Jörg Schmiedeskamp

Hyperpolarised 3He MRI versus HRCT in COPD and normal volunteers: PHIL trial

The aim of the present study was to apply hyperpolarised (HP) 3He magnetic resonance imaging (MRI) to identify patients with chronic obstructive pulmonary disease (COPD) and α1-antitrypsin deficiency (α1-ATD) from healthy volunteers and compare HP 3He MRI findings with high-resolution computed tomography (HRCT) in a multicentre study. Quantitative measurements of HP 3He MRI (apparent diffusion coefficient (ADC)) and HRCT (mean lung density (MLD)) were correlated with pulmonary function tests. A prospective three centre study enrolled 122 subjects with COPD (either acquired or genetic) and age-matched never-smokers. All diagnostic studies were completed in 94 subjects (52 with COPD; 13 with α1-ATD; 29 healthy subjects; 63 males; and 31 females; median age 62 yrs). The consensus assessment of radiologists, blinded for other test results, estimated nonventilated lung volume (HP 3He MRI) and percentage diseased lung (HRCT). Quantitative evaluation of all data for each centre consisted of ADC (HP 3He MRI) and MLD measurements (HRCT), and correlation with forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) indicating airway obstruction, and the diffusing capacity of the lung for carbon monoxide (DL,CO) indicating alveolar destruction. Using lung function tests as a reference, regional analysis of HP 3He MRI and HRCT correctly categorised normal volunteers in 100% and 97%, COPD in 42% and 69% and α1-ATD in 69% and 85% of cases, respectively. Direct comparison of HP 3He MRI and CT revealed 23% of subjects with moderate/severe structural abnormalities had only mild ventilation defects. In comparison with lung function tests, ADC was more effective in separating COPD patients from healthy subjects than MLD (p<0.001 versus 0.038). ADC measurements showed better correlation with DL,CO than MLD (r = 0.59 versus 0.29). Hyperpolarised 3He MRI correctly categorised patients with COPD and normal volunteers. It offers additional functional information, without the use of ionising radiation whereas HRCT gives better morphological information. We showed the feasibility of a multicentre study using different magnetic resonance systems.

Magnetic resonance imaging of dissolved hyperpolarized 129Xe using a membrane-based continuous flow system.

A technique for continuous production of solutions containing hyperpolarized (129)Xe is explored for MRI applications. The method is based on hollow fiber membranes which inhibit the formation of foams and bubbles. A systematic analysis of various carrier agents for hyperpolarized (129)Xe has been carried out, which are applicable as contrast agents for in vivo MRI. The image quality of different hyperpolarized Xe solutions is compared and MRI results obtained in a clinical as well as in a nonclinical MRI setting are provided. Moreover, we demonstrate the application of (129)Xe contrast agents produced with our dissolution method for lung MRI by imaging hyperpolarized (129)Xe that has been both dissolved in and outgassed from a carrier liquid in a lung phantom, illustrating its potential for the measurement of lung perfusion and ventilation.

Controlling diffusion of He-3 by buffer gases: A structural contrast agent in lung MRI

To study the influence of admixing inert buffer gases to laser‐polarized 3He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution.

Intrapulmonary 3He gas distribution depending on bolus size and temporal bolus placement.

Objective:Dynamic ventilation 3He-MRI is a new method to assess pulmonary gas inflow. As differing airway diameters throughout the ventilatory cycle can influence gas inflow this study intends to investigate the influence of volume and timing of a 3He gas bolus with respect to the beginning of the tidal volume on inspiratory gas distribution. Materials and Methods:An ultrafast 2-dimensional spoiled gradient echo sequence (temporal resolution 100 milliseconds) was used for dynamic ventilation 3He-MRI of 11 anesthetized and mechanically ventilated pigs. The applied 3He gas bolus was varied in volume between 100 and 200 mL. A 150-mL bolus was varied in its application time after the beginning of the tidal volume between 0 and 1200 milliseconds. Signal kinetics were evaluated using an in-house developed software after definition of parameters for the quantitative description of 3He gas inflow. Results:The signal rise time (time interval between signal in the parenchyma reaches 10% and 90% of its maximum) was prolonged with increasing bolus volume. The parameter was shortened with increasing delay of 3He application after the beginning of the tidal volume. Timing variation as well as volume variation showed no clear interrelation to the signal delay time 10 (time interval between signal in the trachea reaches 50% of its maximum and signal in the parenchyma reaches 10% of its maximum). Conclusions:Dynamic ventilation 3He-MRI is able to detect differences in bolus geometry performed by volume variation. Pulmonary gas inflow as investigated by dynamic ventilation 3He-MRI tends to be accelerated by an increasing application delay of a 3He gas bolus after the beginning of the tidal volume.

Magnetic resonance imaging using hyperpolarized 3He-gas1☆

Abstract Rationale and Objectives. Current imaging procedures of the lung concentrate on visualization of morphology. Computed tomography is the imaging method of choice for the majority of pulmonary diseases. Functional data are commonly obtained from arterial blood gas analysis, spirometry, and body plethysmography, which all suffer from lack of regional information. Materials and Methods. Magnetic resonance imaging (MRI) of the lung has been advanced recently by the use of hyperpolarized 3He as a new contrast mechanism. Four different image acquisition modes are performed during a typical patient study. Results. 3He-MRI yields functional information about the lung with a high spatial and temporal resolution, avoiding the risks of ionizing radiation. The method is currently limited by high costs and restricted availability of the gas. Conclusion. In this article, the experience obtained at the University of Mainz, being Europe’s most experienced center performing 3He-MRI in humans, is reviewed against the international background.

Magnetization of He-3 spin filter cells

A number of valved quartz glass 3He spin filter cells have been repeatedly exposed to various external magnetic fields in order to determine the influence of induced wall magnetization on the relaxation time in the cells. The procedures of magnetizing and degaussing of cells are described. A comparison of T1 measurements performed in the same cell by different methods attest the good reliability of the measurements as well as the time stability of T1 in Cs-coated quartz glass cells. No orientation dependence of the relaxation in fields of 8 G was observed. A strong dependence of T1 on the strengths of external magnetic fields, applied perpendicular to the direction of the guide field used during the measurements, was observed at low and moderate fields. T1 decreases rapidly by increasing the field strength up to values of about 1 kG both in Cs-coated and bare-wall cells. Further increase in the field to 7 kG has no significant influence on the relaxation value, suggesting the saturation of the cell magnetization. Macroscopic magnetization produced in the bulk of the glass as well as Cs-caused magnetization on the surface are proposed to be two different relaxation mechanisms present in the cells. The magnetization induced in cells has been determined independently of the 3He relaxation by SQUID measurements. The influence of Cs coating and of heating on T1 in magnetized cells is discussed.

Transportabler DNP Polarisator zur klinischen Anwendung

Ziele: Entwicklung eines mobilen Hyperpolarisators fur Flussigkeiten zur drastischen Erhohung der MR-Signalintensitat. Der Polarisator kann nahe an einen MR Tomographen herangebracht werden und erlaubt so die effiziente Nutzung der hergestellten Hyperpolarisation, die mit dem T1 der polarisierten Substanz zerfallt. Der Einsatz des Polarisators soll die MR-Bildgebung von Kernen wie 13C und 15N ermoglichen, um so Zugang zu Informationen uber den Metabolismus der hyperpolarisierten und injizierten Substanz zu erhalten, was u.a. in der Tumordiagnostik eingesetzt werden kann. Methode: Der Polarisator beruht auf einem Halbach Magneten mit moderater Feldstarke (0,03–0,30T) und geringem Streufeld. Der verwendete Magnet besteht aus 3 ineinander gesetzten Ringen aus Permanentmagneten in Halbach Anordnung und erlaubt eine genaue Einstellung der gewunschten Feldstarke. Das Gewicht des Magneten betragt 90kg inklusive Zubehor und kann auf einem fahrbaren Tisch mit 2 Ebenen zusammen mit der Mikrowellenquelle transportiert werden. Es wurden 1H-DNP-Experimente mit 3 Radikalen (Triaryl-Radikal (TAM), TEMPOL, Polyelektrolyt mit kovalent gebundenen Nitroxid-Radikalen) durchgefuhrt und die erreichten Verstarkungsfaktoren bei 0.3 T und Raumtemperatur verglichen. Ergebnis: Die Hyperpolarisation der Kernspins konnte im beschriebenen Aufbau erfolgreich und reproduzierbar durchgefuhrt werden. Die Verstarkungsfaktoren von TAM und TEMPOL in Abhangigkeit der Einstrahlfrequenzen der Mikrowelle wurden bestimmt und mit EPR-Spektren uberlagert. Es zeigte sich eine gute Ubereinstimmung. Zusatzlich wurden die DNP-Verstarkungsfaktoren von allen drei Radikalen in Abhangigkeit von der eingestrahlten Mikrowellenleistung gemessen und auf die mit diesem Aufbau maximal erreichbaren Verstarkungsfaktoren extrapoliert (TAM: 27, TEMPOL: 60, Polyelektrolyt: 80). Schlussfolgerung: Der mobile Polarisator stellt ein effizientes Gerat zur drastischen Erhohung der Kernmagnetisierung und damit der Signalintensitat in der MRT dar. Der DNP Effekt, der auf der Ubertragung der hohen Polarisation von ungepaarten Elektronen auf Kernspins beruht, ist bei diesen Feldstarken wesentlich effizienter als im Hochfeld und auch die Eindringtiefe der zur EPR Anregung notwendigen Mikrowellenstrahlung (hier 2–9 GHz) ist zur Anregung klinisch relevanter Probenvolumina pradestiniert. Unser Aufbau erlaubt die Quantifizierung und Optimierung der entstehenden Hyperpolarisation, die in klinischen MR Geraten z.B. in der molekularen Bildgebung eingesetzt werden kann. Korrespondierender Autor: Munnemann K Uniklinikum der Johannes Gutenberg Universitat Mainz, Radiologie/Medizinische Physik, Langenbeckstr. 1, 55131 Mainz E-Mail: muennema@uni-mainz.de