Frameless multimodal image guidance of localized
convection-enhanced delivery of therapeutics in
Imramsjah M J van der Bom,1Richard P Moser,2Guanping Gao,3
Miguel Sena-Esteves,3Neil Aronin,4Matthew J Gounis1
Introduction Convection-enhanced delivery (CED) has
been shown to be an effective method of administering
macromolecular compounds into the brain that are
unable to cross the blood-brain barrier. Because the
administration is highly localized, accurate cannula
placement by minimally invasive surgery is an important
requisite. This paper reports on the use of an
angiographic c-arm system which enables truly frameless
multimodal image guidance during CED surgery.
Methods A microcannula was placed into the striatum
of five sheep under real-time fluoroscopic guidance using
imaging data previously acquired by cone beam
computed tomography (CBCT) and MRI, enabling three-
dimensional navigation. After introduction of the cannula,
high resolution CBCT was performed and registered with
MRI to confirm the position of the cannula tip and to
make adjustments as necessary. Adeno-associated viral
vector-10, designed to deliver small-hairpin micro RNA
(shRNAmir), was mixed with 2.0 mM gadolinium (Gd)
and infused at a rate of 3 ml/min for a total of 100 ml.
Upon completion, the animals were transferred to an MR
scanner to assess the approximate distribution by
measuring the volume of spread of Gd.
Results The cannula was successfully introduced under
multimodal image guidance. High resolution CBCT
enabled validation of the cannula position and Gd-
enhanced MRI after CED confirmed localized
administration of the therapy.
Conclusion A microcannula for CED was introduced into
the striatum of five sheep under multimodal image
guidance. The non-alloy 300 mm diameter cannula tip
was well visualized using CBCT, enabling confirmation of
the position of the end of the tip in the area of interest.
Recent developments in genetics and virology have
resulted in viral vectors, antibodies and immuno-
toxins showing promise as therapeutic agents for
neurodegenerative disorders such as Huntington’s
or Parkinson’s disease. Although studies have
shown their efficacy in preclinical trials, the
administration of these new therapeutic agents
remains a challenge because their macromolecular
size prevents them from crossing the blood-brain
barrier, ruling out systemic administration.1
Intrathecal administration, which is completely
driven by free diffusion, leads to non-localized
In convention-enhanced delivery (CED), thera-
peutic compounds are forced directly into the
region of interest through a needle or cannula by
applying a low pressure gradient.3e11A great
advantage of CED-based therapy is that it is not
limited by the molecular size of the compound, and
localized delivery lowers the required volume
compared with systemic administration, thus
limiting toxicity. Since CED is a localized tech-
nique, it is an important requirement that the
cannula tip is placed in the target area with a high
level of accuracy.
The placement of cannulas, probes and needles is
stereotactic surgery. These procedures are usually
planned using preoperative three-dimensional (3D)
patient image data. During the procedure a rela-
tionship is established between the image and the
patient by a surgical navigation system which
enables tracking of surgical tools relative to a fixed
reference frame usually attached to the patient.
a robust relationship between the image and the
patient has been established.12 13Although non-
invasive methods to obtain this relationship are
available, the most reliable methods include fiducial
markers or reference frames that are fixed to the
skull with surgical screws, which is itself an
Modern angiography suites are equipped with
flat panel c-arm systems that provide two-dimen-
sional (2D) x-ray imaging and also serve as an in
situ 3D cone beam CT (CBCT) system. CBCT data
are generated by a rotational sweep of the c-arm
around the subject, producing a large number of
x-ray images. Due to the advancements in flat panel
technology and reconstruction software, the image
quality is comparable to that of multidetector
CT which has enabled the use of numerous
applications.14e23Owing to the geometric calibra-
tion of the c-arm system, fluoroscopic and in situ
acquired CBCT data are coupled, enabling truly
frameless navigation. As a result, CBCT data can be
used for preoperative planning and for 3D naviga-
tion of the procedure by registration with real-time
fluoroscopy. Frameless CBCT guidance with real-
time fluoroscopy overlay has been shown to be
feasible, safe and reliable for various biopsy and
provides excellent 3D spatial information, it does
not provide sufficient soft tissue contrast to enable
1Department of Radiology,
University of Massachusetts,
2Department of Neurosurgery,
University of Massachusetts,
3Department of Microbiology
and Physiological Systems,
Gene Therapy Center, University
of Massachusetts, Worcester,
4Department of Medicine, Cell
Biology, University of
Dr Matthew Gounis,
Department of Radiology,
University of Massachusetts,
55 Lake Ave N, SA-107R,
Worcester, MA 01655, USA;
Received 21 October 2011
Accepted 22 November 2011
Published Online First
22 December 2011
J NeuroIntervent Surg 2013;5:69–72. doi:10.1136/neurintsurg-2011-01017069
accurate placement of CED devices into a specific region of the
brain. MRI accommodates such contrast, and MRI guidance
during CED-based surgery would therefore be desirable.
A study was undertaken to establish the feasibility of adeno-
associated viral vector (AAV) delivery of small-hairpin micro
huntingtin to slow or block the pathogenesis of Huntington’s
disease.29To evaluate the safety of the approach and the
distribution of AAV-shRNAmir, CED infusions into sheep
striatum were performed. In this paper we report on the use of
a commercially available truly frameless navigation module
(XperGuide, Philips Healthcare, Best, The Netherlands) that
enables multimodal image guidance during a CED procedure in
a non-invasive manner. Preoperative MRI and CBCT data were
registered with real-time fluoroscopy during minimally invasive
surgery for CED of this novel therapeutic compound into the
striatum of sheep.
knockdown of mutant
MATERIALS AND METHODS
The experiments were approved by our Institutional Animal Care
and Use Committee. As a preclinical trial, surgery was performed
in order to perform CED into the striatum of five purposely bred
sheep (mean weight 26.5 kg). The animals were anesthetized by
intramuscular injection of acepromazine (0.05 mg/kg), bupre-
norphine (0.01 mg/kg), glycopyrrolate (0.01 mg/kg) and thio-
pental (15.0 mg/kg) and intravenous injection of ketamine
(3e6 mg/kg) and diazepam (0.1e0.3 mg/kg). Anesthesia was
maintained duringthe entire procedure.Ventilationwas
performed mechanically with 2% isoflurane in oxygen. Physio-
logical monitoring including heart rate, blood pressure, arterial
oxygen saturation, temperature, end tidal CO2and blood gases
was performed and recorded every 15 min during the procedure.
Prior to surgery, MRI was performed on a 3 Tesla whole body
MRI scanner (Achieva, Philips Healthcare) using an eight-
channel knee coil to obtain subject-specific data. Multislice T1-
and T2-weighted turbo spin echo (TSE) and 3D magnetization
prepared rapid gradient echo (MPRAGE) images were acquired
with a field of view of 1283128380 mm3, an in-plane resolution
of 131 mm and slice thickness of 2 mm. The total imaging time
was approximately 25 min. Upon completion, the animals were
transferred to the adjacent angiography suite and prepared for
sterile surgery. They were secured on the non-radio-opaque table
with a surgical beanbag. A non-invasive frame designed to hold
and manipulate the access sheath was mounted onto the
animal’s skull. A single incision and burr hole (0.5 cm diameter)
were created approximately 1 cm anterior of the coronal suture
and 1 cm mediolateral to the sagittal suture. A metal sheath was
inserted into the manipulator with the distal end touching the
dura mater. CBCT data were acquired for surgery planning and
navigation using an angiographic c-arm system (Allura FD20,
Philips Healthcare). Preoperative MRI data were imported into
the corresponding work station and registered with CBCT data.
The path of the CED microcannula was planned on merged
datasets using XperGuide. This dedicated navigation software
provides real-time guidance of radio-dense medical devices by
fluoroscopic imaging shown relative to 3D multimodal image
coronal slices of (A) T2-weighted turbo
spin echo (T2w-TSE), (B) T1-weighted
turbo spin echo (T1w-TSE), (C)
magnetization prepared rapid gradient
echo (MPRAGE) and (D) cone beam CT
(CBCT) image data of sheep brain prior
to convection-enhanced delivery of
therapeutic compound. The burr hole
and distal end of the sheath in CBCT
data are indicated by the arrow.
Examples of corresponding
module used for surgical navigation
during convection-enhanced delivery.
Real-time x-ray images (gray scale) are
superimposed onto cone beam CT
(CBCT) (red scale) and MRI (blue scale)
data. (A) The entry point, target point
and planned path are indicated by the
pink and green circles and green dots,
respectively. After each alteration of the
position and orientation of the sheath
the x-ray image was updated. Optimal
alignment was achieved by alternating
the orientation between the entry view
(B, C) and progression view (D, E).
Snapshots of navigation
70J NeuroIntervent Surg 2013;5:69–72. doi:10.1136/neurintsurg-2011-010170
data and the planned path in a single view. Fluoroscopic data
were updated in conjunction with every adjustment of the
manipulator in order to see the effects in relation to 3D image
data and the planned path. By alternating between the entry
view (ie, parallel to the planned path) and progression view (ie,
perpendicular to the planned path), both automatically calcu-
lated and provided by navigation software, the sheaths were
readily aligned with the planned paths. The cannula with
a distal tip length of 3.0 mm and outer diameter of 300 mm was
introduced and progressed towards the end position without
fluoroscopic guidance because the cannula tip was not visible
with x-ray imaging. Instead, progression depth measured from
the dura mater during the planning phase was applied. The end
position of the cannula tip was validated by acquisition of high
resolution CBCT data (XperCT) using a 22 cm detector size and
an unbinned reconstruction algorithm.19High resolution CBCT
was registered to T2w-TSE data to confirm the position of the
cannula tip and, if necessary, the cannula was progressed by
distance to the target measured on the fused image data.
In order to visualize the approximate spread of the injected
substance with MRI, the therapeutic compound was mixed
with 2.0 mmol/l gadolinium (Gd). The mixture was infused at
a rate of 0.3 ml/min for a total of 100 ml using a syringe pump
(PHD 2000 Infusion, Harvard Apparatus, Holliston, Massachu-
setts, USA). After infusion, the skull and wound were closed and
the animal was transferred to the MRI system where the same
image data were acquired as before surgery. Upon completion,
the animals were recovered.
CED surgery was planned on preoperatively acquired MRI
(figure 1AeC) and CBCT data obtained after creation of the burr
hole (figure 1D). Cannulae were successfully introduced under
multimodal image guidance. Figure 2 shows snapshots of fluo-
roscopic data (gray scale) overlaid with CBCT data (red scale)
and MRI data (blue scale). The cannula tip, of outer diameter
300 mm (figure 3A), was visualized in vivo using high resolution
CBCT (figure 3B), and registration with MRI enabled validation
of the position relative to the striatum (figure 3C). Gd-enhanced
MRI after CED confirmed the localized administration of
the compound and was used to measure the approximate
distribution volume (figure 4).
CED has been shown to be an effective method of administering
macromolecular drugs into the brain. However, accurate place-
ment of a delivery device remains a challenge that requires
excellent surgical skills. Advancements in imaging and naviga-
tion technology may be of great value in assisting the surgeon
during this procedure. In this short report, we demonstrate the
use of a commercially available truly frameless navigation
module that provides multimodal image guidance during surgery
a comparison with other navigation techniques was performed,
we have shown that the XperGuide module can be of value for
CED and other procedures that may require accurate positioning
such as biopsy, ablation and stimulation.
A great advantage of frameless navigation is that it does not
require the use of invasive fiducials or additional navigation
machinery. Due to calibration of the c-arm system, the rela-
tionship between the image and the patient is simply established
by in situ acquisition of 3D image data which can subsequently
be used for navigation or merged with other patient data.
With high resolution CBCTwe were able to image the small
distal end of the microcannula in vivo. Using MRI data, this
enabled us to visualize the exact end position of the cannula tip
and to make adjustments to the depth as necessary. This
represents a significant advantage over other surgical navigation
a quantitative analysisnor
end of the microcannula. The cannula
tip (arrows) has a length of 3 mm and
a diameter of 300 mm. (B) Maximum
intensity projection of a 0.2 mm slab of
a high resolution cone beam CT (CBCT)
(red scale) acquired after introduction of
the convection-enhanced delivery
cannula. The small detector size and
unbinned reconstruction algorithm
enables in vivo visualization of the
complete cannula. (C) CBCT was
registered with preoperative T2-weighted
turbo spin echo (gray scale) to confirm the
end position and make adjustments in the direction of progression if necessary.
(A) Scale image of the distal
coronal slices of (A) T2-weighted turbo
spin echo (T2w-TSE), (B) T1-weighted
turbo spin echo (T1w-TSE) and (C)
magnetization prepared rapid gradient
echo (MPRAGE) image data of sheep
brain after convection-enhanced
delivery of therapeutic compound mixed
with gadolinium. The spread of the
therapeutic compound is assumed to be
similar to that of gadolinium, which is
clearly visible on both T1-weighted
Examples of corresponding
J NeuroIntervent Surg 2013;5:69–72. doi:10.1136/neurintsurg-2011-010170 71
systems in that direct rather than inferred confirmation of the
cannula position can be obtained.
A limitation of using truly frameless navigation is that it
requires the acquisition of CBCT data and real-time fluoroscopy,
which exposes the patient to additional ionizing radiation. The
acquisition of a single CBCT dataset produces a radiation dose of
approximately 50 mGy, which can be lowered by using a low-
dose CBCT protocol, although at the cost of signal-to-noise.
Another limitation of the navigation method used is that
a relationship between the patient and the image will only be
maintained provided the patient does not move during the
procedure. Although extensive research has been performed to
realign patient and volumetric data using fluoroscopic images
when the patient has moved,30currently a relationship can only
be re-established by acquiring new CBCT data.
State-of-the-art angiographic c-arm systems contain hardware
and software technology that enable truly frameless multimodal
image guidance which may be of great value during minimally
Acknowledgments The authors acknowledge Philips Healthcare and Lundbeck Inc.
Funding This research was funded by a grant from Lundbeck Inc.
Competing interests NA is a member of the NIH sponsored DERC (DK 032520).
Contributors IMJvdB: study design, data collection, data analysis, manuscript
preparation. RPM: study design, operating neurosurgeon, manuscript editing. GG:
study design, material production, manuscript editing. MS-E: study design, manuscript
editing. NA: PI. MG: study design, data analysis, manuscript preparation.
Provenance and peer review Not commissioned; externally peer reviewed.
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