High spatial resolution whole-body MR angiography featuring parallel imaging: initial experience.

PURPOSE: To combine whole-body multi-station three-dimensional contrast enhanced magnetic resonance angiography (3D CE MRA) using a self-developed rolling table platform with parallel imaging strategies (PAT) in order to increase the spatial resolution of the 3D MRA data sets. MATERIALS AND METHODS: Whole-body multi-station MRA was performed with a rolling table platform (AngioSURF) on 5 volunteers in two imaging series: 1) standard imaging protocol, 2) modified high-resolution protocol employing PAT using the generalized autocalibrating partially parallel acquisitions (GRAPPA) algorithm with an acceleration factor of 3. For an intra-individual comparison of the two MR examinations, the arterial vasculature was divided into 30 segments. Signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were calculated for all 30 arterial segments of each subject. Vessel segment depiction was qualitatively assessed applying a 5-point scale to each of the segments. Image reconstruction times were recorded for the standard as well as the PAT protocol. RESULTS: Compared to the standard protocol, PAT allowed for increased spatial resolution through a 3-fold reduction in mean voxel size for each of the 5 stations. Mean SNR and CNR values over all specified vessel segments decreased by a factor of 1.58 and 1.56, respectively. Despite the reduced SNR and CNR, the depiction of all specified vessel segments increased in PAT images, reflecting the increased spatial resolution. Qualitative comparison of standard and PAT images showed an increase in vessel segment conspicuity with more detailed depiction of intramuscular arterial branches in all volunteers. The time for image data reconstruction of all 5 stations was significantly increased from about 10 minutes to 40 minutes when using the PAT acquisition. CONCLUSION: The implementation of PAT into the concept of whole-body MRA enabled to increase the spatial resolution in all examined territories, which resulted in more detailed MR angiograms.

0.5 M Gd chelate (Magnevist) versus 1.0 M Gd chelate (Gadovist): dose-independent effect on image quality of pelvic three-dimensional MR-angiography.

To compare the effect on image quality of a 1.0 M gadolinium (Gd) chelate to that of a conventional 0.5 M Gd chelate, five healthy volunteers and seven patients with angiographically documented aorto-iliac disease underwent a mono-station three-dimensional magnetic resonance angiography (MRA) exam (Siemens SONATA, Erlangen, Germany) twice, once using Gadovist 1.0 and the other time using Magnevist as the contrast agent. All subjects received a fixed volume of Gadovist 1.0, corresponding to a dose between 0.1 and 0.15 mmol/kg body weight followed by a saline flush. For the Magnevist exam, the contrast agent volumes and flow rates were doubled. For both quantitative and qualitative analysis of the angiographic data sets, the arterial tree was divided into nine segments. 1 M Gadovist 1.0-enhanced three-dimensional MRA data sets were characterized by significantly higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) values compared to 0.5 M Magnevist-enhanced images. The data revealed mean SNR/CNR increases exceeding 70% (P < 0.01). Although there was no statistically significant difference in the rating of image quality (P > 0.05), the Gadovist 1.0 exam led to better delineation of the arterial morphology, especially of small vessels.

MR colonography without colonic cleansing: a new strategy to improve patient acceptance.

OBJECTIVE: MR colonography permits accurate detection of colonic polyps larger than 8 mm. Patient acceptance remains limited because of the need for bowel cleansing. The aim of this study was to develop and assess a strategy obviating colonic cleansing by performing MR colonography in conjunction with fecal tagging based on the oral administration of barium. SUBJECTS AND METHODS: Six healthy volunteers and six patients with suspected colorectal tumors, undergoing conventional colonoscopy within 1 week of MR imaging, were included in this study. For fecal tagging, 200 mL of a barium-containing contrast agent was ingested with each of four principal meals preceding the examination. For MR colonography, the colon was filled with a barium and water mixture while gadobenate dimeglumine (0.2 mmol/kg) was injected IV. RESULTS: The combination of fecal tagging and colonic filling with barium resulted in a homogeneously low signal throughout the colonic lumen in all 12 subjects. IV injection of gadolinium caused avid enhancement of the colonic wall. Similarly, lesions arising from the colonic wall enhanced avidly. In the six evaluated patients, MR colonography correctly identified two colonic carcinomas in two patients and one polyp in each of another two patients. CONCLUSION: Fecal tagging obviates bowel cleansing and should, therefore, enhance patient acceptance for MR colonoscopy. Barium used as the tagging agent is promising because it is inexpensive, commercially available, and characterized by an excellent safety profile.

[Contrast-enhanced 3D MR venography of central thoracic veins: preliminary experience]. / Kontrastmittelverstärkte 3D-MR-Venographie der oberen Thoraxapertur: Erste Erfahrungen.

PURPOSE: To evaluate the usefulness of three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) venography for evaluation of thoracic central veins. MATERIALS AND METHODS: Over a 4-month period, 14 patients with suspected central venous abnormalities were examined on a 1.5 T scanner (Magnetom Sonata, SIEMENS, Germany) by means of MR venography. A FLASH-3D sequence using the following parameters was employed: TR 1.6 ms, TE 0.6 ms, TA 3.74 s, flip: 15 degrees, slab thickness 110 mm, effective slice thickness: 2.75 mm, 40 partitions, FOV 360 mm, matrix 140 x 256. 10 s prior to imaging 20 ml of Gd-DOPTA (Multihance, BRACCO, Italy) were automatically injected (MEDRAD, Pittsburgh, USA) flushed by 20 ml of normal saline (flow 4 ml/s). Six 3D data sets were acquired in immediate succession in under 24 s. Results were corroborated with findings from duplex sonography. RESULTS: MR venograms were of diagnostic quality for all 14 patients. Compared to duplex sonography thromboses, post-thrombotic changes as well as functional compressions were reliably detected. Unsuspected findings were found in two patients. CONCLUSION: The outlined strategy allows for dynamic diagnostic imaging of central thoracic veins. Gadolinium-enhanced breath-hold 3D MR venography is easy to perform, well tolerated and highly accurate in assessing central venous pathology.

Rapid magnetic resonance angiography for detection of atherosclerosis.

BACKGROUND: Choice of treatment for atherosclerosis depends on various clinical factors and radiological techniques. We aimed to assess the diagnostic accuracy of a new three-dimensional magnetic resonance angiography (3D MRA) strategy for the display of arterial vasculature from supra-aortic arteries to distal runoff vessels in 72 s. METHODS: We examined five healthy volunteers and six patients over 6 weeks. Conventional digital subtraction angiography (DSA) was available as reference standard in all six patients. Magnetic resonance imaging was done on a commercially available 1.5 Tesla scanner. The imaging technique was based on the acquisition of five 3D data sets in rapid succession with an optimum single injection protocol. FINDINGS: Compared with conventional catheter angiography, according to the findings of two independent and masked readers, whole-body MRA had overall sensitivities of 91% (95% CI 0.76-0.98) and 94% (0.8-0.99), and specificities of 93% (0.85-0.97) and 90% (0.82-0.96) for the detection of substantial vascular disease (luminal narrowing >50%), interobserver agreement for assessment of whole-body magnetic angiograms was very good (kappa=0.94; 95% CI 0.9-0.98). INTERPRETATION: The technique provides a comprehensive non-invasive approach for morphological screening assessment of the arterial vasculature from supra-aortic arteries to the distal runoff arteries.

Dynamic 3D MR angiography of the pulmonary arteries in under four seconds.

Although 3D MRA has been shown to provide excellent depiction of the pulmonary arterial tree, its clinical use has been limited due to lengthy breath-holding requirements. Employing the newest gradient generation (1.5 T MR system, amplitude of 40 mT/m and a slew rate of 200 mT/m/msec), we evaluated a technique permitting the dynamic acquisition of 3D data sets of the entire pulmonary tree in under 4 seconds. Coronal image sets were collected using a repetition time of 1.64 msec and an echo time of 0.6 msec, resulting in an acquisition time of 3.74 seconds. Three volunteers and eight dyspneic patients with known or suspected pulmonary embolism underwent MRI of the pulmonary arteries. The pulmonary arterial tree was visible to a subsegmental level in all examined subjects. Regarding the presence of pulmonary emboli in four patients, there was complete concordance between MR angiographic findings and those of corroborative studies. We conclude that diagnostic MRA of the pulmonary vasculature can be obtained even in patients with severe respiratory distress.

Improved multi-station peripheral MR angiography with a dedicated vascular coil.

Delineation of small branch vessels can be crucial for assessing the peripheral arterial system of patients requiring surgical grafting. Thus signal-to-noise needs to be maximized. We evaluated the performance of a dedicated peripheral vascular coil in four subjects by comparing it to the body coil using DSA as the standard of reference. SNR and CNR values of the dedicated peripheral coil exceeded those obtained with the body coil by a mean of 398%, thus permitting improved delineation of the infrapopliteal arterial morphology.

[Whole-body MRA on a rolling table platform (AngioSURF)]. / Ganzkörper-MRA auf einer rollenden Tischplattform (AngioSURF).

PURPOSE: Development of a technique for whole-body MR angiography based on a rolling table platform and integration of a surface coil. MATERIAL AND METHODS: The developed rolling table platform AngioSURF (System for Unlimited Rolling Field-of-view) with integrated surface coil can be mounted on top of the original patient table of a Siemens Symphony System. Data acquisition was performed with a standard body array surface coil. The system was tested on three volunteers and one patient with angiographically documented vascular pathology. Data acquisition was performed with a 3D-FLASH-sequence (TR/TE 2.1/0.7 ms, flip angle: 20 degrees, FOV 40 x 40 cm, 80 partitions, matrix 512 x 420 with zero interpolation). Five data sets were collected in immediate succession during continuous injection of a paramagnetic contrast agent. Time of acquisition per data set was 10 seconds. Table repositioning was performed manually within 3 seconds. Thus the total acquisition time amounted to 72 seconds. RESULTS: No problems with handling occurred in any of the four cases. The excellent image quality enables detailed assessment of the displayed vascular territories. CONCLUSIONS: The rolling table platform with integrated surface coil (AngioSURF) allows diagnostic display of the arterial vascular system from supraaortic vessels to the distal trifurcation arteries in only 72 seconds.