documentclass[a4paper, extrafontsizes]{memoir}
            usepackage{calc,lipsum}

            newcommandYUGE{fontsize{48}{60}selectfont}

            makeatletter
            makechapterstyle{myChapStyle}{
                chapterstyle{komalike}
                setlength{beforechapskip}{40pt}
                renewcommand{printchaptername}{}
                renewcommand{chapternamenum}{}
                renewcommand{chapnumfont}{normalfontYUGEbfseries}
                renewcommand{printchapternum}{}%chapnumfont thechapterspace}
                renewcommand{afterchapternum}{}
                renewcommand*{printchapternum}{%
                    @hangfrom{chapnumfont YUGEthechapterenspace}}%
            }
            chapterstyle{myChapStyle}
            makeatother

            % Section/subsec/subsubsec fonts
            setsecheadstyle{normalfontLargebfseriessffamily}
            setsubsecheadstyle{normalfontlargebfseriessffamily}
            setsubsubsecheadstyle{normalfontnormalsizebfseriessffamily}

            % Set the desired depth of subsections
            setcounter{secnumdepth}{3}

            begin{document}
                chapter{Fundamentals of medical imaging and continuum mechanics}
                lipsum[1]

                section{Section 1}
                lipsum[1]

                subsection{Subsection 1}
                lipsum[1-3]
            end{document}