In vivo imaging of graftversus-host disease and graftversus-leukemia - Immune Biology of Allogeneic Hematopoietic Stem Cell Transplantation - page 59

Table 4.1 Comparison of Different Imaging Modalities

Spatial
Resolution

Sensi-
tivity

Tissue
Penetration

Multiple
Probes?

Disadvan-
tages Device Signal Detector Advantages

CT X-rays Charge-

coupling
diode

High
(50-100 μ m)

N/A Good

(> 300 mm)

N/A Good anatomic

resolution

Uses ionizing
radiation

PET/
SPECT

γ -rays Scintillating

crystal

Low
(1-2 mm)

V. high Unlimited Yes

(SPECT
only)

Excellent sensi-
tivity and tissue
penetration,
multiple report-
ers possible
with SPECT

Low anatomic
resolution,
requires
radioactive
materials, high
cost

MRI Radio-

waves

Receiver coil V. high

(25-100 μ m)

Low Good

(> 300 mm)

No Excellent soft

tissue resolution
and contrast,
non-ionizing
radiation

High cost

Ultra-
sound

Sound
waves

Drum detec-
tor

High
(50-100 μ m)

N/A Medium

(1-200 mm)

N/A Good anatomic

resolution,
non-ionizing
radiation

Propagates
poorly through
gaseous
medium and
bone

60

Optical Light

waves

Digital cam-
era

Low
(2-5 mm)

Medi-
um-
high

Poor
(1-20 mm,
depending
on wave-
length)

Yes Inexpensive,

high-through-
put, multiple
reporters, can
measure cell
viability and
function

Low anatomic
resolution

Bioluminescence imaging

Bioluminescence imaging (BLI) is based on measuring light emitted
from living cells expressing enzymes which catalyze a light-producing
reaction. These enzymes, known as luciferases, are present in over 700
genera, with 80% of these being marine species [1] . Several luciferases
have been cloned from marine and terrestrial species, but the principal
ones which have been developed as reporter genes are from the cope-
pod Gaussia princeps , the sea pansy Renilla reniformis , the click beetle
Pyrophorus plagiophalamus and the North American firefly, Photinus
pyralis [2,3] .

Gaussia and Renilla luciferase enzymes emit light in the blue/green region
of the visible spectrum. As these wavelengths are scattered and absorbed
by tissues, there are limitations in the spatial resolution and sensitivity pos-
sible with these enzymes. The click beetle and firefly luciferases, on the
other hand, can emit ~60% of their light at >600 nm, in the red and near-
infrared regions of the spectrum, which is more efficiently transmitted
through tissues [4,5] . These wavelengths also avoid most of the scattering