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Objective: To investigate the ability of magnetic resonance imaging (MRI) adiabatic relaxation times in the rotating frame (adiabatic T1ρ and T2ρ) to detect structural alterations in meniscus tissue of mild OA patients and asymptomatic volunteers. Method: MR images of 24 subjects (age range: 50–67 years, 12 male), including 12 patients with mild osteoarthritis (OA) (Kellgren–Lawrence (KL) = 1, 2) and 12 asymptomatic volunteers, were acquired using a 3 T clinical MRI system. Morphological assessment was performed using semiquantitative MRI OA Knee Score (MOAKS). Adiabatic T1ρ and T2ρ (AdT1ρ, AdT2ρ) relaxation time maps were calculated in regions of interest (ROIs) containing medial and lateral horns of menisci. The median relaxation time values of the ROIs were compared between subjects classified based on radiographic findings and MOAKS evaluations. Results: MOAKS assessment of patients and volunteers indicated the presence of meniscal and cartilage lesions in both groups. For the combined cohort group, prolonged AdT1ρ was observed in the posterior horn of the medial meniscus (PHMED) in subjects with MOAKS meniscal tear (P < 0.05). AdT2ρ was statistically significantly longer in PHMED of subjects with MOAKS full-thickness cartilage loss (P < 0.05). After adjusting for multiple comparisons, differences in medians of observed AdT1ρ and AdT2ρ values between mild OA patients and asymptomatic volunteers did not reach statistical significance. Conclusions: AdT1ρ and AdT2ρ measurements have the potential to identify changes in structural composition of meniscus tissue associated with meniscal tear and cartilage loss in a cohort group of mild OA patients and asymptomatic volunteers.

Purpose: The aim of the present work was to validate and optimize adiabatic T1ρ and T2ρ mapping for in vivo measurements of articular cartilage at 3 Tesla (T). Methods: Phantom and in vivo experiments were systematically performed on a 3T clinical system to evaluate the sequences using hyperbolic secant HS1 and HS4 pulses. R1ρ and R2ρ relaxation rates were studied as a function of agarose and chondroitin sulfate concentration and pulse duration. Optimal in vivo protocol was determined by imaging the articular cartilage of two volunteers and varying the sequence parameters, and successively applied in eight additional subjects. Reproducibility was assessed in phantoms and in vivo. Results: Relaxation rates depended on agarose and chondroitin sulfate concentration. The sequences were able to generate relaxation time maps with pulse lengths of 8 and 6 ms for HS1 and HS4, respectively. In vivo findings were in good agreement with the phantoms. The implemented adiabatic T1ρ and T2ρ sequences demonstrated regional variation in relaxation time maps of femorotibial cartilage. Reproducibility in phantoms and in vivo was good to excellent for both adiabatic T1ρ and T2ρ. Conclusions: The findings indicate that sequences are suitable for quantitative in vivo assessment of articular cartilage at 3 T.

Purpose: To evaluate adiabatic T₁ρ and T₂ρ of articular cartilage in symptomatic osteoarthritis (OA) patients and asymptomatic volunteers, and to determine their association with magnetic resonance imaging (MRI)‐based structural abnormalities in cartilage and bone. Materials and Methods: A total of 24 subjects (age range: 50–68 years; 12 female) were enrolled, including 12 early OA patients and 12 volunteers with normal joint function. Patients and volunteers underwent 3T MRI. T₂ρ, adiabatic T₁ρ, and T₂ρ relaxation times of knee articular cartilage were measured. Proton density (PD)‐ and T₁‐weighted MR image series were also obtained and separately evaluated for morphological changes using the MRI OA Knee Scoring (MOAKS) system. Comparisons using the Mann–Whitney nonparametric test were performed after dividing the study participants according to physical symptoms as determined by Western Ontario and McMaster Universities (WOMAC) score or presence of cartilage lesions, bone marrow lesions, or osteophytes. Results: Elevated adiabatic T₁ρ and T₂ρ relaxation times of articular cartilage were associated with cartilage loss (P = 0.024–0.047), physical symptoms (0.0068–0.035), and osteophytes (0.0039–0.027). Elevated adiabatic T₁ρ was also associated with bone marrow lesions (0.033). Conclusion: Preliminary data suggest that elevated adiabatic T₁ρ and T₂ρ of cartilage are associated with morphological abnormalities of cartilage and bone, and thus may be applicable for in vivo OA research and diagnostics.

Purpose: To investigate the association of quantitative magnetic resonance imaging (qMRI) parameters with arthroscopic grading of cartilage degeneration. Arthroscopy of the knee is considered to be the gold standard of osteoarthritis diagnostics; however, it is operator-dependent and limited to the evaluation of the articular surface. qMRI provides information on the quality of articular cartilage and its changes even at early stages of a disease. Methods: qMRI techniques included T₁ relaxation time, T₂ relaxation time, and delayed gadolinium-enhanced MRI of cartilage mapping at 3 T in ten patients. Due to a lack of generally accepted semiquantitative scoring systems for evaluating severity of cartilage degeneration during arthroscopy, the International Cartilage Repair Society (ICRS) classification system was used to grade the severity of cartilage lesions. qMRI parameters were statistically compared to arthroscopic grading conducted with the ICRS classification system. Results: qMRI parameters were not linearly related to arthroscopic grading. Spearman’s correlation coefficients between qMRI and arthroscopic grading were not significant. The relative differences in qMRI parameters of superficial and deep cartilage varied with degeneration, suggesting different macromolecular alterations in different cartilage zones. Conclusions: Results suggest that loss of cartilage and the quality of remaining tissue in the lesion site may not be directly associated with each other. The severity of cartilage degeneration may not be revealed solely by diagnostic arthroscopy, and thus, qMRI can have a role in the investigation of cartilage degeneration.

Objectives: To evaluate the association between radiographically-assessed knee osteoarthritis and femoral neck bone characteristics in women with mild knee radiographic osteoarthritis and those without radiographic osteoarthritis. Methods: Ninety postmenopausal women (mean age [SD], 58 [4] years; height, 163 [6] cm; weight, 71 [11] kg) participated in this cross-sectional study. The severity of radiographic knee osteoarthritis was defined using Kellgren-Lawrence grades 0=normal (n=12), 1=doubtful (n=25) or 2=minimal (n=53). Femoral neck bone mineral content (BMC), section modulus (Z), and cross-sectional area (CSA) were measured with DXA. The biochemical composition of ipsilateral knee cartilage was estimated using quantitative MRI measures, T2 mapping and dGEMRIC. The associations between radiographic knee osteoarthritis grades and bone and cartilage characteristics were analyzed using generalized linear models. Results: Age-, height-, and weight-adjusted femoral neck BMC (p for linearity=0.019), Z (p for linearity=0.033), and CSA (p for linearity=0.019) increased significantly with higher knee osteoarthritis grades. There was no linear relationship between osteoarthritis grades and knee cartilage indices. Conclusions: Increased DXAassessed hip bone strength isrelated to knee osteoarthritis severity. These results are hypothesis driven that there is an inverse relationship between osteoarthritis and osteoporosis. However, MRI assessed measures of cartilage do not discriminate mild radiographic osteoarthritis severity. peerReviewed

Objectives: To investigate whether neuromuscular performance predicts lower limb bone strength in different lower limb sites in postmenopausal women with mild knee osteoarthritis (OA). Methods: Neuromuscular performance of 139 volunteer women aged 50-68 with mild knee OA was measured using maximal counter movement jump test, isometric knee flexion and extension force and figure-of-eight-running test. Femoral neck section modulus (Z, mm³) was determined by data obtained from dualenergy X-ray absorptiometry. Data obtained using peripheral quantitative computed tomography was used to asses distal tibia compressive (BSId, g2/cm4) and tibial mid-shaft bending (SSImaxmid, mm3) strength indices. Results:After adjustment for height, weight and age, counter movement jump peak power production was the strongest independent predictor for Z (β=0.44; p

Analysis of an image texture (TA) is an efficient way to increase the information obtained from medical images. Mathematical computations are performed to evaluate and quantitatively characterize the structure and pathology of the target tissue. Resulting variables may provide complementary information regarding the subtle macromolecular changes occurring in various diseases, such as knee osteoarthritis (OA). OA is a common chronic disease that is characterized by disabling pain, joint dysfunction, and morphological alterations in multiple synovial joint structures. One of the structures affected in OA is the articular cartilage (AC) that provides frictionless movement and load-dampening properties for the joint articulation. Current diagnostic tools lack sensitivity for the early stage of OA. TA combined with quantitative magnetic resonance imaging techniques, such as T2 relaxation time mapping, allow sensitive evaluation of AC degeneration and disease onset, and may lead to more accurate diagnostics, individualized treatment planning, and better patient outcomes. The aim of this thesis was to assess two texture analysis methods, gray level co-occurrence matrix (GLCM) and local binary pattern (LBP), on the Oulu knee osteoarthritis (OKOA) dataset which comprises 80 confirmed OA patients and an equal number of healthy controls. The TA method’s ability to discern OA subjects from healthy subjects was evaluated on the whole dataset and on an early OA -stage simulating subset. Texture analyzed data included T2, T1ρ and T2ρ relaxation time maps and DESS images. Developed techniques were compared against the current mean relaxation time analysis scheme. Furthermore, the parametric outcomes of TA were subjected to machine learning classification algorithms and tested for automatic segregation of the study groups. TA demonstrated excellent performance in discerning the study groups and appears to be more sensitive to the early changes than the current mean relaxation time focused analysis methods. TA can be applied on various quantitative contrasts and resulting outcomes can be utilized in automated classification pipelines for OA detection. TA demonstrates great potential for further research evaluations and clinical applications and these findings warrant further inquiries into the topic. Tiivistelmä Kuvan tekstuurin tutkiminen mahdollistaa lääketieteellisten kuvien rakenteissa piilevän strukturaalisen informaation esittämisen kvantitatiivisessa muodossa. Tekstuurianalyysimenetelmät tuovat erilaisten sairauksien, kuten polven nivelrikon, aiheuttamien kudosmuutosten seuraukset esiin laskennallisin keinoin. Polven nivelrikko on yleinen, elämänlaatua laajasti heikentävä sairaus. Nivelrikossa polven ruston makromolekyyliympäristö muuttuu ja kudosta koossa pitävät tukirakenteet heikkenevät. Normaalisti nivelrusto vastaa nivelen lähes kitkattomasta liikkeestä ja toimii merkittävänä iskuja vaimentavana tukityynynä. Ruston vaurioituminen aiheuttaakin usein huomattavia kipuja sekä nivelen toiminnan ja yleisen toimintakyvyn merkittävää heikkenemistä. Nivelruston uusiutumiskyky on erittäin heikko, ja alkavat muutokset tulisi näin ollen pyrkiä tunnistamaan mahdollisimman varhaisessa vaiheessa. Nykyisin nivelrikkodiagnostiikassa käytettävät menetelmät eivät ole erityisen herkkiä alkavan vaurion tunnistamisessa. Tekstuurianalyysimenetelmät yhdistettyinä ruston rakenneosasten koostumusta mittaaviin kvantitatiivisiin kuvantamismenetelmiin, kuten T2-relaksaatioaikakartoitukseen, mahdollistavat uudenlaisen työkalun kehittämisen. Työkalulla voidaan parantaa diagnostiikan tarkkuutta, potilaan ennustetta ja hoitomenetelmiä. Tässä väitöskirjassa tutkitaan kahden erilaisen tekstuurianalyysimenetelmän soveltuvuutta nivelrikkodiagnostiikkaan. Käytetyt menetelmät ovat gray level co-occurrence matrix, joka perustuu harmaasävyjen yhteisesiintyvyyksiin kuvassa, ja local binary pattern, jossa tutkitaan kynnysarvoistetun kuvan rakenteiden suuntautumista. Menetelmien herkkyyttä erottaa nivelrikkopotilaat terveistä verrokeista tutkitaan testiaineistolla ja verrataan nykyisin käytössä oleviin menetelmiin. Analyysit suoritettiin T2-, T1ρ- ja T2ρ-relaksaatioaikakartoille sekä DESS-kuville. Tekstuurianalyysin tuottamaa parametrimuotoista dataa käytetään lisäksi koneoppimispohjaisten luokittelualgoritmien kehittämisessä. Algoritmien tavoitteena on erottaa tutkittavat ryhmät automaattisesti toisistaan. Tekstuurianalyysimenetelmät osoittautuivat tässä väitöskirjatutkimuksessa erittäin herkiksi työkaluiksi nivelrikon aiheuttamien muutosten tunnistamisessa. Myös alkavan vaiheen nivelrikon tunnistaminen onnistui luotettavasti. Tekstuurianalyysia voidaan soveltaa monenlaisiin lähdekuviin, ja tuotettu data soveltuu automaattisten luokitinalgoritmien kehittämiseen.

Osteoarthritis (OA) is a common chronic condition that reduces the quality of life of millions of individuals worldwilde. In OA, the progressive degradation of articular cartilage (AC) and bone can cause joint pain and disability. Currently there is no effective treatment available for OA besides gross joint replacement surgery. This is largely due to the lack of accurate biomarkers to test potential drugs and treatments that could stop or reverse the disease progression. The primary tools in use for OA diagnostics are inadequate in the early stage of the disease and merely allow its late manifestations to be visualized. Quantitative MRI (qMRI) has demonstrated the ability to distinguish degenerated from intact AC prior to radiographic changes. Moreover, so-colled rotating frame relaxation time parameters are sensitive to the slow molecular motion domain, relevant for clinical applications. T1ρ and T2ρ relaxation time measurements using adiabatic spin-lock pulses (AdT1ρ and AdT2ρ) have shown superior sensitivity to cartilage degeneration in vitro over conventional qMRI parameters. This thesis aimed to compare the differences that exist between established qMRI methods for AC against arthroscopic evaluation as well as optimize and validate AdT1ρ and AdT2ρ mapping of cartilage in vivo. The findings showed that T1 and T2 relaxation time and delayed gadolinium enhanced MRI of cartilage (dGEMRIC) were able to discriminate among different arthroscopic grades of cartilage lesions. However, arthroscopic findings and qMRI parameters were not correlated, supporting the viewpoint that qMRI may be able to elicit more comprehensive information on the quality of remaining cartilage tissue as compared to diagnostic arthroscopy, which detects cartilage loss. AdT1ρ and AdT2ρ mapping of cartilage in vivo were successfully implemented and validated on a clinical MRI system. AdT1ρ and AdT2ρ were able to overcome limitations of the existing methods (continuous wave spin-lock approach), which are challenging to implement on clinical settings for their susceptibility to field inhomogeneity and relatively high power deposition in tissue. The association of AdT1ρ and AdT2ρ with cartilage and bone marrow lesions and osteophytes was demonstrated. The findings indicate the utility of AdT1ρ and AdT2ρ mapping as potential biomarkers for evaluation of early cartilage degeneration in OA research and clinical applications. Tiivistelmä Nivelrikko on tavallinen krooninen sairaus, joka huonontaa miljoonien ihmisten elämänlaatua ympäri maailman. Nivelrikossa nivelruston ja luun asteittain etenevä rappeuma voi aiheuttaa nivelkipua ja liikuntakyvyttömyyttä. Tällä hetkellä nivelrikkoon ei ole muuta tehokasta hoitokeinoa kuin tekonivelleikkaus. Tämä johtuu suuremmaksi osaksi tarkkojen biomarkkereiden puutteesta, joiden avulla voitaisiin kokeilla mahdollisia nivelrikon pysäyttäviä tai tautia parantavia lääkkeitä tai hoitokeinoja. Nykyisin nivelrikon diagnostiikassa käytetyimmät menetelmät ovat riittämättömiä sairauden alkuvaiheessa, ja ne tunnistavat vain sairauden loppuvaiheet. Kvantitatiivisilla magneettikuvausmenetelmillä pystytään erottamaan rappeutunut ja ehjä nivelrusto toisistaan ennen röntgenkuvissa havaittavia muutoksia. Nk. pyörivän koordinaatiston relaksaatioaikaparametrit ovat herkkiä havaitsemaan hidasta molekyyliliikettä, jolla on merkitystä kliinisissä sovelluksissa. Kokeellisissa olosuhteissa T1ρ- ja T2ρ-relaksaatioaikojen mittaaminen käyttäen adiabaattisia spin-lukkopulsseja (AdT1ρ ja AdT2ρ) on osoittautunut erityisen tarkaksi nivelruston rappeutumisen toteamiseksi verrattuna perinteisiin kvantitatiivisiin magneettikuvausmenetelmiin. Tämän väitöskirjan tavoitteena oli vertailla vakiintuneita nivelrikon kvantitatiivisia magneettikuvausmenetelmiä sekä optimoida ja validoida AdT1ρ- ja AdT2ρ-menetelmien käyttöä ihmisen ruston tutkimisessa. Tulokset osoittivat, että T1- ja T2-relaksaatioajat sekä varjoainetehosteinen nivelruston magneettikuvaus pystyivät erottelemaan niveltähystyksessä määritettyjä nivelrikon eri asteita. Kuitenkaan niveltähystyslöydökset ja kvantitatiiviset magneettikuvausparametrit eivät korreloineet viitaten kvantitatiivisen magneettikuvauksen kykyyn osoittaa tarkemmin jäljellä olevan ruston laatua verrattuna niveltähystykseen, jossa arvioidaan ruston puutosta. Nivelruston AdT1ρ- ja AdT2ρ-relaksaatioaikamittaukset onnistuttiin suorittamaan ja validoimaan vapaaehtoisilla koehenkilöillä kliinisellä magneettikuvauslaitteella. AdT1ρ ja AdT2ρ eivät kärsineet samoista puutteista kuin tavanomaiset jatkuva-aaltoiset spin-lukkomenetelmät, joka ovat herkkiä kenttäepähomogeenisuuksille ja aiheuttavat suuremman radiotaajuusaltistuksen. Tutkimuksessa osoitettiin AdT1ρ- ja AdT2ρ-mittausten ja luuödeemin sekä osteofyyttien välinen yhteys. Tulokset osoittivat, että AdT1ρ- ja AdT2ρ-mittaukset ovat potentiaalisia biomarkkereita varhaisen nivelruston rappeuman havaitsemiseksi tutkimus- ja kliinisessä käytössä.