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Magnetic Resonance Angiography 115
or turbulent flow, inappropriate slice thickness, and/or
inadequate time for the signal repetition (TR) all have an
impact on signal characteristics, and thus may mimic vascular pathology. TOF venography uses 2 D sequential plane
imaging as this is more sensitive to slow flow compared to
3D acquisition.
Phase-contrast Magnetic Resonance Angiography
Flow velocity is the decisive factor of this technique that
requires data acquisition with and without flow encoding
in three different planes with subsequent image subtraction. Thus complete background suppression is achieved,
superior to TOF MRA. Yet, acquisition time as compared
with TOF MRA is increased by up to four times, because
flow encoding can only be performed along one axis at a
time. Attention has to be paid to the velocity encoding
(VENC) gradient as a VENC mismatch to the true velocity
might lead to image artifacts, which may mimic stenosis.
Contrast-enhanced 3D Magnetic Resonance
Angiography
This technique requires intravenous gadolinium administration for vessel visualization, as the signal is based on the
intravascular T1-shortening effect of gadolinium. A short
TR is chosen, as well as short scan time to allow for breathhold imaging. These prerequisites are met when a FLASH
technique is applied, spoiling residual transverse magnetization subsequent to signal read out. To optimize signal
intensity, proper bolus timing is essential, either by measuring circulation times beforehand or applying care bolus
techniques.AscomparedwithTOFandPCMRA,image
artifacts are reduced, in-plane (= longitudinal) vessel
imaging (large field-of-view) and dynamic imaging techniques are possible. Special focus on k-space data collection can help increase the signal-to-noise ratio, as the
contrast information is located in the k-space center; this
informationshouldbereadoutearlywhenmaximum
intravascular bolus concentration is given (Klingebiel et
al. 2007, Zhang et al. 2007). Comparable sensitivity and
specificity values have been reported for ce 3D MRA and
DSA for assessment of stenoocclusive disease of the supraaortic arteries including the circle of Willis (Willinek et al.
2005). Compared with precontrast 3D TOF MRA, postcontrast 3D TOF MRA has also been shown to improve the
assessment of intracranial vessel patency in acute stroke
despite the potential pitfall caused by enhancement from
tissue and venous structures (Yang et al. 2002).
With the introduction of parallel imaging, a recently
developed family of techniques that takes advantage of
the spatial information inherent in phased-array radiofrequency coils, reduction in acquisition times and improvements in spatial resolution have become possible (Glockner et al. 2005, Zhang et al. 2007). A comparable image
quality to CT angiography and DSA (for detection of arterial
stenoses), by using a highly accelerated parallel acquisi-
tionina3Tesla(T)scannerhasrecentlybeendescribed
(Nael et al. 2007). Although these techniques are already
commercially available from different manufacturers and
suppliers, and will most likely become part of standard
clinical practice, they are usually restricted to MRI referral
centers at present. A reduction to 2 minutes of scan time
for 3D TOF MRA by using parallel imaging in a 3 T scanner
has been reported to provide comparable image and spatial resolution as standard 3D TOF MRA in a 1.5 T scanner,
whichusuallyrequires6to8minutesofscantime.
Strengths and Disadvantages
TOF and PC MRA have the advantage that administration of
contrast medium can be avoided and this could be of
benefit in pregnancy or during breastfeeding. In fact, recent evidence suggests that there is no detrimental effect
on the fetus following maternal gadolinium administration. Only tiny amounts of gadolinium-based contrast medium given to a lactating mother reach the milk, and only a
minute proportion entering the baby’sgutisabsorbed.The
very small potential risk associated with absorption of
contrast medium may be considered insufficient even to
warrant stopping breastfeeding for 24 hours (Webb et al.
2005). Nevertheless ce MRA may not be considered a safe
alternative for CT/CTA in patients with impaired kidney
function because acute renal failure (Ergun et al. 2006) as
well as nephrogenic systemic fibrosis may be induced
(Broome et al. 2007, Thomsen 2006).
An inherent advantage of MRA, as compared with the
competingangiographic techniques, isthat inMRA thereis
no exposure to ionizing radiation, which is particularly
important in pregnancy and early childhood. With respect
to emergency imaging studies, such as for acute stroke,
intracranial MRA acquisition time (about 6 minutes) is
significantly higher than cervico-cranial multislice CTA
by a 64-slice scanner (6 seconds), potentially obscuring
image quality due to motion artifacts in noncompliant
patients.
Electronically, magnetically, and mechanically activated
implants, electronically operated devices such as defibrillators and cardiac pacemakers, and ferromagnetic foreign
bodies if not encapsulated subcutaneously by fibrous tissue are considered to be absolute contraindications to MRI
scanning. Yet, recent studies indicate that MRI can potentially be safely performed in patients with selected implantable pacemaker and defibrillator systems given appropriate precautions(Rognin et al. 2008). Relative contraindications are cochlear implants, noncardiac pacemakers
(e. g., nerve stimulators or insulin pumps). Lead wires pose
a risk because of the potential of current induction in a
powerful magnetic field. Most prosthetic heart valves are
exposed to a higher stress by cardiac hemodynamics than
exerted by the MR scanner. Osteosynthesis material is
usually anchored, but might cause heating through induction and image quality may be severely degraded. The
majority of other metallic implants such as surgical clips
6 Angiographic Techniques in Neuroradiology116
do not represent a hazard. Nevertheless in any individual
case, the patient has to be thoroughly investigated with
respect to these contraindications. Vascular stents, commonly encountered nowadays in older patients, have been
shown to suffer from deflection forces that may exceed
safety limits in high-field scanners in an experimental
setting (Shellock 2002). Yet, in patients who are scheduled
forMRIseveralweeksafterstentangioplasty,endothelial
overgrowth of the implant device makes stent displacement very unlikely. Tattoos and, as quite recently encountered in our department, permanent makeup, even without iron constituents, maycause skin burns and the patient
should be informed accordingly (Franiel et al. 2006).
Disadvantages of TOF MRA are limited spatial resolution
and the exaggeration of the degree of stenosis as the flow
within the vessel and not the vessel diameter itself defines
the signal. As a hemodynamically relevant vessel stenosis
seems more pronounced on TOF images, this technique
provides a high sensitivity for stenosis detection, but not
yet for grading. TOF MRA is inappropriate for differentiating a high-grade stenosis or near occlusion from an occlusion. 3D TOF MRA also is inappropriate for aneurysm detection, as turbulent intraaneurysmal flow may obscure
the pathology. Nevertheless, 3D TOF MRA as well as ce 3D
MRA may be expected to closely approximate multislice
CTA in terms of spatial resolution when using advanced
MR techniques, suchas parallelimaging, and will thusgain
increasing importance when assessing patients in whom
mid-sized and smaller vessels are of interest.
2 D TOF is a technique that has been widely used for
ruling out dural sinus venous thrombosis, but inherently
suffers from image artifacts that may simulate the pathology and therefore ought to be phased out (Ayanzen et al.
2000). For these reasons, 2 D TOF venography has been
widely replaced by contrast-enhanced venography (Klingebiel et al. 2007).
Cross-sectional MR images (for detecting intramural
hematoma) together with cc MR images (for detecting
intramural hematoma) is a proven modality when internal
carotid artery (ICA) and/or vertebral artery dissection is
presumed. Due to its technique, including image subtraction, vascular pathology close to the skull is easily depicted
without interference with osseous structures as in unsubtracted CTA.
Computed Tomographic Angiography
Historical Development
Computed tomography is a technique that uses X-rays to
generate cross-sectional images derived from serial and
digitally processed images taken around a single axis of
rotation. The Greek words “tomos” (slice) and “graphein”
(to write) represent the term’s origin.
X-rays are emitted through the body plane and the
difference between emitted signal intensity and intensity
measured by the detector elucidates the attenuation char-
acteristics within the body plane of interest. In order to
reconstruct the image, an inversion of the radon transformation is used. G. Hounsfield was awarded a Nobel
Prize in 1979 for his work on several prototypes of CT
scanners (Ambrose and Hounsfield 1973) together with
A.M. Cormack, a physicist. The first CT studies in humans
were performed in 1971.
Subsequenttechnicalimprovements led to several scanner generations, with the introduction of multislice CT
(MSCT) in 1999 as one of the milestones in the history of
CT (Hu 1999). Although CT applications for assessing intracranial vascular pathology have been described as early as
1976 (Michels et al. 1977, Solis et al. 1976), it was not until
the introduction of helical CT (also called “spiral”) in 1990
by W. Kalendar that this technique was considered an
alternative for conventional angiography in selected cases
(Kalender and Polacin 1991, Napel et al. 1992).
Technical Aspects
Until the introduction of MSCT into clinical imaging, comprehensive cervico-cranial (cc) vascular imaging by helical
CT was limited by the heat-load capacity of the X-ray tube
as well as radiation exposure issues. The introduction of
MSCT not only meant 4, 16, 32, 64 up to 320-row-scanners
instead of just one row, but was also associated with an
increased rotational speed (0.35–0.5 s/rotation) and an
increase in heat-load capacity. Taken together these qualities permit comprehensive high-resolution cc vascular
assessment starting from the aortic arch up to the superior
sagittal sinus (Klingebiel et al. 2001, Klingebiel et al. 2002).
Almost simultaneously, workstations for post-processing
of the high-image-load delivered by MSCT were introduced to the market. These workstations significantly facilitated 2 D as well as 3D rendering of up to about 800
slices (cc CTA),enabling meaningfulcondensation ofabundant image information into just a handful of color-coded
photo-realistic image reconstructions. Although even the
first MSCT scanner generation of the year 2000 permitted
ultimate image resolution, it was not until the introduction
of 32 and 64 slices that maximum resolution did not
necessarily result in a significant radiation exposure increase. Overbeaming and overscanning became important
keywords in the discussion of radiation exposure with
MSCT scanning. Overbeaming refers to extending the
cone beam beyond the outer borders of activated detectors
to avoid critically low doses with respect to image quality
in the detector outskirts of the detector row. In consequence, the border zone areas are redundantly exposed
causing increased radiation exposure to the patients (Tzedakis et al. 2005). Overscanning means that in order to be
able to reconstruct the images, the multislice scanner
needs an extra rotation at the start and at the end of the
helical scan. With respect to scan lengths of more than
30–35 cm such as in cc CTA, this effect is negligible. The
aspect of overbeaming is significantly reduced in 64-slice
as compared with four-slice scanners, when using the
Computed Tomographic Angiography 117
Tab l e A6 . 2 Charité Stroke imaging protocol, including unenhanced cranial CT, CT perfusion, and CTA
Parameter CCT c PCT cc CTA
kV 120 120 120
mAs 450 150 150
Pitch 0.75
FOV (mm) 240 240 240
Slice thickness (mm) 4 (basis)/ 8 32 (4× 8) 0.5
Increment (mm) 0.3
Rotation time 1.5 s/360° 1s/360° 0.5 s/360°
Scan area Standard Lentiform nucleus Arch–vertex
Scan time (s) 50 6**–24*
Contrast medium (mL) 50 80
Flow (mL/s) 5 4
c: cerebral, cc: cervico-cranial, FOV: field of view, kV: kilovolt, mAs: miliampere-second, PCT: perfusion CT, CTA: CT angiography
*16-slice scanner, **64-slice scanner
ultimate resolution; overbeaming in this case does not
happenineveryfourthslicebutinevery64thslice.This
makesMSCTscannerswithahighernumberofdetector
rows more suitable for cc CTA than the basic platform of
four-slice scanners.
The recently introduced 320-row scanner generation
provides a detector width of 160 mm instead of a maximum of 32 mm as in preceding scanner generations, thus
covering the whole brain by just one rotation in 0.5mm
thin slices. This new scanner typeis able to simultaneously
acquire and generate high-resolution whole brain perfusion data as well as time-resolved (dynamic) digital subtraction CT-angiography. Even though clinical experience
is still quite limited, a significant impact of 320-row scanners on stroke patient care can be predicted due to its 4D
imaging (volume and time resolution) capability.
The Charité University Hospital protocol for cc CTA is
shown in Tab l e A6. 2 .
After ensuring adequate intravenous access by using
18–20gaugevenouscannula,thepatientisconnectedto
a power injector. If possible, the side of minor clinical
interest should be chosen for venous access, as the high
injection pressure may push the contrast medium upward
into the cervical vessels, obscuring the contours of the
proximalICAaswellasthatoftheCCA,particularlyin
patients with venous valvular insufficiency. There are usually two ways of starting the scan: Either a low-dose,
dynamic scan is performed at the level of the ICA and the
helical scan is then initiated as soon as the operator detects
contrast medium arrival at the chosen level or a so-called
“sure start” protocol is applied; this protocol usually
means that a region-of-interest is placed into the aortic
arch or descending aorta, where a predefined density level
automatically triggers helical scan initiation. Correct ve-
nous line placement still is an important issue, although
injection velocities up to 20 mL/s, as initially required in
stroke imaging protocols (CT perfusion) (Koenig et al.
1998) are no longer applied, due to the widespread use
of deconvolution algorithms in CT perfusion imaging
(Hoeffner et al. 2004). Routinely, a total of 80 mL of contrast medium (nonionic, iodinated contrast medium, containing 370 mg/mL iodine) is administered over 20 seconds, followed by a bolus of 30 mL isotonic saline solution.
Subtraction CTA has been described recently, and will
most probably narrow the already small image quality gap
between invasive catheter angiography and multislice CTA
(MSCTA) (Tomandl et al. 2006).
Strengths and Disadvantages
Radiation exposure is a general concern with CT imaging.
In every single patient, an individual decision has to be
made by the radiologist whether the required diagnostic
information could be obtained by an alternative procedure
that is less invasive or does not involve radiation exposure.
The competing techniques of ultrasound and MRI as well
as invasive catheter angiography are available in most
major hospitals during normal office hours. Yet, the majority of stroke patients are beyond reproductive age and
are critically ill. Time-efficient, operator independent,
round the clock, comprehensive cervico-cranial vasculature assessment is required, with minimal vital parameter
monitoring as is possible. No other modality combines
these qualities, making MSCT the undisputed first line
imaging modality in stroke patients.
Given the technically correct CTA performance, high
intravascular contrast is achieved, ensuring 2D and 3D
reconstructions of unprecedented image quality. Often,
6 Angiographic Techniques in Neuroradiology118
the strikingly short data acquisition figures for comprehensive cc CTA are mentioned when time efficiency is the
issue in stroke imaging. Yet, it is common knowledge in
neuroradiology that it is not the “data acquisition time”
that is a limiting determinant but a time span better addressed as the “clinical imaging time.” The clinical imaging
time takes into consideration the image data reconstruction, transfer of up to 800 image slices, and the postprocessing before the final radiological study report can
be delivered to the referring neurologist. Thus, time effi-
ciency, in the assessment of stroke patients is not just a
matter of the number of detector rows but of appropriate
internal network structures and postprocessing facilities.
Contraindications to CTA are the same as any radiographic study requiring iodine and include impaired renal
function, hyperthyroidism, and iodine allergy. Yet, for vital
diagnostic purposes these contraindications might be
overcome by either kidney protective measures such as
intravenous fluids and/or dialysis, thyroid-blocking drugs,
or pretreatment with antihistamine drugs as well as intravenous cortisone.
Spatial resolution as well as vessel-to-background ratio
are decisive factors for delineating small vascular details in
very fine vessels. Spatial resolution with conventional,
invasive angiography and in high-resolution MSCTA is
quite similar (Fig. A6.4), ending up in 0.35 mm resolution
for CTA (smallest pixel size) as compared to approx.
0.3 mm in most conventional angiography suites using a
1024 matrix (Villablanca et al.2002).Yet,signal-to-background ratio has remained superior in DSA as compared
with CTA, making DSA indispensable in assessing smallvessel disease (Klingebiel et al. 2008, in press) such as
primary angiitis of the CNS. In a recent comparative study
of DSA and MSCTA the smallest arterial size reliably detected with MSCTA was 0.7 mm versus 0.4 mm for DSA
(Villablanca et al. 2007).
A disadvantage of MSCTA is encountered when there is
vascular pathology nearby or within the skull base, such as
with vessel dissection and/or small aneurysms. Due to
border obscurity between high intravascular density and
the adjacent high-density skull base, the automated segmentation tools which have been introduced throughout
Fig. A6.4 MSCTA without
(A)andwith(B)theintro-
duced digital subtraction
mode. MSCTA, lateral MIP
(C) and DSA, lateral projection (D). The two techniques
provide comparable vessel
information with respect to
the anterior cerebral artery
branches.
the past decade also eliminate vessel pixels together with
the target, the skull base. Recently, bone subtraction
MSCTA has been proposed (Tomandl et al. 2006), which
seems promising although complete bone removal was
achieved in only one-third of the CTA investigations.
Powerful digital subtraction will not only enable skull
base removal but improve vessel-to-background ratio in
MSCTA and thus further reduce the differences in image
quality between these techniques. In recent studies, evidence has been presented that MSCTA may be comparable
or even superior to DSA with respect to assessment of
small aneurysms (Villablanca et al. 2002).
A major advantage of high-resolution MSCTA lies in its
cross-sectional imaging character; the inadequate visualization of vessel pathology due to a limited number of
projection images, such as described in Case 14 (p. 210),
may not occur (see also Case 14, p. 210).
Preoperative evaluation of ICA stenosis remains a common indication for angiography, although the same inherent limitations of the projection technique apply. Direct
measurement of carotid stenosis, vessel wall soft tissues,
and CT plaque imaging is now possible with the highresolution anatomic data present in MSCTA, alleviating
the need for ratios and inaccurate mathematic estimations
of carotid anatomy for carotid stenosis quantification
(Bartlettetal.2007).
Oneshouldbeawarewhenchoosingapost-processing
technique for MSCTA that high-grade and/or circular vessel wall calcifications cannot be assessed by widely used
maximum intensity projection (MIP) images. Here, multiplanar and curviplanar reformatted images are indicated
and advanced vessel analysis tools allow continuous crosssection area measurements at given vessel levels.
Current Algorithm at the Charité University Hospital
A variety of different angiographic techniques based on
cross-sectional imaging (MRI/CT) as well as invasive angiography are at the disposal of the neuroradiologist. The
optimal technique for any given indication is a constantly
changing issue due to ongoing technical and scientific
advancements. Before choosing one of these techniques,
the neuroradiologist has to define the imaging focus, such
as intra- or extracranial pathology, arterial and/or venous
vasculature, detection and/or quantification of vessel
stenosis, applicable contraindications, etc.
The use of DSA studies for diagnostic purposes has dramatically declined over the past decade, down to a level,
where even in academic referral centers, resident training
is hampered. The evaluation of AVMs, presumptive cerebral vasculitis and assessment of cerebrovascular hemodynamics are generally looked on as the remaining indications for diagnostic DSA.
With respect to assessment of acute ischemia and
chronic stenoocclusive disorders, at the present time,
Current Algorithm at the Charité University Hospital 119
Fig. A6.5 320-row stroke CT. (A–B) A territorial right-sided MCA
ischemia (arrows) is depicted on the 3D-rendered lateral view (A)as
well as in the coronal reformatted slice (B). (C) Dynamic 320-row
digital subtraction CT angiography in a different patient with an
acute intracranial hemorrhage; an AVM nidus (arrows) is shown,
fed by abnormally strong right pericallosal and callosomarginal arteries and predominantly draining into the superior sagittal sinus.
CTAisthemostpowerfultoolforassessment ofccvasculature, by combining robust, rapid, and cost-efficient
round-the-clock imaging with high-resolution data acquisition, closely approximating spatial resolution of invasive angiography.
With the latest 320-row scanner generation, new stroke
imaging issues as specified above (whole brain perfusion,
dynamic CTA) have evolved, the clinical benefit of which is
currently under investigation. Yet, preliminary experience
underlines the suitability of 320-row CT to assess cerebral
hemodynamics in vascular malformations as well as for
collateral blood flow evaluation in high-grade vessel
stenosis and occlusion. Comprehensive visualisation of
brain ischemia including tissue at risk has also beenshown
whereas the sensitivity for detecting circumscribed or
lacunar infarction, especially in the posterior cerebral circulation, remains to be determined (Fig. A6.5). Thus 320row CT scan protocols are not yet part of our imaging
routine.
Stroke
Stroke MSCTA is able to address all major vessel issues in
acute cerebrovascular insufficiency, starting from embolic
or in-situ vessel stenosis/occlusion, presumptive supraaortic sources of embolism, i. e., ulcerated plaques, and
vessel wall dissection to numerous vessel variants as
well as collateral pathways (Fig. A6.6–A6.8). In contrast
6 Angiographic Techniques in Neuroradiology120
with MR and invasive angiography, CTA visualizes the
plaque nature (soft/hard), assesses the risk of embolization
(“vulnerable” plaques), permits precise stenosis grading
(Bartlettetal.2007),anddemonstrateshypoperfused
brain tissue.
Acute stroke patients presenting within the time window for systemic or intraarterial thrombolysis are predominantly assessed by unenhanced CT, MSCTA, and CT
perfusion in our institution. When lacunar infarction is
considered, or ischemia of the posterior circulation, particularly within a circumscribed brain stem or cerebellar
infarction, MRI and MRA are performed, including diffusion and perfusion protocols. When a clear lacunar infarction is depicted, MRA could beavoided as it predominantly
shows major vessel pathology.
If the posterior circulation is the region of interest, we
prefer a contrast-enhanced cc MRA, the advantage of
which is a comprehensive assessment from the aortic
arch to the anterior middle and posterior cerebral artery
circulation. Because of the large field-of-view, the detail
resolution is limited when compared to MSCTA. Nevertheless, clinically important findings, such as vertebral
artery (VA) occlusion, dissection, and smaller aneurysms,
as well as anatomic vessel variants are detected with
sufficient sensitivity and specificity. Stroke in the posterior
circulation may be caused by VA dissection, making visualization of the intramural hematoma an important issue.
MRI obliges by applying thin slice (3 mm) T1- or T2weighted images, with or without fat saturation, at the
level of interest. This algorithm applies unless acute basilar
artery occlusion is considered. These patients are either
directly transferred to the neuroangiography suite or
undergo immediate MSCTA if there is any doubt of the
diagnosis.
Both CT and MRI can comprehensively assess the cc
vasculature and provide any information necessary for
decision making and treatment planning in stroke patients. However, scanner availability, patient compliance
and safety issues as well as time- and cost-effectiveness
are all in favor of CT-based evaluation.
Intracranial Aneurysm
Although the literature still is somewhat contradictory
about the value of MSCTA in detecting small aneurysms
(< 5 mm) (Ogawa et al.1996, Villablanca etal. 2002, Yoonet
al. 2007), in our experience small and/or atypical aneurysms (i. e., mycotic aneurysms) of 2–3mm diametermay
be reliably detected, when using appropriate imaging protocols in CTA (Fig. A6.9). However, in a major referral hospital with an interventional neuroradiology service, noninvasive angiography might be bypassed in subarachnoid
hemorrhage (SAH) patients, as DSA will be preferred, either to double-check the aneurysm-negative CTA or to coil
the aneurysm(s) shown by CTA, if suitable.
When neurosurgery is involved, the diagnostic algorithm is frequently adapted to the surgeon’s needs. Under
Fig. A6.6 Various stroke-associated vascular pathologies (arrows),
depicted by multislice CTA. Curviplanar reformatted ICA images,
lateral (A) coronal (B)andaxial(C)views.A A freely floating throm-
buswiththetipinthecavernousICAsegmentisshown.B Asmall
pseudoaneurysm of the right ICA is seen in a typical location (below
the skull base).
these circumstances, MSCTA is a powerful technique for
supporting interdisciplinary case discussion and treatment planning by interactive 3D visualization of the vessel
site, for example, at a dedicated volume-rendering workstation.
TOF MRA might be used as preliminary imaging tech-
nique, if neither MSCTA nor DSA is available, but it has a
Current Algorithm at the Charité University Hospital 121
A
Fig. A6.7 Acute stroke,assessed byMSCT. (A) Whereas unenhanced
CT does not show early signs ofischemia, (B)CTA, (axial MIP) depicts
right MCA branch occlusion (arrow). (C) CT perfusion images show
increased mean transit time (MTT) (arrows), (D) without significant
limited sensitivity for aneurysm assessment due to the
previously mentioned flow artifacts.
When subarachnoid hemorrhage (SAH) is present, vasospasm is a major complication that by itself may lead to a
devastating outcome even though the cause for SAH, the
ruptured aneurysm, has been treated appropriately.
MSCTA has been shown to detect vasospasm after SAH
with accuracy equal to that of DSA (Otawara et al. 2005).
Moreover, perfusion CT provided quantitative measurements of regional flow and transit time that showed high
concordance rates with the clinical course, vasospasm
severity, and hemodynamic impairments in patients with
aneurysmal SAH (Sviri et al. 2006).
D
alterations of regional cerebral blood volume (rCBV). These findings
indicate a significant penumbra and confirm the persistent thrombotic vessel occlusion, as the target of thrombolysis.
Vasculitis
In patients with suspected inflammatory vascular disorders, such as in suspected primary angiitis of the CNS,
often indicated by otherwise unexplainable ischemic lesions with or without blood–brain barrier disruption, medium-sized and smaller peripheral vessels are of interest.
Assessment of these vessels demands the highest spatial
resolution and is one of the rare indications for invasive
diagnostic angiography. As immunosuppressive treatment
is carried out in presumptive cerebral vasculitis, for limiting further ischemic brain tissue damage, timely and comprehensive diagnostic assessment is required. In our in-
6 Angiographic Techniques in Neuroradiology122
Fig. A6.8 MSCTA, coronal MIPs. Differing degrees of collateral cir-
culation in patients with M1-MCA occlusive disease (arrows). Acute
M1-MCA occlusion with insufficient (A) and good collateral vessel
perfusion (B). C Chronic proximal MCA and ACA occlusive pathology
in moyamoya disease. Characteristic small vessel collaterization is
depicted (arrows).
Fig. A6.9 DSA (A)andMSCTA(B) comparison for aneurysm assess-
ment. Atypical presumptive mycotic aneurysm at the right-sided T-
junction level (arrows). Both techniques provide equivalent diagnostic information.
Current Algorithm at the Charité University Hospital 123
Fig. A6.10 Cerebral vas-
culitis, posteroanterior
(A)andcoronal(B, C)
projections. A DSA, left
ICA injection, shows multiple vessel irregularities
(arrows), some of which
are more pronounced on
MSCTA images (B)oreven
3D TOF MRA (C). Middle
carotid artery stenosis
seems exaggerated by
TOF MRA (C), indicating
increased stenosis sensitivity but inefficient
stenosis grading. Moreover, detail resolution
clearly is inferior to DSA
and CTA.
ments are involved such as described for tuberculosis or
syphilis. In these cases CTA (Fig. A6.10), sometimes even
3D TOF MRA, will be sufficient for disclosure of vascular
pathology.
stitution, invasive angiography is preferred over stepwise
diagnostic escalation (from MRA over CTA to DSA) in these
patients.
Even so, the sensitivity of DSA itself to establish the
diagnosis of cerebral vasculitis is limited. According to
the literature, only about one-third of cerebral angiographies show positive results in patients with histologically
proved vasculitis (Vollmer et al.1993). Yet combined with
other diagnostic tests such as CSF studies, the sensitivity of
DSA may increase up to almost 100 % (Calabrese and Duna
1995). Ultimate small-vessel delineation may not be required in secondary vasculitis, when major vessel seg-
Cerebral Venous Thrombosis
Cerebral venous thrombosis (CVT) is not an uncommon
differential diagnosis, especially in younger patients without a history of migraine who present to the emergency
room with headache of unknown origin. For these patients,oftenfemalesofchild-bearing-age,CTA,although
a powerful and rapid technique (Fig. A6.11A), is not the
desirable first line modality, becauseof radiationexposure.
In consequence, MR venography, commonly performed
as contrast-enhanced (Fig. A6.11B)or2DTOFMRA
(Fig. A6.11C), has been used throughout the past decade.
However, 2 D MR venography (MRV) has important pitfalls, because of signal artifacts induced by slow and/or
alternating flow. Sometimes, patients with a hyperintense
signal within the transverse sinus on FLAIR Fluid-Attenuated Inversion Recovery) images and a corresponding signal loss at 2 D TOF MRA are misdiagnosed as having CVT,
leading to unnecessary and potentially endangering anticoagulation treatment. In our institution, modified 3D elliptic-centric, ce MRA is routinely used for these patients
(Klingebiel et al. 2007). Thistechnique does not sufferfrom
flow-associated artifacts and closely approximates the
sensitivity and specificity of CTA as the new gold standard.
Even though CTA has proven high sensitivity for venous
assessment, unimpaired by projection technique limitation as in conventional angiography, its value for specific
subsetsofvenouspathology,suchascorticalvenous
thrombosis (Fig. A6.11D), thrombosis of the cavernous si-
6 Angiographic Techniques in Neuroradiology124
Fig. A6.11 Various venography techniques. A MSCT venography,
semitransparent 3D rendering, superoposterior view. Extended
superior sinus venous thrombosis is delineated by the tram-track
sign (arrows). B Contrast enhanced 3D GE venography (lateral MIP),
providing vessel resolution, that closely approximates that of CT
nus, and thrombosis of the internal cerebral veins remains
to be addressed by further studies (Linn 2007). It is mandatory for the neuroradiologist to be familiar with the
numerous anatomic variants present in the venous vasculature, independent of the angiographic technique applied
(Leach et al. 1996, 2006).
venography, superior to 2 D TOF MRV (lateral MIP) in the same
patient (C). D MSCT venography, semitransparent 3D rendering,
top down view. A cortical venous thrombosis (arrow) is recognizable
in this patient with circumscribed ipsilateral hemorrhage in the
frontoparietal region on unenhanced CT scans (not shown).
Peri-therapeutic Imaging
As previouslymentioned, CTA is the appropriate technique
for assessment of carotid artery bifurcation as it has been
shown to precisely support and correlate with various
grading techniques for ICA stenosis (cross-section, diameter ratios) (Bartlett et al. 2007). Delineate the vessel wall
including different plaque components and assess any
intracranial sequel of proximal ICA stenosis as well as to