Background – The analysis of irregularly shaped tumour ROIs is hindered by the fact that most image analysis methods apart from first-order statistics are compatible only with rectangular ROIs. We thus aimed for the first implementation and testing of the 1-D MRI image analysis method that is fully compatible with irregular ROIs. Method – The retrospective prediction model of osteosarcoma chemoresponsiveness included T2-weighted MRI scans obtained before OsteoSa MAP neoadjuvant cytotoxic chemotherapy. Osteosarcoma morphology was quantified by calculating the one- and two-dimensional (1-D, 2-D) Higuchi dimensions (Dh), directionally and non-directionally. Results – The non-directional 1-D Dh reached a predictive AUC of 0.88, while the directional 1-D analysis along 180 radial lines robustly improved the predictive performance, reaching an AUC of 0.95, P<0.001 that is widely considered as nearly ideal. The optimal directional range was between 90o and 97o. Conclusions – We report the first validity testing of the 1-D analysis approach that is fully compatible with irregular ROIs. Such analytical adaptation to ROI shape in MRI has enhanced the osteosarcoma prediction performance over the previously reported standard 2-D analyses. The clinical importance of the early chemoresponsiveness prediction rests on its potential to prolong the survival of chemoresistant patients through personalised treatment adjustments.