T1 weighted scans because of relatively long T1 relaxation values which were significantly longer than T1 relaxation times of adjacent normal renal parenchyma.     

Quantitative assessment of hepatic fibrosis in an animal model with magnetic resonance elastography.

Chronic liver disease is a world-wide problem that causes progressive hepatic fibrosis as a hallmark of progressive injury. At present, the gold standard for diagnosing hepatic fibrosis is liver biopsy, which is an invasive method with many limitations, including questionable accuracy and risks of complications. MR elastography (MRE), a phase-contrast MRI technique for quantitatively assessing the mechanical properties of soft tissues, is a potential noninvasive diagnostic method to assess hepatic fibrosis. In this work, MRE was evaluated as a quantitative method to assess the in vivo mechanical properties of the liver tissues in a knockout animal model of liver fibrosis. This work demonstrates that the shear stiffness of liver tissue increases systematically with the extent of hepatic fibrosis, as measured by histology. A linear correlation between liver stiffness and fibrosis extent was well-defined in this animal model. An additional finding of the study was that fat infiltration, commonly present in chronic liver disease, does not significantly correlate with liver stiffness at each fibrosis stage and thus does not appear to interfere with the ability of MRE to assess fibrosis extent. In conclusion, MRE has the potential not only for assessing liver stiffness, but also for monitoring potential therapies for hepatic fibrosis.     

Real-time display of artifact-free electroencephalography during functional magnetic resonance imaging and magnetic resonance spectroscopy in an animal model of epilepsy.

Simultaneous recording of electroencephalogram (EEG) and functional MRI (fMRI) or MR spectroscopy (MRS) can provide further insight into our understanding of the underlying mechanisms of neurologic disorders. Current technology for simultaneous EEG and MRI recording is limited by extensive postacquisition processing of the data. Real-time display of artifact-free EEG recording during fMRI/MRS studies is essential in studies that involve epilepsy to ensure that they address specific EEG features such as epileptic spikes or seizures. By optimizing the EEG recording equipment to maximize the common mode rejection ratio of its amplifiers, a unique EEG system was designed and tested that allowed real-time display of the artifact-free EEG during fMRI/MRS in an animal model of epilepsy. Spike recordings were optimized by suppression of the background EEG activity using fast-acting and easily controlled inhalational anesthesia. Artifact suppression efficiency of 70-100% was achieved following direct subtraction of referentially recorded filtered EEG tracings from active electrodes, which were located in close proximity to each other (over homologous occipital cortices) and a reference electrode. Two independent postacquisition processing tools, independent component analysis and direct subtraction of unfiltered digital EEG data in MATLAB, were used to verify the accuracy of real-time EEG display.     

Sequential diffusion-weighted magnetic resonance imaging study of lysophosphatidyl choline-induced experimental demyelinating lesion: an animal model of multiple sclerosis

PURPOSE: To differentiate the surrounding edema from the focal demyelinating lesion during the early phase of the lesion using an apparent diffusion coefficient (ADC), and to monitor the changes in ADCs during the complete progression of a lysophosphatidyl choline (LPC)-induced experimental demyelinating lesion, an animal model of multiple sclerosis (MS). MATERIAL AND METHODS: Eighteen rats divided into two groups-demyelinating lesion (group I, N = 12) and vehicle group (saline injected; group II, N = 6)-were studied. A 0.2-microl quantity of 1% LPC solution in isotonic saline was injected in the rat brain internal capsule (IC) area to create the demyelinating lesion. Six rats were used exclusively for histology. Diffusion-weighted (DW) images were acquired at different diffusion weightings on the 3rd, 5th, 10th, 15th, and 20th days after LPC injection. ADC was measured from three regions of interest (ROIs) within the IC: focal demyelinating lesion (area A), surrounding area of the lesion (area B), and contralateral IC area (area C). RESULTS: Histology revealed demyelination of the IC area during the early phase of lesion progression up to day 10 and remyelination thereafter. Elevated ADCs were observed for the surrounding edematous area (area B), compared to the focal demyelinating lesion (area A) during the early phase of the demyelination process, while substantial reduction of ADCs was noticed during remyelination for both regions. CONCLUSION: Measurement of ADC showed clear differentiation of the surrounding edema from the LPC-induced focal demyelinating lesion in rats, especially during the early phase of the lesion progression.     

Imaging of osteomyelitis with special reference to children

Infection of bone in children represents a diagnostic and therapeutic challenge to the pediatrician, the surgeon, the radiologist, and the pathologist. The pattern of manifestation varies and is dependent on the site of involvement, the initiating event, the infecting organism, and the acute or chronic nature of the illness. Early diagnosis allows prompt treatment, which can prevent many of the dreaded complications of this disease. Plain radiographs remain the initial imaging modality used in the diagnosis and differential diagnosis of osteomyelitis. However, with the advent of newer imaging techniques such as scintigraphy, ultrasonography, computed tomography, and magnetic resonance imaging, a higher degree of accuracy in diagnosis and definition of the extent of the disease has been achieved. The time interval between the onset of symptoms and diagnosis has also been significantly reduced. Although magnetic resonance imaging has the additional advantage of multiplanar capability, greater anatomic detail, and excellent soft tissue resolution, it is a relatively expensive technique, which somewhat limits its use. Following a brief review of the classification and pathophysiology of osteomyelitis, we have tried to elucidate the utility of various imaging modalities in the diagnosis of osteomyelitis in children, outlining their relative strengths and weaknesses. Certain entities specific to children and a brief review of differential diagnosis are also presented.     

Depicting adoptive immunotherapy for prostate cancer in an animal model with magnetic resonance imaging

Genetically modified natural killer (NK) cells that recognize tumor‐associated surface antigens have recently shown promise as a novel approach for cancer immunotherapy. To determine NK cell therapy response early, a real‐time, noninvasive method to quantify NK cell homing to the tumor is desirable. The purpose of this study was to evaluate if MR imaging could provide a noninvasive, in vivo diagnosis of NK cell accumulation in epithelial cell adhesion molecule (EpCAM)‐positive prostate cancers in a rat xenograft model. Genetically engineered NK‐92‐scFv(MOC31)‐ζ cells, which express a chimeric antigen receptor specific to the tumor‐associated EpCAM antigen, and nontargeted NK‐92 cells were labeled with superparamagnetic particles of iron‐oxides (SPIO) ferumoxides. Twelve athymic rats with implanted EpCAM positive DU145 prostate cancers received intravenous injections of 1.5 × 10⁷ SPIO labeled NK‐92 and NK‐92‐scFv(MOC31)‐ζ cells. EpCAM‐positive prostate cancers demonstrated a progressive and a significant decline in contrast‐to‐noise‐ratio data at 1 and 24 h after injection of SPIO‐labeled NK‐92‐scFv(MOC31)‐ζ cells. Conversely, tumor contrast‐to‐noise‐ratio data did not change significantly after injection of SPIO‐labeled parental NK‐92 cells. Histopathology confirmed an accumulation of the genetically engineered NK‐92‐scFv(MOC31)‐ζ cells in prostate cancers. Thus, the presence or absence of a tumor accumulation of therapeutic NK cells can be monitored with cellular MR imaging. EpCAM‐directed, SPIO labeled NK‐92‐scFv(MOC31)‐ζ cells accumulate in EpCAM‐positive prostate cancers. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Functional magnetic resonance imaging of auditory cortex: with special reference to the side of aural stimulation.

PURPOSE: To determine whether left- or right-side uniaural stimulation produces different fMRI activation patterns. METHODS: Subjects were 12 volunteers (8 right-handed, 4 left-handed) with normal hearing. Functional imaging using FE-type multishot echo planar imaging was obtained in the axial plane during pure-tone and pseudoword tasks. Auditory stimuli were presented to each ear individually. In pure-tone tasks, subjects heard clustered sequences at 2000 Hz. In pseudoword tasks, subjects heard spoken Japanese syllables. The numbers of activated pixels in the auditory cortex were counted and compared for pure-tone and pseudoword tasks, as was activation according to the side of aural stimulation. RESULTS: In right-handed subjects, prominent activation in pure-tone tasks was noted in the dominant hemisphere in 100% of cases and was unrelated to the side of the stimulation. In pseudoword tasks, prominent activation was noted on the side contralateral to the stimulus in 62.5-100% of cases. In left-handed subjects, prominent activation was noted on the side contralateral to the stimulus in both pure-tone and pseudoword tasks. CONCLUSION: Left- and right-side stimulation produced differences in fMRI responses, especially between pure-tone and pseudoword tasks. Moreover, right-handedness and left-handedness affected results. This type of auditory fMRI may be a noninvasive indicator of language lateralization.     

Application of magnetic resonance to animal models of cerebral ischemia.

The present review has been compiled to highlight the role of magnetic resonance imaging (MRI) and MR spectroscopy (MRS) for the investigation of cerebral ischemia in the animal experimental field of basic research. We have focused on stroke investigations analyzing the pathomechanisms of the disease evolution and on new advances in both nuclear MR (NMR) methodology or genetic engineering of transgenic animals for the study of complex molecular relationships and causes of the disease. Furthermore, we have tried to include metabolic and genetic aspects, as well as the application of functional imaging, for the investigation of the disturbance or restitution of functional brain activation under pathological conditions as relates to controlled animal experiments.     

Diffusion-weighted magnetic resonance imaging of focal hepatic nodules in an experimental hepatocellular carcinoma rat model

RATIONALE AND OBJECTIVES: We sought to investigate the value of diffusion-weighted MR imaging in evaluating focal hepatic nodules in an experimental hepatocellular carcinoma (HCC) rat model. MATERIALS AND METHODS: Forty rats with chemically induced primary hepatic nodules ranging pathologically from regenerative nodules (RNs) to dysplastic nodules (DNs) to HCC were examined with diffusion-weighted imaging. The apparent diffusion coefficient (ADC) values of hepatic nodular lesions were calculated. Tukey's HSD post hoc test was used to compare the difference in ADC values between different hepatic nodular lesions. RESULTS: Eight RNs, 16 DNs, 7 well-differentiated HCCs (HCCwell), 11 moderately differentiated HCCs (HCCmod), and 14 poorly differentiated HCCs (HCCpoor) were evaluated. There was no significant difference between RNs and DNs (P > 0.05). Although the ADC values of HCCwell were slightly lower than those of DNs, there was no significant difference between them (P > 0.05). The ADC values of HCCmod and HCCpoor were significantly higher (P < 0.05) than those of other nodules, and no significant difference was seen between HCCmod and HCCpoor (P > 0.05). CONCLUSION: Diffusion-weighted magnetic resonance imaging can be useful in characterizing focal hepatic nodular lesions, but ADC values cannot be used efficiently to distinguish HCCwell from DNs.     

Massive unilateral non-functioning hydronephrosis in horseshoe kidney.

The occurrence of non-function in one half of a horseshoe kidney resulting from hydronephrosis can, if unrecognized, create a serious surgical as well as medical problem. The anterior position of the ureter in relation to the isthmus, as well as strictures and accessory vessels increase the incidence of hydronephrosis, which if severe enough, can go on to non-function. The key diagnostic factor is the observation of the visualised side, which shows the characteristic malrotation of the calyces and the deviation of the long axis of the kidneys; these are associated with a mass effect on the obstructed side, with or without a 'crescent' sign. Five cases of this unusual occurrence are presented.     

Pathological animal models in the experimental evaluation of tumour microvasculature with magnetic resonance imaging

PURPOSE: The purpose of this study was to evaluate the applications of magnetic resonance imaging (MRI), and in particular, dynamic contrast-enhanced MRI (DCE-MRI), in the assessment of tumour microvasculature by means of animal tumour models evaluated before and after antiangiogenic treatment. MATERIALS AND METHODS: Forty-two MRI exams were performed with intravascular contrast media in 21 rats: tumours were induced by subcutaneous injection of colon carcinoma cells in 7 rats and mammary adenocarcinoma cells in 14 rats. Perfusion and permeability parameters of the implanted tumours were evaluated by using two contrast media (B22956/1 and Gd-DTPA37-albumin) to establish response to treatment with two different antiangiogenic drugs (tamoxifen and SU6668). These parameters were correlated with histology to obtain a radiological-histological map of tumour microvasculature. RESULTS: DCE-MRI revealed greater enhancement in the peripheral area than in the central area in all the examined animal models. In the mammary carcinoma experiment, vascular permeability measured by means of B22956/1 in the animals treated with the antiangiogenic drug (0.0043317+/-0.0040418 ml/min(-1)/ml(-1)) was significantly less than in untreated animals (0.0090460+/-0.0043680 ml/min(-1)/ml(-1)), whereas no significant difference was observed with Gd-DTPA-albumin (13.14+/-13.94 ml/min(-1)/ml(-1) in treated animals and 18.07+/-11.92 ml/min(-1)/ml(-1) in untreated animals). In the colon carcinoma experiment, mean permeability and perfusion decreased by 51% (from 5.2+/-1.1 to 2.5+/-0.8 ml/100 ml) and 59% (from 0.00165+/-5.1 to 0.0067+/-4.8 ml/min(-1)/ml(-1) of tissue), respectively, in all animals after antiangiogenic drug administration. CONCLUSIONS: DCE-MRI permits a noninvasive evaluation of tumour microcirculation and in particular of its dynamic characteristics and vascularity before and after antiangiogenic treatment.     

Rapid, contrast-enhanced, diuretic magnetic resonance imaging of unilateral partial ureteral obstruction. An experimental study in micropigs

The value of rapid, contrast-enhanced, diuretic magnetic resonance (MR) imaging (using ferrioxamine B and furosemide) in demonstrating partial unilateral ureteral obstruction and the potential of such MR imaging in differentiating obstructive from nonobstructive hydronephrosis was assessed in six micropigs. MR imaging (0.35 Tesla, partial-flip technique with repetition time [TR] of 125 milliseconds, echo-delay time [TE] of 20 milliseconds, and flip angle of 70 degrees) was performed before, and at 5, 12, and 19 days after partial ureteral obstruction. Additionally, MR images were acquired 5, 12, and 19 days after release of obstruction. The diuretic was injected 10 minutes after the contrast medium. MR findings were correlated with results from nuclear scintigraphy (99mTc-DMSA uptake). MR images provided good morphologic detail from which renal size, parenchymal thickness, and degree of hydronephrosis could be determined. Contrast medium allowed assessment of cortical uptake and urinary excretion. The course of cortical signal enhancement best characterized the difference between obstructive and nonobstructive hydronephrosis. Normal kidneys and kidneys with nonobstructive hydronephrosis showed progressive decrease in cortical signal enhancement (-11.7% within 40 minutes) after furosemide injection. The kidneys with obstructive hydronephrosis demonstrated a plateau of signal enhancement without decrease (-0.7% within 40 minutes). These results demonstrate the utility of rapid contrast-enhancing, diuretic MR imaging in differentiating obstructive from nonobstructive hydronephrosis.     

Sonographic monitoring of hepatic cryosurgery in an experimental animal model

Several cryosurgical techniques for freezing hepatic parenchyma have been developed. To assess the efficacy of sonographic monitoring of hepatic cryosurgery, an experimental animal model was devised. Real-time sonography was used to monitor the in vivo evolution of hypothermically induced hepatic cryolesions in four mongrel dogs. The results suggest that sonography is an effective and accurate means of monitoring the entire freezing and thawing cycle in hepatic cryosurgery.     

Lymphatic imaging in experimental filariasis using magnetic resonance.

RATIONALE AND OBJECTIVES. To evaluate acquired lymphatic abnormalities caused by filariasis, the authors examined the peripheral lymphatic system in normal ferrets and those chronically infected with Brugia malayi using magnetic resonance imaging (MRI). The findings were compared with previously obtained lymphangioscintigraphic (LAS) images in ferrets both with and without experimental filariasis. METHODS. Fifteen ferrets (11 infected with B. malayi and four noninfected controls) underwent whole body coronal MRI using a quadrature transmission-receive head coil at 0.5 Tesla operating at a resonant frequency of 21.5 mHz for protons with a 25-cm field of view. RESULTS. In contrast to normal animals, infected ferrets showed dilated hindlimb dermal lymphatic collaterals, enlarged high-signal intensity groin lymph nodes with punctate low-signal intensity centers and separate low-signal intensity spots with irregular thin channels, suggestive of nests of viable adult nematodes within tortuous lymphatics and nodes. MRI correlated with the LAS findings, and the interpretations were supported by light, scanning electron, and video microscopy. CONCLUSIONS. T2-weighted MRI in conjunction with LAS accurately depicts the peripheral lymphatic system in filarial-infected ferrets. These two modalities are useful complementary techniques to examine disorders characterized by lymphatic insufficiency.