Presentations

Abstract

Introduction:

DaTscans are used to detect defects in dopaminergic pathways aiding in the diagnosis of Parkinson's disease. It is also beneficial for differentiating between dopamine-deficient Parkinson's, Lewy Body Dementia and Alzheimer's¹⁵. This exam decreases the time to diagnosis and start of treatment.¹ Given the important role DaTscan has in patient management, proper imaging technique is essential to provide diagnostic imaging quality for confident interpretation. Our case highlights the importance of suboptimal scan recognition, and will discuss the differential for poor image quality and applicable correction methods.

Many factors are involved with performing a DaTscan accurately. The patient must be prepped appropriately, including blocking the thyroid gland with potassium iodide a hour before the exam and stopping certain medications, such as phenylephrine and antidepressants.⁴ The patient is injected intravenously with radioactive iodine, ¹²³Iofluplane, which has a high affinity for the presynaptic dopamine transporters at the nigrostriatal pathway. The patient is imaged several hours later.⁵ Imaging the patient involves placing them in head, arm, and knee restraints to minimize movement; the head is then rotated about 12-15cm. The cerebellum is not imaged as the structures of interest are above the ears.⁴

A typical, negative scan will demonstrate symmetric radiotracer uptake at the basal ganglia with an appearance described as a 'comma', and minimal uptake in the remainder of the brain (Figure 1: Normal DaT scan).

Case Information:

The patient is a 75-year-old female with a two-year history of suspected Parkinsonism. She initially reported difficulty picking up her feet, getting up from a seated position, worsening handwriting, and throwing objects in her sleep. On exam, she had slightly increased tone in the left upper extremity, left greater than right decrement with finger taps, concern for gait freezing, decreased left arm swinging, stooped posture and en bloc turning. She was started on a trial of carbidopa levodopa which initially yielded an intermediate improvement in symptoms, but eventually the patient reported a return of symptoms. Due to her symptoms and abnormal physical exam, she underwent a DaTscan.

The patient's initial scan had an overall low count appearance (Figure 2a), and the quality of the exam was questioned by the radiologist. While one may call this abnormal positive for Parkinson's Disease, the confidence level is low. Quality assessment of any nuclear examination should be done when the images do not fall within expected normal limits. Review of the raw data images (Figure 2b) revealed inclusion of the salivary glands, which appeared quite intense. Repeat imaging was performed above the ears, to exclude the normal salivary gland activity, resulting in an improved image quality (Figure 3a and 3b). On the repeat scan, there was a more convincing loss of dopaminergic neurons in the posterior basal ganglia bilaterally, and a more definitive interpretation of a positive DaT Scan.

Discussion:

DaTscans detect defects in the nigrostriatal pathway. The ratio of caudate to putamen uptake, and varying degrees of symmetry are crucial to measure qualitatively and/or quantitatively.³ If there is interference with basal ganglia count detection because the image acquisition is too wide and the scaling is incorrect, as seen in this patient, the results will diminish diagnostic quality. Other artifacts that can cause abnormal imaging findings include improper head positioning, movement artifacts, medications that interfere with ¹²³I uptake, and patient history of previous infarcts.⁴ Improper head positioning can be observed on raw data review, and corrected with reorientation tools. If that is unavailable, repeat imaging would be advised. Motion should be assessed on raw data imaging as this can cause diminution or distortion of the basal ganglia, and would also be corrected with repeat imaging. When faced with an overall low count study, some additional technical considerations include medication interference and dose infiltration. Review of the patient intake form and scanning of the injection site help exclude these confounding factors.

Conclusion:

A DaTscan is clinically useful for diagnosing Parkinson's Disease. The examination requires proper patient preparation, image acquisition, and processing. This case highlights basic nuclear medicine principles and the importance of the knowledge to produce quality diagnostic images.