SPECT & TMJ DISEASE

SPECT analysis in TMJ disease

SPECT (Single Proton Emmission Computerised Tomography)

SPECT using Tc99m is a sensitive and specific assessor for bone age determination, and in particular for assessing arrest of development in TMJs. It is used best for assessment for asymmetric jaw growth, particularly with assessing the extent of condylar hypertrophy, and for precise intra-lesional localisation of hot-spot activity.

Tc99m is used as the specific tracer radionucleotide for SPECT imaging, and is linked to either HDP or MDP which acts as the carrier into bone tissue. SPECT specifically is advantageous for allowing imaging in 3 planes, and for 3-D reconstruction, improving spatial orientation of hot spots and for precise anatomical localisation.

The latest development with SPECT is the fusion of SPECT images with conventional low dose, multi slice helical conventional CT imaging, and for co-analysis of both 3-D SPECT and 3-D conventional CT anatomical rendering.

The best single report on the use of Tc99m for TMJ disease is

Kaban LB et al. Assessment of growth by skeletal scintigraphy. Journal of Oral & Maxillofacial Surgery. 1982. Vol40. 18-22.

The leading nuclear radiologists in this field for the Hunter region is lead by Dr Doug Howarth, and who in 2001 established a definitive protocol for use of SPECT in TMJ imaging.

BONE SCAN PROTOCOL (Hunter Imaging, Newcastle)

Radiopharmaceutical

Adult Dose:  740-900 MBq Tc99m hydroxy-methylene diphosphonate (HDP) or Tc-99m methylene diphosphonate (MDP).

Paediatric Dose: Adjusted according to weight using doses ranging from 185-740 MBq.

N.B. If upper extremity imaging is required, ensure that the injection is given in the contralateral normal arm, waiting at least five minutes after release of the tourniquet before injecting the bolus and ensuring thorough normal saline flush.

Dose/Scan interval

Flow study: Imaging commences immediately after the injection.

Whole-body, spot views, SPECT: Imaging commences 2 hours after injection if using Tc-99m HDP or 3 hours if using Tc-99m MDP. For extremities imaging commences at least 3 hours after injection for any agent used.

Views Obtained

The number of views depends upon the indications for the examination, as set out below.

 

Indications

In a Nuclear Radiology practice bone scintigraphy is mostly used to assess patients with bone or joint pain and cancer patients for evidence of metastatic bone disease. Bone scan is a very sensitive test for the detection of fracture, tumour or infection. Early phase bone scan imaging (blood flow and blood pool imaging) can demonstrate active inflammation, and is very helpful in assessing patients with possible arthritis or infection. Early phase imaging may also help in determining whether the abnormalities detected on delayed scan imaging are recent.

This discussion is limited to assessment for TMJ disease

Principle

It is not clear how Tc-99m labelled diphosphonates are incorporated into bone at the molecular level; however, it appears that regional blood flow, osteoblastic activity, and extraction efficiency are the major factors that influence uptake. In areas of increased osteogenic activity, active crystals of hydroxyapatite with large surface areas appear to be the most suitable sites for chemisorption of the diphosphonate ligands.

 

Patient Preparation

The patient should drink 2-3 glasses of water between the time of injection and the scan. The patient should empty the bladder before scanning, and remove all metal objects from area to be scanned.

Instrument Specifications

Gamma Cameras.

 

  • CARDIFF:              1. Toshiba 7200 (double head)

                                      2. Toshiba 901 (single head)

                                      3. Siemens multi-SPECT MS2 (double head)

                                      4. Siemens orbiter (single head)

B. MAITLAND              1. GE Millenium (double head)

                                      2. Toshiba 7200 (double head)

Collimator.

Low energy high-resolution parallel-hole collimator.

On occasion, pin-hole imaging of paediatric hip joints may be required.

Energy Setting.

140 keV 20% window for Tc-99m HDP or MDP.

Computing and Software Systems.

Each gamma camera has its own dedicated computer with appropriate software for data analysis.

Image Hardcopy.

Film printer (24cm x 30 cm).

Imaging Procedure (General)

Whole body views:

  • At 2-3 hours after injection, position the patient supine on the whole-body imaging table. Adjust the upper detector to minimise the distance between the patient and collimator. If the patient has discomfort lying on the back, place a pillow under the knees. Place a Velcro strap around the feet to prevent rotation of the legs during acquisition.

  1. Acquire anterior and posterior whole body images at a scan speed of 10 cm/min on an analogue formatter and on computer (1024 x 256 matrix).

  2. After the detector head passes the badomen, reposition its height for proximity to the lower extremities (or use auto-contour setting).

 

Variations:

Cancer patients where no focal abnormality is being investigated. No flow or pool is required.

Rheumatology patients (that is patients referred from a specialist rheumatologist (e.g. Drs Mathers, Glass, Ratnarajah, Major) or patients investigated for polyathralgias. These patients require whole body blood pool sweep or multiple spot blood pool to cover as many joints as possible. Always include hands and wrists. If in doubt, check with the Nuclear Medicine Physician. These patients also require whole-body delayed images and static views of hands and wrists (palmar).

Spot views-Trunk:

The number of counts per image depends upon the region being imaged; however as a general rule, for a large field-of-view system, 1,000 kct should be acquired over the thoracic spine, with other images being acquired for a similar time per image. All images should be acquired using 256 x 256 matrix size.

Minimum views:

 Lumbar spine: Anterior, posterior. Always include pelvis and hips. Check with the Nuclear Medicine physician to see if oblique views or SPECT is required.

Thoracic spine: Anterior, posterior. Check with the Nuclear Medicine physician to see if oblique views or SPECT is required. Blood flow and pool imaging may not be required-check with Nuclear Medicine physician.

Cervical spine: Anterior, flexed posterior view. Check with the Nuclear Medicine physician to see if oblique views or SPECT is required.

Skull: Anterior, posterior, laterals (performed individually, not with two camera heads simultaneously).

Facial bones: Anterior, laterals (performed individually), Check with the Nuclear Medicine physician to see if pin-hole views or SPECT is required. Note: usually mandibular condyles are the region of interest.

Assessment of Mandibular growth:

    1. Blood flow and blood pool imaging of the head and neck (anterior view).
    2. Planar imaging of head and neck: anterior, true lateral views.
    3. Image lumbar spine (posterior), as reference region.
    4. Regions of interest (ROIs) drawn on mandibular condyles, mandibular rami and mandibular bodies, as well as L4 and non-renal para-lumbar soft tissue (background counts).
    5. SPECT imaging of head and neck
    6. Where possible SPECT/CT imaging of facial bones/skull.
    7. Uptake ratio calculated from the following formulae:                                                   
UR=  ROI mandible-background

                                       ROI L4 – background

   Where counts/pixel are measured in each ROI.

                       8. Mandibular skeletal maturity assessed by linear regression analysis,

                           as per Kaban et al. J Oral Maxillofac surg 1982;40:18-22.                

Ribs: Anterior, posterior, obliques (either anterior or posterior obliques, depending on the area of interest). Usually no flow/pool is required.

Shoulder girdle: Anterior (arms down), posterior including cervical spine(arms down). Check with the Nuclear Medicine physician to see if oblique views or arms raised view is required, particularly where interest is focused on the scapula.

Spot views-Extremities:

  1. Images of hands, wrists, feet and ankles should be acquired for 400-800 kcts per view in 256 x 256 matrix. Small sandbags should be used to help keep the extremities still during the scan. For the palmar view of hands/wrists the patient’s hands are placed flat upon the gamma camera face. For dorsal views, the hands are placed flat on the bed and the gamma camera repositioned above the dorsum of the hands, as close as possible. Dorsal views should not be performed as an extra view with a double-headed camera, nor should they be performed with the patient’s hands supinated (palms up) on the camera.
  2. All extremity imaging should have a right marker placed on every view, preferable by Co-57 point source.
  3. If early phase images were acquired, then at a minium, acquire spot views of these regions for comparison.

 

Minimum Views.

Elbows: Posterior with arms extended and hands pronated (palmar), lateral views where medial injury investigated, with the patient sitting and flexed elbow placed on the horizontal camera (hand palmar), or lateral views where lateral injury investigated, with the patient sitting and flexed elbow leaned against the upright camera face, patients palm placed on his/her abdomen.

Wrists and Hands: Palmar view with maximum magnification. Check with the Nuclear Medicine physician to see if anterior or oblique views are required.

Lower Limbs: Anterior views of pelvis/hips, knees/thighs, legs/feet, posterior views of lumbar spine, pelvis/hips, lateral views of knees/thighs, feet/legs.

Knees: Anterior view knees and hips, lateral view knees.

Hips: Anterior view hips/pelvis and knees. Posterior view lumbar spine. Check with the Nuclear Medicine physician to see if lateral knee views or lumbar spine SPECT are required.

Pelvis: Anterior view pelvis. Posterior view pelvis and lumbar spine. Squat (Tail on detector) view if history indicates sacrum, coccyx or lower pelvis involved. Lateral views if sacrum or coccyx involved. Check with Nuclear Medicine physician if sacroiliac joint to sacrum ratios are required.

Ankles: Anterior views, posterior views ,lateral views.

 

Feet: Anterior, plantar and lateral views.

Pin-hole views-Hips:

Pinhole images of the hip should be acquired using a pinhole collimator with a 6-mm aperture. Images should be acquired for 200-250 kct for the abnormal hip, with the same time per image being used for the contralateral hip. Images should be acquired in 256 x 256 matrix size.

SPECT study:

For a dual head system, acquire 64 views over 360 degrees into A 128 X 128 word mode matrix at 20 seconds per view using a high-resolution collimator and appropriate body contouring to minimise patient-to-collimator distance. Note. The time frame should be increased to 30-40 seconds for large patients (men greater than 100 kg, women greater than 80 kg). Check that all loose clothing and straps are tucked away because they may interfere with a body-contouring orbit.

Computer Analysis

No analysis is required for whole-body views.

For planar views of the pelvis where sacroiliitis is suspected, sacroiliac joint (SIJ) to sacral ratios may be required. These should be performed using a posterior view of pelvis. Small rectangular regions of interest (ROI) should be placed over the SIJ, ensuring that the ROI does not extend outside the SIJ. A similar ROI is placed over the sacrum at the same level. The ratio is calculated by the number of counts/pixel in the sacral ROI to that in the sacral ROI, for each side. Normal is less than 1.4 in average sized adult patients.

Patients assessed for condylar hyperplasia, may require semi-quantitative analysis of uptake (and ratios) in the mandible condyles. A well-fitted ROI is placed around each condyle and the reference area, left or right frontal bone also has a similar sized ROI. Ratios are calculated by counts/pixel in the condyle to the frontal bone, as well as left to right ratios.

For SPECT studies, the following steps should be performed:

  1. Where necessary apply uniformity and centre-of-rotation correction to the data, if not done automatically by the system used.

  2. If possible, pre-filter the planar data. A suggested filter is a Butterworth, order 10-12, cut-off at 0.4-0.5 Nyquist.

  3. Reconstruct 1-pixel-thick transaxial slices. The back-projection filter may be a Ramp or Ramp-Butterworth with a cut-off at 0.6-0.8 Nyquist.

Information on Film

On each analogue and computer film, ensure that the following information is recorded:

  1. Patient name

  2. Date and type of scan

  3. Orientation of each image (e.g. anterior, posterior).

Interpretation

Normal skeletal structures are usually visualised clearly, and activity is seen in the kidneys and bladder. Most skeletal abnormalities are focal areas of increased uptake. Focal cold areas may reflect absence of bone blood supply or bone destruction/resection.

Radiation Dosimetry

The estimated absorbed doses in organs and tissues of an average (70 kg) subject from an intravenous dose of 740 MBq include:

Bone total 7 mGy, Bladder wall (2 hour void) 26.0 mGy, (4.8 hour void) 62.0 mGy, ovaries 2.4 mGy and total body 1.3-2.5 mGy.

Approximate Uptake Ratio by Age taken from Regression Analysis

                          AGE                                       RATIO

 

                         0 - 2                                 2.0 – 1.85                    

 

                         2 – 5                                1.85 – 1.65

 

                         5 – 10                              1.65 – 1.30

 

                        10 – 15                             1.30 – 1.10

 

                        15 – 20                             1.10 – 0.70

                         20                                     < 0.70