Biomedical subjects

Lars E Olsson

Publications and source records attributed to Lars E Olsson.

6 recordsLinked to original sources

PubMed2003

Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) in early knee osteoarthritis.

Delayed contrast-enhanced MRI of cartilage (dGEMRIC) is a noninvasive technique to study cartilage glycosaminoglycan (GAG) content in vivo. This study evaluates dGEMRIC in patients with preradiographic degenerative cartilage changes. Seventeen knees in 15 patients (age 35-70) with arthroscopically verified cartilage changes (softening and fibrillations) in the medial or lateral femoral compartment, knee pain, and normal weight-bearing radiography were included. MRI (1.5 T) was performed precontrast and at 1.5 and 3 hr after an intravenous injection of Gd-DTPA(2-) at 0.3 mmol/kg body weight. T(1) measurements were made in regions of interest in medial and lateral femoral cartilage using sets of five turbo inversion recovery images. Precontrast, R(1) (R(1) = 1/T(1), 1/s) was slightly lower in diseased compared to reference compartment, indicating increased hydration (P = 0.01). Postcontrast, R(1) was higher in diseased than in reference compartment at 1.5 hr, 3.45 +/- 0.90 and 2.64 +/- 0.58 (mean +/- SD), respectively (P < 0.01), as well as at 3 hr, 2.94 +/- 0.60 and 2.50 +/- 0.37, respectively (P = 0.01). The washout of the contrast medium was faster in diseased cartilage as shown by a higher R(1) at 1.5 than at 3 hr in the diseased but not in the reference compartment. In conclusion, dGEMRIC can identify GAG loss in early stage cartilage disease with a higher sensitivity at 1.5 than 3 hr.

Adult↗

PubMed2003

Hyperpolarized 13C MR angiography using trueFISP.

A (13)C-enriched water-soluble compound (bis-1,1-(hydroxymethyl)-1-(13)C-cyclopropane-D(8)), with a (13)C-concentration of approximately 200 mM, was hyperpolarized to approximately 15% using dynamic nuclear polarization, and then used as a contrast medium (CM) for contrast-enhanced magnetic resonance angiography (CE-MRA). The long relaxation times (in vitro: T(1) approximately 82 s, T(2) approximately 18 s; in vivo: T(1) approximately 38 s, T(2) approximately 1.3 s) are ideal for steady-state free precession (SSFP) imaging with a true fast imaging and steady precession (trueFISP) pulse sequence. It was shown both theoretically and experimentally that the optimal flip angle was 180 degrees. CE-MRA was performed in four anesthetized live rats after intravenous injection of 3 ml CM. The angiograms covered the thoracic/abdominal region in two of the animals, and the head-neck region in the other two. Fifteen consecutive images were acquired in each experiment, with a flip-back pulse at the end of each image acquisition. In the angiograms, the vena cava (SNR approximately 240), aorta, renal arteries, carotid arteries (SNR approximately 75), jugular veins, and several other vessels were visible. The SNR in the cardiac region was 500. Magnetization was preserved from one image acquisition to the next using the flip-back technique (SNR(cardiac) approximately 10 in the 15th image).

Animals↗

PubMed2003

MAGIC-type polymer gel for three-dimensional dosimetry: intensity-modulated radiation therapy verification.

A new type of polymer gel dosimeter, which responds well to absorbed dose even when manufactured in the presence of normal levels of oxygen, was recently described by Fong et al. [Phys. Med. Biol. 46, 3105-3113 (2001)] and referred to by the acronym MAGIC. The aim of this study was to investigate the feasibility of using this new type of gel for intensity-modulated radiation therapy (IMRT) verification. Gel manufacturing was carried out in room atmosphere under normal levels of oxygen. IMRT inverse treatment planning was performed using the Helios software. The gel was irradiated using a linear accelerator equipped with a dynamic multileaf collimator, and intensity modulation was achieved using sliding window technique. The response to absorbed dose was evaluated using magnetic resonance imaging. Measured and calculated dose distributions were compared with regard to in-plane isodoses and dose volume histograms. In addition, the spatial and dosimetric accuracy was evaluated using the gamma formalism. Good agreement between calculated and measured data was obtained. In the isocenter plane, the 70% and 90% isodoses acquired using the different methods are mostly within 2 mm, with up to 3 mm disagreement at isolated points. For the planning target volume (PTV), the calculated mean relative dose was 96.8 +/- 2.5% (1 SD) and the measured relative mean dose was 98.6 +/- 2.2%. Corresponding data for an organ at risk was 34.4 +/- 0.9% and 32.7 +/- 0.7%, respectively. The gamma criterion (3 mm spatial/3% dose deviation) was fulfilled for 94% of the pixels in the target region. Discrepancies were found in hot spots the upper and lower parts of the PTV, where the measured dose was up to 11% higher than calculated. This was attributed to sub optimal scatter kernels used in the treatment planning system dose calculations. Our results indicate great potential for IMRT verification using MAGIC-type polymer gel.

Ascorbic Acid↗

PubMed2002

MRI-guided thermal therapy of transplanted tumors in the canine prostate using a directional transurethral ultrasound applicator.

PURPOSE: To evaluate MRI-based techniques for visual guidance, thermal monitoring, and assessment during transurethral ultrasound thermal therapy of implanted tumors in an in vivo canine prostate model. MATERIALS AND METHODS: Transmissible venereal tumors (TVT) were grown in the right lobe of the prostate in four dogs. High-temperature thermal therapy was selectively applied to the tumor-bearing lobe using a transurethral ultrasound applicator with a 180 degrees directional heating pattern. Temperature-sensitive MRI (MRTI) using a fast interleaved gradient-echo echo-planar (iGE-EPI) imaging sequence was used for cumulative thermal dose calculations in multiple image planes during the treatment. The results from MRTI-based dose maps and post-treatment MRI were compared to those from histologic analysis. RESULTS: MRTI monitoring in multiple planes across the prostate guided the use and control of a directive ultrasound applicator for the selective ablation of the sections of the prostate that contained implanted tumors. Findings in gadolinium enhanced MRI obtained immediately after thermal therapy slightly underestimated the size of tissue necrosis after treatment, as verified by histopathologic analysis. CONCLUSION: The use of multiplanar MRTI with a transurethral ultrasound applicator shows significant potential for selective thermal ablation of prostate tumor and tissue.

Animals↗

PubMed2002

Multiplanar MR temperature-sensitive imaging of cerebral thermal treatment using interstitial ultrasound applicators in a canine model.

PURPOSE: To study the feasibility of an interleaved gradient-echo, echo-planar imaging (iGE-EPI) sequence for multiplanar magnetic resonance temperature imaging (MRTI) to monitor intracerebral thermal treatment three-dimensionally using multielement ultrasound applicators. MATERIALS AND METHODS: Transmissible venereal tumor (TVT) fragments were injected into the right cerebral hemisphere of five dogs. Guided by MRI, an interstitial ultrasound applicator was inserted into the tumor or normal brain tissue. The iGE-EPI sequence was used to estimate temperature changes by computing the complex phase-difference induced by temperature-dependent shifts in the proton resonance frequency of water. The thermal dose maps were updated every 6-8 seconds for five to seven image planes during treatment. The results of MRTI were compared with those of post-treatment MRI and histologic analysis. RESULTS: The multiplanar MRTI monitored temperature and thermal dose distributions in tumor and normal brain tissue over the entire user-defined treatment volume. The ultrasound applicators produced contiguous areas of coagulative necrosis, resulting in 1.5-4.0 cm(3) volumes of tissue necrosis. MRTI-based assessments of thermal-dose distributions were consistent with the results of post-treatment MRI and histologic analysis. CONCLUSION: Multiplanar MRTI is feasible for measuring necrosing thermal doses during intracerebral thermal delivery by interstitial ultrasound applicators.

Animals↗

PubMed2002

Separation of arteries and veins using flow-induced phase effects in contrast-enhanced MRA of the lower extremities.

In 3-D contrast-enhanced magnetic resonance (MR) angiography of the lower extremities the goal is most often to enhance arterial structures while keeping veins and surrounding tissue unenhanced. Imaging during steady-state concentration of a blood pool agent or during poor timing of an extra-cellular contrast medium may result in simultaneous venous enhancement, making interpretation of the angiogram difficult. The aim of this study was to develop a post-processing method to separate the arteries from the veins in standard contrast-enhanced MR angiograms. The method was based on the different accumulation of flow-induced phase in the arteries and veins of the lower extremities. The method was tested in both phantom experiments and volunteers undergoing 3-D contrast-enhanced MR angiography using both an extra-cellular contrast medium and a blood pool agent. In the phantom studies, opposite directional flow was successfully separated at mean flow velocities as low as 9 cm/s. In the volunteer studies, the larger veins were successfully extinguished while the larger arteries were left unaffected. In smaller vessels with low flow velocities the separation was less successful. This was most apparent in vessels not oriented superior-inferior. The method developed here is promising for separating arteries from veins in contrast-enhanced MR angiography although the results could be further improved by either a different pulse sequence design or combining this method with other segmentation methods.

Arteries↗