4D Flow Quantification with MRI

Measurement of intra-cardiac blood flow, flow velocities, abnormal flow in
terms of valvular regurgitation or shunting, and flow-based estimation of
intra-cardiac pressures are essential in the therapeutic management of patients
with congenital and acquired heart disease. While direct intra-cardiac
measurement of these parameters are considered as gold standard, in clinical
practice non-invasive echocardiography with Doppler is preferred, particularly
for repetitive measurements and follow-up. It is safe, portable, readily
available, and is easy to perform. Echocardiography has practical limitations.
It does not directly measure total blood flow, image quality depends on the
experience of the operator and the acoustic accessibility of the patient, and
some valves are difficult to assess by position (pulmonary valve) or the
presence of foreign material (percutaneous valve implantations).
Cardiac magnetic resonance (CMR) has a growing role in the field of
intra-cardiac blood flow measurements, particularly in adult congenital heart
disease (ACHD). Cardiovascular MR flow is nowadays assessed with
two-dimensional phase-contrast sequence (2D PC) which allows accurate
assessment of total transvalvular flow, regurgitant fractions, regurgitant
volumes and shunt calculations. However, an MRI generally consists of a series
of sequential scans, each relying on images from previous acquisitions. Not
only is this time consuming, but also it is dependent on technician*s
experience and often require direct supervision during planning by an
experienced cardiovascular radiologist .This is particularly true in patients
with congenital heart disease with complex and varied native and postsurgical
anatomy. In addition, flow quantification is limited to the vessels targeted
during the scan. Several factors can influence the accuracy of flow
quantification, including the presence of complex flow and eddy-current phase
offsets. With 2D PC , to measure blood flow in multiple vessels , multiple
oblique plans have to be prescribed, which may lead to spatial aliasing,
causing abrupt phase discontinuities in the images .
4D Flow is the new MR technique that might overcome these disadvantages. It
allows scanning of the entire chest in approximately 7 minutes (depending on
field of view, heart rate and resolution). The images may be reconstructed in
any plane, avoiding the need to precisely defined cross-sectional planes during
acquisition for each vessel. Occult jets or dynamic jets are easier detected.
Also it does not require from the technician special knowledge of the complex
anatomy. As opposed to 2D PC, there is no additional scan time required to
evaluate other vessels in the imaging volume. With a volumetric data
acquisition, spatial aliasing is easier to avoid, and thus eddy current
correction can be more easily performed. Recently, arterial flow
quantification has been shown to be more accurate and precise with 4DPC than
2DPC in congenital heart diseases. Ultimately, total examination could be
shortened because all needed information (both contractile function and flow)
is acquired in approximately 7 minutes. This will be an important improvement
for patient comfort, special for patients with structural heart disease that
have difficulties with breath holding and lying still in the magnet. This
sequence does not require breath-holding. The only disadvantage for the moment
is that the temporal resolution is lower than 2D PC which may affect accurate
measurement of short lasting, high-velocity jets.

4D Flow in children with congenital, structural heart disease
Common protocols for the assessment of 2D flow in current clinical practice
include atrioventricular valve planes, semilunar valve planes and large
vessels. It is not uncommon in clinical practice to perform up to 6 or 8 2D
flow measurements in a single study in a patient. A single 4D acquisition of
flow encompassing flow in the heart and large vessels may be faster and more
accurate and reproducible than traditional 2D flow measurements. This may
results in important reductions of scan time, which is particularly important
in children.
Preliminary studies have demonstrated that 4D Flow can better identify
pulmonary and tricuspid insufficiency than echography and intracardiac shunts
(ASD, patent foramen ovale, aortic baffle leak, VSD patch leak), some of which
were not identified on 2D MR (1).
MR imaging is considered a safe imaging technique, that is clinically used in
children. Cardiac MR is well established in the clinical care of children with
congenital heart disease at the Erasmus MC. The generation R population study
illustrates that children tolerate MRI examinations well, also in the context
of research. The sequence that we will investigate has been safely used at the
Stanford University for more than 10 years, both in adults and children.
We will explain to the child and parents in an age-appropriate manner about the
sequence and ask the child if he volunteers at the end of the clinical
examination to lie in the magnet for 7 more minutes. The environment will be
child friendly. Because it does not require breath-holding, the child can relax
and listen to his favorite music.

Primary Objective:
• Intracardiac blood total flow and maximum flow velocity measured by 4D MR,
and compared with 2D MR.
Secondary Objective(s):
• Intracardiac pressures as assessed by 4D MR , compared with 2D MR, invasive
catheterization and echography.
• Intracardiac shunting as assessed by 4D MR, compared with 2D MR, invasive
catheterization and echography.

Prospective explorative study to assess intra-cardiac blood flow velocities
using 4D MR. Comparative data will be used for technical validation: 2D MR,
echocardiography, and invasive measurements, where they are available. The
expected study duration is 12-18 months.

There are no additional risk for the participating patient. The sequence adds 7
minutes to the total duration of the scan.