1. CTA-Source Images: Volume or Flow Weighted?
Sharma et al. AJNR In Press

2. stroke <1 hr - R hemisphere

3. ICA, MCA, ACA termination occlusion

4. stroke <1 hr - CTA source images (SI)
Aviv et al Clin Radiol. 2007;62:447

5. CT-Perfusion matched defects: no penumbra! no brain at risk to salvage!
mean transit time MTT
matched CBV = infarction
blood volume CBV
blood flow rCBF
Murphy et al. Stroke :1771
Aviv et al. AJNR 2007; 28:1975
Murphy et al. Radiology :818

6. CBV for infarction identification
CT perfusion match or mismatch
Murphy, Fox, Lee et al, Stroke :1771

7. CT stroke protocol - 4 (64 +) slice CT
NON CONTRAST CT ~ 20 sec
CTA NECK & HEAD ~ 20 sec MIP-MRPs (2D) - coronal, sagittal, rotating obliques (secs)
MIP MPRs done immediately by techs *
CT-P 2cm (8cm) BASAL GANGLIA & VENTS ~ 40 sec
rCBF (cerebral blood flow ml/100 g brain/minute)
CBV (blood volume)
MTT (transit time)
flow maps done immediately by techs
POST CONTRAST CT ~ 20 sec
TOTAL SCANNING ~100 sec NOT MUCH MORE TIME THAN SIMPLE NCCT ALONE
* no time waste time for rendering; MPRs off operating console by techs
* main advantage of CT over MR stroke protocol is time

8. CTA-Source Images: Volume or Flow Weighted?
Sharma et al. AJNR In Press

9. INTRODUCTION CTA Source Images –
valuable for more than for angio images
previously correlated to MR-DWI
predicts final infarct volume >than NCCT
matched final infarct after re-canalization confirmed by study using ASPECTS
assess infarct extent in absence of DWI
CTA shows vascular contrast filling. When we look beyond blood vessels, we also see parenchymal filling. There have been correlations of CTA source images with DWI of the same cases to predict infarction volume. Can we use CTA source images instead of DWI?
Schram et al;Camargo et al;Kloska at al;Warach et al;Coutts et al;Aviv et al

10. INTRODUCTION cont’d
NCCT, CTA-SI, CBV maps: seeking unsalvageable tissue despite reperfusion
BUT . . .
observed CTA-SI ↓ density often larger than CTP-CBV defect
CTA-SI
CTP-CBV ?
Here we have on right CBV – showing infarction as volume defect with a gray scale map, compared to CTA source image on left. The reduced density on CTA SI is much wider than that of the CBV, a small region in deep right frontal lobe. Why is this?

11. INTRODUCTION contd AIM
correlate CTA-SI and PCCT ↓ density with CTP-CBF (ischemic) and CTP-CBV (infarcted) defects
HYPOTHESES
CTA-SI – more CBF (ischemic) defect
PCCT - more CBV (infarcted) defect
This study was aimed to compare CTA-SI and post contrast CT densities with CBF and CBV, with the hypothesis of CTA-SI closer to CBF and post contrast CT closer to CBV

12. MATERIALS & METHODS Research Ethics Board approval
64 cases (M:35,F:29) stroke database (Jun07-Jan 09)
entry data documented (ASPECTS, NIHSS, time to scan, rtPA dose, vessel occlusion, etc)
64 slice CT; CTA-SI mm → 4mm slab, 2mm gap
image co-registration- SPM 5.0/Analyze 8.0
CTA-SI, PCCT, CTP-CBF, CTP-CBV tracings by 3 NR using MIPAV; volumes calculated
For the CTA-SI we combine adjacent mm slices to 4 mm. 3 neuroradiology readers completed tracings for the multiple images. Volumes calculated from results.

13. Spearman correlation (r) for association
MATERIALS & METHODS
STATISTICAL METHODS
Spearman correlation (r) for association
univariate linear regression analysis seeking relation between CTA:CBF, CTA:CBV, PCCT:CBF, PCCT:CBV
- BLAND-ALTMAN TECHNIQUE
calculations with SAS 9.2
There were multiple statistical analyses.

14. RESULTS defect mean volumes (cm3): CTA-SI 81.84 PCCT 35.30
mean time to CT: 117±54
median NIHSS: 14.5
vessel occluded: ICA 7, ACA 14, MCA M1-M4 43
defect mean volumes (cm3):
CTA-SI PCCT 35.30
CBF CBV
Spearman correlations:
CTA-SI & CBF: r=0.89; p<0.0001
PCCT & CBV: r=0.79; p<0.0001
CTA-SI & CBV: r=0.50
PCCT & CBF: r=0.52
There are many points here. The key results are that CTA-SI and CBF show affected volume close in size while PCCT and CBV are very close.

15. OUTLIERS: residuals > Q3+ 0.5 IQR or < Q1+ 0.5 IQR
RESULTS contd.
SCATTER PLOTS
CTA:CBF
CTA:CBF
log PCCT:log CBV
log PCCT:log CBV
Curve for CTA-SI and CBF is linear, and PCCT and CBV are linear for the log.
OUTLIERS: residuals > Q IQR or < Q IQR
residuals = differences predicted/actual values

16. RESULTS – “outliers”: worse infarcts, ↑NIHSS, ↓ASPECTS
comparison: data of outliers/others for CTA with CBF
Demographics N
Mean
p-value
age (mean±SD; yrs)
Non Outlier 47
68.43±15.65
0.6702
Outlier 17
69.47±10.33
male gender n (%)
26 (55%)
0.8660
9 (53%)
rTPA administration n (%)
34 (72%)
0.8905
12 (71%)
ASPECTS (median(Q1-3))
7.00 (6-9)
0.0141
6.00 (4-8)
NIHSS (median(Q1-3))
12.00 (7-18)
0.0168
18.00 (14-20)
onset to CT Scan (median(Q1-3); min) 44
( )
0.2703
95.00 (72-126)
Time bolus trigger to mid-infarct
(median(Q1-3); min; secs)
21.00 (16-32)
0.1429
36.00 (16-46)
Recanalization n (%)
0.5755
11 (65%)
There are many data points here. From Mans CTA-SI outliers had lower ASPECTS and higher NIHSS score meaning those patients had severer infarcts to begin with. This in turn means that there is no surprise that these outliers seemed to have more 'volume weightage'. I think it is ok to exclude the data sheet unless you want to show how complicated the whole thing is!

17. matched CBF-CBV defect = infarction
PCCT
CTA SI
matched infarction implies CBF from SI matches infarction of PCCT

18. comparison: demographic data of outliers for PCCT with CBV
RESULTS contd.
comparison: demographic data of outliers for PCCT with CBV
Demographic N
Mean
p-value
Age (mean±SD; yrs)
Non Outlier 48
68.48±13.72
0.8160
Outlier 16
69.38±16.59
Male gender n (%)
27 (56%)
0.7744
8 (50%)
rTPA administration n (%)
35 (73%)
0.7563
11 (69%)
ASPECTS (median(Q1-3))
7.00 (6-9)
0.9622
6.50 (6-8.5)
NIHSS (median(Q1-3))
16.00 ( )
0.3018
11.50 (8-18.5)
Onset to CT Scan (median(Q1-3); min) 46
(80-157)
0.1153 15
80.00 (65-118)
Recanalization n (%)
26 (55%)
0.7739
11 (65%)
No baseline features were significantly related to CBV outliers
For CBV, there were no correlates with outliers.

19. RESULTS contd. Outliers:
↑↑NIHSS & ↓↓ASPECT score - CTA ischemic volume ~ CBV volume. i.e. CTA-SI more CBV weighted
larger baseline CTA-SI defects (worse infarcts, matched CB-P) vs non-outliers (118±51 cm3 vs 78±42 cm3; p=0.002)
longer mean time from smart prep completion to slice levels of ischemia
With increased NIH stroke score and decreased ASPECTS score, CTA volume more approximates CBV, or infarction. Larger CTA-SI defects

20. PATIENT 1 CTP – CBF CTP – CBV CTA-SI PCCT CTP-CBV map CTP-CBF map
PCCT image map
CTA-source images
Case We show colour maps and grey scale maps, which have the same information. On upper left, there is a large blood flow defect showing ischemia. On lower left, the CTA-SI shows the same ischemic defect. On upper right, there is a blood volume defect smaller in the centre, showing infarction. On lower right, the infarction is seen on post contrast CT equivalent to CBV. CTA-SI shows brain at risk, NCCT shows completed infarction.
CTP – CBF
CTP – CBV
CTA-SI
PCCT

21. IMAGES PATIENT 2 CTP – CBF CTP – CBV CTA-SI PCCT CTP-CBV map
CTP-CBF map
IMAGES
PATIENT 2
PCCT image map
CTA-source images
Another case. Upper left CBF shows large flow defect in right MCA territory. Lower left shows the same extent on CTA-SI. Upper right shows CBV map without notable infarction defect whole lower right shows the post contrast CT with no defect. CTA-SI shows ischemic region of brain at risk, NCCT shows completed infarction, not seen here.
CTP – CBF
CTP – CBV
CTA-SI
PCCT

22. PATIENT 4 CTP – CBV CTA-SI PCCT CTP – CBF CTP-CBF map (a) (b) (c) (d)
CTP-CBV map
PCCT image map
CTA-source images
(this has CBV weighting, not there on the prev version) Upper left CBF shows large flow defect in left MCA territory, as well as the infarction shown in on right images. Lower left shows the same extent on CTA-SI. Upper right shows CBV map with infarction defect while lower right shows the post contrast CT with infarction in putamen, capsule and operculum. CTA-SI shows ischemic region of brain at risk, NCCT shows completed infarction.
CTP – CBF
CTP – CBV
CTA-SI
PCCT

23. DISCUSSION
CTA-SI defects correlate highly with CTP-CBF (ischemia) rather than CTP-CBV (infarction)
exceptions: large, severe infarcts
↑↑NIHSS, ↓↓ASPECTS, extensive baseline CTA-SI
cases with matched defects of infarction and blood flow defects
For patients with mismatched ischemic and infarction defect, CTA-source images, merged into slabs, show range of ischemic brain, while post contrast CT can show range of infracted brain.

24. DISCUSSION: CTA SI scan time
older scanners - CTA - long prep delay, long scan times,  contrast rates - steady state arterial & tissue contrast – more volume-weighted* (infarct)
steady state no longer true ** with faster MDCT CTA (inj rates: 5-7 ml/s; prep delay times: s – time-attenuation curve shape changed
faster MDCT: CTA-SI more flow-wt than volume-wt
PCCT delayed, in steady state, volume weighted
Scanner time is also a factor. 4-slice machines took longer to do CTA, and are more likely to produce CTA with a steady state of contrast through a CTA scan cycle, and therefore shows infarction, like CBV. Faster machines like 64 or more can show equivalence of CBF, Post contrast CT has a steady state.
* Axel L. Radiology 1980;137:679-86
Hamberg LM, Hunter GJ, Kierstead D, et al. AJNR 1996;17:
Hunter GJ, Hamberg LM, Ponzo JA, et al. AJNR 1998;19:29-37
** Konstas AA, Goldmakher GV, Lee TY, et al. AJNR 2009;30:662-68

25. DISCUSSION pathophysiology of hypodensities:
NCCT (& PCCT): extra-to-intra-cellular shift H2O
CTA-SI : change in blood/contrast distribution
earlier CTA reports, AHA guidelines - CTA-SI volume-weighted (infarction)*
timing of CTA-SI determines flow or volume-weighted; whether contrast steady state
current fast CTA-SI flow-weighted (ischemia)
* Camargo EC, Furie KL, Singhal AB, et al. Radiology 2007;244:541-48
Coutts SB, Lev MH, Eliasziw M, et al. Stroke 2004;35:
Lev MH, Segal AZ, Farkas J, et al. Stroke 2001;32:
Lin K, Rapalino O, Law M, et al. AJNR Am J Neuroradiol 2008;29:931-36
Latchaw RE, Alberts MJ, Lev MH, et al. Stroke 2009;40:

26. DISCUSSION implications:
CTA-SI important in acute stroke CT, especially in absence of DWI
whole brain coverage CTA vs limited CTP
automated console-generated processing – faster availability
CTA-SI + PCCT aspire to CBF and CBV
limitations:
1) correlations with CTP, not “final” infarcts ) differences of + and - outliers with baseline demographics

27. CONCLUSION CTA-SI are CBF rather than CBV wt’d
study supports hypothesis that currently
CTA-SI are CBF rather than CBV wt’d
i.e CTA-SI show tissue at risk, not infarct
CTA-SI aspire as CBF (ischemia), & PCCT as CBV and/or DWI (infarction)
Thanks !