Biomedical subjects

Lars E Olsson

Publications and source records attributed to Lars E Olsson.

11 recordsLinked to original sources

PubMed2006

MR coronary angiography in pigs with intraarterial injections of a hyperpolarized 13C substance.

A new diagnostic application of a water-soluble contrast medium (CM) based on the hyperpolarization of a 13C substance is introduced. The degree of polarization achieved is >30%, which is about a factor of 10(5) higher than the thermal equilibrium polarization level at 1.5 T. Imaging of hyperpolarized (HP) CM during a cardiac interventional MRI procedure was studied. Catheters were positioned in the left and right coronary arteries of pigs. A coil tuned to 13C was used for nonproton imaging. The HP-13C CM ( approximately 5 ml, 0.5 M, approximately 30% polarization) was injected during projection imaging using a fully balanced steady-state free precession (SSFP) pulse sequence with and without cardiac gating. The contrast agent-filled catheter was clearly visible during the procedure. The coronary arteries were well depicted and the signal-to-noise ratios (SNRs) were in the range of 10-40. The use of HP-13C CM may provide a new diagnostic procedure for interventional MRI.

Animals↗

PubMed2006

Magnetic resonance imaging of experimental mouse colitis and association with inflammatory activity.

BACKGROUND: Ulcerative colitis and Crohn's disease are the major chronic inflammatory bowel diseases affecting the gastrointestinal tract in humans. Imaging techniques such as endoscopy and computed tomography are used to monitor disease activity. Magnetic resonance imaging (MRI) is emerging as a diagnostic modality, and studies have shown that MRI can be used in the diagnostic procedure of patients with inflammatory bowel disease. The aim of the present study was to investigate the role of MRI in quantitatively reflecting inflammation in an experimental mouse colitis model. METHODS: Colonic inflammation was induced by exposing mice to dextran sulfate sodium. MRI was used to assess colon wall thickness, T2-weighted (T2w) signal, and contrast-enhanced T1-weighted (T1w) signal in inflamed and healthy animals in vivo. Haptoglobin and interleukin-1beta served as systemic and local inflammatory markers, and macroscopic ex vivo scoring of the colon was performed to assess colonic inflammation. RESULTS: Dextran sulfate sodium-exposed animals displayed increased levels of inflammatory markers and higher inflammatory score compared with healthy animals. Colon wall thickness and contrast-enhanced T1w signal were significantly increased in dextran sulfate sodium-exposed compared with healthy animals. In addition, the T2w signal was positively correlated with haptoglobin levels and colon wall thickness in the inflamed animals. CONCLUSIONS: Our results show that MRI can be used to depict healthy and inflamed mouse colon and that the T2w signal, contrast-enhanced T1w signal, and colon wall thickness may be used to characterize inflammation in experimental colitis. These potential biomarkers may be useful in the evaluation of putative drugs in longitudinal studies in both mice and humans.

Animals↗

PubMed2005

3He MRI-based assessment of posture-dependent regional ventilation gradients in rats.

A recently developed method for quantitative assessment of regional lung ventilation was employed for the study of posture-dependent ventilation differences in rats. The measurement employed hyperpolarized (3)He MRI to detect the build-up of the signal intensity after increasing numbers of (3)He breaths, which allowed for computation of a regional ventilation parameter. A group of six anesthetized rats was studied in both supine and prone postures. Three-dimensional maps of the ventilation parameter were obtained with high spatial resolution (voxel volume approximately 2 mm(3)). Vertical (dorsal-ventral) gradients of the ventilation index, defined as the regional ventilation normalized by the average ventilation within the whole lung, were investigated. Variations in the regional distribution of the ventilation parameter, as well as of the ventilation index, could be detected, depending on the posture of the rats. In supine posture, ventilation was elevated in the dependent parts of the lungs, with a linear gradient of the ventilation index of -0.11 +/- 0.03 cm(-1). In prone posture, the distribution of ventilation was more uniform, with a significantly (P < 0.001) smaller gradient of the ventilation index of -0.01 +/- 0.02 cm(-1). It is concluded that the (3)He MRI-based method can detect and quantify regional ventilation gradients in animals as small as the rat and that these gradients depend on prone or supine posture of the animal.

Administration, Inhalation↗

PubMed2004

Linear energy transfer dependence of a normoxic polymer gel dosimeter investigated using proton beam absorbed dose measurements.

Three-dimensional dosimetry with good spatial resolution can be performed using polymer gel dosimetry, which has been investigated for dosimetry of different types of particles. However, there are only sparse data concerning the influence of the linear energy transfer (LET) properties of the radiation on the gel absorbed dose response. The purpose of this study was to investigate possible LET dependence for a polymer gel dosimeter using proton beam absorbed dose measurements. Polymer gel containing the antioxidant tetrakis(hydroxymethyl)phosphonium (THP) was irradiated with 133 MeV monoenergetic protons, and the gel absorbed dose response was evaluated using MRI. The LET distribution for a monoenergetic proton beam was calculated as a function of depth using the Monte Carlo code PETRA. There was a steep increase in the Monte Carlo calculated LET starting at the depth corresponding to the front edge of the Bragg peak. This increase was closely followed by a decrease in the relative detector sensitivity (Srel = Dgel/Ddiode), indicating that the response of the polymer gel detector was dependent on LET. The relative sensitivity was 0.8 at the Bragg peak, and reached its minimum value at the end of the proton range. No significant effects in the detector response were observed for LET < 4.9 keV microm(-1), thus indicating that the behaviour of the polymer gel dosimeter would not be altered for the range of LET values expected in the case of photons or electrons in a clinical range of energies.

Electrons↗

PubMed2004

Interleaved echo-planar imaging for fast multiplanar magnetic resonance temperature imaging of ultrasound thermal ablation therapy.

PURPOSE: To develop a multiplanar magnetic resonance temperature imaging (MRTI) technique based on interleaved gradient-echo echo-planar imaging (EPI), verify in phantom, develop software tools to process and display data on a clinical scanner in near real-time, and demonstrate feasibility to monitor ultrasound thermal ablation therapy in vivo. MATERIALS AND METHODS: Temperature estimation used complex phase-difference subtraction of the EPI MRTI data to indirectly measure the temperature-dependent water proton-resonance-frequency shift. Software tools were developed to run on a clinical 1.5-T MR scanner that processed and displayed relevant temperature and thermal dosimetry data during the course of thermal ablation treatments in canine brain and prostate in vivo. RESULTS: EPI MRTI provided multi-planar acquisitions and increased temperature sensitivity and lipid suppression. Relative to a single-plane fast gradient-echo MRTI sequence at comparable spatial and temporal resolutions in phantom, EPI MRTI demonstrated a three-fold increase in sensitivity and slice coverage per TR. In vivo monitoring of ultrasound thermal ablation therapy in canine brain and prostate demonstrated the usefulness of the temperature and thermal dose information. CONCLUSION: Multi-planar MRTI allowed progression of thermal damage to be monitored and treatment parameters adjusted in near real-time (less than five second delay). EPI MRTI is an effective multi-planar monitoring method during ultrasound thermal ablation procedures.

Animals↗

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↗