Page 367 - fbkCardioDiabetes_2017

Cardio Diabetes Medicine 2017 343

Myocardial Imaging Products :

Continuing Evolution For The Better

Dr. N. Ramamoorthy Dr. Meera Venkatesh
Ph.D. Chemistry

Retiree from BARC-DAE, Mumbai; Chairman,
SARCAR, AERB, Mumbai; Adjunct Faculty,
SoAHS, Manipal Univ. Mysore.

Abstract: specificity and sensitivity, was a challenge.This led
The role of myocardial imaging in nuclear medicine to investigating a range of products providing valu-
(NM) has been well recognized in the management able information of different nature and there has
of patients of coronary artery diseases. It is reported been an evolution over time, both in products and
that nearly 40-50% of all diagnostic imaging done imaging instrumentation. This article tries to briefly
in NM (over 40 million studies per annum) is of the capture the salient developments and the ever-con-
myocardium (depending upon the region/country), tinuing changes for the better.
and thus nuclear cardiology(NC) has become an im-
portant branch of NM. The radiopharmaceuticals and Myocardial perfusion markers:
techniques evolved over time are for mapping mainly The search for a suitable radioisotope tracer for myo-
the blood flow to myocardium (using potassium ionic cardial imaging as a mimic of intra-cellular K (due to
+
analogs: 201 Tl , NH , Rb , [ 99m Tc(X) ] ), and demon- non-availability of a suitable potassium radionuclide
+
13
+
82
+
+
n
4
strating viability (trapping of fatty acid analog ( I - (RN)) with the then prevalent planar gamma camera
123
fatty acid) or glucose analog ( FDG)). The advent of was the starting point in the evolution of myocardial
18
SPECT and PET-CT has helped enhance the image perfusion imaging (MPI) agents. In mid-1970s the ad-
quality as well as quantitation capability, strength- vent of 201 Tl tracer - mimic of K due to similarity of
+
+
ening the NC practices further. The dream-wish in ionic size and charge - heralded a major milestone
the continuing evolution is to develop an efficacious in the history of radiopharmaceutical and nuclear
product, which can medicine.
specifically image the atherosclerotic lesions within Thallium-201 as TlCl (74 h half-life; Eg 135 & 167
201
coronary arteries, although many challenges need to keV; 69-80 keV Hg X-rays): The following features
be addressed. of 201 TlCl led to its facile deployment: high myocar-
dial extraction of 201 Tl ensuring that 3-4% of the
+
Preamble: administered dose of 201 Tl (50-75 MBq (about 1.5-2
mCi)) being taken up by the myocardium; relative-
Myocardial imaging has been an extremely import- 201 +
ant contribution of nuclear medicine (NM) for the ly slower uptake and slower wash-out of Tl from
management of patients of coronary artery diseas- ‘compromised but viable’ myocardial tissue (ischemic
es (CAD, IHD). The role of NM imaging,to map the areas), as compared to normal myocardial cells; fast
blood flow to the myocardium (myocardial perfusion), blood clearance; excretion by renal system, etc. This
as well as to demonstrate viability of myocardial seg- helped obtain stress and rest images of myocardial
201
ments, has been of considerable value to cardiolo- perfusion, with a single injection of TlCl and im-
gists in planning management strategies, and/or for aging twice, early (injection of tracer at peak exer-
subsequent follow-up. Though one of the early aims cise and imaging soon after) and a delayed image
201
of diagnostic nuclear medicine imaging was to visu- at 3-4 h p.i.). This led to the success of Tl imaging
alise the myocardium so as to assess the functional in NM, despite the relatively low resolution images
adequacy, the path of developing and deploying suit- obtained with the planar gamma camera (GC). The
able radiopharmaceutical products, of the required term ‘redistribution’ was much used for information
Cardio Diabetes Medicine