A device for detecting circulating tumor cells (CTCs) in a biological fluid sample, comprising - a microfluidic device having an inlet portion for receiving the biological fluid sample into said microfluidic device, and an outlet portion for discharging the received biological fluid sample from said microfluidic device; characterized in that said microfluidic device further houses a micro flow restrictive element extending between the inlet portion and the outlet portion of said microfluidic device; wherein inner cross-section area of the inlet portion of the microfluidic device is larger than inner cross-section area of said micro flow restrictive element; and this reduction in inner cross-section area between the microfluidic device and the micro flow restrictive element configured to induce a rapid drop in pressure of the biological fluid sample flowing through inlet zone of said micro flow restrictive element to a critical level, which is equal to or below saturated vapor pressure of said fluid sample at room temperature; - an ultrasonic signal processing system including: an ultrasonic transmitter configured for transmitting ultrasound waves on said biological fluid sample while it is flowing through said micro flow restrictive element; an ultrasonic receiver configured for receiving ultrasound waves reflected from said biological fluid sample; and an ultrasonic signal processor configured for analyzing information obtained from the ultrasonic transmitter and the ultrasonic receiver and configured for detecting presence of CTCs within the flowing biological fluid sample by considering variation of the monitored reflected ultrasound waves due to generation of cavitation inception based on said rapid pressure drop within the micro flow restrictive element. - a microfluidic device having an inlet portion for receiving the biological fluid sample into said microfluidic device, and an outlet portion for discharging the received biological fluid sample from said microfluidic device; characterized in that said microfluidic device further houses a micro flow restrictive element extending between the inlet portion and the outlet portion of said microfluidic device; wherein inner cross-section area of the inlet portion of the microfluidic device is larger than inner cross-section area of said micro flow restrictive element; and this reduction in inner cross-section area between the microfluidic device and the micro flow restrictive element configured to induce a rapid drop in pressure of the biological fluid sample flowing through inlet zone of said micro flow restrictive element to a critical level, which is equal to or below saturated vapor pressure of said fluid sample at room temperature; - an ultrasonic signal processing system including: an ultrasonic transmitter configured for transmitting ultrasound waves on said biological fluid sample while it is flowing through said micro flow restrictive element; an ultrasonic receiver configured for receiving ultrasound waves reflected from said biological fluid sample; and an ultrasonic signal processor configured for analyzing information obtained from the ultrasonic transmitter and the ultrasonic receiver and configured for detecting presence of CTCs within the flowing biological fluid sample by considering variation of the monitored reflected ultrasound waves due to generation of cavitation inception based on said rapid pressure drop within the micro flow restrictive element. an ultrasonic transmitter configured for transmitting ultrasound waves on said biological fluid sample while it is flowing through said micro flow restrictive element; an ultrasonic receiver configured for receiving ultrasound waves reflected from said biological fluid sample; and an ultrasonic signal processor configured for analyzing information obtained from the ultrasonic transmitter and the ultrasonic receiver and configured for detecting presence of CTCs within the flowing biological fluid sample by considering variation of the monitored reflected ultrasound waves due to generation of cavitation inception based on said rapid pressure drop within the micro flow restrictive element.