Case Author(s): Eric Hutchins, M.D. and Jerold Wallis, M.D. , 12/03/04 . Rating: #D., #Q.

Diagnosis: Intra-arterial Injection of Tl-201

Brief history:

67 year old female with chest pain.


Single projection image of the raw data.

View main image(mi) in a separate image viewer

View second image(mc). Image of arms.

View third image(mi). Raw data image and arm image combined.

Full history/Diagnosis is available below

Diagnosis: Intra-arterial Injection of Tl-201

Full history:

67 year old female with chest pain. Her cardiac risk factors include hypercholesterolemia, hypertension, and smoking.


201-thallous chloride


The raw image of the thorax does not demonstrate adequate counts.

The image of the arms shows that most of the activity is in the left upper extremity.

On the combined image of the chest and arms, the chest contains 22,823 counts and the arm contains 133,113 counts.


When the number of counts is too low, the etiology could be due to problems with the radiopharmaceutical, the patient, or the camera/computer.

Was the correct radiotracer injected? Was the correct dose administered? Was the radiotracer infiltrated or injected into an artery rather than a vein? Does the patient have abnormal anatomy or physiology that caused an abnormal biodistribution of radiopharmaceutical? Was the correct collimator used? Was the camera set to the correct photopeak?

These are some of the questions to ask when presented with a noisy image.

201-Tl chloride acts as a "chemical microsphere" and localizes to myocardial cells in proportion to tissue perfusion. The normal extraction efficiency of 201-Tl chloride by myocardial cells is 88%. In this case the skeletal muscle of the left upper extremity extracted the majority of the injected activity.


The patient was re-injected with 201-Tl chloride through a new intravenous access and the images were satisfactory.

Note that the local radiation dose from an infiltrated thallium dose can be significant. In this case, the dose was spread out over the arm, making the change of an adverse effect much less likely. Nonetheless, this is to be avoided, and care must be taken during injection to verify good venous access.

View followup image(). SPECT images of the heart after re-injection of Tl-201 through new intravenous access. The study is normal.

Major teaching point(s):

If study is count-poor, image the site of injection.

ACR Codes and Keywords:

References and General Discussion of Myocardial Imaging (Anatomic field:Heart and Great Vessels, Category:Normal, Technique, Congenital Anomaly)

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Case number: mi030

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