Assessment of Neurovascular Coupling - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 345

changes, autoradiography, two-photon microscopy, analysis of
optical intrinsic signals (OISs) and hemoglobin spectroscopy, and
magnetic resonance imaging (MRI) or positron emission tomogra-
phy (PET) scans ( 2, 29-36 ). These methods have specifi c advan-
tages and disadvantages. LDF instruments have very good temporal
resolution, but recordings are one-point measurements.
Autoradiography has good spatial resolution, but does not follow
changes over time in single subjects. Functional MRI and PET
acquire depth-resolved images over time, but the spatial and tem-
poral resolution is still limited in rodent species. Speckle and OIS
techniques are able to provide two-dimensional images with good
spatial and temporal resolution, but have limited depth penetra-
tion. LDF, laser speckle imaging, and optical imaging of intrinsic
signals, specifi cally optical spectroscopy, are most frequently used
methodologies, available from different manufacturers, and easily
implemented into an existing in vivo setup. These methods are
shortly introduced. In addition, capillary blood fl ow measurements
by two-photon microscopy are described, which currently provide
ultimate temporal and spatial resolution for studies on the cerebral
microcirculation.

LDF offers a low-effort method for continuous noninvasive blood
fl ow measurements in tissue. LDF measures blood fl ow based on
the Doppler shift of coherent light induced by moving blood cells
(Fig. 4 ). The invention of LDF has widely replaced techniques that
require injection of radioactive tracers to assess rCBF. Besides non-
invasiveness, the major advantage is the ability to measure perfu-
sion changes in the microcirculation and the ability to track fast

4.1. Laser Doppler
Flowmetry

Fig. 4. LDF measures blood fl ow based on the Doppler shift ( blue ) of coherent light induced
by moving blood cells.