Dr. Nunn: But the Auger electrons have very short range,
and it is unlikely that you would get your iodine into old
parts of the tumor, especially the central part.
Dr. Norman: The contrast medium probably is excluded
from the cells, and so not all of the radiation emitted by the
iodine is effective in killing the cells. But as we could see
from the comparison of the calculated versus the experimen-
tal data in cells, apparently most of the iodine energy release
from the iodine atom does in fact contribute to cell killing.
So I assume that the range of the photoelectric plus the char-
acteristic x-rays are really contributing to cell killing. Prob- ably, the Auger electrons do not. I think the ordinary iodi-
nated contrast medium is as good as anything else that we
Dr. Mattrey to Dr. Saini: I understand the agent has a very
long blood half-life, and I realize the blood is bright, but how much of that is from contrast, and how much of that is signal
entry because of the gradient-echo image you showed here? Do we really see blood enhancement 24 hours later?
Dr. Saini: It is true that gradient-echo images will get some
entry slice phenomenon signal in the blood vessels, but if you compare the pre- and postcontrast images, there is un-
equivocal image signal within blood vessels throughout the
imaging volume, and it can be seen quite far out into the pe-
riphery of the organs such as the liver. You can even begin to
discriminate the bile ducts from blood vessels. So there is no question that there is intravascular signal.
Dr. Mattrey to Dr. Wisner: Did you actually measure node
enlargement, or was this a visual thing?
Dr. Wisner: We did measure a subset of the node population
Dr. Mattrey: There is a problem with that unless there is a
dramatic change in size, because when you've made the
CT number higher, you recruit more partial volume. Part
of the lymph node that you might have otherwise not ap- preciated on the pre comes in because it is now brighter.
Secondly, measuring size by CT is somewhat susceptible to window level, because the curve is not the perfect square wave. It is actually kind of a bell-shaped curve, and
where you measure along that curve will depend on how you set your window. I accept the fact that the lymph
nodes probably enlarge in size, but I would want to be careful measuring from the CT scan and actually correlate them anatomically, but that would be tough to do.
Dr. Wisher: I agree wholeheartedly with you. That is wh 3
I didn't present the precontrast data; we were using that only as a guide.
Dr. Mat t rey to Dr. Clement: It has been shown that
when the leg was perfused from the arterial side, some- thing like 90% of the enhancement came through the inter-
stitium. Is there a discrepancy?
Dr. Clement: There have been many discrepancies in the literature about this subject. In our previous study pub- lished in the proceedings from the last CMR, we saw it was 50/50, and now with this study I presented today,
what we are seeing is that the vascular route to each indi-
vidual lymph node is of minor importance.
Dr. Mattrey: I have another question for you regarding the animal model. Since you gave the contrast material be- fore you cannulated the thoracic duct and therefore dis-
rupted a great deal of lymphatic and interstitial spaces, could that have been contaminated by your surgery that you did after you gave the contrast? Could that have mud-
died the data some?
Dr. Clement: The procedure to cannulate the thoracic
lymph duct is retroperitoneal, and so when you open the abdomen, you do not touch the organs inside. So probably
you do not chance a capillary leak inside these organs.
Dr. Dawson to Dr. Norman: Your technique involves in- jecting directly in order to get a high enough iodine level in brain tumors in dogs, and it may be fine in other super- ficial tumors, even in man, but why not employ the interventional radiologist to do selective infusions? You
could give a loading dose and then maybe repeat boluses during the therapy to keep the levels topped up both intra- vascularly and interstitially. You could argue that in dogs, in man and brain tumors, catheters for longer periods in the carotid artery might not be a good idea, but certainly in
other tumors in man you could consider catheters present for some time, and I would have thought in dogs with brain tumors you could take the risk of an intraarterial
catheter and repeat boluses.
Dr. Norman: I can only tell you that while it sounds like
an attractive idea, the radiologists at UCLA do not like the idea at all. They claim that they have too many problems on intraarterial injections. I want to emphasize that the dogs we have been treating are pet animals, and we cannot even mention the word experimental around the owners. We are treating them in order to cure them hopefully, and
this is why from a straight scientific standpoint our data
are incomplete, because many of the dogs are simply never returned. The owners decide that they should be euthanized, and that is the end of the thing. So I think we have done remarkably well, given the constraints.
Dr. Weinmann to Dr. Lanza: You put some gadolinium DTPA onto the emulsion; can you explain how you did that?
Dr. Lanza: Essentially they are fatty acids, coupling the DTPA to the surface of the lipids. It actually would be ga-