Marjut Timonen

MRI quality assurance using the ACR phantom in a multi-unit imaging center

Abstract Background. Magnetic resonance imaging (MRI) instrumentation is vulnerable to technical and image quality problems, and quality assurance is essential. In the studied regional imaging center the long-term quality assurance has been based on MagNET phantom measurements. American College of Radiology (ACR) has an accreditation program including a standardized image quality measurement protocol and phantom. The ACR protocol includes recommended acceptance criteria for clinical sequences and thus provides possibility to assess the clinical relevance of quality assurance. The purpose of this study was to test the ACR MRI phantom in quality assurance of a multi-unit imaging center. Material and methods. The imaging center operates 11 MRI systems of three major manufacturers with field strengths of 3.0 T, 1.5 T and 1.0 T. Images of the ACR phantom were acquired using a head coil following the ACR scanning instructions. Both ACR T1- and T2-weighted sequences as well as T1- and T2-weighted brain sequences in clinical use at each site were acquired. Measurements were performed twice. The images were analyzed and the results were compared with the ACR acceptance levels. Results. The acquisition procedure with the ACR phantom was faster than with the MagNET phantoms. On the first and second measurement rounds 91% and 73% of the systems passed the ACR test. Measured slice thickness accuracies were not within the acceptance limits in site T2 sequences. Differences in the high contrast spatial resolution between the ACR and the site sequences were observed. In 3.0 T systems the image intensity uniformity was slightly lower than the ACR acceptance limit. Conclusion. The ACR method was feasible in quality assurance of a multi-unit imaging center and the ACR protocol could replace the MagNET phantom tests. An automatic analysis of the images will further improve cost-effectiveness and objectiveness of the ACR protocol.

Boron neutron capture therapy (BNCT) in Finland: Technological and physical prospects after 20 years of experiences

Boron Neutron Capture Therapy (BNCT) is a binary radiotherapy method developed to treat patients with certain malignant tumours. To date, over 300 treatments have been carried out at the Finnish BNCT facility in various on-going and past clinical trials. In this technical review, we discuss our research work in the field of medical physics to form the groundwork for the Finnish BNCT patient treatments, as well as the possibilities to further develop and optimize the method in the future. Accordingly, the following aspects are described: neutron sources, beam dosimetry, treatment planning, boron imaging and determination, and finally the possibilities to detect the efficacy and effects of BNCT on patients.

A novel mutation of the GAA gene in a Finnish late‐onset pompe disease patient: Clinical phenotype and follow‐up with enzyme replacement therapy

Pompe disease is a rare, progressive disease leading to skeletal muscle weakness due to deficiency of the acid α‐glucosidase (GAA) enzyme. Herein we report the first diagnosed Finnish patient with a phenotype compatible with the late‐onset form of Pompe disease. Molecular genetic analysis of the GAA gene revealed a novel missense mutation, 1725C>A (Y575X), combined with a previously reported mutation, 1634C>T (P545L). Human recombinant α‐glucosidase enzyme (alglucosidase‐α) treatment was initiated for this patient at age 20 years. After 12 months she was no longer fully wheelchair‐bound, and muscle strength had improved. No disease progression was visible on muscle magnetic resonance imaging of the lower limbs, and the energy state of the muscle cells increased by 46% on phosphorus magnetic resonance spectroscopy. Overall, our findings suggest that enzyme replacement therapy is indicated, even in patients with late‐onset Pompe disease, to halt disease progression and improve the quality of daily life. Muscle Nerve, 2009

1H MRS of a boron neutron capture therapy 10B-carrier, L-p-boronophenylalanine-fructose complex, BPA-F: phantom studies at 1.5 and 3.0 T.

The quantification of a BNCT 10B-carrier, L-p-boronophenylalanine-fructose complex (BPA-F), was evaluated using 1H magnetic resonance spectroscopy (1H MRS) with phantoms at 1.5 and 3.0 T. For proper quantification, relaxation times T1 and T2 are needed. While T1 is relatively easy to determine, the determination of T2 of a coupled spin system of aromatic protons of BPA is not straightforward with standard MRS sequences. In addition, an uncoupled concentration reference for aromatic protons of BPA must be used with caution. In order to determine T2, the response of an aromatic proton spin system to the MRS sequence PRESS with various echo times was calculated and the product of the response curve with exponential decay was fitted to the measured intensities. Furthermore, the response curve can be used to correct the intensities, when an uncoupled resonance is used as a concentration reference. BPA was quantified using both phantom replacement and internal water referencing methods with accuracies of +/- 5% and +/- 15%. Our phantom results suggest that in vivo studies on BPA concentration determination will be feasible.

Aspects of forward scattering from the compression paddle in the dosimetry of mammography.

The best compression paddle position during air kerma measurement in mammography dosimetry was studied. The amount of forward scattering as a function of the compression paddle distance was measured with different X-ray spectra and different types of paddles and dose meters. The contribution of forward scattering to the air kerma did not present significant dependency on the beam quality or of the compression paddle type. The tested dose meter types detected different amounts of forward scattering due to different internal collimation. When the paddle was adjusted to its maximum clinical distance, the proportion of the detected forward scattering was only 1 % for all dose meter types. The most consistent way of performing air kerma measurements is to position the compression paddle at the maximum distance from the dose meter and use a constant forward scattering factor for all dose meters. Thus, the dosimetric uncertainty due to the forward scatter can be minimised.

Synthesis and in vitro phantom NMR and MRI studies of fully organic free radicals, TEEPO-glucose and TEMPO-glucose, potential contrast agents for MRI

Two organic radical contrast agents, TEMPO-Glc and TEEPO-Glc, were synthesized and their stabilities and contrast enhancing properties were tested with in vitro NMR and MRI experiments. Owing to the glucose moieties in the prepared compounds, this study presents potential candidates for a tumor targeting fully organic contrast agents for MRI.

Risk for metabolic syndrome predisposes to alterations in the thalamic metabolism

Risk factors for the metabolic syndrome (MetS) affect brain function and associate with asymptomatic brain infarctions in healthy individuals. We studied whether MetS risk factors alter cerebral metabolism. Eighteen non-smoking men (36 ± 6years) were stratified into two groups according to their risk of developing the MetS. Individuals in the Risk group had a family history of type 2 diabetes, were pre-obese, had mild hypertension and higher fasting plasma glucose and serum insulin compared to the Control group with no risk factors. N-acetyl aspartate, choline, total creatine (tCr), myo-inositol, and glucose were studied in the thalamus, frontal cortex, and frontal white matter with proton magnetic resonance spectroscopy. The plasma glucose was 13% higher (p < 0.01) in the Risk group, but the brain glucose levels were comparable between the groups. In the Control group, the thalamic tCr correlated with the thalamic glucose level (r = 0.81, p = 0.015). In the Risk group, the tCr was 17% higher (p = 0.006) and correlated with the fasting plasma glucose concentration (r = 0.78, p = 0.013), but not with the thalamic glucose level. In conclusion, the increased tCr level in the Risk group suggests that a family history of type 2 diabetes together with MetS risk factors alters thalamic energy metabolism.

Conformance of mean glandular dose from phantom and patient data in mammography.

In mammography dosimetry, phantoms are often used to represent breast tissue. The conformance of phantom- and patient-based mean glandular dose (MGD) estimates was evaluated mainly from the aspect of diagnostic reference levels. Patient and phantom exposure data were collected for eight diagnostic and three screening mammography devices. More extensive assessments were performed for two devices. The average breast thickness was close to the nationally used reference of 50 mm in diagnostic (50 mm, SD = 13 mm, n = 5342) and screening (47 mm, SD = 13 mm, n = 395) examinations. The average MGD for all breasts differed by 2% from the MGD determined for breasts in the limited compressed thickness range of 40-60 mm. The difference between phantom- and patient-based MGD estimations was up to 30%. Therefore, phantom measurements cannot replace patient dose data in MGD determination.

Synthesis, Stability and Relaxivity of TEEPO-Met : An Organic Radical as a Potential Tumour Targeting Contrast Agent for Magnetic Resonance Imaging

Cancer is a widespread and life-threatening disease and its early-stage diagnosis is vital. One of the most effective, non-invasive tools in medical diagnostics is magnetic resonance imaging (MRI) with the aid of contrast agents. Contrast agents that are currently in clinical use contain metals, causing some restrictions in their use. Also, these contrast agents are mainly non-specific without any tissue targeting capabilities. Subsequently, the interest has notably increased in the research of organic, metal-free contrast agents. This study presents a new, stable organic radical, TEEPO-Met, where a radical moiety 2,2,6,6-tetraethylpiperidinoxide (TEEPO) is attached to an amino acid, methionine (Met), as a potentially tumour-targeting moiety. We describe the synthesis, stability assessment with electron paramagnetic resonance (EPR) spectroscopy and relaxation enhancement abilities by an in vitro nuclear magnetic resonance (NMR) and phantom MRI studies of TEEPO-Met. The new compound proved to be stable notably longer than the average imaging time in conditions mimicking a biological matrix. Also, it significantly reduced the relaxation times of water, making it a promising candidate as a novel tumour targeting contrast agent for MRI.