Current Telemedicine and eHealth activities can be classified according to the technology used, the type of activity, or the target group. One of the most important aspects of classification is the distinction between real time and store-and-forward.

Two major types of TM & eH activities exist:

• Synchronous, or Real-Time – implies direct real-time contact between the TM service provider (for example, a remote consultant) and end-user (such as a patient or another physician), through videoconferencing, or real-time data acquisition (ultrasound, ECG etc).

In this type of service, the classic example of which is videoconsultation, the interaction between the participants is "live" and they can interact immediately. The advantage of this approach is that it enables optimum transfer of information between the participants. The disadvantages are that it is logistically difficult to manage large-scale services and they tend to be relatively expensive.

• Asynchronous, or Store-and-Forward – implies collecting patient’s data (such as pictures or videos, ECG traces, lab reports, radiology images or pathology slides) and sending them later to a remote site for reviewing, diagnosis and treatment planning.

Store and forward services are less expensive and easier to manage as there is no "live" interaction. One participant gathers information (text, data, images, etc) in electronic form and sends it to the other participant, who views it at a subsequent convenient time and reports back. The classic example here is dermatology second opinions.

Choice as to which of the above approaches is preferable varies with the type of service required; neither is universally preferable.

The spectrum of TM & eH services includes:

• Specialist and primary care consultations (Teleconsulting).

A patient or a primary care physician “seeing” (another) medical specialist over a live video connection (may include diagnostic procedures such as ultrasound or endoscopy). Almost 60 different medical subspecialties have successfully used distant consulting.

• Distant diagnostic
  or therapeutic manipulation.

This is the most advanced type of live (real-time) telemedicine services; includes complex interventions (such as endoscopy or a surgical procedure) performed by a distant specialist over a telecommunication link (Telesurgery). The pictures show the first Transatlantic surgical procedure performed in 2001 by an operating surgeon (Professor J. Marescaux) located in New-York, on a patient in Strasburg, using surgical robotic system ZeusTM and a high-speed (10 Mbps) connection [57].