J Gieseke

Noninvasive detection of steno-occlusive disease of the supra-aortic arteries with three-dimensional contrast-enhanced magnetic resonance angiography: A prospective, intra-individual comparative analysis with digital subtraction angiography

Background and Purpose— Concomitant disease of the supra-aortic arteries can influence the outcome of surgical treatment of carotid artery stenosis. However, sensitivity and specificity data of noninvasive contrast-enhanced 3-dimensional (3D) magnetic resonance angiography (CE MRA) for the detection of steno-occlusive disease of the entire supra-aortic arteries including the circle of Willis remain unclear. We aimed to intra-individually compare high-spatial-resolution CE 3D MRA and digital subtraction angiography (DSA) for the assessment of steno-occlusive vascular disease of the supra-aortic arteries. Methods— CE MRA and DSA of the supra-aortic arteries were prospectively performed in 50 consecutive patients. Intra-individual comparison of CE MRA and DSA was available in 833 arteries. High-spatial-resolution CE MRA comprised a measured voxel size of 0.81 mm × 0.81 mm × 1 mm (0.66 mm3). Steno-occlusive vascular disease of the 833 arteries was assessed independently by 2 radiologists according to the NASCET criteria. Results— CE MRA had a sensitivity of 100% (73/73), a specificity of 99.3% (760/765), a positive predictive value of 93.6% (73/78), and a negative predictive value of 100% (760/760) by using a 70% to 99% threshold of arterial diameter stenosis. For detection of occlusion, sensitivity, specificity, PPV, and NPV value of CE MRA were 100%, respectively. Conclusions— Noninvasive high-spatial-resolution CE MRA is suited to replace diagnostic DSA for the detection of steno-occlusive disease of the supra-aortic arteries.

Impact of oxygen as a vasodilator on respiration-related Gontan hemodynamics assessed by real-time phase-velocity MRI

Background Inhalative administration of oxygen increases pulmonary blood flow by vasodilation. Currently, flow rate quantification using conventional two-dimensional phase-contrast MRI (PC-MRI) is not capable to study short-term effects due to averaging of flow information. The aim of this study was to examine the impact of oxygen supply on respiration-related flow rate variations by non-electrocardiographic triggered real-time phase-contrast MRI (PC-MRI) in patients after total cavo-pulmonary connection (Fontan).

Clinical Cardiac MR at 3.0 Tesla using parallel RF transmission with patient-adaptive local RF shimming: initial experience

Purpose: The use of high-field MRI scanners has introduced new challenges for cardiac imaging, associated with B1- and B0-field inhomogeneities. A dual – source RF transmission system may help reduce dielectric effects, thus improving image contrast and reducing local SAR peaks of cardiac TSE and SSFP sequences, thereby allowing a shorter minimum TR and TE of SSFP sequences. Thus, the aim of our study was to evaluate the impact of dual – source parallel RF transmission with patient adaptive RF-shimming on image quality and diagnostic confidence for routine clinical CMR using a 3.0 T dual – channel transmit whole – body MRI system. Materials and Methods: A clinical 3.0 T MRI system (Achieva 3.0T-TX, Philips Healthcare, Best, Netherlands), equipped with a dual-source RF transmission system was used. The effect of parallel RF transmission with patient adaptive B1 shimming (multi transmit=MTx) vs. conventional (single transmit=STx) RF transmission on SSFP sequences and TSE Black-Blood (TSE BB) sequences was evaluated. Images were analyzed independently by two experienced readers for homogeneity and diagnostic confidence on a 4-point grading-scale. Also, the presence of off-resonance artefacts in the SSFP images was rated on a 4-point grading scale. CNR between interventricular septum and blood pool was determined. Results: A total of 21 patients were included into the study. For both, TSE BB and SSFP -images, the use of MTx resulted in a significant improvement of image homogeneity and diagnostic confidence in the left and right ventricle. As a side effect, off-resonance artefacts were significantly reduced in the acquired SSFP images. Interrater agreement for all ratings was very good. The quantitative measurements revealed a significant increase of CNR in the RF shimmed images using MTx compared to the images acquired with STx.((BR))Conclusions: Patient adaptive local RF-shimming using parallel dual source RF-transmission significantly improves image homogeneity, diagnostic confidence and contrast of cardiac SSFP and TSE BB sequences.

Modulation des Refokussierungswinkels in TSE Sequenzen mit FAS (Flip Angle Sweep).

Ziele: Die Verwendung von TSE (FSE) -Sequenzen mit zahlreichen 180° Refokussierungspulsen ist bei 3T durch die SAR Begrenzungen limitiert. Eine Erniedrigung der SAR ist unter anderem durch eine Reduzierung des Refokussierungwinkels wahrend eines Echozuges moglich (Hyperecho/FAS). Diese Studie untersucht den Einfluss der FAS-Technik (Flip Angle Sweep) auf den Bildkontrast bei Leberuntersuchungen. Methode: 7 Probanden wurden an einem 3T System (Intera, Philips MS, Best NL) unter Verwendung einer Oberflachenspule (Syn-cardiac) untersucht. Es wurden atemgetriggerte T2 gewichtete TSE Sequenzen (TR/TE: >4000/80ms, SD/Matrix: 8mm/256, ETL: 18) mit unterschiedlichen FAS-Winkeln (ohne FAS, 150°, 120°, 90°, 75°, 60°, 30°) akquiriert. SNR Messungen wurden in Leber, Fett, Muskulatur, Nieren und Milz sowie in einer Wasserprobe und einer Manganlosung (0,6 mmolar) durchgefuhrt. Hieraus wurden entsprechende Kontrastwerte im Verhaltnis zur Leber berechnet. Ergebnis: Mit abnehmenden Refokussierungswinkeln reduzieren sich die gemessenen SNR Werte insbesondere der Gewebe/Proben mit primar hoher Signalintensitat um 35–50% (180° vs. 30°), die SNR Werte der Leber und der Muskulatur hingegen werden nur geringfugig reduziert. Als Folge kommt es zu einer Abnahme der Kontraste zwischen Leber und den ubrigen parenchymatosen Organen bzw. Flussigkeiten. Die Manganlosung mit kurzen T1 und T2 Zeiten weist hingegen eine deutliche Zunahme der SNR mit reduzierten Refokussierungswinkeln auf (ca. 300%). Schlussfolgerung: Die Reduktion des Refokussierungswinkels in TSE Sequenzen fuhrt zu einer Abnahme der SNR-Werte sowie des Kontrastes der Gewebe des Oberbauches. Die Ursache, insbesondere in Zusammenschau mit dem SNR Anstieg der Manganlosung, ist in erster Linie auf einen verstarkten T1 Effekt zuruckzufuhren. Die Auswirkungen auf die Detektion fokaler Leberlasionen ist unklar, der Einsatz der genannten Verfahren sollte jedoch mit entsprechender Vorsicht erfolgen. Korrespondierender Autor: von Falkenhausen M Radiologische Universitatsklinik Bonn, Sigmund Freud Str. 25, 52105 Bonn E-Mail: marcus.von_falkenhausen@ukb.uni-bonn.de

DTI Measurements of Fractional Anisotropy at 3 Tesla: Sequence optimization and reproducibility

Purpose: To determine suitable parameters for rapid DTI acquisition at 3 tesla, to assess the reproducibility of fa-measurements which are one of the core information for fiber trackings, and to quantify the influence of noise reduction and averaging high b-values on resulting FA-maps. Methods: The study collective consisted of 10 volunteers for the issue of sequence optimization and 2 volunteers for reproducibility assessment and testing for the use of noise decorrelation and high b averaging. Concerning sequence optimization, the following constant parameters were used: a single shot SENSE imaging protocol with 2×2x2mm spatial resolution, covering sixty slices and measuring 15 diffusion directions. Parameters varied during sequence optimization were b-values (400, 600, 800s/mm2) and SENSE-factors (1 to 4), with the number of trackable callosal fibers as the criterion for parameter comparison. To assess the reproducibility of DTI sequences, we performed three independent measurements per session on two separate days, and these sequences were acquired with and without averaging of high b-values and noise reduction, which resulted in a total of 12 acquisitions per day. Results: The highest number of trackable callosal fibers, was achievable with a b-value of 600s/mm2 and a SENSE factor of 2. Acquisition times were ranking from a maximum of 10 down to 4 and a half minutes. Concerning reproducibility, the highest relative standard deviation around the mean of repeated acquisitions, was ranking around 6 percent. The impact of noise reduction algorithms and averaging of the high b-values was low, so that the use of noise decorrelation and averaging high b may be withdrawn in favour of acquisition time. Conclusion: SENSE-DTI at 3 Tesla allows for rapid DTI acquisition and yields highly reproducible FA measurements.