Dr Iain Duncan

To biopsy or not -the thyroid nodule dilemna

Thyroid nodules are very common and a small percentage of these are malignant. Ask 10 thyroid specialists about their approach to biopsy and diagnosis and you will get 10 different approaches. All will be rational and based on reasonable scientific data and on experience. The different approaches arise because the research is varied in its […]

How useful are lung scans in 2012? Iain’s view…

Lung scan renaissance

Lung scans fell out of favour with the advent of multislice CT pulmonary angiography (CTPA) which offered a great improvement on the accuracy of lung scans shown by the PIOPED study done in the 1980’s. There is no doubt that CTPA is a readily available test for diagnosing pulmonary embolism.  Nuclear technology has also moved on since the PIOPED study and more recent studies from various centres tend to suggest that there is very little difference in accuracy between the two modalities. In practice it is the appropriate use and application of the test that is more important than whether it is CTPA or V/Q lung scanning. The PIOPED II STUDY (New Engl J Med 2006,354:2317) showed the overall sensitivity of  CTPA for the diagnosis of pulmonary embolism was 83% and the specificity was 96%. However, these data excluded CT studies that were technically inadequate or un-interpretable . When all the studies are included the sensitivity and specificity fall to 78% and 90% respectively. The positive predictive value was 86% and the negative predictive value was 95%. Most notably the positive predictive value was only 58% when the clinical probability was low.  Therefore additional testing is necessary when clinical probability is inconsistent with the scan results.

Yellow=perfusion and green=ventilation

Wang, Feng MD et al in Clinical Nuclear Medicine July 2009 (Volume 34 – Issue 7 – pp 424-427) concluded V/Q lung scan, perfusion scan combined with CR and CTPA all show high efficacy in diagnosing pulmonary embolism.

In a head to head comparison (all patients had both tests) of CTPA and SPECT-CT lung scans Gutte et al (V/Q SPECT AND LOW-DOSE CT VS MDCT IN PE. J Nucl Med 2009; 50:1987–1992)  found  SPECT-CT lung scans had a sensitivity of 97% and specificity of 100%.  CTPA  alone had a sensitivity of 68% and a specificity of 100%.

 

In a  very recent study done at the Charles Gairdner Hospital Perth (Ling  et al. Internal medicine Journal 2012;42:1257-1260)   they demonstrated that the addition of low dose CT increases the diagnostic yield by providing alternative diagnoses and contributed to a final diagnosis in 36%.   Their  use of SPECT-CT for the diagnosis of pulmonary embolism had a  sensitivity , specificity, and negative predictive values of  93%,100%, and 97% respectively. 

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SPECT-CT lung adds specificity

This middle aged female was referred with shortness of breath and a CXR reported as showing oligaema in the left upper zones that could indicate pulmonary embolism. The reconstructed planar lung scan showed a large matched defect corresponding to the left upper lobe. The SPECT-CT scan shows a large airspace is responsible for the abnormality -most […]

Nuclear Medicine = New Clear Medicine

When I started in nuclear medicine it was often cynically stated by other physicians that nuclear medicine was “unclear” medicine. Unfortunately like so many jokes this one had more truth than I was comfortable with.  Nuclear medicine was great at finding the problem but not telling you what it was.  We could find “hot spots” […]

SPECT-CT in nuclear medicine

Nuclear Medicine Update: Dr Iain talks about the value of SPECT-CT in bone scanning “Nuclear Medicine functional imaging is now directly combined with CT anatomical scanning to create SPECT-CT. It is the first technology to combine the power of SPECT with the precision of diagnostic multi-slice-CT. It makes it possible to pinpoint the exact location, […]

Nuclear Medicine for Dummies

Indication Scan Comments Arthritis & joint symptoms Bone scan Helps assess distribution, activity and extent Back and neck pain Bone scan Useful in determining whether focal abnormalities are present (facet joint arthritis, fractures) or to determine the level and location of symptoms Bile leak or obstruction HIDA scan Biliary disease HIDA scan This scan detects […]