Per Åkeson

Cardiac metabolism measured noninvasively by hyperpolarized (13)C MRI.

Pyruvate is included in the energy production of the heart muscle and is metabolized into lactate, alanine, and CO2 in equilibrium with HCO  3− . The aim of this study was to evaluate the feasibility of using 13C hyperpolarization enhanced MRI to monitor pyruvate metabolism in the heart during an ischemic episode. The left circumflex artery of pigs (4 months, male, 29–34 kg) was occluded for 15 or 45 min followed by 2 hr of reperfusion. Pigs were examined by 13C chemical shift imaging following intravenous injection of 1‐13C pyruvate. 13C chemical shift MR imaging was used in order to visualize the local concentrations of the metabolites. After a 15‐min occlusion (no infarct) the bicarbonate signal level in the affected area was reduced (25–44%) compared with the normal myocardium. Alanine signal level was normal. After a 45‐min occlusion (infarction) the bicarbonate signal was almost absent (0.2–11%) and the alanine signal was reduced (27–51%). Due to image‐folding artifacts the data obtained for lactate were inconclusive. These studies demonstrate that cardiac metabolic imaging with hyperpolarized 1‐13C‐pyruvate is feasible. The changes in concentrations of the metabolites within a minute after injection can be detected and metabolic maps constructed. Magn Reson Med 59:1005–1013, 2008.

Brain metastases--comparison of gadodiamide injection-enhanced MR imaging at standard and high dose, contrast-enhanced CT and non-contrast-enhanced MR imaging.

The aim was to compare the abilities of contrast-enhanced CT, non-contrast-enhanced MR imaging and contrast-enhanced MR imaging using standard (0.1 mmol/kg b.w.) and high (0.3 mmol/kg b.w.) doses of Gadodiamide injection to detect brain metastases (i.e. blood-brain barrier damage). Sixteen patients with at least 2 metastases found by CT were evaluated by MR imaging using non-contrast-enhanced spin-echo, T1-weighted, T2-weighted sequences, and contrast-enhanced spin-echo T1-weighted sequences at 2 dose levels. Gadodiamide injection was first given at the dose of 0.1 mmol/kg b.w. After imaging, another 0.2 mmol/kg b.w. was given, yielding a cumulative dose of 0.3 mmol/kg b.w. No contrast media-related adverse events were recorded. The images were evaluated openly by one and blindly by 2 investigators and the number of metastases, size, delineation (open study) and diagnostic certainty (blind study) of each individual metastasis noted. High-dose MR imaging showed significantly more and smaller metastases than any other examination, and gave a higher diagnostic certainty. All high-dose images were superior to those with the standard dose MR imaging when compared blindly in pairs. We conclude that spin-echo MR imaging with a high dose of Gadodiamide injection is an efficient way to improve the detection of brain metastases, in particular of small ones.

Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC): intra- and interobserver variability in standardized drawing of regions of interest.

Purpose: To establish the reproducibility of a standardized region of interest (ROI) drawing procedure in delayed gadolinium‐enhanced magnetic resonance imaging (MRI) of cartilage (dGEMRIC). Material and Methods: A large ROI in lateral and medial femoral weight‐bearing cartilage was drawn in images of 12 healthy male volunteers by 6 investigators with different skills in MRI. The procedure was done twice, with a 1‐week interval. Calculated T1‐values were evaluated for intra‐ and interobserver variability. Results: The mean interobserver variability for both compartments ranged between 1.3% and 2.3% for the 6 different investigators without correlation to their experience in MRI. Post‐contrast intra‐observer variability was low in both the lateral and the medial femoral cartilage, 2.6% and 1.5%, respectively. The larger variability in lateral than in medial cartilage was related to slightly longer and thinner ROIs. Conclusion: Intra‐observer variability and interobserver variability are both low when a large standardized ROI is used in dGEMRIC. The experience of the investigator does not affect the variability, which further supports a clinical applicability of the method.

Hyperpolarized (3)He apparent diffusion coefficient MRI of the lung: Reproducibility and volume dependency in healthy volunteers and patients with emphysema.

To measure the apparent diffusion coefficient (ADC) of hyperpolarized (HP) 3He gas using diffusion weighted MRI in healthy volunteers and patients with emphysema and examine the reproducibility and volume dependency.

Validity of apparent diffusion coefficient hyperpolarized 3He-MRI using MSCT and pulmonary function tests as references.

PURPOSE To compare apparent diffusion coefficient (ADC) measurements from hyperpolarized (HP) helium ((3)He)-magnetic resonance imaging (MRI) with quantitative data from multislice Computed Tomography (CT) (MSCT) of the whole lungs and pulmonary function tests (PFT). MATERIALS AND METHODS Twenty-seven subjects, 22 with established emphysema and 5 with preclinical emphysema defined by PFT criteria, were examined with HP (3)He-MRI and MSCT. Mean age was 55 (+/-12) years, 18 female and 9 male. Mean ADC from (3)He-MRI was compared with emphysema index (EI), 15th percentile and mean lung density (MLD) values from MSCT. Both mean ADC and MSCT data were compared to PFT, especially percent of predicted diffusing capacity of carbon monoxide (%predicted DLCO), using Pearsons correlation test. RESULTS Mean ADC and standard deviation values were 0.392+/-0.119 cm(2)/s for the established emphysema group and 0.216+/-0.046 for the pre-clinical emphysema group. MSCT values for the established emphysema group and pre-clinical emphysema group were: EI (%) 11+/-12 and 0.4+/-0.6, respectively; 15th percentile (Hounsfield Units (HU)), -956+/-25 and -933+/-13, respectively and MLD (HU) -877+/-20 and -863+/-15, respectively. Correlations between mean ADC and EI and 15th percentile were both r=0.90 and for MLD r=0.59. There was higher correlation between mean ADC and %predicted DLCO (r=0.90) than between EI and %predicted DLCO (r=0.76). CONCLUSION HP (3)He-MRI correlates well with density measurements from MSCT and agrees better than MSCT with %predicted DLCO which is the PFT most related to emphysema.

Time-dependency in brain lesion enhancement with gadodiamide injection

Purpose: To determine the effective time window for MR imaging of tumors with blood-brain barrier (BBB) damage after injection of Gd-containing contrast media. Material and Methods: Eleven patients with 15 brain lesions (metastasis, glioma, abscess) were studied with a T1-weighted spin-echo sequence repeated over periods of up to 43 min after contrast injection. A quotient was calculated between the signals in the lesion and in the gray matter, and plotted against time. Results: All lesions reached 70% of the maximum RATIO within 3.5 min. After 25 min 12 out of 15 lesions showed persistent enhancement within 15% of the maximal RATIO. Conclusion: The peak enhancement of BBB damage occurs around 3.5 min after injection. The effect does not change during the next 25 min. Scanning should not be started until 2–5 min after injection of the contrast medium, and there is no advantage in waiting longer as no major increase (or decline) of contrast can be expected.

Progression of Emphysema in a 12-month Hyperpolarized 3 He-MRI Study: Lacunarity Analysis Provided a More Sensitive Measure than Standard ADC Analysis 1

RATIONALE AND OBJECTIVES Inhaled hyperpolarized (3)He magnetic resonance (MR) imaging has been used to measure alveolar size in patients with emphysema. The aim of this study was to test the hypothesis that (3)He MR images could be used to develop a biomarker of emphysema progression. MATERIALS AND METHODS Twelve healthy controls and 18 patients with emphysema (eight current smokers, 10 ex-smokers) were imaged at baseline and 6 and 12 months. An additional nine subjects with alpha-1 antitrypsin deficiency (four with emphysema, six without symptoms) were also imaged at baseline and at 6 months. Each subject was imaged at two lung volumes: functional residual capacity (FRC) and FRC plus 15% of total lung capacity. Means and standard deviations of apparent diffusion coefficients (ADCs) were calculated from coronal images of the entire lung and correlated with pulmonary function test results. The lacunarity hypothesis was tested and calculated from the data using a range of 2 x 2 x 2 to 6 x 6 x 6 voxels, and the average was calculated. RESULTS There was no change in the mean ADC at either lung volume in any subject over the 6- or 12-month period. FRC and residual volume increased over the 12 months, suggesting air trapping. The lacunarity of images collected at FRC increased at 6 and 12 months in smokers only (P = .063 and P = .023, respectively). CONCLUSIONS The mean ADC calculated from MR images of the lungs with helium was not sufficiently sensitive to detect changes over a 12-month period. However, lacunarity captured more of the spatial information in the images and detected emphysema progress in the smokers.

Safety aspects of gadofosveset in clinical practice--analysis of acute and long-term complications.

PURPOSE The purpose of this retrospective study was to systematically search for acute adverse reactions and long-term complications in all patients that had been administered gadofosveset at our hospital. MATERIALS AND METHODS We identified 67 gadofosveset administrations during 2006-2009 in 62 patients from 8 to 84years of age. Radiological information system (RIS) and clinical patient records were analyzed for suspected acute adverse reactions and long-term complications including nephrogenic systemic fibrosis (NSF). The gadofosveset doses ranged between 0.024 and 0.060mmol/kg bodyweight with a mean dose of 0.031-mmol/kg bodyweight. Follow-up time of the patients ranged from less than 1year up to 4years with a mean follow-up time of 2.1years. RESULTS No acute adverse events or technical failures related to the contrast medium were recorded in the RIS. No dermatological and nephrological diseases related to the gadofosveset administration were found in the clinical patient records. Four patients died during follow-up without any apparent relation to the gadofosveset exposure. CONCLUSIONS Based on our clinical material we conclude that gadofosveset is safe for a mixed patient population with no acute adverse events or any indications of long-term complications during the follow-up time up to four years.

Thoracic magnetic resonance venography using Gadofosveset in patients with venous pathology—A comparative study of image quality and inter-rater variability

Background High-quality non-invasive imaging of the deep venous system in the thorax is challenging, but nevertheless required for diagnosis of vascular pathology as well as for patient selection and preoperative planning for endovascular procedures. Purpose To compare the diagnostic quality of Gadofosveset-enhanced thoracic magnetic resonance venography, seven consecutive patients with suspected or known disease affecting the central thoracic veins were compared to seven consecutive magnetic resonance venography using conventional gadolinium-based contrast agents. Materials and methods Diagnostic capability, defined as the ability to assess vessel patency and pathologic conditions, for the major thoracic deep venous segments was assessed by two-independent readers. Both reviewers rated the overall subjective image quality on a four-graded scale, and inter-rater variability was analyzed using unweighted and weighted Cohens kappa values. Results Diagnostic capability was generally considerably higher in the Gadofosveset group for all examined vessel segments. The overall images quality rating was significantly higher for the Gadofosveset group with a mean rating of 2.9 and 2.7 for the two-independent readers, compared to 1.2 and 1.0 for the control croup. Inter-rater variability showed less variability for the Gadofosveset group with a quadratic-weighted Cohens Kappa value of 0.58 compared to 0.36 for the control group. Conclusion Our results show that Gadofosveset-enhanced magnetic resonance venography of the central thoracic veins is a reliable technique in clinical routine practice that results in diagnostic images, superior to conventional gadolinium-based contrast medium.

Gadofosveset-enhanced magnetic resonance venography in patients with venous pathology of the lower limbs – Comparison of diagnostic image quality and inter-rater variability with gadobutrol venography and computed tomography venography

Purpose This study was performed to compare the diagnostic quality of Gadofosveset-enhanced magnetic resonance venography with Gadobutrol-enhanced magnetic resonance venography and computed tomography venography for the deep veins of the lower extremities in patients with iliocaval venous pathology. Materials and methods Diagnostic capability and image quality were assessed by two independent readers. Inter-reader variability was analyzed by unweighted and quadratic weighted Cohen’s kappa values. Results The diagnostic capability was equal to or higher in the Gadofosveset group for all examined vessel segments compared with both control groups. The image quality score was significantly higher for the Gadofosveset group compared to both control groups. Inter-reader variability expressed by quadratic weighted Cohen’s kappa value (k) showed less variability in the Gadofosveset group compared to the control groups. Conclusion Our results show that Gadofosveset-enhanced magnetic resonance venography is a reliable technique in clinical routine practice, with image quality superior to both Gadobutrol-enhanced magnetic resonance venography and computed tomography venography.