Eur Radiol (2008) 18: 1473–1483DOI 10.1007/s00330-008-0885-1 MAGNETIC RESONANCE

Michael FenchelKambiz NaelAchim SeegerUlrich KramerRoya SalehStephan Miller

Received: 30 August 2007Revised: 1 December 2007Accepted: 16 January 2008Published online: 15 February 2008# European Society of Radiology 2008

Whole-body magnetic resonance angiography

at 3.0 Tesla

Abstract The quality of magneticresonance (MR) angiography couldbe substantially improved over thepast several years based on theintroduction and application ofparallel imaging, new sequence tech-niques, such as, e.g., centric k-spacetrajectories, dedicated contrast agents,and clinical high-field scanners. All ofthese techniques have played animportant role to improve imageresolution or decrease acquisition timefor the dedicated examination of a

single vascular territory. However,whole-body MR angiography maybe the application with the potentialto profit most from these technicaladvances. The present review articledescribes the technical innovationswith a focus on parallel imaging athigh field strength and the impacton whole-body MR angiography.The clinical value of advanced whole-body MR angiography techniquesis illustrated by characteristic cases.

Keywords Magnetic resonanceimaging . Magnetic resonanceangiography . Whole body .Three Tesla . MRI

Introduction

Magnetic resonance (MR) angiography has evolved into astandard clinical examination for a variety of vascularregions, such as MR angiography of the carotid arteries[1–4], abdominal aorta and its main branches [5–7], andperipheral vessels [8–11]. It has replaced diagnostic invasiveangiographic procedures in many cases. The main advan-tages of MR angiography are its non-invasiveness, the lackof ionizing radiation, the combination of morphologic andfunctional information in a single examination, and the

postprocessing capabilities of the three-dimensional (3D)datasets.

Up to now, MR angiography has predominantlyremained locally focused on the symptomatic clinicalregion. Nonetheless, many vascular diseases, such as, e.g.,atherosclerosis, diabetic vasculopathy, and inflammatoryvessel changes such as Takayasu arteriitis, have to beconsidered as systemic diseases that simultaneously affectmultiple regions of the body. Consequently, whole-bodyimaging may detect the extent of vascular pathologies forimproved assessment of patients’ prognosis and guidance

M. Fenchel (*) . A. Seeger .U. Kramer . S. MillerDepartment of Diagnostic Radiology,Eberhard-Karls-University Tuebingen,Hoppe-Seyler-Str. 3,72076 Tuebingen, Germanye-mail: michael.fenchel@med.uni-tuebingen.deTel.: +49-7071-2985837Fax: +49-7071-295845

K. Nael . R. SalehDepartment of Radiological Sciences,David Geffen School of Medicine,University of California,Los Angeles, CA, USA

of appropriate therapy. Several investigators have eval-uated the feasibility of contrast-enhanced whole-body MRangiography [12–15], which, with the exception of thecoronary arteries and intracranial vessels, involves theanatomic coverage of all vascular territories.

In the beginning, in order to assess vascular abnormal-ities in more than one vascular region, investigators had toreposition the surface coils on the patient and repeatedlyinject contrast agent, which was quite cumbersome. Firstmulti-station MR examinations without moving individualcoils were performed by Riederer et al. using a continuoustable movement approach [16] and Ruehm et al. who havecompounded a dedicated rolling table platform (Angio-SURF) with receiver coils that were immovably placed inthe center of the magnet bore [12, 13]. These devices werecombined with fast imaging modalities to depict the arterialvasculature from the supra-aortic to the lower leg regionwithin short examination times [17]. Although initialresults have been promising, the resulting image qualityand spatial resolution were lower compared to a single-station approach. In consecutive studies since dedicatedwhole-body MR scanners became commercially available,multi-station MR angiography has been performed for theassessment of the entire vascular system without patientrepositioning [14, 18] or manual table movement. Still,limitations and compromises in spatial resolution oranatomic coverage were described, mainly because of thelimited time available for data acquisition, which is due tothe rapid bolus passage of the contrast agent. In order toextend the duration of the arterial phase, severalapproaches, such as semicircular cushions placed belowthe patient’s knee or thigh compression with dedicatedpressure cuffs [19, 20], have been tested for reducedvenous overlap of peripheral runoff vessels.

A major improvement concerning data acquisition speedwas the implementation of parallel imaging techniques at1.5-T (T) MR imagers, as well as on high-field-strengthscanners (e.g., 3.0 T) [21–23]. Parallel imaging allowed areasonably fast acquisition of large 3D datasets. The signal-to-noise penalty that comes along with parallel imaging canbe, at least partly, offset by imaging at 3.0 T. In theory, thetwo-fold increase in SNR moving from 1.5 to 3.0 T cancompensate the signal loss imposed by an accelerationfactor of 4. This means that, maintaining the SNR ofimaging at 1.5 T, a four-fold increase in acquisition speedcan be realized at 3.0 T. However, the signal gain from3.0 T may also be used to further enhance the imageresolution or reduce the amount of contrast agent used.Generally, almost the same amount of contrast agent isused for whole-body MR angiography compared to state-of-the-art examinations focused on only one body region.Therefore, whole-body angiography can be considered asutilizing the applied contrast bolus more efficiently. Withthe recently claimed association of gadolinium administrationwith nephrogenic systemic fibrosis (NSF)-a severe andpotentially lethal disease encountered in patients with

reduced renal function-a minimization of the gadoliniumdose seems to be advisable [24]. MR angiography at 3.0 Tcould potentially reduce the amount of contrast agent applied,while maintaining high diagnostic image quality.

This review article focuses on relevant new technicalconcepts and describes clinical applications of state-of-theart whole-body MR angiography.

Whole body MR angiography

In the past years, patients and primary care physicians haveincreasingly recognized the clinical burden of athero-sclerotic disease [25, 26]. As new advances in the treatmentcontinue to reduce mortality and morbidity, patients andphysicians will increasingly confront the problem ofconcomitant arterial and end-organ disease, remote fromthe presently symptomatic region. Therefore, treatmentstrategies that include surgical and percutaneous catheter-based interventions, as well as pharmacological treatment,necessitate an accurate assessment of all atheroscleroticmanifestations with respect to the location, extent, andseverity of arterial involvement [27–28]. Although multi-modal whole-body cardiovascular imaging was performedmany years ago by several institutions [29, 30], up to now thediagnostic approach to atherosclerosis has predominantlyremained locally focused on the symptomatic clinicalproblem. This is mainly due to limitations that are inherentto the selected imaging techniques, risks associated withinvasive procedures, contrast and radiation-dose limitationsas well as monetary and time constraints. Recently, whole-body examination protocols were introduced [14, 15, 31, 32]using MRI for the assessment of nearly all vascular regionsof the body.

‘Competing’ modalities such as digital subtractionangiography (DSA), which is still considered the goldstandard for regional examinations, or multi-slicecomputerized tomography (CT) imaging provide highspatially resolved datasets. Especially the quality ofmulti-slice CT imaging is continuously increasing dueto data acquisition with up to 64-detector rows simul-taneously, faster gantry rotation, or using two separateradiation sources (dual-source CT). Isotropic voxel sizesof up to 0.6×0.6×0.6 mm3 can be achieved with modernCT scanners.

This underscores the necessity to provide high spatiallyresolved 3D data sets with MR angiography, although theformer modalities use ionizing radiation and may not besuited for whole-body applications.

MR angiography at 1.5 T, using dedicated surface coilsand parallel imaging, provides in-plane resolutions ofabout 1.2×1.2 mm2, with a slice thickness often exceeding1.5 mm, impeding the depiction of fine anatomicalstructures and subtle pathological changes in small vessels.Previous phantom studies have suggested that, in order toreliably detect and grade stenoses, spatial resolution should

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be high enough so that the size of the vessel examinedincludes at least three pixels in-plane [33, 34]. For the renalarteries, for instance, this would result in an in-planeresolution of at least 0.8×0.8 mm2 with a similar slicethickness.

Additionally to the prerequisites mentioned above, fastdata acquisition is also mandatory in order to comply withpatients’ breath-hold capabilities when imaging thoracic orabdominal vessels [35, 36]. Recent technical developmentsin combination with higher field strength imaging allowsfor these demands to be met with the acquisition ofisotropic, sub-millimeter MR angiographic datasets in 20 sor less.

Technical considerations

Multi-coil technology and parallel imaging

The introduction of surface array coils in addition toadvances in parallel imaging has significantly improvedMR imaging techniques. Newly designed coils normallycomprise several small coil elements arranged in an arrayor matrix-like structure. Compared to applications using

the integrated body coil, this results in improved SNR andflexible parallel imaging capabilities, both being mandatoryfor high imaging quality, high spatial resolution and fast dataacquisition [37–39].

The general idea behind parallel imaging is to acquireimage data simultaneously by two or more receiver coilswith different spatial sensitivities. Reducing the linesampling density of k-space by a certain factor (typically2 or 3) leads to a reduction in acquisition time by the samefactor as well as an image with a reduced field of view inthe phase-encoding direction. However, by using thecomplementary data from different receiver coils, the‘missing’ lines in k-space can be calculated during imagereconstruction. Generally, the signal-to-noise ratio (SNR)in parallel acquisition techniques is decreased compared toacquisitions with the full k-space data. Additionally,parallel imaging techniques suffer an SNR penalty due tothe applied reconstruction schemes: this effect mainlydepends on the efficacy of the geometry of the coildistribution and is represented by the so-called ‘geometryfactor’ g [40]. As a result, appropriately designed coilarrays with better sensitivity profiles will improve theoverall SNR and the efficiency of parallel imaging and willresult in higher spatial resolution [38].

Fig. 1 Four sequential stationswere used for whole-body MRangiography

Table 1 Typical sequence parameters for multi-station whole-body CE-MRA at 3.0 T

Station Head/neck Chest/abdomen Pelvis/thighs Calves

TR/ TE [ms] 2.9/1.2 3.0/1.2 3.0/1.2 3.3/1.4

Flip angle [°] 25 25 25 25

Bandwidth [Hz/Px] 670 670 670 650

Field of view (mm2) 460×358 460×382 460×382 400×360

Matrix 576×358 576×384 576×384 640×449

Partitions* 80 (80%) 80 (80%) 80 (65%) 88 (75%)

Acquired voxel size (mm) 1.0×0.8×1.0 1.0×0.8×1.0 1.0×0.8×1.0 0.8×0.6×0.8

Parallel acquisition** GRAPPA × 3 GRAPPA ×3 GRAPPA ×4 GRAPPA ×4

Centric reordering (time to k-space center) [s] 5.0 5.0 2.0 2.0

Scan time (s) 18 19 13 20

*The value in the parentheses is the resolution in the slice direction**GRAPPA was applied in the left-to-right phase-encoding direction; 24 reference linesAn asymmetric k-space sampling scheme (partial Fourier 80%) and zero interpolation were applied along all three axes (kx, ky, kz)

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The obvious advantage of parallel imaging is theacceleration of data acquisition due to the reduced numberof phase-encoding lines. This can be used to decrease theoverall examination time and/or increase spatial resolution,and therefore improve examination efficiency.

Higher magnetic field (3.0 T)

Recent hardware developments have led to MR scannerswith faster gradients, higher magnetic field strengths, up to32 parallel receiver channels and dedicated coil systems.State-of-the-art gradients now achieve a gradient strength ofup to 45 mT/m and a slew rate of 200 mT/m per millisecondin each spatial direction. Strong gradient systems allow forultra-fast repetition times (TR) of less than 2 ms. MRangiographic techniques benefit from the shorter repetitiontime with reduced spin dephasing. However, fast gradientswitching may exceed stimulation limits, and therefore a TRon the order of 2.0–2.5 ms is frequently chosen.

One of the main determinants of SNR is the staticmagnetic field strength (B0) [41] Theoretically, imaging at3.0 T leads to a two-fold increase in SNR compared to1.5 T as the signal increases with B2

0 , whereas noisecontributions are linearly dependent on magnetic field

strength. Hence, MR imaging at 3.0 T holds the promise toovercome some of the SNR limitations, especially fortechniques with borderline SNR at 1.5 T (e.g., myocardialperfusion or myocardial viability imaging). The higherSNR at 3.0 T can also be used to increase the spatialresolution and/or reduce imaging time by means of parallelimaging, which means undersampling of k-space inconjunction with multi-element coils for spatially resolvedsignal detection [40, 42]. The increased speed andefficiency associated with parallel MRI may be convertedinto extra diagnostic value for high-field cardiovascularMRI in various ways, including enhancing image qualityand overcoming physiological (RF power deposition,peripheral nerve stimulation, acoustic noise) and physical(gradient switching rate dB/dt) constraints [43]. In addition,it has been predicted that high field strengthsmay also reducenoise amplification in parallel imaging techniques [44, 45].

The longitudinal relaxation times T1 of most tissues aresignificantly longer at higher field strength. Changes in T1

relaxation times at 3.0 T range between 5% for skeletalmuscle and nearly 40% for white matter in the brain andliver parenchyma [46]. This leads to improved backgroundsuppression [47] since the relaxivity of most paramagneticcontrast media (e.g., Gd-DTPA) in blood remains nearlyunchanged [48].

Fig. 2 a A 51-year-old malepatient with bilateral claudica-tion (thigh type) without evidentstenosis in Doppler ultrasoundexamination. Accessory renalartery supplying the lower poleof the left kidney. High-gradestenosis at the branching of theaccessory artery (white arrow).Double right-sided renal artery,which shows an early branching(1.2 cm distal of the ostium,arrowhead). Irregular vesselwall of distal superficial femoralarteries without hemodynami-cally relevant stenosis. Highbranching of the right anteriortibial artery as normal anatomicvariation (curved arrow). b En-larged view showing the renalarteries of the patient in a,showing the high-grade stenosisat the branching of the accessoryartery supplying the left lowerpole (white arrow). The renalpelvis is already filled withcontrast agent from the previoustiming bolus (asterisks)

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In the range of clinically used field strengths, however,SAR roughly increases quadratically with field strengthSAR1B2

0

� �. Therefore, the SAR at 3.0 T is about four

times higher when compared with that of 1.5 T. This canbecome a limiting factor especially when high-performancesequences such as fast 3D gradient-recalled-echo (GRE)techniques are used. Compromises (e.g., decreasing the flipangle or increasing the RF pulse duration) have to bemade tocomply with the safety regulations. Alternatively, thecombination with parallel imaging techniques reducesenergy deposition in the patient and may help to reduce theSAR. This means by using parallel imaging short TRstogether with high flip angles can be achieved, which isessential for high-resolution imaging.

Further expected problems for large FOV imaging at3.0 T include radiofrequency (RF) non-uniformity andmagnetic susceptibility effects. These factors may result inregional shading and focal T2*-induced signal loss,respectively. Thus, signal losses caused by T2* dephasingwere an initial concern for 3.0-T contrast-enhanced MRangiography. Although no data are available investigatingT2* effects for abdominal imaging at higher field strength,it was reported that signal losses from T2* dephasingappear to be comparable to 1.5 T [49]. In our experience,using a somewhat lower injection rate of approximately1.0–1.2 ml/s, in order to keep the gadolinium concentrationin the blood relatively low, we did not observe any effectsrelated to T2* dephasing at 3.0 T, which compromisedimage quality.

A further potential source of reduced image quality isdiminished RF penetration at higher field strengths, whichmight cause an inhomogeneous RF transmit field (B1

field), and as a result leads to location-dependent flipangles and receiver-coil sensitivities. In our initial experi-ence at 3.0 T, magnetic susceptibility effects were notsignificantly limiting, likely due to the short TE (1.1 ms)employed in the contrast-enhanced MR angiographysequence. We have, however, observed some artifactualsignal loss in the proximal part of the left femoral artery(imaging station III) in a subset of subjects. This is mostlikely due to dielectric resonance and radiofrequency eddycurrents, which resulted in local B1-field variations. Thiseffect seems more pronounced when, due to SAR limits, alow flip angle has to be used in the GRE sequence. Furtheroptimization of the present transmit coil system mayovercome these technical challenges in the future.Furthermore, utilization of B1 insensitive RF pulses (e.g.,adiabatic pulses) [50] or application of dielectric pads canbe beneficial to increase the signal homogeneity of theacquired images.

Intravascular contrast agents and injection protocol

Application of new contrast materials may prove beneficialto increase the performance of whole-bodyMR angiography

applications. The use of contrast agents with higher concen-tration or compounds with higher T1 relaxivity representsanother strategy to raise the baseline SNR [51, 52]. Since thelongitudinal relaxation time (T1) of unenhanced blood andbackground tissue increases with the field strength, thesensitivity to the injected gadolinium agents is heightened at

Fig. 3 Inverted MIP of a44-year-old male patient withclaudication of the left leg. Ahemodynamically significantband-like stenosis is evident inthe left common iliac artery(black arrow). Hypoplastic rightvertebral artery (black arrowhead)

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3.0 T [53]. This in turn can be translated to faster acquisitiontime and higher spatial resolution data sets throughout thewhole body.

Initially, whole-body MR examinations were conductedwith a single biphasic protocol for contrast injection andsuccessive image acquisition from head to foot. However,especially when using whole-body protocols with lowparallel imaging factors, the assessment of smaller sizedtrifurcation arteries in the distal station may be hamperedby venous contamination, as has been reported in several

studies [13, 12]. Also due to rapid transit time andbidirectional blood flow between the carotid arteries anddescending aorta, venous contamination of renal arteriesmay result when the acquisition of the head-neck station issuccessively followed by the data collection for thethoraco-abdominal station in single contrast injectionprotocols. The optimal timing between carotid arteriesand renal arteries differs merely by 3–4 seconds [54, 55].

A two-step contrast injection strategy such as a hybriddual-acquisition protocol has been used successfully for

Fig. 4 a Several coronal MPRs of a 53-year-old male patient withclaudication of both legs (Fontaine stage IIb). b Inverted MIP of thesame patient as in a. Status post bilateral stent placement in iliacarteries several years ago (black arrows). Hemodynamic relevantplaque stenosis in the right common iliac artery (curved arrow).

Also, a stenosis at the branching of the left superficial femoral artery(approximately 70% luminal narrowing, small arrowhead) and leftpopliteal artery (approximately 70% luminal narrowing, largearrowhead) can be appreciated

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lower extremity MR angiography [56]. The same techniquecan be easily applied to a whole-body contrast-enhancedMR angiography procedure. This is facilitated by the multi-coil technology with flexible coil arrangement and a widerange of table movement, which enables the imaging ofdifferent vascular territories in a deliberate order. Severalinstitutions prefer the acquisition of station I followed bystation IV in the first contrast injection [14, 57], resulting inoptimal image quality of the calf vessels. However,acquiring the abdominal/pelvic station after a secondinjection poses several problems. The abdominal/pelvicstation is usually prone to low SNR, not only in obesepatients, and may be further compromised by residualcontrast agent in the vessels as well as artifacts arising frominsufficient subtraction of enhancing structures (e.g., renalpelvis and ureter). Therefore, other groups [18, 15] preferthe acquisition of station II, III and IV with the first contrastinjection. All the more as the quality of the lower legstation was shown not to be significantly reduced [18, 15].

In summary, implementing a refined imaging protocol,using a hybrid dual-acquisition, combined with different

k-space trajectory schemes, has the potential to enhance theperformance of whole-body contrast-enhanced MR angi-ography protocols, in terms of diagnostic image quality andminimal venous contamination [58, 15].

Examination protocol for whole-body MRA at 3.0 T

At most institutions whole-body MR angiography studiesare performed using a 32-channel MR system with highgradient performance (amplitude: 45 mT/m, slew rate:200 mT/m/ms). The angiography stations comprise: (1)head-neck-upper chest, (2) lower chest-abdomen-pelvis, (3)pelvis-thighs, and (4) calves-feet, where the z-displacement,Dz, between adjacent stations was 450mm, having a field-of-view of 480–500 mm (Fig. 1). This setting results inmaximum cranio-caudal (z) coverage of 1,850 mm, whichobviates the need for subject repositioning in most of thepatients.

The contrast injection protocol consists of a hybrid two-step injection protocol. The initial timing measurement

Fig. 5 a A 55-year-old male patient with known infrarenal aorticaneurysm. Size of the infrarenal abdominal aortic aneurysm (curvedarrow) was 3×4.4 cm, reaching about 1.8 cm above the bifurcation.Additionally, an accessory renal artery supplying the right kidneywas demonstrated (black arrow). Irregular vessel wall in femoral

arteries bilaterally, without significant stenosis of the vessel lumen.b Same patient as in a. Presented are inverted MIPs of theabdominal/pelvic station (lateral view, 40° left anterior oblique andanterior-posterior projection). The excentric infrarenal AAA can beappreciated (curved arrows)

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involves a single injection of 2ml of contrast at 1.0–1.2 ml/s,followed by 30-ml saline flush, using an automated powerinjector. Arrival of the timing bolus in the ascending aorta ismonitored in real-time. Following the timing measurements,the MR angiography is performed using a total dose of0.2 mmol/kg of Gd. The contrast agent is infused in twoseparate injections at a rate of 1.0–1.2ml/s followed by 30mlof saline at the same injection speed.

‘Mask’ images are acquired at each station prior tocontrast infusion and MRA. Following the first contrastinjection (60–70% of contrast volume), stations II, III, andIV are acquired. Mask images of station I are recordedprior to the second contrast injection, after which station Iis measured. The phase-encoding order differs betweenstation I and II, and station III and IV, in order to ensureoptimal timing for the arterial vessel segments. The timeto k-space center (which determines the image contrast) is5 s for station I and II and approximately 2 s for stationsIII and IV. Subjects are instructed to hold their breathduring acquisition of stations I and II. Table 1 showstypical sequence parameters used at our institution inclinical protocols for whole-body contrast-enhancedMRA at 3.0 T.

For 1.5-T protocols, usually the GRAPPA parametersare set to an acceleration factor of two in all four stations.These protocols yield stable results in terms of image

quality and spatial-resolution with voxel sizes raging in theorder of 1.5 mm3 throughout the whole body [14, 15, 57].

The increased SNR at 3.0 T allows for even higheracceleration factors (GRAPPA ×3 or 4). Using higheracceleration factors and decreased minimum scan time hasresulted in acquisition of isotropic high spatial-resolution3D data sets with voxel sizes of less than 1 mm3 throughoutthe whole body without prolongation of scan time andcompromising image quality [58]. In contrast to 1.5 T,having nearly identical anatomical coverage and acquisitiontimes, MR angiography at 3.0 T has resulted in significantimprovements in spatial resolution. The acquired voxel sizecould be decreased by 50–70% compared to values that canbe achieved at 1.5 T.

For the distal runoff vessels (calves’ feet), usually themost problematic region in whole-body MR angiographyprotocols, a matrix of 640 or higher is used in readoutdirection. In combination with an acceleration factor offour, imaging time is not substantially prolonged, yieldingan improved spatial resolution with voxel sizes of up to0.8×0.6×0.8 mm3. This may increase the diagnosticaccuracy for the assessment of the infra-popliteal vessels,including the pedal arteries. The increased spatial resolutionreflects an improvement in voxel volume by about 75%(0.38 mm3 versus 1.5 mm3) in comparison to current state-of-the-art 1.5-T whole body protocols.

Fig. 6 a A 42-year-old female patient with history of Takayasuarteriitis. The inverted MIP shows an infrarenal occlusion of theabdominal aorta (Leriche syndrome) (black arrow). Large collateralssupplying the lower extremities (arrowhead). b Same patient as in a.The first and second station are shown in volume-rendering

technique (VRT). Besides the infrarenal occlusion of the abdominalaorta (right image, white arrow), a proximal occlusion of the leftsubclavian artery (subclavian steal syndrome) could be demonstra-ted (left image, white arrowhead)

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Application of whole-body contrast-enhanced MRangiography at 3.0 T

Whole body MR angiographic examinations are mainlyperformed in patients with atherosclerosis to simultaneous-ly assess all vascular regions (except coronary arteries) ofthe body (Figs. 2, 3 and 4). In these patients MRangiography may be combined with the assessment ofheart and brain in order to provide a comprehensive examof the predilection organs of atherosclerotic disease.

Although in most patients with long-standing or uncon-trolled diabetes mellitus small-vessel disease is the leadingpathologic entity, macro-vascular manifestations of the lowerleg arteries are also of concern and are regularly assessed inour department by MR angiography. Whole-body MRangiography at 3.0 T can provide high-resolution imageswith the same amount of contrast agent as compared to adedicated scan of the lower leg arteries. This results in datafromother vascular territories ‘for free’without any additionalexamination or contrast application with almost identicalimage quality. Furthermore, a subgroup of our patients withdiabetes suffered an episode of myocardial infarction, whichmay be clinically not evident due to associated neuropathy. Acomprehensive examination protocol may assess cardiacfunction andmyocardial viability in these patients to optimizemedical or interventional therapy.

Other patients who may profit from whole-body MRangiography are patients with AAA (Fig. 5) or systemicvascular disease such as, e.g., Takayasu arteriitis (Fig. 6).Hallmark of the disease is the inflammation of the vesselwall of large arteries, which regularly causes stenoses of

the large vessels, predominantly of thoracic and supra-aortic vessels, in these patients. MR angiography helps tofollow-up patients and guide appropriate therapy.

Summary and future directions

In conclusion, using multi-coil technology in combina-tion with multi-channel RF systems, whole body MRangiography appears promising at 3.0 T. Effectiveimplementation of high-acceleration parallel acquisitionand adapted contrast injection protocols increasedspatial resolution and resulted in acquisition of isotropicsub-millimeter data sets. The procedure is feasible andconvenient for both the patient and technician, eliminat-ing the need for coil or patient repositioning. Never-theless, more extensive clinical testing is warranted toexplore the boundaries and limitations of the whole-body approach at 3.0 T.

Novel techniques such as, e.g., total imaging matrix withcontinuous table movement (Tim CT, Siemens MedicalSolutions, Erlangen, Germany), are presently implementedon 1.5-T scanners. This technique provides seamless 3Ddata from head to toe with continuous table movement.However, currently the spatial resolution is limited to about1.5×1.5 mm in-plane due to technical restrictions. As soonas these principal limitations have been overcome, thetechnique will benefit from higher field-strength imaging,exactly the same as the presented multi-station approach.

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