Plant structural changes due to herbivory : Do changes in Aceria-infested coconut fruits allow predatory mites to move under the perianth ? Being minute in size , eriophyoid mites can reach places that are small enough to be inaccessible to their predators . The coconut mite , Aceria guerreronis , is a typical example ; it finds partial refuge under the perianth of the coconut fruit . However , some predators can move under the perianth of the coconut fruits and attack the coconut mite . In Sri Lanka , the phytoseiid mite Neoseiulus baraki , is the most common predatory mite found in association with the coconut mite . The cross-diameter of this predatory mite is c. 3 times larger than that of the coconut mite . Nevertheless , taking this predator 's flat body and elongated idiosoma into account , it is -- relative to many other phytoseiid mites -- better able to reach the narrow space under the perianth of infested coconut fruits . On uninfested coconut fruits , however , they are hardly ever observed under the perianth . Prompted by earlier work on the accessibility of tulip bulbs to another eriophyoid mite and its predators , we hypothesized that the structure of the coconut fruit perianth is changed in response to damage by eriophyoid mites and as a result predatory mites are better able to enter under the perianth of infested coconut fruits . This was tested in an experiment where we measured the gap between the rim of the perianth and the coconut fruit surface in three cultivars -LRB- ` Sri Lanka Tall ' , ` Sri Lanka Dwarf Green ' and ` Sri Lanka Dwarf Green × Sri Lanka Tall ' hybrid -RRB- that are cultivated extensively in Sri Lanka . It was found that the perianth-fruit gap in uninfested coconut fruits was significantly different between cultivars : the cultivar ` Sri Lanka Dwarf Green ' with its smaller and more elongated coconut fruits had a larger perianth-fruit gap . In the uninfested coconut fruits this gap was large enough for the coconut mite to creep under the perianth , yet too small for its predator N. baraki . However , when the coconut fruits were infested by coconut mites , the perianth-rim-fruit gap was not different among cultivars and had increased to such an extent that the space under the perianth became accessible to the predatory mites . Introduction To reduce the predation risk , some organisms show behavioural or morphological changes that are induced by their predators -LRB- Wiackowski and Starońska 1999 ; Buskirk and McCollum 2000 ; Oku et al. 2003 -RRB- . Some have adapted to find refuge in such a way that predators can not reach them . Eriophyoid mites have a worm-like body with a very small cross-section diameter -LRB- 40 -- 100μm -RRB- that allows them to reach concealed plant parts or to live in self-induced , small plant galls where they find protection from biotic and abiotic stresses -LRB- Sabelis and Bruin 1996 -RRB- . The coconut mite , Aceria guerreronis Keifer -LRB- Acari : Eriophyidae -RRB- , feeds on the meristematic tissue beneath the perianth covering the base of the coconut fruit . Here it not only profits from the relatively nutritious value of this tissue , but also from the reduced risk of predation due to the perianth . Among the predatory mites that have been reported to be associated with the coconut mite in Sri Lanka , Neoseiulus baraki Athias-Henriot -LRB- Acari : Phytoseiidae -RRB- is the most frequently found species -LRB- Fernando et al. 2003 ; Moraes et al. 2004 -RRB- . This species was previously referred to as N. aff. paspalivorus -LRB- Fernando et al. 2003 -RRB- , but was later confirmed as N. baraki -LRB- Moraes et al. 2004 -RRB- . It has a flat and elongated idiosoma -LRB- Moraes et al. 2004 -RRB- and we suggest this might make this predator -- relative to other phytoseiid mites -- better suited to creep into narrow spaces . When the coconut mites are outside the perianth they are exposed and vulnerable to predators , but under the perianth of the coconut fruit they face less risk of being eaten . In the absence of natural enemies , coconut mite populations may grow exponentially and , consequently , the development of the coconut fruit will be impaired . Therefore , we expect the coconut palms to defend themselves directly against the coconut mites and/or indirectly by promoting the efficiency of predators against these herbivores -LRB- e.g. Sabelis et al. 2007 -RRB- . In this article , we investigate whether coconut fruits exhibit a mode of indirect defence that is similar to that observed in tulip bulbs by Lesna et al. -LRB- 2004 -RRB- . These authors have found that , when tulip bulbs are attacked from within by the eriophyoid mite Aceria tulipae Keifer -LRB- Acari : Eriophyidae -RRB- , bulbs increase the gap between scales to such an extent that predatory mites can enter the interior of the bulbs . This prompted us to hypothesize that mite-infested coconut fruits undergo a change in perianth structure with the effect that predatory mites have better access to the space underneath the perianth and thereby to the coconut mites . To test this hypothesis we measured the gap between the perianth and the surface of coconut fruit -LRB- `` perianth-fruit gap '' -RRB- when uninfested and when infested by coconut mites , and compared the size of the gap with the size of the predatory mite N. baraki . The perianth functions as a protective cover to the female flower and the tender meristematic zone of the growing coconut fruit . In young coconut fruits -LRB- i.e. 1 -- 2 months after fertilization -RRB- the perianth is tightly appressed to the surface of the coconut fruit -LRB- Howard and Abreu-Rodriguez 1991 -RRB- , but , as the coconut fruit grows , the perianth-fruit gap increases slightly , but apparently just sufficient for the coconut mites to move under the perianth and feed on the meristematic zone of the coconut fruit . Tightness of the perianth -LRB- Howard and Abreu-Rodriguez 1991 -RRB- , bract arrangement -LRB- Moore 1986 -RRB- and shape -LRB- Mariau 1986 -RRB- of the coconut fruit have been shown to affect the susceptibility of coconut fruit to the coconut mites . Thus , perianth structure affects the probability of coconut mite infestation , but the extent of the effect depends on the growth phase of the coconut and on the palm cultivar . Coconut mites usually do not infest the meristematic zone of unfertilized coconut flowers -LRB- Mariau and Julia 1970 ; Hall and Espinosa-Becerril 1981 ; Moore and Alexander 1987 -RRB- . After fertilization , coconut fruits of all stages are susceptible to mite attack but in general , peak populations occur in 3 - to 7-months-old coconut fruits -LRB- Moore and Alexander 1987 ; Ramaraju et al. 2002 ; Fernando et al. 2003 -RRB- . For our experiments we used 4-month-old coconut fruits of three cultivars , commonly grown in Sri Lanka . We measured the perianth-fruit gap for each of these cultivars when uninfested and when infested by coconut mites . Finally , we compared the size of the gap with that of the predatory mite , N. baraki , to make inferences on accessibility of the space under the perianth to the predators of coconut mites . Materials and methods Perianth-fruit gap measurement Four-month-old coconut fruits -LRB- i.e. 4 months after fertilization -RRB- were collected from palms of the three cultivars : -LRB- 1 -RRB- cultivar ` Sri Lanka Dwarf Green ' -LRB- DG -RRB- , which has usually small , elongated coconut fruits , -LRB- 2 -RRB- cultivar ` Sri Lanka Tall ' -LRB- SLT -RRB- with larger and more round-shaped coconut fruits , and -LRB- 3 -RRB- a hybrid ` Sri Lanka Dwarf Green × Sri Lanka Tall ' -LRB- DGT -RRB- . After bringing the coconut fruits to the laboratory they were first split transversely into two halves to remove nut water . This made it easier to dissect the coconut fruit into four longitudinal sections across the perianth -LRB- Fig. 1 -RRB- . Dissected coconut fruits with disturbed perianth structure and loosened fibres at the coconut fruit surface were discarded from the measurements . Fig. 1Bract arrangement of the perianth on a coconut fruit . Longitudinal sections were taken along line A and B. OB-Outer bracts of the perianth , IB-Inner bracts of the perianth After splitting coconut fruits into four sections , the perianth-fruit gap was measured at two different places on each section -LRB- Fig. 2 -RRB- using a stereomicroscope with a graticule . The first measurement -LRB- L1 -RRB- was made at the rim of the perianth where it touches the coconut fruit surface -LRB- Fig. 2 -RRB- . The edge of each bract of the perianth has two different positions : -LRB- 1 -RRB- the edge that directly touches the surface of the coconut fruit , -LRB- 2 -RRB- the edge that overlaps -LRB- or is overlapped by -RRB- another bract . Measurements were not taken at the latter position , as it was difficult to dissect the coconut fruits along this position of the bract without disturbing the structure of the perianth . The second measurement -LRB- L2 -RRB- was taken 1 cm away from position L1 , higher up along the surface of the coconut fruit -LRB- Fig. 2 -RRB- . These two perianth-fruit gaps were measured in 157 infested -LRB- 61 from SLT , 39 from DG and 57 from DGT -RRB- and 114 uninfested -LRB- 43 from SLT , 28 from DG and 43 from DGT -RRB- coconut fruits . Fig. 2Longitudinal section of a coconut fruit showing position L1 at the edge of the bract touching the coconut fruit and position L2 , 1 cm away from L1 along the surface of the coconut fruit Mite census After measuring the gap between the surface of the coconut fruit and the perianth , bracts of each coconut fruit were removed to count the number of mites on the lower surface of each of them as well as on the underlying surface of the fruit . Counts of total number of mobile stages were done under a stereomicroscope . Total number of N. baraki was counted , whereas the population level of A. guerreronis was estimated by counting the total number of mites from six randomly selected circular -LRB- 1 cm Ø -RRB- patches , three on the lower side of the perianth and three on the surface of the coconut fruit under the perianth . Size of the predatory mites For c. 30 min predatory mites were kept in a Petri dish on wet cotton wool , placed on ice to lower the temperature -LRB- to 3 °C -RRB- , thereby reducing mite activity . Thickness of the soma was taken as a measure of size . This was assessed for 12 female deutonymphs , just before their last moult , and for 20 adult females , ten of which were 1-day-old since their last moult and the other ten were more-than-5-days-old . Measurements in each stage of predatory mites were replicated four times . Because the migratory population of N. baraki mainly consisted of adult females -LRB- Kumara , unpublished data -RRB- and they are more likely to be the first invaders under the perianth of infested coconut fruits , sizes of the larval and protonymphal stages of the predatory mites were not used in our analysis . The other predatory mite that is commonly found under the perianth is N. paspalivorus which occurs mainly in the wet zone of Sri Lanka -LRB- Fernando , unpublished data -RRB- . We did not measure the size of N. paspalivorus in our study since it does not occur in the dry-intermediate zone where we collected the coconuts . Statistical analysis The perianth-fruit gap -LRB- L1 -RRB- appeared to vary with the position along the perianth rim . The mean thickness of adult female N. baraki exceeded the mean value of the measurements taken at four positions along the perianth rim in most coconut fruits . Yet , the soma was less thick than the widest perianth-fruit gap on each coconut fruit . We hypothesized that the predatory mites can find the entrance to the interior of the perianth if there are places with a sufficiently large gap between fruit and perianth . Thus , the mean value of the perianth-rim-fruit gap -LRB- L1 -RRB- is less relevant if it concerns perianth accessibility to the predatory mite . Therefore , it was assumed that the widestgap observed from data obtained from four sites on each coconut fruit was the most relevant variable to be taken into account in the data analysis . Generalized Linear Models -LRB- GLM -RRB- were used to test differences in the perianth-fruit gap between main factors -LRB- category of coconut fruits i.e. infested and uninfested coconut fruits and cultivar -RRB- and to assess the interactions between the main factors . Using only the data on infested coconut fruits it was further investigated whether the perianth-fruit gap is a predictor of predator/herbivore mite density under the perianth . Regression analyses were performed to assess the relation between the widest perianth-fruit gap and the per nut density of coconut mites under the perianth and the per nut density of predatory mites under the perianth . The difference in the density of coconut mites and predatory mites among cultivars were analyzed using one-way ANOVA on log-transformed data . All analyses were carried out using Minitab ® , Version 11 . Results The mean of the widest perianth-fruit gaps at L1 and L2 in infested and uninfested coconut fruits in three cultivars are shown in Fig. 3 . In uninfested coconut fruits these were 41 , 68 and 40 μm at L1 and 39 , 78 and 45 μm at L2 in SLT , DG and DGT , respectively , whereas in infested coconut fruits these were 80 , 75 and 99 μm at L1 and 84 , 107 and 94 at L2 in SLT , DG and DGT , respectively . Thus , the perianth-fruit gap at L1 and L2 was significantly higher in infested coconut fruits than in uninfested coconut fruits -LRB- Table 1 ; see also Figs. 3 and 4 -RRB- . No significant difference was observed in the perianth-fruit gap among cultivars at L1 . However , the perianth-fruit gap was significantly affected by the cultivar at L2 -LRB- Table 1 -RRB- . The interaction between category of the coconut fruit -LRB- infested and uninfested -RRB- and cultivar was significant at L1 , but not at L2 -LRB- Table 1 -RRB- . This significant category-cultivar interaction at L1 arises because the increase in perianth-fruit gap due to coconut mite infestation is significant in two cultivars -LRB- SLT , DGT -RRB- , but not in the third cultivar -LRB- DG -RRB- . It should be noted that the perianth-fruit gap of uninfested fruits from the latter cultivar -LRB- DG -RRB- is very similar to the gap size of infested fruits in the two former cultivars -LRB- SLT , DGT -RRB- -LRB- Fig. 3 -RRB- . Fig. 3Mean -LRB- ± SE -RRB- of the widest gap at L1 and L2 in infested and uninfested coconut fruits of three cultivars : SLT = ` Sri Lanka Tall ' -LRB- white rectangles -RRB- , DG = ` Sri Lanka Dwarf Green ' -LRB- black rectangles -RRB- , DGT = ` Sri Lanka Dwarf Green × Sri Lanka Tall ' hybrid -LRB- grey rectangles -RRB- Table 1Analysis of variance of the gap -LRB- L1 and L2 -RRB- between the perianth and the surface of the coconut fruitSources of variancedfMSFPAt L1Category1254 ,67033.88 < 0.001 Cultivar25 ,9080.790.457 Category × Cultivar240 ,2875.36 < 0.01 Residual2657 ,516 At L2Category1582 ,23549.27 < 0.001 Cultivar256 ,5866.870.001 Category × Cultivar211 ,8311.440.239 Residual2658 ,232 Category refers to classification into infested and uninfested coconuts ; df = Degrees of freedom ; MS = Mean of squares ; P = Critical levelFig . 4Frequency distribution of coconut fruits over classes of widest L1 gaps in infested -LRB- black rectangles -RRB- and uninfested -LRB- white rectangles -RRB- coconut fruits -LRB- all three cultivars together -RRB- To test whether the widest perianth-fruit gap -LRB- L1 -RRB- is a predictor of mite density under the perianth regression analysis was carried out . Because most infested coconut fruits had predatory mites under their perianth , it was not possible to obtain a sufficiently large sample of coconut fruits that had coconut mites only . A scatter plot of the few data points did not show any conspicious trend . Regression of the number of predatory mites under the perianth on L1 measured on the same coconut fruit did not reveal a significant relation -LRB- R2 = 0.04 , slope = 0.011 , P = 0.436 -RRB- . This means that among the infested coconut fruits the perianth-fruit gap is not a reliable predictor of the density of predatory mites under the perianth . The absence of a correlation is not unexpected because the density records are snapshots of a dynamic process involving interactions between predator and prey . Sampling randomly over the time course of such an interaction is bound to show no correlation . The frequency distribution of coconut fruits over different gap classes showed different patterns in infested and uninfested coconut fruits -LRB- Fig. 4 -RRB- . At L1 , 79 % of the uninfested coconut fruits had a widest perianth-fruit gap less than 100 μm whereas 68 % of the infested coconut fruits had a highest perianth-fruit gap exceeding 100 μm . These percentages , i.e. 21 % for uninfested fruits and 68 % for infested fruits , are significantly different according to Chi-square analysis of the 2 × 2 frequency table that can be constructed from the table below Fig. 4 -LRB- X2 = 58.63 >> 10.83 at α = 0.001 -RRB- . The frequency distribution of perianth-fruit gap at L2 followed the same pattern as that at L1 . In conclusion , the gap between perianth and surface of the coconut fruits increased dramatically when infested by coconut mites . The mean thickness -LRB- ± SE -RRB- of the female deutonymphs of N. baraki was estimated to be 95 ± 4 μm -LRB- n = 12 -RRB- . In adult female predatory mites , the mean thickness was 100 ± 4 μm in mites 1-day-old after their last moult -LRB- n = 10 -RRB- and 110 ± 7 μm in mites older than 5 days after their last moult -LRB- n = 10 -RRB- . However , the sizes of deutonymphs and two age classes of adult females were not statistically different from each other . The number of A. guerreronis varied from 0 to 6491 with means of 1,178 , 1,302 and 1,093 in six circular patches of 1 cm diameter in SLT , DG and DGT , respectively -LRB- Fig. 5 -RRB- . Their density -LRB- per six circular patches of 1 cm diameter -RRB- was not significantly different among the infested cultivars -LRB- P = 0.322 , df = 2 and F = 1.14 for log-transformed data -RRB- . The number of N. baraki ranged from 0 to 55 with means of 9 , 13 and 8 mites per coconut fruit in SLT , DG and DGT , respectively -LRB- Fig. 5 -RRB- . There was a significant difference in the density of N. baraki among infested cultivars -LRB- P = 0.024 , df = 2 and F = 3.82 for log transformed data -RRB- : cultivar DG had a significantly higher density of predatory mites than the other two cultivars . We can therefore not exclude the possibility that the densities of coconut mites are blurred by effects of predatory mites . Unfortunately , sample sizes of coconut fruits ` with coconut mites but no predatory mites ' were far too small to warrant further analysis -LRB- e.g. in DG there were only five coconut fruits of this type -RRB- . Fig. 5Mean -LRB- ± SE -RRB- of the number of coconut mites -LRB- white rectangles -RRB- and predatory mites -LRB- black rectangles -RRB- per coconut fruit from three coconut cultivars -LRB- SLT , DG , DGT ; see legend of Fig. 3 -RRB- Discussion We found that the perianth-fruit gap was different among cultivars SLT , DG and DGT of the coconut palm . Except at L1 in infested coconut fruits , among the three cultivars used in our study , cultivar DG had the widest mean gap . In general DG bears smaller and more elongated coconut fruits than the other two cultivars . As observed by Mariau -LRB- 1977 -RRB- , varieties with small coconut fruits are more susceptible to coconut mites than varieties with large coconut fruits . This may well be because the perianth of the smaller coconut fruits is less firmly attached to the coconut fruit , giving mites better access to the space under the perianth . In our study the highest mean number of coconut mites was also found on DG . However , the density of coconut mites did not significantly differ among cultivars . Therefore , the results of our study did not firmly support the idea that the coconut fruits with larger gap between perianth and the surface of the coconut fruit -LRB- in other words fruits with loosely attached perianth -RRB- are more susceptible to the coconut mite . It should be noted that the mean widest gap between the perianth and the surface of the uninfested coconut fruits exceeded 40 μm in all three cultivars , which is larger than the cross-diameter of adult female coconut mites -LRB- 36 -- 52 μm ; Keifer 1965 -RRB- . Hence , the perianth-fruit gap in uninfested coconut fruits of any of the three cultivars is large enough for mature coconut mites to enter the space under the perianth . Hence , we expect the sub-perianth space of the three cultivars in our study to be equally accessible to mature coconut mites . The widest perianth-fruit gap per uninfested coconut fruit was much less than 100 μm -LRB- see Fig. 3 -RRB- in 79 % of the coconut fruits we observed in our study -LRB- Fig. 4 -RRB- . However , the mean cross-diameter of the soma of adult female N. baraki was c. 110 μm . Therefore , it is clear that the perianth-fruit gap of most uninfested coconut fruits is not large enough for adult females of N. baraki to enter the space under the perianth . This largely applies to the deutonymphs of N. baraki as well , since their mean soma cross-diameter is close to 100 μm . Possibly , larvae and protonymphs of N. baraki have a soma small enough to pass the perianth-fruit gap of uninfested coconut fruits . However , juvenile predatory mites are unlikely to be the first invaders under the perianth , because they are much less mobile than adults and because female predatory mites can only lay eggs when there is a sufficient supply of prey . Adult females are therefore more likely to be the first to colonize a coconut , but they can not enter sub-perianth space unless coconut mites have established . Hence , initially coconut mites experience reduced risk of being eaten by predatory mites when feeding on the tissue beneath the perianth . Interestingly , we found that the gap in coconut fruits infested by coconut mites was significantly wider than that in uninfested coconut fruits -LRB- Fig. 4 -RRB- . Of the infested coconut fruits in our study , 68 % had a perianth-fruit gap above 100 μm at L1 which is large enough for N. baraki to creep under the perianth . This suggests the following mechanistic hypothesis to be tested by future experimental analysis : when infested by coconut mites , the coconut fruits increase the gap between the perianth and the surface of the coconut fruit to such an extent that the predators can reach their otherwise-concealed prey . Our results on coconuts are consistent with observations by Lesna et al. -LRB- 2004 -RRB- on tulip bulbs . When infested by the rust mite , A. tulipae , tulip bulbs become attractive to the predatory mite , Neoseiulus cucumeris Oudemans -LRB- Acari : Phytoseiidae -RRB- -LRB- Aratchige et al. 2004 -RRB- . Having a small cross-sectional area , rust mites can easily move into the spaces in between bulbs scales where they are in refuge because the bulb scales in the apex -LRB- so called ` nose ' -RRB- of the bulbs are too tightly packed for predators to move in . However , in response to damage by rust mites , bulbs start to produce ethylene which triggers the bulbs to widen the gap between scales in the ` nose ' of the bulb , apparently to an extent that is just enough to allow the predatory mites to enter the inside of the bulb -LRB- Lesna et al. 2004 -RRB- . More importantly , treating the tulip bulbs with an ethylene blocker causes the space between bulb scales to be more narrow : tight enough to prevent access by predatory mites , but definitely not tight enough for the rust mite to enter the inside . Thus , it is not just the feeding damage to the bulb scale tissue that causes widening of the space between bulb scales -LRB- Lesna et al. unpublished data -RRB- . Whether the structural changes in the perianth of coconut fruits in response to coconut mite attack is herbivore-induced plant response or a by-product of necrosis and suberization of the coconut fruit surface due to herbivory , remains to be elucidated , however . The ` by-product ' hypothesis is not supported by the observation that the perianth-fruit gap of uninfested fruits from cultivar DG is very similar to the gap size of infested fruits from the same cultivar , as well as the two other cultivars -LRB- SLT , DGT -RRB- under study . Thus , coconut mite infestation has no significant effect on perianth-fruit gap in cultivar DG and the space beneath the perianth is always accessible to the predatory mite N. baraki , irrespective of coconut mite infestation . Whereas this shows that increased gap size is not a simple consequence of necrosis and suberization of the meristimatic tissue beneath the perianth , it does not disprove this hypothesis -LRB- e.g. feeding effects on perianth structure may depend on the structure itself -RRB- and -- as yet -- there is no evidence for the ` induction ' hypothesis . Determining whether or not the changes in perianth structure are induced or not , has wider implications . An induced response indicates a net benefit to the coconut palm and hence a reason why it may have been favoured by natural selection . Such an evolutionary response of the plant requires that the association between the eriophyids and the coconut palm has existed for a long enough time and that eriophyids have represented a selective factor of importance . This may not be true for the Americas because Cocos nucifera was introduced some 500 years ago , whereas A. guerreronis , while native to the Americas , has been first described and discovered as a pest in 1965 -LRB- Navia et al. 2005 -RRB- . Moreover , there is insufficient data to make any inference on mite-palm associations for the Asian region . Thus , any speculation on the evolution of induced plant responses in perianth structure rests on the assumption of a sufficiently long association with some eriophyoid species or other herbivore -LRB- e.g. tarsonemid mites ; see Lawson-Balagbo et al. 2007 -RRB- small enough to reach the space beneath the perianth . Alternatively , plants ancestral to coconut palms have been selected to induce a generalized ` open-the-gap ' response to attack by any herbivore small enough to enter and feed in otherwise tight folds of plant tissue . Another crucial assumption is that there are predators small enough to enter sub-perianth space and capable of controlling coconut mites . This may hold for the predatory mite N. baraki since it is frequently found associated with coconut mites -LRB- Fernando et al. 2003 -RRB- , but critical tests to prove its biocontrol capacity are still to be done . For herbivore-induced increase of the perianth-fruit gap to be a plant defense strategy favoured by selection , the benefits should exceed the costs . Clearly , when the perianth-fruit gap is increased , coconut fruits may not only get assistance from predatory mites to combat coconut mites , but they would also become more vulnerable to herbivores that are somewhat larger than eriophyoid mites . This cost may be offset by providing sub-perianth access to a generalist predatory mite , like N. baraki , that can feed on -LRB- juvenile stages of -RRB- slightly larger herbivorous arthropods as well . However , the increased gap width may also provide intraguild predators , such as Proctolaelaps bickleyi -LRB- Acari : Ascidae -RRB- , with access beneath the perianth , as recently shown in an extensive survey in Brazil -LRB- Lawson-Balagbo et al. 2007 -RRB- . Most intraguild predators , including P. bickleyi , are larger than their intraguild prey , and this may either lead to partitioning of refuge space under the perianth depending on predator and refuge size or even to exclusion from the sub-perianth space -LRB- Lawson-Balagbo et al. 2007 -RRB- . We therefore hypothesize that the maximum perianth-fruit gap created by the coconut palm represents a compromise between benefits in terms of protection by predatory mites and costs in terms of desiccation , increased diversity of herbivores and impact of intraguild predators of the effective predators of coconut mites .

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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O B I O O O O O O B O O O B I O O B I O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B I O O O O O B I O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O 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O O O O B O O O O O O O O O O O O O O O O O O B I O O B O O O O O O B O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O 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eriophyidae
coconut mites
coconut
predatory mites
phytoseiidae
perianth
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Vascular complications of prosthetic inter-vertebral discs Five consecutive cases of prosthetic inter-vertebral disc displacement with severe vascular complications on revisional surgery are described . The objective of this case report is to warn spinal surgeons that major vascular complications are likely with anterior displacement of inter-vertebral discs . We have not been able to find a previous report on vascular complications associated with anterior displacement of prosthetic inter-vertebral discs . In all five patients the prosthetic disc had eroded into the bifurcation of the inferior vena cava and the left common iliac vein . In three cases the aortic bifurcation was also involved . The fibrosis was so severe that dissecting out the arteries and veins to provide access to the relevant disc proved impossible . Formal division of the left common iliac vein and artery with subsequent repair was our solution . Anterior inter-vertebral disc displacement was associated with severe vascular injury . Preventing anterior disc displacement is essential in disc design . In the event of anterior displacement , disc removal should be planned with a Vascular Surgeon . Key points Anterior prosthetic disc displacement frequently involves major arteries and veins . Removal of an L45 disc prosthesis is associated with vascular injury . A Vascular Surgeon should be involved in disc removal . Introduction Replacement of the inter-vertebral disc is designed to relieve symptomatic back pain secondary to disc degeneration by preserving segmental function . A successful artificial disc replacement would avoid the significant long-term problems associated with spinal fusion -LSB- 9 -RSB- . We report five consecutive cases of anterior displacement of prosthetic inter-vertebral discs resulting in erosion into the bifurcation of the vena cava and aorta , from a series of only 13 patients . One patient suffered recurrent back pain . These patients had no preoperative vascular symptoms to warn of this vascular involvement and all of these discs were removed in order to prevent further vascular injury . The complications associated with removal are described together with our suggestions on an approach to this challenging surgical problem . Prosthetic disc replacements -LRB- AcroFlex disc , DePuy Acromed , Raynham , MA , USA -RRB- were carried out as part of a clinical trial with ethical approval , regulatory approval and with informed patient consent . All patients had incapacitating back pain . Leg pain was not an exclusion criteria unless directly attributable to a prolapsed inter-vertebral disc . All patients in this study had magnetic resonance imaging evidence of degenerative disc disease . All patients had an Oswestry disability index -LRB- ODI -RRB- greater than 30 % and all had discographically established concordant pain at the target level/s . Inclusion criteria , the follow-up protocol and disc design for this study have been described previously -LSB- 5 -RSB- . Case 1 A 33-year-old woman presented with a 5-year history of low back and right leg pain . A two level artificial inter-vertebral disc replacement was performed at L45 and L5S1 without complication through an anterior transperitoneal approach -LRB- L45 31.5 × 43 × 9 × 5 ° AcroFlex disc and L5S1 34 × 46 × 9 × 10 ° AcroFlex disc -RRB- -LRB- Fig. 1a -- c -RRB- . Fig. 1Postoperative X-ray with satisfactory placement of L45 and L5S1 AcroFlex disc , lateral view -LRB- a -RRB- AP view -LRB- b and c -RRB- with anterior disc displacement at 6 months -LRB- d -RRB- The patient made an uneventful recovery with improved symptoms at 6 weeks . However on X-ray the prosthesis at L45 had moved 5 mm anteriorly . At 6 months there was further L45 prosthesis displacement ; however , mobility was preserved with full lumber flexion and extension at video fluoroscopy -LRB- Fig. 1d -RRB- . The L45 artificial disc was replaced at 15 months with a size 2 SB Charité III disc containing an 8.5-mm spacer -LRB- Waldemar Link GmbH & Co. , Hamburg , Germany -RRB- . At surgery the disc had stretched and eroded into the left common iliac vein . The distal vein was occluded with thrombus . An injury to the medial wall of the left common iliac artery was repaired with 5/0 Prolene and the occluded vein was oversewn with 4/0 Prolene . This provided access and permitted removal of the disc . Postoperative recovery was complicated by a paralytic ileus only . The patient has an L5S1 prosthesis which remains in an acceptable position . She has subsequently become pregnant and had a normal delivery without the need for Caesarian section . Case 2 A 40-year-old woman presented with a 3-year history of lumber back pain . She underwent L45 disc replacement with a 29 × 40 × 9 × 10 ° AcroFlex disc . This surgery was complicated only by a temporary loss of bladder filling sensation . At 6 week follow-up her back and leg symptoms were significantly improved . Unfortunately at 6 months her back pain had returned and she was now suffering pain and tingling in the left L5 dermatome . On X-ray the prosthesis had moved anteriorly . At 1 year the patient agreed to have the prosthesis removed . At operation the prosthesis was eroding into the left common iliac artery and vein . Both vessels were mobilised with difficulty due to dense scar tissue , the inevitable venous and arterial injuries were repaired with 4/0 Prolene . The disc was replaced with a Stabilis cage -LRB- Stryker , UK -RRB- containing artificial bone graft which was secured with a 3.2 × 34 mm screw and washer . Postoperatively the patient wore class II compression hosiery and was prescribed 40 mg Clexane twice daily . Unfortunately , despite this prophylaxis , she suffered left common iliac artery and iliofemoral deep vein thrombosis . Full anticoagulation was achieved with Tinzaparin and subsequently Warfarin . Swelling is controlled by class II compression hosiery . Transluminal angioplasty has been performed for a stenosis of the left common iliac artery at the site of repair . Her claudication has improved and is now thought to be venous . Case 3 A 51-year-old man presented with bilateral leg pain and no motor or sensory loss . He had undergone laminectomy 12 years previously for a disc prolapse . A prosthetic inter-vertebral disc -LRB- 29 × 40 × 9 × 10 ° AcroFlex disc -RRB- was placed in the L45 inter-vertebral space , without complication , using an anterior transperitoneal approach . The postoperative X-ray showed the prosthesis to be in an acceptable position , i.e. centrally placed in the disc space on antero-posterior projection and posteriorly placed on the lateral view -LRB- Fig. 2a , b -RRB- . The patient 's symptoms were improved but the prosthesis had migrated 2 mm anteriorly at 6 weeks and 5 mm by 12 months -LRB- Fig. 2c -RRB- . Fig. 2Satisfactory placement of L45 AcroFlex disc , lateral view -LRB- a -RRB- and AP view -LRB- b -RRB- with anterior displacement at 12 months -LRB- c -RRB- and subsequent spinal stabilisation with plate and pedicle screws -LRB- d -RRB- At operation the disc had migrated into the left common iliac vein posterior to the aortic bifurcation . A tear was made in the left iliac vein while mobilising these vessels . The left common iliac vein was divided transversely to facilitate removal of the disc . A 14-mm carbon fibre cage filled with iliac crest bone graft was inserted and the iliac vein re-anastomosed with 4/0 Prolene . Postoperative duplex scanning showed the left common iliac vein and artery to be patent . The spine was stabilised with a flat plate and pedicle screws 12 days later -LRB- Fig. 2d -RRB- . Case 4 A 47-year-old man presented with lumbar back pain radiating to his thigh and buttock . He underwent L45 and L5S1 disc replacement with a 31.5 × 43 × 11 ° AcroFlex disc and a 31.5 × 43 × 9 ° AcroFlex disc respectively without postoperative complication . At 1 month follow-up he was well with no pain . Anterior displacement of the L45 disc was first seen on plain X-ray at 2 years and the disc was removed 11 months later . Having learned from previous bitter experiences , the vascular surgeon formally divided the left common iliac artery and vein so that there was good access to remove the disc and replace it with a Stabilis cage . The left common iliac artery and vein were then re-anastomosed . Despite this approach the right common iliac vein was injured and required repair . Full deep vein thrombosis prophylaxis was undertaken with pneumatic compression in theatre , peri-operative low molecular weight Heparin , postoperative compression stockings in addition to anticoagulation with Warfarin . Both iliac vessels were widely patent with no thrombus and normal blood flow velocity on duplex imaging at 1 month . Postoperatively he has continued to suffer pain after prolonged standing with occasional sleep disturbance . The L5S1 disc was stable on X-ray at 6 months with fusion progressing between L45 . Case 5 A 44-year-old man who had long standing low back pain had a single level degenerate disc at L5S1 . The L5S1 disc was replaced with a 29 × 40 × 10 ° 11 mm AcroFlex disc . Immediately postoperatively he was well with an improvement in his symptoms . Gradual displacement of the prosthesis occurred from 3 months . The prosthesis was removed at 19 months and fusion performed using a Stabilis cage and cancellous bone graft . During surgery a tear of the left common iliac vein occurred during mobilisation this was repaired with 2.0 Prolene . Formal division of the iliac vein and artery was not necessary as the disc was removed from L5S1 . Preoperatively the ODI was 48 % after fusion it had fallen to 10 % . Discussion The five patients reported here gained early symptomatic relief from low back and leg pain with an artificial inter-vertebral disc . However , in each case , revision following surgery for benign disc degeneration was associated with a major vascular injury . Anterior displacement of the L45 disc caused pressure on the left common iliac vein and artery with stretching of the vessels and erosion into the vessel wall in three cases . It was impossible to mobilise the stretched vessels from the firmly adherent surrounding dense scar tissue without vascular injury . In one case the left common iliac vein was thrombosed while in the others repairs were necessary after almost impossible mobilisation of the vessels to expose the prosthesis . Damage to the left common iliac vein and artery in one case led to both venous and arterial thrombosis . It is likely that this complication will lead to longstanding symptoms of venous insufficiency . The only safe solution for adequate exposure of an anteriorly displaced visco-elastic artificial L45 disc is the formal division and subsequent re-anastomosis of the left common iliac vein and if necessary the left iliac artery ; this strategy was successfully employed in cases 3 and 4 . An anterior transperitoneal approach is essential to allow proximal and distal vessel control before division . A retroperitoneal approach in this type of revision surgery would be extremely hazardous and potentially life threatening due to an inability to control the right common iliac vein or vena cava when there is bleeding from the left common iliac vein . The aortic bifurcation would also be difficult to control . The Link SB Charité disc is currently the most widely implanted inter-vertebral disc . This articulating disc consists of an ultra high molecular weight polyethylene spacer between two separate cobalt -- chromium -- molybdenum alloy plates . Griffith et al. reported displacement or dislocation of the prostheses in 6 of 139 implants with an average follow-up of 11 months . There were six reported vein injuries although it is not clear whether these injuries were associated with displacement or revision surgery or at what level the implant was placed -LSB- 6 -RSB- . Cinotti et al. reported only one anterior displacement of 46 SB Charité III prostheses and no vascular injury , with a minimum follow-up of 2 years -LSB- 3 -RSB- . In a series of 105 patients with 154 SB Charité III discs five vascular problems were reported -LRB- two phlebitis , two pulmonary embolism and one acute leg ischaemia -RRB- although no information on the rate of revision or anterior displacement was presented in this series -LSB- 10 -RSB- . Zeegers et al. reported a prospective study of 50 patients where 75 SB Charité III prosthesis were inserted . None of 38 patients with full 2 year radiographic follow-up had migration of the prosthesis . One patient lost to follow-up had malposition and some slip but was lost to follow-up . Of 12 patients who underwent reoperation only one aortic injury was reported during failed disc re-positioning and subsequent fusion -LSB- 12 -RSB- . These reports are all non-randomised series without any control and in one case retrospective . The only published randomised study of inter-vertebral disc replacement compares the Charité disc with spinal fusion . This study showed that pain and disability scores are equivalent at 24 months follow-up . There was a 4.4 % incidence of venous injury in the arthroplasty group and device failure in 5.1 % compared to 9.1 and 2 % respectively in the spinal fusion group -LSB- 2 -RSB- . This first design of the AcroFlex disc contained a hexane based polyolefin rubber core vulcanised between two titanium plates . A retrospective review of six patients who had AcroFlex discs , with a mean follow-up was 3.5 years , reported a poor outcome in two patients with fracture of the rubber component and persistent symptoms in a second . There were no reported cases of disc displacement or of vascular injury during one revision although the prosthesis was at L5S1 -LSB- 4 -RSB- . Fraser et al. reported a series of 28 patients who had the third generation AcroFlex disc implanted , 17 patients had the same disc design used in this study . Eight of 28 required revision surgery for deterioration of symptoms and failure of the prosthesis . Two of the four patients who had removal of the prosthesis suffered left iliac vein injury during surgery . Fraser et al. inserted the discs through a retroperitoneal approach and suffered one anterior displacement in this case series -LSB- 5 -RSB- . It should be noted that there were two pilot studies . In the first series all patients were implanted in Adelaide . Displacement occurred in series 2 at both test centres but only in Manchester was displacement severe enough to warrant removal for the reasons stated . Disc displacement due to placement of the disc too far anteriorly has been reported with the PRODISC -LSB- 1 -RSB- . The high incidence of disc displacement in this series -LRB- 5 of 13 -RRB- is thought to be associated with an anterior transperitoneal approach and more extensive removal of the annulus rather than malposition . Design is also an important factor in preventing displacement since it occurred in both centres . On revision surgery no osteointegration of these implants was apparent and displacement occurred despite re-design of the endplates , as a result of the series 1 failure , to a domed surface with 4 -- 6 tapered fins on each surface . This redesign was also inadequate . Van Ooij has described a series of 27 patients with anterior displacement of four Charité discs one of which led to compression of the iliac artery causing symptoms of ischaemia -LSB- 11 -RSB- . A systematic review of total disc replacement examined the results from 564 arthroplasties in 411 patients . The majority of the cases considered were the Charité disc and only eight cases of vascular injury were identified -LSB- 8 -RSB- . The authors of both papers concluded that removal of artificial discs is potentially dangerous and no reliable strategy for revision surgery exists for a procedure without proven long-term reliability . The five cases described in this report highlight failure of three design criteria for a disc prosthesis : -LRB- i -RRB- the rapid fixation to bone , -LRB- ii -RRB- fail-safe design to prevent damage to surrounding structure in case of failure and -LRB- iii -RRB- medium-term osteointegration -LSB- 7 -RSB- . If a disc does fail and needs to be removed , surgery can be hazardous with associated vascular injury -LSB- 8 -RSB- . Consequently , we advise that a Vascular Surgeon should be available to try and mobilise or divide and re-anastomose the left common iliac vessels when needed for adequate exposure of a L45 disc . Furthermore , this revision disc surgery is usually difficult and should be planned to include autologous blood transfusion .

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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

inter-vertebral disc replacement
artificial inter-vertebral disc
inter-vertebral arthroplasty


Influence

of

convolution

filtering

on

coronary

plaque

attenuation

values

observations

in

an

ex

vivo

model

of

multislice

computed

tomography

coronary

angiography

Attenuation

variability

-LRB-

measured

in

Hounsfield

Units

HU

-RRB-

of

human

coronary

plaques

using

multislice

computed

tomography

-LRB-

MSCT

-RRB-

was

evaluated

in

an

ex

vivo

model

with

increasing

convolution

kernels

MSCT

was

performed

in

seven

ex

vivo

left

coronary

arteries

sunk

into

oil

followingthe

instillation

of

saline

-LRB-

-RRB-

and

a

solution

of

contrast

material

-LRB-

mgI/ml

iomeprol

-RRB-

Scan

parameters

were

slices/collimation

mm

rotation

time

ms.

Four

convolution

kernels

were

used

smooth

and

An

experienced

radiologist

scored

for

the

presence

of

plaques

and

measured

the

attenuation

in

lumen

calcified

and

noncalcified

plaques

and

the

surrounding

oil

The

results

were

compared

by

the

ANOVA

test

and

correlated

with

Pearson

's

test

The

signal-to-noise

ratio

-LRB-

SNR

-RRB-

and

contrast-to-noise

ratio

-LRB-

CNR

-RRB-

were

calculated

The

mean

attenuation

values

were

significantly

different

between

the

four

filters

-LRB-

p

-RRB-

in

each

structure

with

both

solutions

After

clustering

for

the

filter

all

of

the

noncalcified

plaque

values

-LRB-

HU

with

saline

HU

in

contrast

solution

-RRB-

were

significantly

different

with

the

exception

of

the

pair

for

which

a

moderate-high

correlation

was

generally

found

Improved

SNRs

and

CNRs

were

achieved

by

and

The

use

of

different

convolution

filters

significantly

modifief

the

attenuation

values

while

sharper

filtering

increased

the

calcified

plaque

attenuation

and

reduced

the

noncalcified

plaque

attenuation

Introduction

Multislice

computed

tomography

-LRB-

MSCT

-RRB-

of

the

coronary

arteries

is

becoming

an

established

method

to

exclude

the

presence

of

significant

stenosis

because

of

the

high

negative

predictive

value

-LSB-

-RSB-

Stenosis

however

occurs

in

a

later

stage

of

coronary

artery

disease

-LRB-

CAD

-RRB-

consequently

the

atherosclerotic

plaque

composition

and

morphology

may

represent

a

better

predictor

of

plaque

stability

-LSB-

-RSB-

Until

recently

only

invasive

techniques

such

as

intracoronary

ultrasound

-LRB-

ICUS

-RRB-

have

been

able

to

provide

consistently

reproducible

quantitative

and

qualitative

information

on

plaque

composition

-LSB-

-RSB-

ICUS

however

can

not

be

used

for

routine

evaluation

of

plaque

characteristics

because

of

its

invasiveness

and

related

increased

risk

additional

time

and

cost

Magnetic

resonance

imaging

may

be

used

to

characterize

in

vivo

the

atherosclerotic

plaque

morphology

and

composition

in

carotid

-LSB-

-RSB-

and

coronary

arteries

-LSB-

-RSB-

Several

recent

in

vivo

studies

have

stressed

that

MSCT

can

be

used

to

characterize

coronary

atherosclerotic

plaque

and

has

the

potential

to

become

the

noninvasive

modality

of

choice

for

plaque

imaging

-LSB-

-RSB-

This

technique

is

able

to

provide

information

on

noncalcified

coronary

plaques

which

may

be

useful

to

identify

a

high-risk

plaque

-LSB-

-RSB-

MSCT

plaque

assessment

is

based

upon

the

variable

X-ray

attenuation

of

the

tissue

components

However

several

parameters

such

as

lumen

attenuation

convolution

filtering

body

mass

index

of

the

patient

and

contrast-to-noise

ratio

-LRB-

CNR

-RRB-

of

the

images

are

able

to

modify

the

attenuation

values

that

are

being

used

to

define

the

composition

of

coronary

plaques

The

aim

of

the

present

study

was

to

investigate

the

effect

of

increasing

convolution

filtering

on

plaque

components

with

varying

coronary

attenuation

in

an

ex

vivo

coronary

model

Material

and

methods

Specimens

Seven

ex

vivo

left

anterior

descending

-LRB-

LAD

-RRB-

coronary

arteries

were

obtained

at

autopsy

-LRB-

Fig.

-RRB-

from

seven

deceased

patients

four

male

and

three

female

with

a

mean

age

of

years

five

-LRB-

four

males

and

one

female

with

an

age

between

and

years

-RRB-

jad

died

of

noncardiovascular

diseases

and

two

-LRB-

one

male

and

one

female

with

an

age

of

and

years

respectively

-RRB-

had

died

of

ischemic

heart

disease

The

Institutional

Review

Board

approved

the

study

protocol

Fig.

of

proximal

left

coronary

artery

specimen

CX

Left

circumflex

LAD

left

anterior

descending

artery

LM

left

main

coronary

artery

The

specimens

were

prepared

and

examined

separately

Each

coronary

artery

was

fitted

with

two

cannulas

fixed

with

surgical

thread

in

the

proximal

-LRB-

in

the

left

main

-RRB-

and

distal

ends

-LRB-

in

the

LAD

-RRB-

The

circumflex

artery

had

been

closed

earlier

at

its

end

with

thread

Only

the

LAD

was

used

because

of

the

major

length

-LRB-

segments

considered

with

a

mean

length

of

cm

-RRB-

and

higher

prevalence

of

atherosclerotic

disease

and

for

technical

reasons

-LRB-

ability

to

fix

a

surgical

thread

in

the

left

main

without

hampering

the

evaluation

of

the

proximal

LAD

-RRB-

Contrast

material

Two

solutions

were

used

a

saline

and

a

dilution

of

contrast

material

-LRB-

mgI/ml

Iomeprol

Bracco

Italy

-RRB-

The

attenuation

values

-LRB-

Hounsfield

Units

HU

-RRB-

of

the

two

solutions

measured

in

a

syringe

after

dilution

were

HU

-LRB-

defined

as

saline

no

contrast

material

was

diluted

-RRB-

and

HU

-LRB-

defined

as

contrast

solution

-RRB-

We

preferred

to

use

a

dilution

to

achieve

a

mean

coronary

in-lumen

density

HU

which

is

not

typically

achieved

in

in

vivo

cardiac

computed

tomography

angiography

-LRB-

CTA

-RRB-

studies

in

order

to

emphasize

the

difference

with

the

saline

solution

Our

study

benefits

from

two

consecutive

scans

of

the

same

vessel

-LRB-

e.g.

with

and

without

contrast

media

-RRB-

for

a

comparative

evaluation

of

plaques

which

is

not

truly

feasible

during

in

vivo

studies

due

to

high

radiation

exposure

Experimental

settings

A

box

was

filled

with

olive

oil

Prior

to

positioning

the

specimen

in

the

oil

saline

was

injected

through

the

sheaths

to

wash

out

the

air

bubbles

in

the

lumen

as

much

as

possible

Once

the

specimen

had

sunk

into

the

oil

which

simulated

epicardial

fat

the

solution

was

instilled

through

the

sheaths

using

a

syringe

from

the

proximal

end

of

the

specimen

The

injection

was

finished

when

the

solution

was

observed

leaking

out

of

the

distal

end

of

specimen

The

leaking

solution

was

removed

from

the

specimen

using

a

syringe

The

same

procedure

was

used

to

fill

the

LAD

with

both

solutions

The

specimen

was

kept

for

all

investigations

in

the

same

longitudinal

position

-LRB-

head-LM-to

feet-distal

end

of

LAD

-RRB-

to

obtain

direct

cross-section

images

Scan

parameters

A

MSCT

scan

-LRB-

Somatom

Sensation

Siemens

Germany

-RRB-

was

performed

following

the

intra-coronary

injection

of

two

solutions

Scans

were

performed

at

the

following

parameters

slices/collimation

mm

rotation

time

ms

feed

per

rotation

mm

-LRB-

pitch

mm

-RRB-

kv

mAs

effective

slice

thickness

mm

reconstruction

increment

mm

field

of

view

-LRB-

FOV

-RRB-

mm

Four

convolution

filters

were

used

-LRB-

smooth

-RRB-

-LRB-

medium

smooth

-RRB-

-LRB-

medium

-RRB-

and

-LRB-

sharp

-RRB-

Based

on

our

clinical

experience

in

routine

evaluation

was

used

instead

of

because

of

a

better

delineation

of

the

coronary

arteries

and

atherosclerotic

lesions

The

scan

geometry

was

based

on

a

retrospective

electrocardiogram

-LRB-

ECG

-RRB-

gated

protocol

-LRB-

the

same

used

for

the

in

vivo

examination

-RRB-

This

protocol

is

based

on

a

low

pitch

that

allows

a

retrospective

reconstruction

of

multiple

phases

within

the

cardiac

cycle

A

demo-ECG

was

switched

on

and

a

heart

rate

of

occurred

during

the

scan

The

half-rotation

reconstruction

algorithm

brought

the

effective

temporal

resolution

down

to

ms.

Data

collection

and

analysis

A

radiologist

with

a

level

expertise

in

cardiac

CT

-LSB-

-RSB-

loaded

the

data

sets

into

a

dedicated

workstation

-LRB-

Leonardo

Siemens

Germany

-RRB-

and

performed

orthogonal

views

of

all

specimens

for

each

convolution

filter

with

two

solutions

One

operator

performed

all

of

the

measurements

Each

specimen

was

evaluated

for

the

presence

of

atherosclerotic

plaque

The

coronary

wall

thickening

of

plaque

-LRB-

minimum

size

observed

-RRB-

was

clearly

visible

from

the

surrounding

oil

with

low

attenuation

and

from

the

lumen

after

injection

of

contrast

material

Plaques

were

targeted

regardless

of

their

size

The

operator

loaded

the

two

data

sets

for

each

solution

of

the

same

specimen

into

a

workstation

screen

scrolling

the

data

sets

in

parallel

with

standard

soft-tissue

window

settings

-LRB-

window

width

HU

window

center

HU

-RRB-

Once

a

plaque

was

detected

in

the

two

solutions

by

means

of

a

comparative

evaluation

the

operator

drew

four

regions

of

interest

-LRB-

ROIs

-RRB-

for

the

contrast

material

in

the

lumen

of

the

vessel

-LRB-

defined

as

lumen

-RRB-

the

soft

tissue

of

the

coronary

plaque

-LRB-

defined

as

noncalcified

plaque

-RRB-

the

calcification

within

the

coronary

artery

wall

-LRB-

defined

as

calcified

plaque

-RRB-

and

the

oil

surrounding

the

plaque

-LRB-

defined

as

surrounding

-RRB-

The

ROIs

-LRB-

minimum

size

-RRB-

were

drawn

as

large

as

possible

while

avoiding

the

borders

of

each

structure

in

order

to

limit

the

partial

volume

effect

Once

the

four

ROIs

were

drawn

the

operator

could

copy

and

paste

these

into

other

stacks

of

images

The

two

data

sets

for

each

solution

were

then

evaluated

using

four

convolution

filters

-LRB-

and

-RRB-

For

each

ROI

the

mean

and

the

standard

deviation

of

the

attenuation

value

were

collected

Overall

attenuation

values

were

obtained

Statistical

analysis

The

attenuation

values

are

presented

as

means

and

standard

deviations

The

signal-to-noise

ratio

-LRB-

SNR

-RRB-

was

calculated

as

the

mean

attenuation

value

of

the

ROI/standard

deviation

of

the

surrounding

oil

attenuation

value

The

standard

deviation

HU

value

of

the

surrounding

air

is

often

used

for

the

estimation

of

noise

However

we

did

not

include

the

air

in

our

images

The

standard

deviation

of

the

surrounding

oil

can

estimate

the

noise

because

of

its

reliable

signal

SNRs

are

presented

as

means

for

each

kernel

The

contrast-to-noise

ratio

-LRB-

CNR

-RRB-

was

calculated

as

-LRB-

mean

attenuation

A

mean

attenuation

B

-RRB-

image

noise

-LRB-

defined

as

the

standard

deviation

of

the

surrounding

oil

-RRB-

CNRs

of

-LRB-

lumen

noncalcified

plaque

-RRB-

-LRB-

noncalcified

plaque

surrounding

-RRB-

-LRB-

calcified

plaque

noncalcified

plaque

-RRB-

and

-LRB-

calcified

plaque

lumen

-RRB-

were

calculated

and

presented

as

average

for

each

kernel

and

solution

Statistical

evaluation

was

performed

with

dedicated

software

-LRB-

SPSS

ver

SPSS

Chicago

Ill.

-RRB-

A

one-way

ANOVA

test

was

performed

to

analyze

the

statistical

difference

between

kernels

in

each

structure

for

two

solutions

A

p

was

considered

for

statistical

significance

The

Tukey

HSD

test

evaluated

the

statistical

absolute

difference

between

any

two

groups

of

values

The

Pearson

's

correlation

was

also

tested

between

all

the

different

convolution

filters

After

clustering

for

kernel

and

structure

the

attenuation

values

obtained

with

the

two

solutions

were

compared

with

Student

's

t-test

and

correlated

with

Pearson

's

test

Results

A

total

of

sections

containing

mixed

plaques

-LRB-

n

-RRB-

were

evaluated

in

the

seven

coronary

specimens

Two

solutions

and

four

convolution

kernels

were

available

-LRB-

slices

-RRB-

at

each

level

and

four

ROIs

-LRB-

lumen

surrounding

calcified

plaque

noncalcified

plaque

-RRB-

were

sampled

in

each

slice

A

total

of

measurements

were

performed

The

results

are

summarized

in

Table

The

attenuation

values

were

all

significantly

different

between

the

convolution

filters

in

each

structure

with

both

solutions

-LRB-

p

-RRB-

The

results

of

the

Tukey

HSD

to

test

the

difference

between

pairs

of

four

filters

showed

that

the

noncalcified

plaque

attenuation

values

were

all

significantly

different

using

both

solutions

-LRB-

p

-RRB-

with

the

exception

of

pair

The

attenuation

values

between

and

were

significantly

different

at

a

high

concentration

in

calcified

plaques

whereas

for

the

same

pair

of

filters

the

attenuation

values

of

the

lumen

and

the

surrounding

were

not

significantly

different

After

clustering

the

paired

attenuation

values

of

the

four

structures

for

the

convolution

filter

a

moderate-high

correlation

was

generally

found

with

the

exception

of

pairs

in

surrounding

-LRB-

r

-RRB-

in

lumen

-LRB-

r

-RRB-

and

surrounding

-LRB-

r

-RRB-

in

lumen

-LRB-

r

-RRB-

and

-LRB-

r

-RRB-

in

lumen

in

the

saline

solution

Table

of

the

attenuation

values

measured

in

each

structure

in

the

two

solutions

-LRB-

e.g.

saline

and

contrast

solutions

-RRB-

with

increasing

convolution

filter

.140.429.952.140.59.448.236.019.123.56.01.8

.193.7209.8312.685.544.0334.191.7169.7331.3138.317.8

Noncalcified

.839.18.014.235.82.414.032.04.03.232.40.3

.766.639.368.263.39.266.366.525.948.560.02.4

Calcified

Plaque

.5392.0327.0758.5360.3133.6785.7388.5294.91145.8517.487.8

.4333.8498.0838.7364.2116.0885.6382.6488.71194.8520.761.0

Contrast

Whereas

the

convolution

filter

did

not

significantly

affect

the

attenuation

values

of

the

lumen

and

the

surrounding

sharper

filters

decreased

the

attenuation

of

the

plaque

and

conversely

increased

the

attenuation

of

the

calcification

with

both

solutions

-LRB-

Fig.

-RRB-

Fig.

attenuation

of

the

four

structures

in

the

two

solutions

-LRB-

e.g.

saline

and

contrast

-RRB-

with

increasing

convolution

filters

Whereas

the

convolution

filter

does

not

significantly

affect

the

attenuation

values

of

the

lumen

and

the

surrounding

sharper

filters

decrease

the

attenuation

of

the

noncalcified

plaque

and

conversely

increase

the

attenuation

of

the

calcified

plaque

with

both

solutions

The

SNR

values

appear

to

have

a

common

trend

with

increasing

convolution

filtering

and

both

solutions

However

the

best

SNR

was

achieved

with

the

and

filters

Plaque

values

follow

the

lumen

values

while

the

surrounding

and

calcification

patterns

are

similar

-LRB-

Fig.

-RRB-

Fig.

SNR

values

appear

to

have

a

common

trend

with

increasing

convolution

filtering

and

both

solutions

-LRB-

e.

g.

saline

and

contrast

-RRB-

However

the

best

SNR

is

achieved

with

and

filters

Noncalcified

plaque

values

follow

the

lumen

values

while

the

surrounding

and

the

calcified

plaque

patterns

are

similar

The

CNR

values

were

calculated

between

structures

with

increasing

convolution

filters

and

different

solutions

-LRB-

Table

-RRB-

Improved

CNRs

were

achieved

with

the

and

filters

The

lumen-noncalcified

plaque

CNR

was

particularly

improved

with

the

and

filters

using

a

high

solution

of

contrast

media

The

noncalcified

plaque-surrounding

CNR

was

improved

with

the

and

filters

in

contrast

solution

Calcified

plaque-noncalcified

plaque

CNR

increased

with

the

contrast

solution

with

the

and

filters

while

it

decreased

using

the

and

filters

The

filter

was

found

to

be

ideal

for

calcified

plaque-lumen

contrast

since

it

improved

the

CNR

at

contrast

solution

Table

of

CNR

values

calculated

between

structures

with

increasing

convolution

filters

and

different

solutions

noncalcified

Non

calcified

Calcified

plaque

noncalcified

Calcified

plaque

Contrast

solutionLumen

noncalcified

Noncalcified

plaque

Calcified

plaque

noncalcified

Calcified

plaque

After

clustering

the

paired

attenuation

values

obtained

for

the

four

structures

in

order

to

test

the

statistical

difference

between

saline

and

contrast

solution

for

each

convolution

filter

values

were

all

significantly

different

-LRB-

p

-RRB-

apart

from

surrounding

with

and

calcification

with

Pearson

's

test

has

shown

good

correlation

only

between

the

attenuation

values

of

calcification

-LRB-

r

r

r

r

with

respectively

-RRB-

Discussion

The

evaluation

of

the

coronary

artery

wall

is

a

data

set

that

has

become

available

since

the

introduction

of

coronary

MSCT

Several

studies

have

reported

the

ability

of

MSCT

to

detect

coronary

plaques

and

subsequently

characterize

their

tissue

composition

-LRB-

i.e.

calcified

mixed

noncalcified

-RRB-

-LSB-

-RSB-

In

an

in

vivo

study

Kopp

et

al.

showed

an

excellent

correspondence

between

ICUS

criteria

-LRB-

soft

intermediate

and

calcified

plaques

-RRB-

and

MSCT

attenuation

values

-LSB-

-RSB-

Schroeder

et

al.

subsequently

found

a

strong

correlation

between

tissue

density

measurements

within

the

plaque

and

the

qualitative

ICUS

criteria

The

CT

attenuation

results

were

HU

for

plaques

classified

by

ICUS

as

soft

-LRB-

i.e.

predominantly

lipid

-RRB-

plaques

HU

for

plaques

classified

by

ICUS

as

intermediate

-LRB-

i.e.

predominantly

fibrous

-RRB-

plaques

and

HU

for

plaques

classified

by

ICUS

as

calcified

These

researchers

reported

no

overlap

in

the

mean

attenuation

among

the

three

groups

-LSB-

-RSB-

Leber

et

al.

showed

that

lesion

echogenity

correlated

well

with

MSCT

attenuation

measurements

in

coronary

plaque

with

MSCT

correctly

classifying

of

sections

containing

hypoechoic

plaque

areas

-LRB-

soft

plaques

-RRB-

of

sections

containing

hyperechoic

plaque

areas

-LRB-

fibrous

plaques

-RRB-

and

of

sections

containing

calcified

plaque

tissue

The

MSCT

density

measurements

within

coronary

lesions

revealed

significantly

different

values

for

hypoechoic

hyperechoic

and

calcified

plaques

-LSB-

-RSB-

The

close

correlation

between

ICUS

and

MSCT

in

terms

of

the

detection

of

calcified

and

noncalcified

coronary

plaques

was

also

shown

by

Achenbach

et

al.

although

this

group

found

a

sensitivity

of

only

for

exclusively

noncalcified

plaque

-LSB-

-RSB-

Becker

et

al.

compared

the

atherosclerotic

lesions

of

human

cadaver

heart

specimens

detected

by

MSCT

with

the

histopathological

macroscopic

findings

according

to

American

Heart

Association

criteria

They

concluded

that

MSCT

is

a

promising

tool

for

the

characterization

of

atherosclerotic

coronary

plaques

-LSB-

-RSB-

Such

information

is

of

great

value

since

the

risk

of

acute

coronary

syndromes

caused

by

plaque

disruption

and

thrombosis

depends

on

plaque

composition

-LRB-

i.e.

noncalcified

predominantly

lipid

plaques

with

positive

remodeling

-RRB-

rather

than

stenosis

severity

-LSB-

-RSB-

Reliable

and

reproducible

non-invasive

methods

for

the

assessment

of

plaque

constitution

could

be

important

in

risk

stratification

of

patients

with

CAD

Nevertheless

several

aspects

-LRB-

i.e.

the

impact

of

lumen

attenuation

convolution

filters

body

mass

index

of

the

patient

CNR

of

the

images

and

coronary

calcification

-RRB-

of

the

methodology

need

to

be

better

addressed

in

order

to

validate

the

accuracy

of

attenuation

values

measured

within

the

coronary

plaques

using

MSCT

It

is

controversial

if

the

absolute

HU

values

are

valid

measurements

for

determining

the

plaque

composition

and

identifying

the

corresponding

tissue

A

phantom

study

revealed

that

intracoronary

attenuation

can

significantly

affect

the

measured

plaque

attenuation

so

that

accurate

plaque

tissue

differentiation

may

be

influenced

-LSB-

-RSB-

Furthermore

Cademartiri

et

al.

recently

reported

that

the

intravascular

attenuation

modifies

significantly

the

attenuation

of

the

coronary

atherosclerotic

plaques

in

an

ex

vivo

coronary

specimen

-LSB-

-RSB-

Therefore

the

characterization

of

the

plaque

on

the

basis

of

absolute

attenuation

values

should

be

reported

with

caution

and

the

intraluminal

attenuation

should

also

be

reported

The

calibration

of

tissue

attenuation

values

with

contrast

in-lumen

values

may

improve

accurate

tissue

component

identification

New

possibilities

for

coronary

artery

plaque

imaging

may

be

offered

by

dual-source

CT

which

provides

robust

diagnostic

image

quality

independent

of

the

heart

rate

Potential

applications

of

dual-energy

CT

include

tissue

characterization

and

Ca

quantification

of

atherosclerotic

plaques

-LSB-

-RSB-

In

our

experimental

study

we

addressed

the

issue

of

the

variability

of

coronary

plaque

attenuation

by

varying

the

convolution

filters

-LRB-

Fig.

-RRB-

Fig.

of

plaque

with

increasing

filtering

using

a

saline

and

contrast

solution

The

direct

back

projection

of

CT

attenuation

profiles

results

in

unsharp

images

To

prevent

unsharp

and

approximate

images

each

projection

has

to

be

convolved

with

a

predetermined

mathematical

function

the

convolution

kernel

this

kernel

represents

a

filtering

procedure

that

is

able

to

enhance

or

reduce

object

boundaries

Convolution

influences

image

characteristics

by

the

choice

and

design

of

the

kernel

-LRB-

i.e.

smooth

sharp

-RRB-

A

smooth

filter

reduces

spatial

resolution

as

well

as

image

noise

a

sharp

filter

increases

spatial

resolution

as

well

as

image

noise

The

noise

is

caused

by

the

fluctuations

in

the

number

of

X-ray

quanta

registered

by

the

detector

and

is

affected

by

convolution

and

dose

The

SNR

evaluates

the

ratio

between

the

intensity

of

the

signal

and

its

statistical

fluctuation

Suzuki

et

al.

have

demonstrated

that

the

accuracy

of

a

vascular

diameter

measurement

with

an

automated

software

is

affected

by

the

choice

of

convolution

filtering

-LSB-

-RSB-

Seifarth

et

al.

recently

compared

the

effect

of

different

convolution

filtering

on

the

visualization

of

coronary

artery

stents

Using

the

edge-enhancing

they

observed

a

significant

improvement

in

lumen

assessment

compared

to

the

conventional

-LSB-

-RSB-

Our

study

shows

how

the

use

of

different

convolution

filters

significantly

affects

the

measured

coronary

plaque

attenuation

-LRB-

Fig.

-RRB-

The

use

of

sharper

convolution

filters

produces

an

increase

in

the

mean

attenuation

value

of

the

calcified

component

of

plaque

Increasingly

sharper

filtering

produces

a

reduction

in

the

mean

attenuation

values

of

the

noncalcified

plaque

component

On

the

basis

of

our

results

it

is

still

challenging

to

rely

on

absolute

HU

values

since

the

protocol

used

in

coronary

MSCT

has

not

been

standardized

Furthermore

absolute

plaque

attenuation

values

determined

in

the

various

studies

are

not

comparable

It

is

reasonable

to

use

a

proper

convolution

filtering

with

improved

SNR

and

CNR

to

better

focus

on

plaque

components

The

intermediate

filter

obtained

a

slight

decrease

of

noncalcified

plaque

attenuation

and

an

increase

of

calcified

plaque

attenuation

However

improved

SNRs

and

CNRs

were

also

achieved

by

the

and

filters

The

underestimated

the

noncalcified

plaque

attenuation

and

overestimated

the

calcified

plaque

attenuation

in

the

likely

attempt

to

weigh

both

components

There

are

several

limitations

to

our

study

The

first

one

is

inherent

to

the

lack

of

an

evaluation

of

intra

and

inter-observer

variability

A

second

limitation

is

related

to

the

fact

that

the

coronary

specimens

were

collected

from

elderly

patients

with

a

high

prevalence

of

calcification

The

blooming

artifacts

of

calcification

may

impair

coronary

noncalcified

plaque

visualization

and

characterization

based

on

HU

values

-LSB-

-RSB-

Furthermore

we

did

not

investigate

the

influence

of

mAs

and

voltage

-LRB-

kV

-RRB-

on

the

blooming

effect

Nevertheless

it

has

been

reported

that

the

voltage

setting

employed

-LRB-

i.e.

kV

-RRB-

might

be

reasonably

chosen

during

in

vivo

studies

-LSB-

-RSB-

In

vivo

studies

should

also

better

address

the

issue

of

body

mass

which

affects

coronary

plaque

measurements

-LSB-

-RSB-

Moreover

according

to

data

mined

from

the

literature

it

is

reasonable

to

expect

that

plaque

size

-LRB-

especially

in

calcified

plaques

-RRB-

and

lumen

area

would

be

influenced

by

the

use

of

different

convolution

filters

due

to

variable

partial

volume

effect

Edge-enhancing

sharper

reconstruction

filters

are

reported

to

increase

the

visible

in-stent

lumen

diameter

-LSB-

-RSB-

The

pathological

correlation

has

not

been

provided

since

the

aim

of

our

study

was

not

to

compare

pathology

with

MSCT

but

to

assess

the

influence

of

convolution

filtering

on

plaque

attenuation

measurement

In

conclusion

the

use

of

different

convolution

filtering

significantly

modified

plaque

attenuation

values

Therefore

convolution

filtering

should

be

reported

when

attenuation

values

are

shown

in

order

to

provide

a

standardization

of

the

methodology

Sharper

convolution

kernels

increased

the

attenuation

of

the

calcium

within

the

coronary

plaques

and

reduced

the

attenuation

of

soft

plaque

tissues

Improved

SNR

and

CNR

were

achieved

by

using

the

and

filters

A

smooth

filter

-LRB-

e.g.

-RRB-

may

be

used

for

clinical

routine

evaluation

while

a

medium

filter

-LRB-

e.g.

-RRB-

may

be

considered

the

best

choice

for

the

assessment

of

highly

calcified

or

stented

vessels

The

use

of

a

proper

filtering

according

to

plaque

type

could

give

a

more

reliable

assessment

of

plaque

attenuation

values

in

terms

of

HU

O O O O O B I O O O O O O O O O O B I I B I O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

multislice computed tomography
coronary angiography
coronary plaque