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Minimally Invasive Therapy Unit & Endoscopy Training Centre
University Department of Obstetrics and Gynaecology
Royal Free Hospital
Pond Street
Hampstead
London NW3 2QG, UK

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Computer capture of surgery using a personal computer

The visual recording of surgical procedures either as still images or movies is becoming standard practice across many specialities. Analogue recording using film or video is gradually being replaced by digital technology for reasons of quality and convenience. Commercial systems are available but are expensive and have limited capabilities and capacity. We have been using a digital system based around a standard personal computer since 2003 to record all our surgery.

System 1 The original system consisted of a standard Windows ® PC with a 250 GB internal hard disk linked to the camera system by a Canopus AV-100 analogue-digital converter. This system was based on software compression using the freely available DivX codec. We used VirtualVCR, another freeware programme, to make the recordings in real-time.

We used a Canopus ADVC-100 analogue/digital converter linked to the PC with a firewire cable as the interface between the analogue signal from the camera unit and the computer. To avoid interference from the theatre equipment, use the 4 pin firewire output from the A/D converter.

The digital signal was captured in real-time using the freeware (free) video capture application VirtualVCR (available from http://virtualvcr.sourceforge.net). The program provides real-time capture statistics of variables such as the number of frames captured, dropped frames, compression ratio, size of the file and the time left on the hard disk for further recording which can be saved along with the recording. VirtualVCR allows the Windows mouse pointer to be used within the image for teaching, etc.

As it is being recorded, the video signal was compressed in real time using the DivX ® MPEG-4 encoder/decoder (available for free for non-commercial use from http://ww.divX.com). Raw video images take up a lot of memory (e.g. 10 minutes of uncompressed video requires approximately 15 Gb hard disk space), so compression is desirable; for instance, we can save over 230 hours of surgery on our 250 Gb hard disk using the settings described below. It is also preferable to compress the video in real time (i.e. as the procedure is being recorded) rather than afterwards to avoid delays in subsequent recordings. DivX ® provides good compression without over compromising quality.

Our settings for the DivX ® Pro codec (version 5.1.1), which can be accessed within VirtualVCR, were as follows:

 

The above settings produced an approximately 11-fold compression (e.g. 10 minutes of compressed video required about 180 Mb hard disk storage), and was twice the compression of conventional DVD recordings in MPEG-2:

We saved screen shots during surgery using the freeware programs WinGrab (available from http://home.no.net/wingrab ) or after surgery with VirtualDub (see below).

If required, we edited recordings using the freeware programme VirtualDub (available from http://www.virtualdub.org). Editing can be done on a frame-by-frame basis, and individual frames can be copied and pasted into standard photo editing programs to provide still images. Numerous freely available filters can be used with VirtualDub to change the size of the output, crop edges, adjust the colour balance, apply logos, etc.

Recordings could be played back using software such as Microsoft Windows ® Media Player which comes free with the Windows ® operating system for PCs (provided the DivX ® codec has been installed). We prefered to use the freeware programme Zoom Player (available from http://www.inmatrix.com/zplayer) or GOM player (available from http://www.gomplayer.com). Movies and still pictures could also be integrated into presentation software such as Microsoft ® PowerPoint, but only after conversion to a different format (there is no such problem with Apple computers running the OS X operating system). Still pictures could be printed to provide hard copies for patients and medical notes, and movies burnt to CD or DVD.

System 2 In 2006, our system was upgraded to utilising a Plextor ConvertX PX-M402U AV converter which allowed for hardware-based compression. Although this system also makes MPEG-1 and MPEG-2 (DVD quality) compression possible, we continued to use the DivX codec as this codec provides superior compression at similar quality. We used the Home Theatre LP configuration (1 hour of recording is approximately 1 GB).

System 3 Most recently, and for convenience, we have changed to a laptop-based system by adding an external hard drive for saving the video recordings. An external hard drive gets round the problem of most laptops, namely a relatively slow hard disk; it also allows a much greater capacity for recording (our current hard disk is 500 GB).

The picture above shows the laptop with the ConvertX AV converter underneath on the left, and the external hard drive on the right. We still use VirtualDub for editing and converting the recordings if needed.

Taken from: Magos A, Kosmas I, Sharma M, Buck L, Chapman L, Taylor A. Digital recording of surgical procedures using a personal computer. Eur J Obstet Gynecol Reprod Med 2005, 120, 206-9.

Note: Local guidelines must be followed when any visual recordings are made of patients. In the UK, the General Medical Council has issued guidelines which state that, in the case of laparoscopic images or images of internal organs, permission or consent is not required from patients provided the recording are effectively anonymised by removal of any identifying marks (further details are available at http://www.gmc-uk.org/guidance/current/library/making_audiovisual.asp#5.

A good surgeon operates with his hand, not with his heart.

Alexandre Dumas Père (1802-1870)