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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.
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