[HSF] Image of the Week - Fixing a tube :)(OT)

Thu Feb 1 21:38:45 EST 2007

Largely agree with Ed.

EBCT has much less resolution, but also much less radiation. A non-efficiently done diagnostic cath and MDCT have similar "exposure".

The resolution of the 16 MDCT is the roughly the same as the 64. The difference is the length of time (breath hold) required to get the same pictures. This (16) makes a lot of sense both economically and medically for OP who usually are more fit. (More spins, same speed, but slightly less radiation.) Some manufacturers also allow gating of the energy to be less during part of the cardiac cycle to further reduce radiation exposure, if the rhythm is stable.

CMR may make rapid progress over the next 12-24 months. There are some incredible ideas out there. (Okay, I get get excited about almost any idea.) A therapeutic or virtual transcardiac MR procedure is very interesting. (There was a talk on 3D TEE for the same at STS). MR images are much more crisp unless one is looking at thin valve tissue, but I am uncertain as to how they would be acquired in real (operative type) time. 

TEA

----- Original Message ----
From: "DukeB60 at aol.com" <DukeB60 at aol.com>
To: OpenHeart-L at lists.hsforum.com
Sent: Thursday, February 1, 2007 10:43:03 PM
Subject: Re: [HSF] Image of the Week - Fixing a tube :)(OT)

There is no question that the imaging capabilities  of the 64 slice scanner 
will, if it hasn't already, revolutionize  cardiology imaging with it's ability 
to acquire an amazing amount of data in a  short time.  Temporal and spatial 
resolution allow for very detailed images  even of the constantly moving 
heart.  The ability to obtain a block of data  with 64 sources of radiation and 64 
detectors simultaneously, in a relatively  short time period representing only 
a partial rotation of the gantry, allows for  imaging of an organ previously 
impossible to clearly visualize due to the fact  it is a moving target.  A 
huge amount of data acquisition accompanied by  remarkable and relatively user 
friendly software applications make for a very  appealing modality.  So 
appealing, in fact, it has been marketed  relentlessly so that everyone thinks they 
need one - or two.  
    While there is a rational debate about whether CTA  is ready to supplant 
conventional coronary angiography (CCA), few would argue  that at some time in 
the near future CT based imaging will be a routine method  of coronary 
imaging, and at some centers it already is.  
    MRI will also play a role for structural and  functional cardiac imaging 
that may rival echo. in the near future. Tea has been  investigating this 
modality for some time and we are actually contemplating a  hybrid OR that may 
include real time MRI to allow more accurate positioning of  percutaneous and/or 
trans-apical aortic valves with greater accuracy than  traditional echo.  It 
may not happen for some time in the future, but it is  likely coming.  An 
additional appeal of MRI is the absence of ionizing  radiation exposure, which, as 
Prasanna pointed out, has not been lost on the MRI  manufacturers.
    While the 64 slice CT has a unique use in cardiac  imaging, due to the 
fact the target is constantly in motion, it is doubtful that  the 64 slice 
machine is necessary, or even desirable, for imaging non-moving  targets such as 
the brain, lungs, abdominal viscera or extremities.  16  slice or even 4 slice 
machines give superb images with a relatively longer, but  not very 
significantly prolonged, data acquisition time.  Using the  software packages of the 64 
slice machine, superb images can be obtained that  satisfy all diagnostic needs 
with less ionizing radiation.  
    What is at issue here is not the capability of the  64 slice  to obtain 
beautifully rendered images but, rather, the  fact that the exposure to 
radiation for diagnostic radiographic procedures,  especially in instances where 
repeated follow-up imaging my be required, becomes  a not insignificant factor.  
Concerns arise, then, as to whether we  may begin to see neoplasms primarily 
due to such repeated exposure to excessive  amounts of diagnostic radiation. "We 
do not know yet the long term effects  of getting our atoms jerked 
around." (John Flege), but it very well may  not be good.  Many are voicing 
concern.
Prasanna's post  was alarming inasmuch as it may have come to the attention 
of the lawyers  that a patient may have a cause of action for a malignancy that 
may have been  induced by diagnostic radiation exposure.
    While the 64 slice machine gives beautiful images,  obtaining them comes 
at a cost we never paid much attention to previously -  that is, the fact we 
may be creating a public health problem,  purely iatrogenic in nature, due to 
the indiscriminate and, perhaps,  irresponsible use of such a high dose of 
radiation when it is not strictly  necessary to obtain the desired images.  
    When I say we did 1200 scans last month on the 64  slice machine it is 
very doubtful they were all of a nature that required the  unique ability of the 
64 slice scanner to image a moving object.  Rather,  the 64 slice machine was 
likely chosen because reimbursement is higher  and the data acquisition time 
is shorter maning higher throughput  - more scans per day means more cash 
flow.  But at what public health  cost?  That is the important question.  I'm not 
at all  certain we know for sure the consequences "of jerking our atoms  
around" but have heard from enough sources that we should not be cavalier  in the 
use of the 64 slice scanner when it isn't really necessary.  (I  think this was 
actually longer than some of Ani's posts.)

              Ed

Edward P.  Raines, M.D., J.D.
BryanLGH Cardiothoracic Surgery
BryanLGH Medical Center  East
1600 South 48th Str.
Lincoln, Nebraska 68506
Office:  402-481-8430
Cell: 402-730-9242
Fax:  402-481-8429
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