Table 2.

ctDNA detection techniques

Detection Methods	Detection Principle	Role	Advantages	Disadvantages	Reference
ddPCR	DNA amplification, sample microtitration and reading of the starting concentration of target molecules by fluorescence signaling	Detection of single nucleotide variants, quantification of nucleotides	High sensitivity and specificity, relatively low cost for specific DNA detection, short time to achieve absolute quantification of target molecules, suitable for long-term monitoring of patients with known mutations	It cannot process a large amount of sequence information at the same time and can only amplify known sequences.	98
NGS	Sequence information is read after DNA amplification using signals emitted at base insertion into the DNA strand with the help of chemical markers	Whole exome sequencing (WES) as well as whole genome sequencing (WGS), detection of nucleotide variants	Large amount of sequence information can be processed at the same time, detection time is not long, suitable for patient screening of unknown mutations, lower cost compared to ddPCR for large amount of DNA detection	The sensitivity and specificity are not as good as ddPCR.	99,100