 3d - tess t2mapping provides clinically comparable results to cpmg in shorter scan - time .
 clinical and investigational studies may benefit from high temporal resolution of 3d - tess . 
transverse relaxation time ( t2 ) mapping in articular cartilage has been previously reported as a reliable marker for the evaluation of collagen matrix and water content .
the changes in t2 values have been demonstrated to correlate with alterations in water content , as well as collagen structure and organization , and are linked to changes in hyaline cartilage and its depletion [ 13 ] . to date , t2 mapping of cartilage has been successfully used in many applications related to biomechanical and biochemical analysis of cartilage tissue [ 417 ] .
although the loss of glycosaminoglycans is an early sign of osteoarthritis ( oa ) and collagen depletion occurs in later stages , the potential of t2 as a marker for the grading of cartilage degeneration in oa has also been demonstrated .
t2 maps are typically calculated from a series of t2-weighted images acquired with different echo times .
however , the accuracy and reliability of the resulting t2 maps is highly dependent on the method used to record the initial t2-weighted images .
a multi - spin - echo pulse sequence [ e.g. , carr - purcell - meiboom - gill ( cpmg ) ] is a widely used method for in vivo t2 mapping .
this sequence acquires signals from multiple time points along the t2 decay for each k - space line during a single repetition time .
the complete t2 decay curve is also time - consuming and frequently requires segmented imaging strategies .
it is well known that maps generated with a series of single - echo spin - echo ( se ) images suffer from steady state effects ( i.e. , different t1 weightings ) in the images . to prevent this , long transverse relaxation ( tr ) times are necessary , which may limit clinical applications .
in addition , the total scan time is substantially longer compared to cpmg because the sequence must be repeated for each echo time separately .
recently , a triple - echo steady - state ( tess ) relaxometry method was introduced for fast and accurate t2 and t1 mapping [ 22 , 23 ] .
this sequence has several advantages over conventional t2 mapping : it is very fast , the data are acquired in a single scan , and the quantification of t2 is markedly insensitive to b1 . to date , the clinical performance of 3d - tess for t2 mapping in cartilage has not yet been evaluated .
therefore , the purpose of this study was to assess the clinical relevance of t2 relaxation times , measured by three - dimensional ( 3d ) triple - echo steady - state ( 3d - tess ) , in knee articular cartilage compared to conventional multi - echo spin - echo t2-mapping .
the right knees of 10 patients ( 35.1  10.5 years ) with a focal cartilage lesion and 13 age - matched volunteers ( 31.4  9.4 years ) were measured in this prospective study .
the local ethics committee approved this study , and all participants gave written , informed consent .
inclusion criteria for volunteers were : no signs of any cartilage lesion in the knee joint on standard morphological magnetic resonance ( mr ) sequences ; and no meniscal and ligament damage . in patients ,
three patients underwent surgical procedures on the femoral cartilage ( matrix - associated chondrocyte transplantation [ mact ] , pridie drilling , and mosaicplasty ) , and the remaining patients were diagnosed with chondropathy grade 2 to 4 according to the international cartilage repair society ( icrs ) classification .
all subjects underwent mr examinations of the knee joint on a 3 tesla tim trio mr scanner ( siemens healthcare , erlangen , germany ) . an eight - channel knee coil ( siemens healthcare ,
the examination consisted of two methods : a multi - echo multi - slice spin echo sequence ( cpmg ) as a reference method for t2 mapping ; and a 3d - tess with the exact same geometry settings as in the cpmg sequence but with two modifications , a standard ( tesss , acquisition time 4:35 min ) and a quick ( tessq , acquisition time 2:05 min ) sequence .
for tessq , the total acquisition time was reduced by using a phase - and - slice partial fourier acquisition .
the abbreviation tess refers to tesss throughout the entire manuscript . with tess imaging , the three steady - state free precession signal amplitudes ( f1 , f0 , and f-1 )
were acquired within separate radiofrequency cycles ( each signal within one at the same echo time ) to enable a shorter repetition time and mitigate possible susceptibility effects .
cpmg t2 maps were calculated using the syngo console tool mapit ( siemens , erlangen , germany ) , and , for 3d - tess , the scripting framework iceluva was used . to ensure the possibility of evaluating all t2 maps at once by copying regions - of - interest ( rois ) ,
the frequency calibration was double - checked before each scanning to avoid chemical shift artefacts .
the summary of all sequence parameters is in the table 1.table 1sequence parameters used for cpmg t2 mapping and novel 3d - tess t2 mappingsequence parametercpmg3d - tesss3d - tessqslice thickness3 mm3 mm3 mmslice spacing3 mm3 mm3 mmrepetition time2060 ms1114 ms1114 msecho time[11.9 , 23.8 , 35.7 , 47.6 , 59.5 , 71.4 , 83.3 , 95.2 ] ms5.065.06averages111frequency sampling100 % 100 % 100 % phase sampling100 % 100 % 100 % phase partial fouriernono6/8slice partial fouriernono7/8acquisition matrix320  320320  320320  320field - of - view160  160160  160160  160flip angle1801515total acquisition time4:30 min4:36 min2:05 minpixel bandwidth161
hz / pixel446 hz/ pixel446 hz/ pixel sequence parameters used for cpmg t2 mapping and novel 3d - tess t2 mapping t2values were compared in six different regions in the femoral ( anterior afc , mid mfc , posterior pfc ) and tibial ( anterior atc , mid mtc , posterior ptc ) cartilage ( fig .
the rois were selected in the jivex dicom viewer ( jivex 4.3 ; visus technology transfer gmbh , bochum , germany ) by a radiologist ( n.n . ) with 16 years of experience . to assess inter - observer variability , another two observers ( n.n .
, 15 years of experience ) , blinded to previous results , evaluated five volunteers and five patients , and the coefficient of variation was calculated.fig .
1roi selection on 3d - tess image ( the second acquired mr image , referred to as f0 ) .
afc : anterior femoral cartilage , mfc : mid femoral cartilage , pfc : posterior femoral cartilage , atc : anterior tibial cartilage , mtc : mid tibial cartilage , and ptc : posterior tibial cartilage roi selection on 3d - tess image ( the second acquired mr image , referred to as f0 ) .
afc : anterior femoral cartilage , mfc : mid femoral cartilage , pfc : posterior femoral cartilage , atc : anterior tibial cartilage , mtc : mid tibial cartilage , and ptc : posterior tibial cartilage the difference between absolute t2 values calculated with different mapping techniques ( cpmg versus 3d - tess and 3d - tessq versus 3d - tesss ) was expressed as a p - value calculated by a wilcoxon signed ranks test .
pearson correlation coefficients were calculated , and standard deviations ( sds ) of the rois were compared . both absolute values and percentage differences between cpmg and 3d - tess were evaluated . in patients , the t2 values from focal chondral lesions were compared to the adjacent native cartilage and the ability to differentiate between healthy and depleted cartilage was assessed .
all statistical calculations were performed in spss version 19.0 ( spss inc . , chicago , il ) and a p - value less than 0.05 was considered statistically significant .
the right knees of 10 patients ( 35.1  10.5 years ) with a focal cartilage lesion and 13 age - matched volunteers ( 31.4  9.4 years ) were measured in this prospective study .
the local ethics committee approved this study , and all participants gave written , informed consent .
inclusion criteria for volunteers were : no signs of any cartilage lesion in the knee joint on standard morphological magnetic resonance ( mr ) sequences ; and no meniscal and ligament damage . in patients ,
three patients underwent surgical procedures on the femoral cartilage ( matrix - associated chondrocyte transplantation [ mact ] , pridie drilling , and mosaicplasty ) , and the remaining patients were diagnosed with chondropathy grade 2 to 4 according to the international cartilage repair society ( icrs ) classification .
all subjects underwent mr examinations of the knee joint on a 3 tesla tim trio mr scanner ( siemens healthcare , erlangen , germany ) .
an eight - channel knee coil ( siemens healthcare , erlangen , germany ) was used for all mr scans .
the examination consisted of two methods : a multi - echo multi - slice spin echo sequence ( cpmg ) as a reference method for t2 mapping ; and a 3d - tess with the exact same geometry settings as in the cpmg sequence but with two modifications , a standard ( tesss , acquisition time 4:35 min ) and a quick ( tessq , acquisition time 2:05 min ) sequence .
for tessq , the total acquisition time was reduced by using a phase - and - slice partial fourier acquisition .
the abbreviation tess refers to tesss throughout the entire manuscript . with tess imaging , the three steady - state free precession signal amplitudes ( f1 , f0 , and f-1 )
were acquired within separate radiofrequency cycles ( each signal within one at the same echo time ) to enable a shorter repetition time and mitigate possible susceptibility effects .
cpmg t2 maps were calculated using the syngo console tool mapit ( siemens , erlangen , germany ) , and , for 3d - tess , the scripting framework iceluva was used . to ensure the possibility of evaluating all t2 maps at once by copying regions - of - interest ( rois ) , the frequency calibration was double - checked before each scanning to avoid chemical shift artefacts .
the summary of all sequence parameters is in the table 1.table 1sequence parameters used for cpmg t2 mapping and novel 3d - tess t2 mappingsequence parametercpmg3d - tesss3d - tessqslice thickness3 mm3 mm3 mmslice spacing3 mm3 mm3 mmrepetition time2060 ms1114 ms1114 msecho time[11.9 , 23.8 , 35.7 , 47.6 , 59.5 , 71.4 , 83.3 , 95.2 ] ms5.065.06averages111frequency sampling100 % 100 % 100 % phase sampling100 % 100 % 100 % phase partial fouriernono6/8slice partial fouriernono7/8acquisition matrix320  320320  320320  320field - of - view160  160160  160160  160flip angle1801515total acquisition time4:30 min4:36 min2:05 minpixel bandwidth161
hz / pixel446 hz/ pixel446 hz/ pixel sequence parameters used for cpmg t2 mapping and novel 3d - tess t2 mapping
t2values were compared in six different regions in the femoral ( anterior afc , mid mfc , posterior pfc ) and tibial ( anterior atc , mid mtc , posterior ptc ) cartilage ( fig .
the rois were selected in the jivex dicom viewer ( jivex 4.3 ; visus technology transfer gmbh , bochum , germany ) by a radiologist ( n.n . ) with 16 years of experience . to assess inter - observer variability , another two observers ( n.n .
, 15 years of experience ) , blinded to previous results , evaluated five volunteers and five patients , and the coefficient of variation was calculated.fig .
1roi selection on 3d - tess image ( the second acquired mr image , referred to as f0 ) .
afc : anterior femoral cartilage , mfc : mid femoral cartilage , pfc : posterior femoral cartilage , atc : anterior tibial cartilage , mtc : mid tibial cartilage , and ptc : posterior tibial cartilage roi selection on 3d - tess image ( the second acquired mr image , referred to as f0 ) .
afc : anterior femoral cartilage , mfc : mid femoral cartilage , pfc : posterior femoral cartilage , atc : anterior tibial cartilage , mtc : mid tibial cartilage , and ptc : posterior tibial cartilage
the difference between absolute t2 values calculated with different mapping techniques ( cpmg versus 3d - tess and 3d - tessq versus 3d - tesss ) was expressed as a p - value calculated by a wilcoxon signed ranks test .
pearson correlation coefficients were calculated , and standard deviations ( sds ) of the rois were compared . both absolute values and percentage differences between cpmg and 3d - tess were evaluated . in patients , the t2 values from focal chondral lesions
were compared to the adjacent native cartilage and the ability to differentiate between healthy and depleted cartilage was assessed .
all statistical calculations were performed in spss version 19.0 ( spss inc . , chicago , il ) and a p - value less than 0.05 was considered statistically significant .
the subjects had the following demographic characteristics : volunteers ( 5 males , mean age 28.8 5.8 years , mean bmi 23.8 3.7 ; 8 females , mean age 33.1 11.1 years , mean bmi 22.8 2.9 ) , patients ( 8 males , mean age 36.8 11 years , mean bmi 24.7 2.6 ; 2 females mean age 28.1 4.7 years , mean bmi 22.9 4.8 ) . both techniques provided artefact - free t2 maps ( figs . 2 , 3 and 4 ) . the t2 values measured with 3d - tess were systematically lower than those measured with cpmg . when all cartilaginous regions were pooled , the average t2 values were 52  10 ms ( cpmg ) and 29  5 ms ( 3d - tess )
. for individual cartilage layers separately , the mean t2 values in the superficial layer were 59  7 ms ( cpmg ) and 33  2 ms ( tess ) , and in the deep layer , 46  9 ms ( cpmg ) and 27  5 ms ( tess ) .
in general , the difference between 3d - tess and cpmg t2 values was statistically significant in all regions .
the t2 values measured by cpmg showed a high correlation with t2 values calculated from 3d - tess , primarily in the weight - bearing zones of the tibia and femur , and the other zones correlated only moderately ( tables  2 and 3).fig . 2the series of mr images acquired with different tes used for the t2 map generation with the cpmg technique .
a : te = 11.9  ms , b : te = 23.8 ms , c : te = 35.7 ms , d : te = 47.6 ms , e : te = 59.5 ms , f : te = 71.4 ms , g : te = 83.3 ms , h : te = 95.2 ms , and i : resulting pseudo - colour - coded t2 mapfig .
a , b , and c : the three base steady - state signal modes ( a : f1 , b : f0 , c : f-1 ) , and d : resulting pseudo - colour coded t2 mapfig .
4a : t2 map acquired by cpmg , pseudo - colour - coded and overlaid on a morphological t2 weighted image from a 32-year - old healthy volunteer ( te  =  11.9  ms ) ; b : t2 map acquired by 3d - tess , pseudo - colour - coded and overlaid on the second acquired mr image ( f0 ) . the typical zonal stratification in cartilage is observable with both techniques .
however , t2(cpmg ) provides apparently higher dynamic contrast of t2 values with better depiction of cartilaginous layerstable 2femoral cartilageafcsafcdd / s [ % ] mfcsmfcdd / s [ % ] pfcspfcdd / s [ % ] t2 ( cpmg ) ( ms)62.453.4014.468.9355.4219.659.3654.298.5t2 ( tess ) ( ms)37.028.3223.432.6923.1029.334.5329.5914.3 
 p - value ( wilcoxon)0.0020.0020.0020.0020.0020.002pearson coefficient0.5350.4550.7010.8080.4970.300 
 cpmg multi - echo multi - slice spin echo sequence ; tess triple echo steady state ; afcs anterior femoral condyle , superficial zone ; afcd anterior femoral condyle , deep zone ; mfcs medial femoral condyle , superficial zone ; mfcd medial femoral condyle , deep zone ; pfcs posterior femoral condyle , superficial zone ; pfcd posterior femoral condyle , deep zone ; d / s deep / superficial ratiotable 3tibial cartilageatcsatcdd / s [ % ]
mtcsmtcdd / s [ % ] ptcsptcdd / s [ % ] t2 ( cpmg ) [ ms]51.1733.5834.452.6538.0027.857.6542.7825.8t2 ( tess ) [ ms]32.0820.4036.430.3923.7821.831.1824.7320.8p - value ( wilcoxon)0.0030.0020.0020.0020.0020.002pearson coefficient0.1360.8060.8070.8650.7400.913 
 cpmg multi - echo multi - slice spin echo sequence ; tess triple echo steady state ; atcs anterior tibial condyle , superficial zone ; atcd anterior tibial condyle , deep zone ; mtcs tibial femoral condyle , superficial zone ; mtcd medial tibial condyle , deep zone ; ptcs posterior tibial condyle , superficial zone ; ptcd posterior tibial condyle , deep zone ; d / s deep / superficial ratio the series of mr images acquired with different tes used for the t2 map generation with the cpmg technique .
a : te = 11.9  ms , b : te = 23.8 ms , c : te = 35.7 ms , d : te = 47.6 ms , e : te = 59.5 ms , f : te = 71.4 ms , g : te = 83.3 ms , h : te = 95.2 ms , and i : resulting pseudo - colour - coded t2 map mr images of different contrasts acquired using 3d - tess .
a , b , and c : the three base steady - state signal modes ( a : f1 , b : f0 , c : f-1 ) , and d : resulting pseudo - colour coded t2 map a : t2 map acquired by cpmg , pseudo - colour - coded and overlaid on a morphological t2 weighted image from a 32-year - old healthy volunteer ( te  =  11.9  ms ) ; b : t2 map acquired by 3d - tess , pseudo - colour - coded and overlaid on the second acquired mr image ( f0 ) .
however , t2(cpmg ) provides apparently higher dynamic contrast of t2 values with better depiction of cartilaginous layers 
 cpmg multi - echo multi - slice spin echo sequence ; tess triple echo steady state ; afcs anterior femoral condyle , superficial zone ; afcd anterior femoral condyle , deep zone ; mfcs medial femoral condyle , superficial zone ; mfcd medial femoral condyle , deep zone ; pfcs posterior femoral condyle , superficial zone ; pfcd posterior femoral condyle , deep zone ; d / s deep / superficial ratio 
 cpmg multi - echo multi - slice spin echo sequence ; tess triple echo steady state ; atcs anterior tibial condyle , superficial zone ; atcd anterior tibial condyle , deep zone ; mtcs tibial femoral condyle , superficial zone ; mtcd medial tibial condyle , deep zone ; ptcs posterior tibial condyle , superficial zone ; ptcd posterior tibial condyle , deep zone ; d / s deep / superficial ratio the sds for tess - t2 were slightly lower than for cpmg - t2 ; however , this difference was not statistically significant ( 28  6 % and 30  12 % , p = 0.579 ) .
when comparing cartilage layers , the sd did not demonstrate any significant differences between the superficial ( tess 26  8 % , cpmg 32  10 % ) and the deep zone ( tess 29  7 % , cpmg 29  8 % ) .
both t2 mapping techniques were able to detect the changes between chondral lesions and native cartilage .
for cpmg , the mean t2 in cartilaginous lesions was 90  50 and in native cartilage , it was 62  25 ms . for 3d - tess ,
the mean t2 in cartilaginous lesions was 32  6 , and in native cartilage , it was 24  8 ms
. example t2 maps of native and damaged cartilage are depicted in fig . 5.fig .
5a : t2 map acquired by cpmg , pseudo - colour - coded and overlaid on a morphological image of a 41-year - old patient with pridie drilling on the medial femoral condyle ( te  =  11.9  ms ) ; the ratio of native and lesion cartilage t2s is 0.81 .
b : t2 map acquired by 3d - tess , pseudo - colour - coded and overlaid on the second acquired mr image ( f0 ) ; the ratio of native and lesion cartilage t2s is 0.83 .
the dynamic range of the cmpg t2 map is higher compared to the 3d - tess t2 map , therefore , the lesion appears to be more diffuse , although the ratios of native and lesion cartilage t2s are comparable between cpmg and 3d - tess a : t2 map acquired by cpmg , pseudo - colour - coded and overlaid on a morphological image of a 41-year - old patient with pridie drilling on the medial femoral condyle ( te  =  11.9  ms ) ; the ratio of native and lesion cartilage t2s is 0.81 .
b : t2 map acquired by 3d - tess , pseudo - colour - coded and overlaid on the second acquired mr image ( f0 ) ; the ratio of native and lesion cartilage t2s is 0.83 .
the dynamic range of the cmpg t2 map is higher compared to the 3d - tess t2 map , therefore , the lesion appears to be more diffuse , although the ratios of native and lesion cartilage t2s are comparable between cpmg and 3d - tess the comparison between tessq and tesss showed almost no difference between t2 values . on average ,
t2(3d - tessq ) was 31  2 ms and t2(3d - tesss ) was 31  3 ms .
the mean pearson correlation coefficient calculated from the whole cartilage in volunteers and patients was 0.816 , ranging from 0.750 to 0.911 in different cartilage regions .
the example of correlation in the femoral and tibial cartilage is depicted in fig . 6.fig .
6a : the correlation of the individual t2 values of an example roi from the femoral cartilage acquired by tessq and tesss ( r  =  0.893 , n  =  433 ) .
b : the correlation of the individual t2 values of this example roi from the tibial cartilage acquired by tessq and tesss ( r  =  0.862 , n  =  544 ) a : the correlation of the individual t2 values of an example roi from the femoral cartilage acquired by tessq and tesss ( r  =  0.893 , n  =  433 ) .
b : the correlation of the individual t2 values of this example roi from the tibial cartilage acquired by tessq and tesss ( r  =  0.862 , n  =  544 ) the mean coefficient of variation between different observers was 6.4 % ( femoral cartilage , t2(cpmg ) ) , 8.1 % ( tibial cartilage , t2(cpmg ) ) , 5.8 % ( femoral cartilage , t2(3d - tess ) ) and 10.8 % ( tibial cartilage , t2 ( 3d - tess ) ) .
the results of our study indicate that t2 relaxation times in the cartilage of the knee joint , calculated from a novel 3d - tess sequence , are highly consistent with those calculated by a classic cpmg sequence .
although the absolute t2 values were significantly lower for 3d - tess , this decrease was systematic , and the t2 values were highly correlated between 3d - tess and cpmg in most of the selected regions . in ref . , the authors demonstrated that tess - based t2 quantification provides accurate t2 values in excellent agreement with single - echo spin echo reference measurements , while cpmg resulted in a substantial overestimation of t2 due to stimulated echo contributions .
the observed significant difference between tess - t2 and cpmg - t2 may , thus , be mainly attributed to stimulated echo contamination present in the cpmg scans .
in addition , the increase of t2 values in the region affected by the magic angle effect ( posterior femoral condyle in our case ) was observable with both techniques . according to mosher et al .
, the greatest variation in cartilage t2 with regard to the magic angle effect is observed in the superficial 20 % of cartilage .
this is in concordance with the presented results , although we divided the cartilage into two layers rather than three because of limited in vivo resolution .
the great advantage of 3d - tess for cartilage t2 mapping is the decrease of total scan time . at our institute , the routine ( cpmg )
t2 mapping at 3 t requires four and a half minutes . in our study , for f comparison purposes , we primarily used a total - acquisition - time - matched version of 3d - tess .
however , we were able to decrease the acquisition time of 3d - tess down to 2:05 min by using a phase - and - slice partial fourier sampling , keeping the resulting cartilage t2 values without a statistically significant change , compared to the total - acquisition - time - matched version of 3d - tess .
this feature would be extremely beneficial in studies where a higher temporal resolution is desired .
a typical example would be the physiological analysis of cartilage changes during in vivo loading .
used cpmg t2 mapping in their in vivo loading study with a 13-minute long cpmg sequence version .
evaluated the unloading effect on articular cartilage prior to and during the mr scan with a 4:09-minute long cpmg - based sequence . in another study
, the changes in cartilage water content in cartilage under compression were detected using t2 mapping , with an acquisition time of 7:30 minutes .
the limitation with all such experiments is that the decrease of t2 values during the mr experiment under loading can not be excluded with certainty .
therefore , there is a need to shorten the acquisition time of t2 experiments to a minimum . in this case
, 3d - tess seems to be the ideal t2 mapping technique for such investigational applications .
however , fast t2 mapping with 3d - tess could also be beneficial for routine clinical applications , providing increased patient comfort and reducing costs .
we also hypothesized that the sd of t2 from rois selected on cartilage would be lower with 3d - tess due to its more robust t2 calculation .
the results , however , showed the sds were the same , no matter which technique was used .
moreover , sds calculated in our study were consistent with those published in other studies ; e.g. , nieminen et al . found an sd of t2 in bovine cartilage ranging from 12.5 to 29 % , and kurkijrvi et al .
, observed an sd of t2 in human cadaver samples between 13.3 - 41.5 %   and 23 - 34 % , respectively .
since all of these studies were performed in vitro , it can be assumed that motion artefacts did not contribute to those high sds .
high sds of t2 in cartilage tissue could be attributed to relatively large tissue anisotropy and heterogeneity due to collagen fibre organization . in has been previously demonstrated that focal cartilage lesions , as well as the cartilage repair tissue , are characterized by t2 elevation [ 14 , 3335 ] .
this focal t2 increase was attributed either to collagen disorganization or to cartilage swelling , accompanied by water volume increase .
similarly , in our study , we observed an increase in t2 differences between native cartilage and lesions .
for cpmg , this difference was slightly larger ( 32 % ) compared to 3d - tess ( 24 % ) .
since both differences were statistically significant , the clinical relevance of both techniques is comparable .
it would be necessary to validate these findings in a larger patient group with the same type of cartilage lesions or repair tissues .
moreover , the lesions selected in our study were quite severe , resulting in relatively large t2 value changes
. it would be interesting , however , to investigate the sensitivity of 3d - tess to subtle t2 changes , where 3d - tess would be expected to perform better as it provides more accurate t2 values .
this is primarily because 3d - tess is less prone to errors , while cpmg substantially overestimates t2 due to stimulated echo contributions .
3d - tess is insensitive to b0 and b1 heterogeneities and may , thus , provide more accurate t2 values with lower sds .
moreover , the three - dimensional nature of 3d - tess allows reformatting of t2 maps in arbitrary planes , expanding the usefulness of this sequence to other tissues ( e.g. , ligaments , menisci ) or more challenging joints for mr imaging ( mri ; e.g. , hip , shoulder , temporo - mandibular ) .
the 3d - tess sequence also produces t1 maps ( not tested in this study ) that may have great clinical potential , but require additional b1 mapping scans .
the results of this study demonstrate the clinical utility of a 3d - tess sequence for t2 mapping of human knee cartilage .
3d - tess provides results similar to those of a conventional multi - echo spin - echo sequence with many benefits , such as shortening of total acquisition time and insensitivity to b1 and b0 changes .
t2 mapping with 3d - tess was able to differentiate between healthy and damaged cartilage tissue , indicating its great potential for clinical studies .
 objectivesto assess the clinical relevance of t2 relaxation times , measured by 3d triple - echo steady - state ( 3d - tess ) , in knee articular cartilage compared to conventional multi - echo spin - echo t2-mapping.methodsthirteen volunteers and ten patients with focal cartilage lesions were included in this prospective study . 
 all subjects underwent 3-tesla mri consisting of a multi - echo multi - slice spin - echo sequence ( cpmg ) as a reference method for t2 mapping , and 3d tess with the same geometry settings , but variable acquisition times : standard ( tesss  4:35min ) and quick ( tessq  2:05min ) . 
 t2 values were compared in six different regions in the femoral and tibial cartilage using a wilcoxon signed ranks test and the pearson correlation coefficient ( r ) . 
 the local ethics committee approved this study , and all participants gave written informed consent.resultsthe mean quantitative t2 values measured by cpmg ( mean : 469ms ) in volunteers were significantly higher compared to those measured with tess ( mean : 315ms ) in all regions . both methods performed similarly in patients , but 
 cpmg provided a slightly higher difference between lesions and native cartilage ( cpmg : 90ms61ms [ 31%],p=0.0125;tess 32ms24ms [ 24%],p=0.0839).conclusions3d - tess provides results similar to those of a conventional multi - echo spin - echo sequence with many benefits , such as shortening of total acquisition time and insensitivity to b1 and b0 changes.key points 3d - tess t2mapping provides clinically comparable results to cpmg in shorter scan - time. clinical and investigational studies may benefit from high temporal resolution of 3d - tess. 3d - tess t2values are able to differentiate between healthy and damaged cartilage . 
None
Introduction
Materials and methods
Patients
MR examinations
MR data evaluation
Statistical analysis
Results
Discussion
Conclusion