There's a review of Medical Imaging technologies entitled: "Evolving and experimental technologies in medical imaging." in the Jan 2006 edition of the Journal "Radiology", it gives some context to the current position of Terahertz Imaging with respect to more established technologies.

http://radiology.rsnajnls.org/cgi/content/full/238/1/16

Terahertz radiation is not only useful im medicine, there are many more applications:
Terahertz radiation can be used for detecting hidden weapons and explosives because radiation at these wavelengths penetrates most container materials. Terahertz radiation has wavelengths that are slightly longer than visible and infrared, but shorter than microwaves. Because their energy is almost a million times lower than that of x-rays, this non-ionizing radiation is not expected to cause any harmful effects to humans or animals.

Spire's terahertz imaging system design will incorporate a nano-engineered miniature quantum cascade laser as a terahertz radiation source. Spire's quantum cascade laser device consists of hundreds of nanometer-thick gallium arsenide-based layers. The entire imaging system is small and portable.

I found the article very interesting not just regarding to the Tetrahertz radiation system also the other imaging methods.
Things are evolving very fast I must say.
It is also very interesting the ways to cure i.e tumors with systems that bhave MRI technology such is the case in :
ExAblate - Magnetic Resonance (MRI) guided Focused Ultrasound (MRgFUS) device that focuses ultrasound energy, to heat and destroy tumor cells inside the body while sparing tissue outside the tumor.
Guy

Terahertz imaging is still not well developed, most of the research is still military. The equipment is real expensive, so if/when it trickles down to major research is hard to say. Yes it is exciting, but don't hold your breath as far as you getting a chance to use it successfully. I work in imaging and microscopy, there are but a handful of companies making the equipment, even fewer making the optics for microscopes to do it right. A very good objective from Westover/AMG, Olympus, Nikon, Mitutoyo or others might work, but you never know. It would probably have to be special objectives from Optec, Spa or some other custom lens manufacturer?

Added note, the Terahertz article mentioned photonic band gap material. Yes there is some new materials on the horizon, but still are not proven. They could change the the cost of Terahertz equipment, but it is years away before they are actually in practical use. The article is missleading stating that this material would lower costs rapidly, because the material will not be available to the general market for some time to come. The big problem with US healthcare and Life Sciences is no one wants to spend money until the Europeans have perfected it and lowered its costs to produce. I recently visited a lab where they where using a $300 DSLR camera mounted on a $500 microscope screening and documenting patient blood samples on hemocytometers!! I showed them equipment that would do the imaging in real time and with fantastic image quality, but they could not afford it!! Their accounting department would not let them spend over certain amounts for any digital camera or microscope!!