Application of micro-CT in small animal imaging Sebastian J. Schambach a , Simona Bag a , Lothar Schilling b , Christoph Groden a , Marc A. Brockmann a, * a University of Heidelberg, Medical Faculty Mannheim, Department of Neuroradiology, Germany b University of Heidelberg, Medical Faculty Mannheim, Division of Neurosurgical Research, Germany a r t i c l e i n f o Article history: Accepted 21 August 2009 Avail able online 23 Augus t 2009 Keywords: Micro-computed tomography (lCT) Imaging Preclinical studies Rodent Mouse Rats Mice Small animal In vivo studies a b s t r a c t Over the past decade, the number of publications using micro-computed tomography ( lCT) imaging in prec linic al in vivo studies has risen expone ntia lly. High er spat ial and tempora l reso lutio n are the key tech nical adv ance ments that have allo wed rese arch ers to capt ure incre asing ly deta iled anat omic al images of small animals and to monitor the progression of disease in small animal models. The purpose of this review is to present the technical aspects oflCT, as well as current research applications. Our objectives are threefold: to familiarize the reader with the basics oflCT techniques; to present the type of experimental designs currently used; and to highlight limitations, future directions, in lCT-scanner research applications, and experimental methods. As a first step we present different lCT setups and components, as well as image contrast generation principles. We then present experimental approaches in order of the evaluated organ system. Finally, we provide a short summary of some of the technical limitations oflCT imaging and discuss potential future developments in lCT-scanner techniques and experime ntal setups. 2009 Published by Elsevier Inc. 1. Introduction Sma ll anim als are esse ntial a s mod els of hum an disease an d the study of organism development. Small animal imaging has a vital role in understanding these models and a key role in phenotyping, as well as drug development and treatment. In the early 1970s, clini cal ima ging was revo lutio nize d by the intro duct ion of com- puted tom ogr aphy (CT ). Until then, the examination of small ro de nts in res ea rch pr oj ects, esp eci all y of mi ce and rat s, was limited by the rela tivel y low geometrical reso lvin g capa city ofclinical CT scanners to 1 mm 3 [1] . Over the past three decades, micro-CT (lCT) imaging has rapidly advanced with higher quality resolution, the int roduction of the cone beam re con str uc tion algorithm, and an increased availability of dedicated scanners for non-invasiv e small animal imaging research [2] . This increased use oflCT has been reflected in a rising number of publications beginning in the early 1980s. Fig. 1graphically depicts this rising number of annu al publ icat ions oflCT in pre clin ical rese arch , unde rlin ing the incre ased imp orta nce of thes e scanners. This grap h is based on a simple query of the public database PubMed using the me sh terms: lCT or MIC RO-CT or ‘‘High Res olu tio n CT” or Mini-CT and ANIMAL. Initially lCT demonst rate d excellent spat ial reso lutio n, but poo r soft tissu e contrast. Ther efo re, earl y pub licat ions imp lementi ng lCT mainly focused on the non-invasive evaluation of high con- trast structur es, such as bones or imp lants. Wit h advancem ents in X-r ay dete ctor sens itivi ty, nota ble imp rovements wer e mad e both in temporal and in geometrical resolution, as well as readout speed. In addition, with the introduction of new contrast agents to elev ate soft tissu e cont rast, lCT could be transferred to in vivo appli cat io ns in pr eclinical re sea rch to evaluate soft tissue structures and vessel morphology. The primary purpose of this review is to familiarize the reader with the underlying technical aspects and application possibilities oflCT imaging in experimental small animal imaging. The objec- tiv es of thi s rev ieware thr eef old : fir st, to pr esent the tec hni cal fun - damenta ls oflCT ; sec ond, to describe successfu lly applied experimental lCT setups incl uding vari ous cont rast gene ratio n mec hani sms and contrast enha ncem ent pos sibil ities in rela tion to the examin ed organ system; and fina lly, to iden tify curren t limitations oflCT-imaging and future directions. 2. Technical aspects oflCT imagingSince the first description oflCT use in preclinical research in the early 1980s[3–6], a number of reviews of the technology and applicatio ns oflCT h ave bee n publ ishe d [1,7–15]. Initi ally , numer- ous sma ll companies spec iali zed in the pro ducti on of ded icate d small animal lCT scan ners, but they were subs equ ently bought by larger competitors with growing interests in lCT technology. 1046-2023/$ - see front matter 2009 Published by Elsevier Inc. doi:10.1016/j.ymeth.2009.08.007 *Co rrespo nding author. Address: Unive rsity of Heid elberg , Medical Facu lty Mannh eim, Depar tmen t of Neuro radio logy, Theod or-Kutzer- Ufer 1-3, 68167 Mannheim, Germany. Fax: +49 621 383 2165. E-mail address: [email protected](M.A. Brockmann). Methods 50 (2010) 2–13 Contents lists available at ScienceDirect Methods journal homepage: www.elsevier.com/locate/ymeth
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Sebastian J. Schambach a, Simona Bag a, Lothar Schilling b, Christoph Groden a, Marc A. Brockmann a,*
a University of Heidelberg, Medical Faculty Mannheim, Department of Neuroradiology, Germanyb University of Heidelberg, Medical Faculty Mannheim, Division of Neurosurgical Research, Germany
a r t i c l e i n f o
Article history:
Accepted 21 August 2009
Available online 23 August 2009
Keywords:
Micro-computed tomography (lCT)
Imaging
Preclinical studies
Rodent
Mouse
Rats
Mice
Small animal
In vivo studies
a b s t r a c t
Over the past decade, the number of publications using micro-computed tomography (lCT) imaging in
preclinical in vivo studies has risen exponentially. Higher spatial and temporal resolution are the keytechnical advancements that have allowed researchers to capture increasingly detailed anatomical
images of small animals and to monitor the progression of disease in small animal models. The purpose
of this review is to present the technical aspects of lCT, as well as current research applications. Our
objectives are threefold: to familiarize the reader with the basics of lCT techniques; to present the type
of experimental designs currently used; and to highlight limitations, future directions, in lCT-scanner
research applications, and experimental methods. As a first step we present different lCT setups and
components, as well as image contrast generation principles. We then present experimental approaches
in order of the evaluated organ system. Finally, we provide a short summary of some of the technical
limitations of lCT imaging and discuss potential future developments in lCT-scanner techniques and
experimental setups.
2009 Published by Elsevier Inc.
1. Introduction
Small animals are essential as models of human disease and the
study of organism development. Small animal imaging has a vital
role in understanding these models and a key role in phenotyping,
as well as drug development and treatment. In the early 1970s,
clinical imaging was revolutionized by the introduction of com-
puted tomography (CT). Until then, the examination of small
rodents in research projects, especially of mice and rats, was
limited by the relatively low geometrical resolving capacity of
clinical CT scanners to 1 mm3 [1]. Over the past three decades,
micro-CT (lCT) imaging has rapidly advanced with higher quality
resolution, the introduction of the cone beam reconstruction
algorithm, and an increased availability of dedicated scanners for
non-invasive small animal imaging research [2]. This increased
use of lCT has been reflected in a rising number of publicationsbeginning in the early 1980s. Fig. 1 graphically depicts this rising
number of annual publications of lCT in preclinical research,
underlining the increased importance of these scanners. This graph
is based on a simple query of the public database PubMed using
the mesh terms: lCT or MICRO-CT or ‘‘High Resolution CT” or
Mini-CT and ANIMAL.
Initially lCT demonstrated excellent spatial resolution, but poor
soft tissue contrast. Therefore, early publications implementing
lCT mainly focused on the non-invasive evaluation of high con-
trast structures, such as bones or implants. With advancements
in X-ray detector sensitivity, notable improvements were made
both in temporal and in geometrical resolution, as well as readout
speed. In addition, with the introduction of new contrast agents to
elevate soft tissue contrast, lCT could be transferred to in vivo
applications in preclinical research to evaluate soft tissue
structures and vessel morphology.
The primary purpose of this review is to familiarize the reader
with the underlying technical aspects and application possibilities
of lCT imaging in experimental small animal imaging. The objec-
tives of this review are threefold: first, to present the technical fun-
damentals of lCT; second, to describe successfully applied
experimental lCT setups including various contrast generationmechanisms and contrast enhancement possibilities in relation
to the examined organ system; and finally, to identify current
limitations of lCT-imaging and future directions.
2. Technical aspects of lCT imaging
Since the first description of lCT use in preclinical research in
the early 1980s [3–6], a number of reviews of the technology and
applications of lCT have been published [1,7–15]. Initially, numer-
ous small companies specialized in the production of dedicated
small animal lCT scanners, but they were subsequently bought
by larger competitors with growing interests in lCT technology.
1046-2023/$ - see front matter 2009 Published by Elsevier Inc.doi:10.1016/j.ymeth.2009.08.007
* Corresponding author. Address: University of Heidelberg, Medical Faculty
Mannheim, Department of Neuroradiology, Theodor-Kutzer-Ufer 1-3, 68167
General Electric acquired Enhanced Vision System Corp. (EVS)
in the year 2002; Siemens bought ImTek Inc. in 2004 and CTI
Molecular Imaging Inc. in 2005, while Varian Security & Inspection
Products acquired Bio-Imaging Research Inc. (BIR) in 2007. A short
market overview can be found in Table 1. To the best of our knowl-
edge, this is a comprehensive overview of the market at the time of
this review. We recognize, however, that other suppliers may also
exist of which we have not listed here.
Fig. 1. The rising number of annual publications of lCT in preclinical research demonstrates the increasing importance of these scanners. This graph is based on a simple
query of the public database PubMed with using the following mesh terms: lCT or MICRO-CT or ‘‘High Resolution CT” or Mini-CT and ANIMAL. A time line was created with
MEDSUM: an online MEDLINE summary tool by Galsworthy, MJ. Hosted by the Institute of Biomedical Informatics (IBMI), Faculty of Medicine, University of Ljubljana,
Slovenia. URL: www.medsum.info.
Table 1
Market overview on micro-CT: manufacturers and their current products.
Company Web site Products
Biomedical Imaging Research (BIR) http://www.bio-imaging.com ACTIS 150/90 Desktop
In the literature, both customized non-destructive testing lCTs
[16] and custom-made lCTs [3,17] adapted for the necessities of animal research are described. The following paragraphs will detail
some of the various lCT scanner designs and discuss the advanta-
ges and limitations of this form of imaging technology.
2.1. lCT setup
2.1.1. Construction principles
Generally, there are two different construction principles with
respect to lCT scanners. The first construction principle involves
scanners with an X-ray detector and radiation source mounted
on a gantry that is rotated around the examined object (Fig. 2A).
In these scanners the source–detector distance (SDD) is construc-
tion-conditioned in most marketed tomographs (with a few excep-
tion where SDD can be adjusted), with a magnification level for theobject in the course of the beam. In these systems the achievable
geometrical resolution depends mainly on the pixel pitch and
matrix size of the detector used, as well as the focusing mode of
the X-ray tube used. Accordingly, scanners are named ‘‘mini-CT”
because the setup is analogous to clinical CTs.
The second construction principle, which is found mostly in
ex vivo specimen lCT scanners and custom built systems, is out-
lined in Fig. 2B. In this design the examined object is rotated within
the light path. The setup allows the free adjustment of source–
object distance (SOD) and object–detector distance (ODD), thereby
allowing SDD adjustment. Free adjustment of SOD and ODD facili-
tates optimization of the geometric magnification level, depending
on the signal-to-noise ratio (SNR) and the penumbra blurring [15].
Thus, for small fields of view, higher maximal resolution can be
achieved as compared to a conventional setup. In these systems,
the object can be rotated horizontally [16] or vertically [17]
orthogonal to the ray path. However, one drawback is the necessity
to fix the examined animal during rotation around its own axis, to
prevent movement blurring in the resulting datasets.
2.1.2. X-ray tubes
The availability of a variety of lCT scanners using a range of
X-ray tube technologies presents both advantages and disadvan-
tages. The majority of marketed scanners use nano- or microfocus
X-ray tubes with transmission targets. In these X-ray tubes an
electron beam is produced on the tip of a hairpin tungsten filament
and focused by several magnetic lenses onto a focal spot of
1–10 lm on a transmission target (Fig. 3).
Transmission targets typically have a thin layer of tungsten
(about 100 lm) electroplated or vapor-deposited on a carrying
material with low atomic number and high thermal conductance
such as beryllium or chemical vapor depositioned (CVD)-diamonds(e.g. Diamond Materials GmbH, Freiburg, Germany). On the outside
of the transmission targets a cone-shaped beam of braking radia-
tion (depending on tube voltage), and characteristic radiation
(depending on the target material) is produced which irradiates
onto a digital X-ray detector.
In contrast to this, in conventional clinical CT or three-dimen-
sional (3D)-rotation angiography systems, X-ray tubes with reflec-
tion targets and focal spot sizes of a minimum of 300lm are
typically used. If tubes of this dimension are used, as per the pro-
tocol of Badea et al. [17], then a low magnification must be used in
order to minimize penumbra blurring caused by the large focal
spot. Reflection target X-ray tubes convert the irradiated electron
energy less efficiently to X-ray photons than transmission target
tubes [18]. On the other hand, reflection targets can absorb moreheat energy without damage because they have a thicker tungsten
anode compared to the tungsten layer on transmission targets.
Therefore, higher energy electron beams can be used in reflection
anode tubes, leading to higher photon flux in these tubes [17].
Reflection anode tubes typically generate power in the range of
kilowatts, whereas microfocus transmission tubes operate in the
range of watts. In 1994, Flynn et al. stated that the output power
of a microfocus tube would generally follow P max = 1.4( x)0.88
[W/lm] where x equals the focal spot size in lm [19]. Due to the
use of advanced target materials, such as CVD-diamonds that have
Fig. 2. Different lCT architectures. In thedesign illustrated under (A), theexamined
object is placed still in the center of the setup and a gantry carrying detector and X-
ray source is rotated around it. The geometrical magnification factor is fixed
structurally by the defined SDD. In the setup outlined in (B), the object is rotated in
the course of the beam and can be freely positioned between detector and source,
which allows for the adjustment of the magnification level.
Fig. 3. (A) Transmission target X-ray tube of the Y.Fox lCT. (B) Sketch of the inside configuration of transmission tubes with the electron beam exiting a hairpin filament
(triangle) that is focused viamagneticlenses(gray bars) on thetransmission target(1) . (C) Reflection anode X-ray tube with rotating anode in closed design and(D) sketchof
a reflecting anode X-ray tube design with electrons exiting from a curled heating cathode and the electrons accelerated onto a reflection target (1). (Image source of (C) and(D): Wikipedia Commons.)
Another novel liposome-based contrast agent tested by Montet
et al., with an iodine content of 70 mg/ml, allows for the measure-
ment of hepatic metastasis of around 250 lm in size, as well as
delineation of the liver and spleen. Furthermore, the iodinated
liposomes have been found to be a suitable contrast agent for
vascular structures [44]. More recently, multimodal contrast
agents are being tested and gaining considerable attention as they
contain both iodine and gadolinium and can therefore be used
either in CT or in MRI [15,45].
3. Application of lCT in experimental imaging
3.1. Osseous structures
The first advances in lCT technique were mainly driven by
imaging needs for the evaluation of bone anatomy and density
[46,47]. These publications have investigated bone density [48];
osteogenesis [49]; ovariectomy [50] and osteoporosis [51]; bone
resorption [52]; bone remodeling [53]; bone regeneration [54]
and fracture healing [55]; bone neoplasm [56] and biocompatible
materials [57]; and many more topics. Various reviews have also
addressed the use of lCT in the evaluation of pathological changesin bone structure [48,58–60].
The high X-ray density of osseous structures allows the precise
lCT-based evaluation of stereology, volume, and trabecular archi-
tecture of bones at micrometer resolution [61]. For the volumetric
estimation of bone density, ex vivo lCT is described as the method
of choice [62]. Furthermore, the non-invasive quality of lCT allows
for the observation of bone structure before and after exposure to
mechanical stress under experimental conditions [12]. An isotropic
resolution of about 50 lm is described as sufficient to evaluate
changes correlated with osteoarthritis [63] and other bone-remod-
eling processes in rats in vivo [64]. In studies of osseous disease,
differences in trabecular structure and mineralization density,
which can have an impact on experimental setup and data collec-
tion, were compared between different mouse strains in vivo [61].
The results showed a higher degree of mineralization in C3H/HeH
mice compared to C57BL/6 mice at identical body weight and body
size in concordance with earlier ex vivo studies [65]. According to
this study, lCT is capable of detecting the impact of illnesses and
therapeutic interventions on bone density and structure [61]. To
provide an example for imaging of osseous structures, Fig. 5 shows
a murine proximal femur volume rendering of a dataset acquired
via lCT ex vivo, where we compared a fast (A: scan time 40 s)
and a slow scan mode (B: scan time 20 min).
Next to the evaluation of changes in trabecular structures, the
quantification of osteopathologic processes is also very important.
For this purpose, lCT is used in fundamental research in oncology
for the quantification of bone metastases [66]. Besides osteolytic
alterations or processes, an increase in bone density, such as
osteopetrosis, manifested in op/op knock out mice, can also be
assessed using lCT [67].
3.2. Vascular structures
To date, approximately 60 articles have been published on the
evaluation of vasculature in small animals via lCT. Starting in
the late 1990s, topics such as angiogenesis [40,68,69] and neovas-
cularization [70] were studied. In addition, the vasculature of mis-
cellaneous organ systems, both in healthy and in diseased
conditions, have been evaluated in terms of renal vasculature
[71–74]; hepatic vasculature [75] and portal hypertension [76];
Fig. 5. Volume rendering of a murine femur dataset, acquired ex vivo with a continuous scan mode lasting 40 s (A) and with an incremental scan mode having 20 minacquisition time (B) using a volume-CT.
Fig. 6. Digital subtraction angiography of the cerebral arteries after superselective
catheterization of the common carotid artery in a rat (cranio-caudal view).
cerebral vasculature [16,77]; coronary arteries [78]; and ocular
vasculature [79].
The in vivo evaluation of vascular structures in small animals
via lCT is only possible by means of contrast agent administra-
tion, which is similar to CT angiography (CTA) in humans. The
earlier, relatively slow lCT scanners with scanning times lasting
up to hours allowed for vessel analysis in rodents after sacrifice
of the animal [13] using perfusion with radiopaque polymerizing
substances [77,80] or shock freezing the contrast agent perfused
specimen [81]. In ex vivo studies there is no need for X-ray dose
reduction, and no anesthesia-dependent limitations in scanning
time, therefore SNR can be maximized by long scans with high
photon flux, resulting in submicron resolution [80]. Recent ad-
vances in X-ray detector technology, leading to faster readout
times, lager pixel matrices, higher X-ray sensitivity, and higher
SNR, allow examination times of less than a minute [16,40].
These advances have in turn lead to a reduction of movement
artifacts, anesthesia incidents, applied radiation dose, and the
use of conventional contrast agents with lCT angiography. Fur-
thermore, not only does using systems with cone-beam geome-
try allow computed tomography to be performed, but also
digital subtraction angiography is possible as demonstrated in
Fig. 6.
Actual examples for high-resolution 3D vessel imaging in vivo
using conventional contrast agents were reported by Kiessling
et al. and Schambach et al., when they imaged tumor supplying
vessels at resolutions of 50 lm [40] and cerebrovascular structures
in mice at 16 lm resolution, respectively [16]. Figs. 7 and 8 show
in vivo datasets of intracranial and extracranial vessels of a mouse
using a conventional contrast agent (Iomerone 300, Bracco Altana)
with 40 s scanning time. These datasets allow not only the analysis
of anatomical differences in brain vasculature between mouse
strains, but also the evaluation of acute vessel diameter alterations
between hypoxia and normoxia.
The use of so-called blood-pool contrast agents for imaging of
vascular structures as well as parenchymal organs in small animals
is well described in the literature [82–91]. Various thoracic and
abdominal murine vascular structures acquired via lCT in vivo
are displayed in Fig. 9 using the liposomal contrast agent Fenestra
VC.
However, some vascular pathologies can be detected without
the application of a contrast agent. For example, Persy et al. evalu-
ated the degree of aortic calcification in a model of chronic renal
failure of rats in vivo without contrast agents anddrew conclusions
about the development and the degree of renal failure in these
animals [92].
Fig. 7. Maximum intensity projections (MIP, A–C) and volume rendering (D) of murine cerebral vessel datasets, acquired with a lCT in vivo using a conventional contrast
agent and bolus technique. Image (A) shows the passage of the internal cerebral artery (ICA) through the skull base and the circle of Willis incorporating the middle cerebral
artery (MCA) and the anterior cerebral artery (ACA), presented in a curved-MIP. In image (B) a transversal view of the circle of Willis of a BALB/c mouse with prominent
posterior communicating artery (PcomA) between posterior cerebral artery (PCA) and superior cerebellar artery (SCA) is shown. Image (C) represents a sagittal view of
murine brain vessels with small branches of the azygos of the pericalosal artery (azPA) visible. The azPA is supplied in mice by a unification of both ACA called azygos of the
ACA(azACA). (D) shows a volumerendering of external cranial vessels of a mouse with arteries such as the commoncarotid a. (CCA), external carotid a. (ECA),internal carotida. (ICA), stapedial a. (SA), occipital a. (OA), caudal auricular a. (CAA), superficial temporal a. (STA), facial a. (FA), and lingual a. (LA) visible.
in diameter in unenhanced scans. Even though a sharp cutoff for
the tumor border could not be defined, it was still possible to dis-
tinguish the lesion from abutting vascular structures with the help
of other slice orientations. In a more recent study, it was possible todelineate pulmonary tumors of 0.85 mm in vivo in a nude mouse
model [95]. One of the latest in vivo studies of mice attained de-
tailed perceptibility of lung tumors of 500 lm using respiratory
gating [96].
Other studies describe the capability of lCT for the monitoring
of lung fibrosis in mice after intratracheal administration of
bleomycin [97]. The fibrotic lung segments present themselves
with a rising compaction of lung parenchyma. In another model,
emphysema was produced in mice via tracheal instillation of pan-
creas elastase and the typical changes in lung architecture could be
detected [98]. The differences in regional lung ventilation were
non-invasively imaged in Wistar rats via xenon gas inhalation
lCT [99].
3.3.3. Cardiac imaging
Hypercholesterolemia and arteriosclerosis can produce oxida-
tive stress, a dysfunction of coronary arteries and myocardial
ischemia, which accompany the expression of growth factors and
can lead to myocardial neovascularization. Using high-resolution
lCT ex vivo, Zhu et al. demonstrated that it was possible to image
the related changes in myocardial micro-vasculature in swine
[100]. In this quantitative analysis, the subendocardial spatial den-
sity of microvessels with a diameter under 200 lm, at an imaging
resolution of 40 lm was significantly higher in swine suffering
from hypercholesterolemia compared to controls.
For in vivo imaging of the heart in rat and mice, projections
must be assigned not only to different breathing phases, but also
to higher frequency heart actions. Cardiac gating in small animalshas been successfully described in the literature in terms of the
application of prospective and retrospective gating techniques
[84,101]. Using pulsed X-ray tubes as done by Badea et al. [84], a
10 ms time window per frame is possible. Temporal resolution of
a dedicated X-ray detector should be high enough to display oneheart cycle in a set of images. Most detectors in use do not exceed
a frame rate of 30 fps. The implication here is that at frame rates of
30 fps the end-diastolic and end-systolic phase can be identified in
animals with a heart rate of up to 300 bpm. Images that we pro-
duced under such conditions via retrospective intrinsic gating in
mice are presented in Fig. 10.
To summarize, in vivo cardio-CT is well established as a valu-
able method of non-invasive investigation in heart pathology mod-
els as well as for the phenotyping of genetically modified small
animals.
3.4. Imaging of abdominal organs
lCT imaging of abdominal organs in small animals is increas-ingly used as the availability of scanners has greatly improved. In
this context, the examination of parenchymatous organs such as
liver, spleen and kidney is of high interest, whereas most studies
focus on oncological problems and the investigation of the kidney
function.
3.4.1. lCT of parenchymatous upper abdominal organs
Relatively long scanning times, in the range of minutes, motion
blurring caused by breathing movements, and the small blood
volume of animals make the evaluation of subphrenic abdominal
organs, like the liver, difficult when using conventional iodinated
contrast agents. As a result, for the imaging of parenchymatous
upper abdominal organs, liver-specific contrast agents are used
on a regular basis. For example, the iodinated contrast agentDHOG (1,3-bis-[7-(3-amino-2,4,6-triiodophenyl)-heptanoyl]-2-oleoyl
Fig. 10. Datasets of the murine heart after retrospective intrinsic gating. Images (A + B) show a short axis view in MIP mode with (A) representing end-systolic and
(B) end-diastolic phase. In (D) a long axis view of the heart in end-diastolic phase with clearly distinguishable left ventricle (LV), right ventricle, atriums and aortic arch (AA).
(C) shows a volume rendering with pulmonal tissue visible in light blue and trachea as well as bronchioli in red. (Intrinsic gating in cooperation with Q. Xie, Experimental
Radiation Oncology, Medical Faculty Mannheim, and S. Bartling, German Cancer Research Centre (DKFZ).)
glycerol; Fenestra LC; Art Technologies, San Diego, CA), which is
internalized by hepatocytes via the ApoE-receptor and leads to a
relevant enhancement of liver contrast after 1–2 h [86,88,102].
DHOG allows for the delineation between healthy, enhancing
hepatocytes and non-enhancing neoplasmatic cells [103] and thusthe non-invasive quantification of liver metastases. The burden-
some ‘‘second look” procedure used in older experimental setups
can, therefore, be abandoned. Furthermore, liposomes are ingested
by phagocytic cells in the spleen, and the red pulp which is
populated mostly by erythrocytes and macrophages. This ingestion
creates a hyper-dense imaging effect [44]. As the half-life of DHOG
can range from several days up to 2 weeks, it may offer the possi-
bility to image the tumor growth repeatedly without the need for
repeated injections, or at least to reduce the dose of the adminis-
tered contrast agent in repeated scans.
The smallest neoplasms that could be confirmed in a respira-
tory-gated DHOG enhanced lCT scan have been reported to be in
the range of 250–300 lm [44]. However, Fig. 11 shows a murine
liver interspersed with metastases with diameters of less than100 lm scanned about 2.5 h after i.v. administration of 400ll
Fenstra LC.
3.4.2. lCT of the kidney
Up to 10 years ago it was difficult to geometrically relate the 3D
anatomical complexity of renal vasculature with the related tubu-
lar sections of the nephron because of methodological limitations.
A recent review on the use of lCT for the evaluation of renal micro-
structural changes addresses the paucity of imaging publications
citing only 16 articles [104]. Most of the cited articles evaluated
anatomy ex vivo to compare 3D anatomy to histological slices from
human specimens.
Likewise, only a few publications describe the use of lCT to
evaluate renal structures in animals. Using lCT, Fortepiani et al.showed that the blockage of nitrogen-oxide synthesis (an experi-
mental approach to elevate blood pressure) leads to a reduction
in renal blood flow and that administration of an AT1-receptor
antagonist inhibited the effects of this blockage. To evaluate vessel
changes, the kidneys were perfusion fixed in situ and perfused
with radiopaque silicon. Furthermore, an elevated heterogeneity
of glomerular volumes in the renal cortex of rats suffering from
diabetic nephropathy was confirmed via lCT [105].
Even fewer studies on the use of lCT for in vivo imaging in
small animals exist. A study by Almajdub et al. describes an
in vivo imaging procedure for mouse kidney anatomy evaluation
using contrast-enhanced high-resolution lCT [106]. They demon-
strate that contrast-enhanced lCT enables accurate in vivo mea-
surement of kidney volume, length and thickness in mice andreport reference parameters for four strains.
Other authors applied lCT of the kidneys in small animals to
evaluate liposomal blood-pool contrast agents by ruling out renal
excretion [43,89].
As an example of renal in vivo lCT imaging, Fig. 12 presents ascan of the renal pelvis and the ureter of a mouse after contrast
agent administration is presented.
3.4.3. Gastrointestinal tract
Colon carcinoma is one of the most frequent tumors in Western
society. Various animal models exist to mimic this disease andlCT
is applied successfully in this research field as well. For example, in
a study by Durkee et al., virtual colonoscopy was performed anal-
ogous to the examination of colon polyps in humans. After nega-
tive contrasting by air insufflation in APC-min-mice, colon polyps
could be visualized and measured [107]. In a subsequent histolog-
ical examination, a high correlation between identified tumor vol-
umes via lCT and histology was found. Using various positivecontrast agents, it was also possible to image spontaneously
Fig. 11. MIP of the murine liver contrasted with Fenestra LC in transversal (A) and coronal (B) view (1200 projections, scan time 40 s, Field of View 3.5 3.5 cm). White
arrows point to hypo dense round structures with a diameter of 100 lm, in the sense of metastases.
Fig. 12. Volume rendering of lCT scan of a C57BL/6 mouse in vivo after injection of
the blood-pool contrast agent Fenestra VC, acquired without cardiac or pulmonary
gating. The numbers refer to the abdominal vena cava (1), the renal vein (2), right
iliac vein (3), spleen (4), kidney (5), and the ureter (6).
Fig. 13. (A) Raw data projection of a murine (APC (min)) virtual colonoscopy dataset acquired in vivo with double contrast, white arrows pointing at the colon polyps.
(B) Volume rendering of a similar dataset, showing the internal surface of a healthy colon.
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