Johan Olsrud

99mTc-Labeled Superparamagnetic Iron Oxide Nanoparticles for Multimodality SPECT/MRI of Sentinel Lymph Nodes

The purpose of this study was to develop multimodality SPECT/MRI contrast agents for sentinel lymph node (SLN) mapping in vivo. Methods: Nanoparticles with a solid iron oxide core and a polyethylene glycol coating were labeled with 99mTc. The labeling efficiency was determined with instant thin-layer chromatography and magnetic separation. The stability of the radiolabeled superparamagnetic iron oxide nanoparticles (SPIONs) was verified in both sterile water and human serum at room temperature 6 and 24 h after labeling. Five Wistar rats were injected subcutaneously in the right hind paw with 99mTc-SPIONs (25–50 MBq, ∼0.2 mg of Fe) and sacrificed 4 h after injection. Two animals were imaged with SPECT/MRI. All 5 rats were dissected; the lymph nodes, liver, kidneys, spleen, and hind paw containing the injection site were removed and weighed; and activity in the samples was measured. The microdistribution within the lymph nodes was studied with digital autoradiography. Results: The efficiency of labeling of the SPIONs was 99% 6 h after labeling in both water and human serum. The labeling yield was 98% in water and 97% in human serum 24 h after labeling. The SLN could be identified in vivo with SPECT/MRI. The accumulation of 99mTc-SPIONs (as the percentage injected dose/g [%ID/g]) in the SLN was 100 %ID/g, whereas in the liver and spleen it was less than 2 %ID/g. Digital autoradiography images revealed a nonhomogeneous distribution of 99mTc-SPIONs within the lymph nodes; nanoparticles were found in the cortical, subcapsular, and medullary sinuses. Conclusion: This study revealed the feasibility of labeling SPIONs with 99mTc. The accumulation of 99mTc-SPIONs in lymph nodes after subcutaneous injection in animals, verified by SPECT/MRI, is encouraging for applications in breast cancer and malignant melanoma.

Magnetic resonance imaging artifacts caused by aneurysm clips and shunt valves: Dependence on field strength (1.5 and 3 T) and imaging parameters

To evaluate artifact sizes at 3 T compared to at 1.5 T, and to evaluate the influence of scanning parameters with respect to artifact size on a 3‐T magnetic resonance imaging (MRI) system.

Feedback interstitial diode laser (805 nm) thermotherapy system: Ex vivo evaluation and mathematical modeling with one and four-fibers

In this study a newly developed microprocessor controlled power regulation and thermometry system integrated with a diode laser (805 nm wavelength) was evaluated with respect to temperature distribution, effectiveness of regulation, and ability to predict temperature distributions by computer simulation.

MRI thermometry in phantoms by use of the proton resonance frequency shift method: application to interstitial laser thermotherapy

In this work the temperature dependence of the proton resonance frequency was assessed in agarose gel with a high melting temperature (95 degrees C) and in porcine liver in vitro at temperatures relevant to thermotherapy (25-80 degrees C). Furthermore, an optically tissue-like agarose gel phantom was developed and evaluated for use in MRI. The phantom was used to visualize temperature distributions from a diffusing laser fibre by means of the proton resonance frequency shift method. An approximately linear relationship (0.0085 ppm degrees C(-1)) between proton resonance frequency shift and temperature change was found for agarose gel, whereas deviations from a linear relationship were observed for porcine liver. The optically tissue-like agarose gel allowed reliable MRI temperature monitoring, and the MR relaxation times (T1 and T2) and the optical properties were found to be independently alterable. Temperature distributions around a diffusing laser fibre, during irradiation and subsequent cooling, were assessed with high spatial resolution (voxel size = 4.3 mm3) and with random uncertainties ranging from 0.3 degrees C to 1.4 degrees C (1 SD) with a 40 s scan time.

MR Evaluation Ex Vivo and In Vivo of a Covered Stent-Graft for Abdominal Aortic Aneurysms: Ferromagnetism, Heating, Artifacts, and Velocity Mapping†

Magnetic resonance imaging (MRI) safety was evaluated at 1.5 T in a covered nickel titanium stent‐graft (Vanguard™) used for endovascular treatment of abdominal aortic aneurysms (AAAs). Imaging artifacts were assessed on MRI with contrast‐enhanced (CE) three‐dimensional (3D) MR angiography (MRA) and spiral computed tomography (CT) in 10 patients as well as ex vivo. Velocity mapping was performed in the suprarenal aorta and femoral arteries in 14 patients before and after stent‐graft placement. For comparison it was also performed in six healthy volunteers. No ferromagnetism or heating was detected. Metal artifacts caused minimal image distortion on MRI/MRA. The artifacts disturbed image evaluation on CT at the graft bifurcation and graft limb junction. No significant differences in mean flow were found in patients before and after stent‐graft placement. Our study indicates that MRI at 1.5 T may be performed safely in patients with the (Vanguard) stent‐graft. MRI/MRA provides diagnostic image information. Velocity mapping is not included in our routine protocol. J. Magn. Reson. Imaging 2000;12:112–121.

Phantom digit somatotopy: a functional magnetic resonance imaging study in forearm amputees

Forearm amputees often experience non‐painful sensations in their phantom when the amputation stump is touched. Cutaneous stimulation of specific stump areas may be perceived as stimulation of specific phantom fingers (stump hand map). The neuronal basis of referred phantom limb sensations is unknown. We used functional magnetic resonance imaging to demonstrate a somatotopic map of the phantom fingers in the hand region of the primary somatosensory cortex after tactile stump stimulation. The location and extent of phantom finger activation in the primary somatosensory cortex corresponded well to the location of normal fingers in a reference population. Stimulation of the stump hand map resulted in an increased bilateral activation of the primary somatosensory cortex compared with stimulation of forearm regions outside the stump hand map. Increased activation was also seen in contralateral posterior parietal cortex and premotor cortex. Ipsilateral primary somatosensory cortex activation might represent a compensatory mechanism and activation of the non‐primary fronto‐parietal areas might correspond to awareness of the phantom limb, which is enhanced when experiencing the referred sensations. It is concluded that phantom sensation elicited by stimulation of stump hand map areas is associated with activation of finger‐specific somatotopical representations in the primary somatosensory cortex. This suggests that the primary somatosensory cortex could be a neural substrate of non‐painful phantom sensations. The stump hand map phenomenon might be useful in the development of prosthetic hand devices.

Functional magnetic resonance imaging at 3t as a clinical tool in patients with intracranial tumors

Purpose: To investigate the potential of functional magnetic resonance imaging (fMRI) at 3T as a clinical tool in the preoperative evaluation of patients with intracranial tumors. High magnetic field strength such as 3T is of benefit for fMRI because signal-to-noise ratio and sensitivity to susceptibility changes are field-strength-dependent. Material and Methods: Twenty patients with tumors close to eloquent sensorimotor or language areas were studied. Motor, sensory, and two language paradigms (word generation, rhyming) were used; their effectiveness was determined as the percentage of patients in whom the functional area of interest was activated. Activation maps were calculated and their quality rated as high, adequate, or insufficient. The influence of fMRI on the neurosurgical decision regarding operability, surgical approach, and extent of the resection, was assessed. Results: Paradigm effectiveness was 90% for motor and 95% for sensory stimulation, and varied from 79% to 95% for word generation and rhyming in combination. Ninety percent of the activation maps held high or adequate quality. fMRI proved useful: in the decision to operate (9 patients), in the surgical approach (13 patients), and in extent of the resection (12 patients). Conclusion: fMRI at 3T is a clinically applicable tool in the work-up of patients with intracranial tumors.

Can resting-state functional MRI serve as a complement to task-based mapping of sensorimotor function? A test-retest reliability study in healthy volunteers.

To investigate if resting‐state functional MRI (fMRI) reliably can serve as a complement to task‐based fMRI for presurgical mapping of the sensorimotor cortex.

Thermal conductivity of uterine tissue in vitro

Thermotherapy of the uterus has emerged as an alternative to hysterectomy in the treatment of menorrhagia, from whence it follows that the thermal properties of uterine tissue have become of importance. This study presents measurements of the thermal conductivity and the water content of uterine tissue in vitro. A steady-state thermal conductivity apparatus, based on the comparison of test samples with a material with known thermal conductivity, is described. Measurements were conducted on tissue samples from eleven patients, directly after hysterectomy. Samples with and without endometrium, as well as coagulated samples, were examined. The thermal conductivity of myometrial tissue was found to be 0.536 +/- 0.012 W m(-1) K(-1) (mean +/- 1 SD) and the corresponding water content was 81.2 +/- 1.5% (mean +/- 1 SD). Measurements on samples with both endometrium and myometrium showed similar thermal conductivity (0.542 +/- 0.008 W m(-1) K(-1), mean +/- 1 SD) and water content (81.6 +/- 0.7%, mean +/- 1 SD). It was also indicated that coagulation causes dehydration, resulting in a lower thermal conductivity.

fMRI memory assessment in healthy subjects: a new approach to view lateralization data at an individual level

We present a comprehensive and clinically applicable fMRI test—including both a verbal and a visuospatial task—for assessment of hemispheric specific memory in the medial temporal lobe (MTL). fMRI data was collected from 15 healthy right-handed volunteers. Whole-brain activation was analyzed as well as activation in two regions of interest: the MTL and the anterior speech area. Laterality indices (LI) and LI-curves were calculated using the LI toolbox of Wilke and Lidzba, 2007. The fMRI paradigms successfully visualized memory-related activity in the MTL, the verbal memory measure also provided information of language lateralization. Eleven subjects showed left lateralized verbal encoding in the MTL, visuospatial memory activation was divided equally between left and right, and 14/15 subjects had left lateralized language. Lateralization data at the group level were consistent with previous studies, but a variety of activation effects were found at the individual level indicating differences in strategy during verbal and visuospatial processing. Further studies using the presented method are needed to determine its clinical usefulness.