DOI:10.2214/AJR.07.0195
AJR 2007; 189:W46
© American Roentgen Ray Society
Reply
Daniel T. Boll
Duke University Medical Center Durham, NC
WEB—This is a Web exclusive article.
The headlining phrase of the letter to the editor by Nijenhuis and Backes
[1] questioning "inlet
arteries or outlet veins of the spinal cord?" accurately broaches both
the most important and yet challenging issues of state-ofthe-art imaging of
the spinal cord vasculature. In this response to the comments of Nijenhuis and
Backes, two scientists who have significantly advanced understanding of spinal
perfusion using MR angiography, we seek to readdress the methods of our study
using CT angiography (CTA) [2]
and, furthermore, we want to emphasize the clinical impact of this study's
results.
A scope of different techniques has been assessed to visualize and
understand spinal vasculature and perfusion. Various degrees of
technique-inherent invasiveness enabled visualization of the artery of
Adamkiewicz with varying sensitivity, specifically by means of autopsy
dissections [3], conventional
spinal angiography [4], and
spinal MR [5,
6] and CT
[5] angiography.
Technique-specific limitations, such as formalin-induced tissue shrinkage;
projection techniques with resulting magnification and parallax effects;
unproportional contrast agent–induced T1 shortening; and varying impact
of image acquisition, reconstruction, and reformation parameter combinations
emphasize that individual assessment of absolute vessel diameters will not
clarify whether subcentimeter arterial or venous vasculature is under
investigation.
The study sought to introduce a new approach to reconstruction of image raw
data sets by using a modified vessel-dedicated brain reconstruction algorithm
with filtering and autocalibration procedures to eliminate beam-hardening
artifacts originating from surrounding high-density osseous structures.
Therefore, a resulting overestimation of vessel diameters was accepted because
the main focus of the study was to enhance detection of the artery of
Adamkiewicz by identifying a continuous vascular tract extending from an
intercostal or lumbar artery via the anterior radiculomedullary artery to the
anterior spinal artery by ascending to the midsagittal surface of the spinal
cord and performing the characteristic hairpin turn
[7].
Studies have shown that the spinal vasculature represents an extensive
intersegmental vascular network with interconnected collateralization along
the spinal cord. To gain dynamic information on spinal flow phenomena, a
multiphasic, time-resolved CTA would have been necessary. Radiation dose
considerations, however, did not justify the implementation of such
multiphasic CTA. Therefore, the monophasic imaging protocol used to visualize
an antegrade-perfused artery of Adamkiewicz relied on a bolus-timing technique
to ensure that the contrast bolus had reached the aortic orifice of
intercostal or lumbar arteries supplying the great anterior radiculomedullary
artery.
Venous contamination had to be accepted. The identification of a continuous
arterial vessel tract extending from the aortic orifice to the anterior spinal
artery [7] was not affected by
surrounding venous structures. Neighboring or crossing spinal veins do not
form vascular junctions with this arterial pathway. If, however, dynamic
information on spinal flow phenomena is warranted, Nijenhuis et al.
[6] have proven the feasibility
of performing biphasic contrast-enhanced MR angiography.
A study population of 100 patients to introduce a different approach for
visualization of the spinal vasculature by means of CTA is definitely not
large enough to derive clinical significance for this novel technique.
However, this study was designed to prove the feasibility of combining
high-resolution MDCT angiography imaging with a modified vessel-dedicated
brain reconstruction algorithm in consideration of the unique morphologic
vascular characteristics of the intrinsic spinal vasculature. Therefore,
promising study results of this feasibility study have to be validated with
larger and dedicated study populations with direct intraoperative or MR
angiographic confirmation to prove clinical significance.
References
- Nijenhuis RJ, Backes W. Inlet arteries or outlet veins of the
spinal cord? (letter) AJR 2007;189
:[web] W45[Free Full Text]
- Boll DT, Bulow H, Blackham KA, Aschoff AJ, Schmitz BL. MDCT
angiography of the spinal vasculature and the artery of Adamkiewicz.
AJR 2006; 187:1054
-1060[Abstract/Free Full Text]
- Koshino T, Murakami G, Morishita K, Mawatari T, Abe T. Does the
Adamkiewicz artery originate from the larger segmental arteries? J
Thorac Cardiovasc Surg 1999;117
: 898-905[Abstract/Free Full Text]
- Kieffer E, Richard T, Chiras J, Godet G, Cormier E. Preoperative
spinal cord arteriography in aneurysmal disease of the descending thoracic and
thoracoabdominal aorta: preliminary results in 45 patients. Ann
Vasc Surg 1989; 3:34
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- Yoshioka K, Niinuma H, Ehara S, Nakajima T, Nakamura M, Kawazoe K.
MR angiography and CT angiography of the artery of Adamkiewicz: state of the
art. RadioGraphics 2006;26
[suppl 1]:S63
-S73[Abstract/Free Full Text]
- Nijenhuis RJ, Mull M, Wilmink JT, Thron AK, Backes WH. MR
angiography of the great anterior radiculomedullary artery (Adamkiewicz
artery) validated by digital subtraction angiography. Am J
Neuroradiol 2006; 27:1565
-1572[Abstract/Free Full Text]
- Yoshioka K, Niinuma H, Ohira A, et al. MR angiography and CT
angiography of the artery of Adamkiewicz: noninvasive preoperative assessment
of thoracoabdominal aortic aneurysm. RadioGraphics2003; 23:1215
-1225[Abstract/Free Full Text]
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