Practical recommendations
M. Neuss, B. Schnackenburg
Angiography
n General problems
n Stents: No solution since stents currently
used effectively shield signal from inside the
stent lumen.
n Timing: It is possible that because of cardiovascular comorbidity not one timing suits all
patients with suspected renal artery stenosis.
Therefore, we recommend not to use a fixed
interval after the injection of contrast agent,
but to time on the fly using a 2D time resolved angio.
Aorta
The approach to imaging of the aorta critically
depends on the information available on the
suspected pathology. A suspected dissection of
the aorta requires a more sophisticated
approach than a simple follow-up of a patient
with an ectatic ascending aorta. The general recommendation given in this section is suitable
for most indications, special indications are
dealt with in an addendum.
The receiver coil to be used depends on the
expected pathology. If there is information
available from other imaging modalities that
changes are limited to the intrathoracic part of
the aorta, we use a five-element phased array
coil in a position that is suitable for a cardiac
examination. If there is more extensive involvement of the aorta, we use a four-element phased
array coil covering the thoracic and abdominal
part of the aorta. In very tall patients in which
additional information on the anatomy of the
iliac arteries is required the use of the coil system built in the magnet may be warranted.
The use of parallel imaging techniques is preferred since they reduce breathhold time or increase spatial resolution if breathhold time is
kept constant.
20 ml of contrast agent (Gd-DTPA derivate),
20 ml of saline, flow 3 ml/s in both. If extensive
aneurysm, increase amount of contrast agent to
25 ml, saline 20 ml, flow 3 ml/s in both.
n Scan procedure
1. Survey in SSFP technique, 3 stacks in transverse, sagittal, coronal orientation, 15–20
slices each, slice thickness 8–10 mm, negative
gap 1 mm.
2. Stack of transverse slices in SSFP technique
covering the area of identified pathology.
Slice thickness 8 mm, negative gap 2–4 mm.
Spatial resolution 1.5 ´ 1.5 ´ 8 mm (M/P/S).
Intrathoracic part of aorta in breathhold or
end-expiratory trigger, abdominal part of the
aorta in free breathing. If unclear pathology,
add stack of oblique sagittal slices in same
technique covering ascending aorta, arch,
and descending aorta.
3. If significant pathology or first examination
acquire proton-density weighted anatomical
images in blackblood technique with identical geometry as step 2.
4. Plan MR angiography in an orientation that
covers side branches of major interest, i.e.,
origin of supraaortic branches in thoracic
part of the aorta and abdominal branches in
abdominal part of the aorta. We use 45–55
slices in a parallel imaging contrast-enhanced
3D-T1TFE-angio technique, slice thickness
1.7–1.8 mm, matrix 352, resulting in a reconstructed voxel size of 1.1 ´ 1.1 ´ 1.7 mm
(M/P/S). For the timing of the angiography
we use a 2D time resolved angiography
started at the injection of the contrast agent.
The actual 3D angiography is started at the
moment when the contrast bolus enters the
region of interest.
5. For printouts of the angiography we reconstruct maximum intensity projections at an
angle of 3o.
n Measurements that need to be part
of the report
n Intrathoracic aorta: Aortic sinuses, proximal
ascending aorta, aortic arch, descending aorta at the level of the diaphragm, maximal diameter.
n Abdominal aorta: Diameter on the level of
the diaphragm, celiac trunc, proximal to the
iliac arteries, common iliac arteries.
If a dissection is present, identify the true and
false lumen and check for signs of complication
like pericardial or pleural effusion and perivas-
cular hematoma. Identification of true and false
lumen can usually be accomplished by acquiring
the angiography in two dynamics: the first dynamic shows a higher signal intensity in the
true lumen, the second dynamic in the false lumen. In cases of doubt use phase contrast angiography to determine flow velocity and direction. In most cases flow in true lumen is faster
and in cephalo-caudal direction. If interventional or surgical correction is planned it is important to localize communications of true and
false lumen. In many cases this can be done in
blackblood technique. If not, use 2D time resolved angiography before 3D angiography with
a contrast bolus of 3–5 ml, injection rate 2 ml/s
followed by a saline flush to localize the communication between true and false lumen.
In aneurysm of the abdominal aorta repair
with stent grafts is feasible in many patients. In
these cases the distance of the aneurysm from
the renal arteries and the diameter of the common iliac arteries need to be part of the report.
If the patient had a graft repair before and
there is suspected infection of the graft T1weighted blackblood images before and after a
single dose of contrast agent need to be compared. A sign of inflammation is contrast enhancement in the tissue surrounding the graft.
The prior implantation of stent grafts reduces
the signal from inside the stent, but in most
stents the struts are spaced wide enough to receive enough signal in spin-echo sequences and
gradient echo sequences using contrast enhancement.