Additional studies by Prvulovich et al in 1997 and Hendel et al in 1999 Localisation
CT can be used
demonstrated improvements in diagnostic specificity in patients with follow-up CT (low resolution or diagnostic quality) can be used in conjunction with SPECT
angiography, in comparison with non-attenuation corrected images
7,8
. It should, to help localise cold or hot areas seen on SPECT imaging. This has particular
with SPECT to
however, be noted that these studies were all conducted using radioisotope and value in cases where there are limited or no anatomical landmarks present on
transmission based attenuation correction units, not CT. In terms of the impact of SPECT imaging and/or when such landmarks are present but greater anatomical
localise cold or
attenuation correction on diagnostic sensitivity of MPI, Duvernoy et al’s study on 28 spatial resolution is required. Examples with the registration of SPECT with CT for
patients with left main coronary artery disease in 2000
9
showed this to be present localisation purposes could include: to aid definitive diagnosis and to give more
hot areas
on 64 per cent of AC images versus seven per cent of uncorrected images. precise lesion localisation as part of surgical work up, such as sentinel lymph
nodes
13
, radiotherapy treatment planning
14
or initial patient treatment work up
15

In the 1980s, the use of external transmission sources such as Ba-133 and Gd-153 (eg neuroendocrine tumours (NET)).
were utilised to provide attenuation correction data. However, issues related to
poor statistical quality has resulted in a limited use of such sources within modern Advancements in computing power and software algorithms have also impacted
clinical practice. Nevertheless, in clinical instances whereby only AC is being upon the ability to compensate for the errors in SPECT imaging. In particular the
performed, as in nuclear cardiology for example, the use of a transmission-based inclusion of an iterative reconstruction model (eg OSEM) for the correction of
system may be justified. Acquiring the required AC data using a transmission based attenuation with SPECT data and providing quantitative information is becoming
system such as Gd-153 takes longer than a CT based method due to the large more common within clinical practice
10
. Numerous studies have identified the
difference in available photon flux and the fact that transmission based systems improved diagnostic accuracy of SPECT/CT over conventional SPECT imaging and
have a limited field of view coverage
3
. the empirical evidence points toward the following areas of clinical practice which
have benefited from the emerging hybrid imaging technology, for example:
CT data may be used to create linear attenuation coefficients based upon Lymphoma
16

anatomical detail specific to each patient. This data (attenuation map) may be Lung Cancer
16

used to correct for the effects of photon attenuation within the subject and, if only Primary and secondary malignant bone disease
17

AC is being undertaken (eg myocardial perfusion imaging), the CT may be acquired Infection and inflammation
18

with a lower statistical quality. Although this reduces the spatial resolution, this Abdominal disease
19

technique reduces the radiation dose to the patient. Endocrinology
15,20

With reference to oncology-based applications, CT AC has particular values. A comprehensive list of potential clinical applications for SPECT-CT has previously
SPECT imaging is increasingly used to quantify the uptake of a particular been published
10
and the majority of applications relate to the anatomical
radiopharmaceutical within tumours/organs. Such targets are quantified in SPECT localisation of tumours using various radiopharmaceuticals. Published research by
as volumes of interest (VOI); these are defined around the region to integrate the Koral et al identified the added value of SPECT-CT in terms of providing valuable
number of counts, which is directly proportional to the activity (expressed as MBq tumour organ uptake and dosimetry data, enabling accurate patient workup prior
or mCi) in the volume defined
10
. to treatment for lymphoma
11,12
. This research involved a range of professional fields
and provides evidence of multiprofessional working.
Accurate quantitative measurement of radioactivity from a SPECT study can be
compromised by the effects of attenuation (and scatter). Such factors may be corrected Case study
by the use of CT AC data. The use of SPECT-CT is beginning to create a new role An eight-year-old male presented with a painful right tibia; the clinical question
for nuclear medicine in terms of accurately quantifying radionuclide uptake within surrounded whether this patient had an osteoid osteoma or leukaemia. A whole
targets, compared to measurements undertaken with SPECT alone. Results from body bone scan was conducted (anterior and posterior) and a focal area of uptake
clinical studies
11,12
have demonstrated the value of SPECT-CT in terms of measuring was noted within the right femur. Subsequently, localised SPECT images of pelvis
response to radiotherapy treatment for patients with non-Hodgkin’s lymphoma and and femora were acquired; the poor resolution could not differentiate the high
radioimmunotherapy. The use of SPECT-CT within oncology is beginning to replicate uptake between cortex and medulla and CT imaging was undertaken (see figure
clinical experience with PET-CT, in terms of improving localisation and extent of disease, 2). Correlation with plain films and a SPECT-CT acquisition of the area show a
and differentiation of physiological and pathological uptake. localised area of thickening and sclerosis of the medial cortex of the upper right
44
|
IMAGING & ONCOLOGY
|
2009
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64