MRI for Subarachnoid Hemorrhage: References
                 ===========================================

Chakeres DW, Bryan RN
Acute subarachnoid hemorrhage: in vitro comparison of magnetic resonance and
computed tomography.
AJNR Am J Neuroradiol 1986 Mar-Apr;7(2):223-8

The computed tomographic (CT) attenuation values and magnetic resonance (MR)
signal intensities of simulated acute subarachnoid hemorrhage were compared
systematically. In vitro MR and CT measurements (T1, T2, and Hounsfield
units) were made of mixtures of normal human cerebrospinal fluid (CSF) and
normal heparinized blood, ranging from 0% to 100% by volume. The mixtures
were measured in a plexiglass phantom with a Siemens DR3 CT scanner for
attenuation measurements (Hounsfield units) and in the Baylor Bruker
Instruments Proton Scanner (6-MHz) using inversion-recovery and spin-echo
pulse sequence techniques for T1- and T2-calculated relaxation times. A
PRAXIS II (10.7 MHz permanent magnet) nonimaging unit was used to measure
the relaxation times of the CSF/blood mixtures independently for comparison.
The Hounsfield measurements of the densest parts of the layered mixtures
showed increasing values with increasing amounts of hemorrhage (0% blood, 0
H; 100% blood, 66 H) in a nonlinear pattern. The T1 times of the mixtures
decreased with increasing amounts of blood, ranging from 2200 msec to 500
msec for 100% CSF and 100% blood, respectively. The inverse of the T1
relaxation times was proportional to the percentage of blood. The T2 data
for the mixtures were similar in character to the T1 relaxation times,
except for shorter T2 times at high concentrations of blood. It was
concluded the MRI distinguishes varying blood/CSF mixtures on the basis of
relaxation times better than does CT on the basis of Hounsfield units. CT
still has an imaging advantage, since high-concentration hemorrhage is
clearly different from normal brain, while concentrated acute subarachnoid
blood has relaxation times similar to normal brain and is nearly isointense
on MRI.


DeWitt LD
Clinical use of nuclear magnetic resonance imaging in stroke.
Stroke 1986 Mar-Apr;17(2):328-31

There are many positive aspects to the use of MRI in the evaluation of
cerebrovascular disease. First, the MR imaging technique appears to be
essentially without hazard. It does not rely on ionizing radiation, and no
intravenous injections of contrast agent are necessary. MRI exploits the
tissue's inherent biophysical characteristics to provide superior contrast.
Infarctions are well delineated by MRI, often better and earlier than CT.
Because of the lack of MRI signal from bone and thus the lack of transverse
artifact from bone often seen with CT, lesions in the posterior fossa are
very well visualized. With MRI it is possible to obtain images in the
transverse, coronal, and sagittal planes, which provides for good evaluation
of lesion size and extent. Arteriovenous malformations have been visualized
by MRI, but it is still too early to know whether MRI has any detection
capability over CT in this disorder. Subdural hematomas have been well
visualized by MRI, including cases of isodense subdurals not visualized by
CT. On the other hand, MRI has not proven to have any advantage over CT in
the evaluation of intracerebral hemorrhage, hemorrhagic infarction, and
subarachnoid hemorrhage. In fact, for detection of intracerebral hemorrhage
and subarachnoid hemorrhage, CT may be better at the present time. In
chronic infarction the surrounding area of Wallerian degeneration may cause
the area of infarction to appear larger than it actually is. Hopefully, with
further research into the use of different pulse sequence techniques and
with good neuropathological correlation, the present limitations of MRI can
be eliminated.(ABSTRACT TRUNCATED AT 250 WORDS)


Magarisawa S, Suzuki A, Yasui N
[Review of cases of ruptured cerebral aneurysm with a history of examination
at our institution prior to the diagnosis of subarachnoid hemorrhage--in
order to improve treatment outcome in patients with intracranial
aneurysms]
No To Shinkei 1994 Apr;46(4):341-7

There were 78 patients who had been examined at our institution prior to the
diagnosis of subarachnoid hemorrhage (SAH) among the 1114 patients with
ruptured aneurysm stet between April 1974 and March 1992. Among these 78
cases these were 35 patients who might have been treated at an earlier
stage, i.e., 26 patients in which the diagnosis was made belatedly and 9
patients in which an unruptured aneurysm was missed. All 26 patients with
belatedly diagnosed SAH had headache without neck stiffness or neurological
deficits and thus were Hunt and Kosnic grade 1-2 while 25 cases were
categorized so called "minor leak". The causes in 6 of the 7 patients with
poor outcome was rerupture or vasospasm due to delay in the diagnosis of
SAH. Because the diagnosis of mild SAH is not always easy, it is important
to take a careful medical history. MRI or lumbar puncture should be
performed when SAH is suspected from the history, even if CT shows no
evidence of SAH. The cause of failure to diagnose unruptured aneurysms, in
addition to misreading was blood vessel overlapping as a result of
non-selective angiography, poor contrast, etc. Angiography should be
performed selectively and the inclusion of oblique, magnified, stereoscopic,
and other imaging techniques is advisable, if an unruptured aneurysm is
suspected, and angiographic follow-up is necessary when an ruptured aneurysm
is uncertain.