and Anatomy of PET/MRI

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© The Author(s), under exclusive license to Springer Nature Switzerland AG 2022
E. E. Kim et al. (eds.)Atlas and Anatomy of PET/MRI, PET/CT and SPECT/

Atlas and Anatomy of PET/MRI

Vanessa Murad1, 2  , E. Edmund Kim3, 4, Jin-Chul Paeng1, Hyung-Jun Im5 and Gi-Jeong Cheon1

Department of Nuclear Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea

Department of Diagnostic Imaging, Fundacion Santa Fe de Bogotá University Hospital, Bogota, Colombia

Department of Radiological Sciences, University of California, Irvine, School of Medicine, Orange, CA, USA

Department of Nuclear Medicine and Department of Molecular Medicine, Graduate School of Convergence Science and Technology, Seoul National University College of Medicine, Seoul, Republic of Korea

Departments of Applied Bioengineering, Molecular Medicine, and Biopharmaceutical Sciences, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Republic of Korea


Positron emission tomography/magnetic resonance image (PET/MRI)18F-Fludeoxyglucose (FDG)OncologyAnatomyCancer

Hybrid positron emission tomography/magnetic resonance image (PET/MRI) has undergone rapid evolution during the last years, moving from a predominantly research field to clinical practice. With the advances in faster silicon photomultiplier detectors, MRI-based attenuation correction, and image reconstruction, significant improvements in equipment and image quality have been achieved. Currently, there are fully integrated PET/MRI systems that allow simultaneous and more rapid acquisition, improving not only the technical quality but also the experience for patients who need a low radiation dose [13]. With this technology comes the possibility of performing multiparametric MRI studies, where detailed anatomical evaluation and functional evaluation are possible, not only considering the qualitative and quantitative data of PET but also integrating multiple parameters such as perfusion (contrast-enhanced sequences), cellularity (diffusion-weighted sequence), metabolites (spectroscopic analysis), and texture analysis. Additionally, recent developments are very promising in giving the possibility of incorporating advanced data and biomarkers to integrate with bioinformatics and allow a better understanding of the disease, as well as an efficient evaluation, prediction of response to treatment, and follow-up [47].

With the growing availability of PET/MRI, its main and differential applications have also been clarified. Nonspecific 18F-fludeoxyglucose (FDG) PET/MRI continues to be the most widely used, and thus new radiotracers are expanding the field to be explored. Among the most frequent applications of 18F-FDG PET/MRI, where its superiority over PET/CT has been demonstrated, are the evaluation of head and neck, colorectal, gynecological, bone and soft tissue tumors, as well as the evaluation and characterization of primary or secondary liver lesions [812]. It has also shown good results in non-tumor pathology such as epilepsy, inflammatory bowel disease, and cardiac sarcoidosis [4, 13].

The creation of new radiotracers that can be imaged both with PET/MRI and PET/CT, depending on the case and availability, has allowed great advances in the evaluation of other oncological and non-oncological pathologies. In the case of neuroendocrine tumors and prostate cancer, targeting somatostatin receptors with 68Ga-DOTATOC, targeting PSMA with 68Ga-PSMA-11 among others available tracers, and the inclusion of 177Lu agents have revolutionized the diagnosis and treatment of these pathologies respectively [14, 15]. In the field of neuroimaging, the wide availability of radiotracers has made it possible to improve the evaluation of multiple targets different from glucose metabolism (FDG), such as DNA synthesis (18F-fluorothymidine), protein synthesis (11C-methionine, 18F-fluoroethyl-L-tyrosine [FET], 18F-fluoro-L-3,4-dihydroxyphenylalanine [DOPA]), and hypoxia (18F-fluoromisonidazole) [16, 17]. In the field of degenerative diseases, where much remains to be explored and research is very promising, examples of emerging invaluable applications are amyloid PET and Tau PET for Alzheimer’s disease, as well as 18FP-CIT PET for Parkinson’s disease [18, 19].

In this chapter, we present multiple demonstrative examples of the different uses of PET/MR, with the most relevant anatomical references for each case.

1 Head and Neck

1.1 Case 1

A 75-year-old male patient, with worsening dizziness and weakness in both legs. Brain malignancy was suspected on brain CT, so 18F- FDG PET/MR was performed. Images revealed marked increased activity in a well-defined enhancing mass involving the corpus callosum, crossing the midline and with subependymal extension. Primary central nervous system (CNS) lymphoma was suspected, and stereotaxic biopsy confirmed a diffuse large B-cell lymphoma (Fig. 1) [20].

Fig. 1

1. Left superior frontal gyrus

2. Left precentral gyrus

3. Left postcentral gyrus

4. Peritumoral edema, right parietal lobe

5. Primary central nervous system lymphoma involving right parietal white matter

6. Primary central nervous system lymphoma involving corpus callosum

1.2 Case 2

A 72-year-old man with diagnosis of lymphoplasmacytic lymphoma (LPL)/Waldenström macroglobulinemia (WM) from marginal zone lymphoma, with central nervous system involvement. After surgery and chemotherapy, complete response was achieved, but the patient attended an early checkup with headache, so 18F-FDG PET/MR was performed. Images showed focal increased activity in a lobulated mass at the periventricular white matter, adjacent to the posterior horn of the left lateral ventricle with perilesional edema, which showed predominantly low signal on T2WI and heterogeneous contrast enhancement, which are frequent findings of lymphoma involvement. With these findings, a relapse was confirmed, and treatment was initiated again (Fig. 2) [21].

Fig. 2

1. Metabolically active lymphoma adjacent to the posterior horn of the left lateral ventricle

2. Normal FDG uptake in gray matter at the frontal cortex

3. Normal FDG uptake in the white matter at the frontal lobe

4. Anterior horns of the lateral ventricles

5. Posterior horns of the lateral ventricles

6. Septum pellucidum

7. Anterior cerebral arteries

8. Falx cerebri, frontal region

9. Perilesional edema

10. Choroid plexus at right lateral ventricle

11. Skull, left parietal area

12. Left temporal muscle

13. Scalp, left parietal area

14. Superior sagittal sinus

1.3 Case 3

A 5-year-old patient with gradual loss of vision in the right eye. Clinical examination and contrast-enhanced MRI were performed and confirmed the diagnosis of retinoblastoma. 18F-FDG PET/MR was performed during initial workup and staging. Minimal uptake was found in the primary tumor and the presence of metabolically active metastases was ruled out (Fig. 3) [22].

Fig. 3

1. Right eye retinoblastoma with minimal diffuse FDG uptake

2. Right medial rectus muscles

3. Right temporal lobe

4. Cerebellar vermis

5. Left optic nerve

6. Left lateral rectus muscle

7. Pons

8. Ethmoid air cells

9. Left eye, anterior chamber

10. Left eye, vitreous chamber

11. Left temporal arachnoid cyst

12. Pituitary gland

13. Left temporal bone

14. Basilar artery

15. Fourth ventricle

1.4 Case 4

A 49-year-old woman with a headache and decreased mobility of the right eye. 18F-FDG PET/MR was performed, and images showed a metabolically active mass with heterogeneous enhancement in the olfactory recess involving the cribriform plate and ethmoid air cells. The lesion produced lateral displacement of the right medial rectus muscle, compression of the optic chiasm, and obstruction of the sphenoid sinuses. Subsequent biopsy confirmed the diagnosis of an olfactory neuroblastoma, also known as esthesioneuroblastoma (Fig. 4) [23].

Fig. 4

1. Metabolically active tumor in the upper olfactory recess

2. Thalamus

3. Pons

4. Genu of corpus callosum

5. Lateral ventricle anterior horn

6. Splenium of corpus callosum

7. Pineal gland

8. Straight sinus

9. Cerebellum

10. Nuchal ligament

11. Spinal cord

12. Sphenoidal sinus with secretion due to obstruction

13. Left optic nerve

14. Basilar artery

15. Cerebellar vermis

16. Right temporal lobe

17. Left eye, vitreous chamber

18. Left ethmoid air cells

19. Optic chiasm

20. Fourth ventricle

1.5 Case 5

A 48-year-old male patient with progressive proptosis, impaired visual acuity, and headaches. 18F-FDG PET/MR was performed, finding diffuse metabolically active infiltration of the soft tissues in both orbits and eyelids, with encasement and displacement of the optic nerves and muscles, without infiltration. Biopsy revealed the diagnosis of an extra nodal marginal zone B-cell lymphoma (EMZBC) (Fig. 5) [22].

Fig. 5

1. Metabolically active bilateral orbital lymphoma infiltration

2. Right anterior ethmoid air cells

3. Right posterior ethmoid air cells

4. Sella turcica (pituitary gland)

5. Right temporal lobe

6. Right superior eyelid with lymphoma infiltration

7. Frontal sinuses

8. Right temporal muscle

9. Pons

10. Right eye lens

11. Right eye vitreous chamber

12. Right optic nerve

13. Left medial rectus muscle

14. Left lateral rectus muscle

15. Left internal carotid artery

16. Basilar artery

17. Fourth ventricle

18. Midbrain, red nucleus

19. Aqueduct of Sylvius

20. Crista galli

21. Left olfactory cortex

22. Left Sylvian fissure

23. Anterior cerebral arteries

24. Midbrain, sustancia nigra

1.6 Case 6

A 55-year-old male patient with sore throat and a soft tissue mass in the right nasopharyngeal wall on physical examination. Biopsy revealed nasopharyngeal squamous cell carcinoma, so 18F-FDG PET/MR was performed for staging. Images showed increased metabolic activity in the right nasopharyngeal area at a soft tissue mass, consistent with the primary tumor. Hypermetabolic, enlarged, metastatic lymph node (LN) was also found in the right neck, level II (Figs. 6 and 7) [24].

Fig. 6

1. Nasal septum

2. Right maxillary sinus

3. Right masseter muscle

4. Right temporalis muscle

5. Right lateral pterygoid muscle

6. Right medial pterygoid muscle

7. Right mandibular ramus

8. Right external auditory canal

9. Right internal carotid artery

10. Right mastoid air cells

11. Metabolically active tumor at the right fossa of Rosenmüller

Fig. 7

1. Tongue

2. Right molar teeth with artifact due to dental implant

3. Right masseter muscle

4. Right mandibular ramus

5. Right medial pterygoid muscle

6. Right palatine tonsil

7. Right external maxillary vein

8. Right parotid gland

9. Metabolically active LN metastasis, right neck level II

10. Oropharynx

11. Spinal cord

1.7 Case 7

A 55-year-old female patient with a growing ulcerated mass in the right sublingual area. Biopsy was performed confirming an adenoid cystic carcinoma with cribriform pattern, so 18F-FDG PET/MR was performed for staging. Images showed a focal hypermetabolic lesion in the right sublingual space, displacing the tongue’s intrinsic muscles, without infiltrating them. Ipsilateral, level II, hypermetabolic lymph node metastasis was also found (Fig. 8) [10].

Fig. 8

1. Metabolically active tumor in the right sublingual space

2. Metastatic LN, right neck level II

3. Genioglossus muscle

4. Epiglottis

5. Larynx

6. Cervical vertebral body

7. Right sternocleidomastoid muscle

8. Posterior cervical muscles (inner to outer): semispinalis, splenius cervicis, and splenius capitis

9. Left submandibular gland

10. Right common carotid artery

11. Left sublingual space

12. Mandible, body

1.8 Case 8

A 55-year-old male patient with a history of persistent dysphagia and cough. Direct endoscopic examination was performed finding a laryngeal mass, consistent with an epiglottic squamous cell carcinoma. 18F-FDG PET/MR was performed for staging, finding a prominent hypermetabolic mass in the superior aspect of the epiglottis, projecting towards the upper airway and decreasing its caliber. No hypermetabolic lymph nodes or distant metastases were observed (Fig. 9) [10].

Fig. 9

1. Metabolically active epiglottic tumor

2. Intrinsic tongue muscles (genioglossus)

3. Left submandibular gland

4. Spinal cord

5. Pituitary gland and stalk

6. Sphenoid sinus

7. Nasopharynx

8. Uvula

9. Oropharynx

10. Larynx

1.9 Case 9

A 21-year-old man with a non-painful, progressively growing right parotid mass. Ultrasound-guided biopsy revealed a secretory carcinoma, so 18F-FDG PET/MR was performed for staging. Images showed a hypermetabolic irregular mass involving both the superficial and deep lobes of the right parotid gland, without associated metastatic lymph nodes (Fig. 10) [25].

Fig. 10

1. Metabolically active right parotid tumor, involving both superficial and deep lobes

2. Right masticator space

3. Spinal cord

4. Left parapharyngeal space

5. Left carotid space

6. Left paraspinal space

7. Left buccal space

8. Oropharynx

9. Longus capitis muscles

1.10 Case 10

A 57-year-old man with a painful, rapidly growing left cervical mass. Ultrasound was performed finding an enlarged, necrotic lymph node, which biopsy revealed a metastatic carcinoma. 18F-FDG PET/MR was performed suspecting primary head and neck malignancy, and images showed a hypermetabolic mass in the hypopharynx, predominantly left side, with multiple metastatic lymph nodes in the left neck. The diagnosis of primary squamous cell carcinoma in this location was confirmed (Fig. 11) [10].

Fig. 11

1. Metabolically active hypopharyngeal tumor

2. Hypermetabolic metastatic neck lymph nodes: left, level III

3. Hypermetabolic metastatic neck lymph node: left, level II

4. Hypermetabolic metastatic neck lymph nodes: left, level IV

5. Right carotid artery

6. Retropharyngeal space

7. Right vertebral artery

8. Epiglottis

9. Left submandibular gland

10. Left carotid artery

11. Left jugular vein

12. Trachea

13. Left thyroid lobe

14. Left common carotid artery

15. Left second rib

16. Vocal cords

1.11 Case 11

A 22-year-old man with headache, occasional fever, and weakness in both arms. Laboratory tests did not show definite abnormalities, so 18F-FDG PET/MR and MRI were performed to rule out unknown origin infection vs occult malignancy. Images showed diffusely increased activity along the spinal cord with corresponding ill-defined high signal intensity lesions in T2WI. With these findings and other neurological tests, the diagnosis of acute disseminated encephalomyelitis (ADEM) was confirmed (Fig. 12) [26].

Fig. 12

1. Diffusely increased activity along the spinal cord

2. Focal increased activity at the vocal cords, physiologic

3. Sphenoid sinus

4. Clivus

5. Nasopharynx

6. Uvula

7. C2, odontoid process

8. Nuchal ligament

9. Oral cavity

10. Oropharynx

11. Left parapharyngeal space

12. Left parotid gland

13. Left vertebral foramen in C1

14. Brainstem

15. C6–C7 Intervertebral disc

16. Trachea

17. Cerebellum

18. Cisterna magna

19. Ill-defined high signal intensity lesions (T2WI)

20. Right vertebral artery

21. Hard palate

22. Longus capitis muscles

23. Left vertebral artery

24. Cerebrospinal fluid

1.12 Case 12

A 67-year-old male patient with a history of left maxillary sinus squamous cell carcinoma, treated 9 years ago with radiotherapy and surgery (resection with flap reconstruction). He attended his annual checkup completely asymptomatic and among other studies 18F-FDG PET/MR was performed. Images showed focal increased activity in the lateral wall of the left nostril on the medial aspect of the surgical flap, which also presented heterogeneous contrast enhancement, which was not evident in the previous study. This finding was confirmed as a local recurrence (Fig. 13) [10].

Fig. 13

1. Metabolically active recurred tumor in the surgical flap

2. Cerebellum

3. Lateral ventricles

4. Thalami

5. C2, odontoid process

6. Nuchal ligament

7. Medulla

8. Epiglottis

9. Tongue

10. Nasopharynx

11. Left occipital condyle

12. Left cervical paraspinal muscles (multifidus, longissimus capitis, splenius capitis)

13. Right maxillary sinus

14. Right masseter muscle

15. Right mandibular ramus

16. Left nostril

17. Left pterygoid muscles

18. Left cerebellar hemisphere

19. Nasal septum

20. Prevertebral muscles (longus capitis and rectus capitis muscles)

21. Proximal vertebral arteries

22. Surgical graft

23. Left mandibular condyle

2 Chest

2.1 Case 1

A 62-year-old male patient with a solitary pulmonary nodule and history of heavy smoking. 18F-FDG PET/MR was performed during staging. Images showed moderately increased activity in a small solid nodule at the left lower lobe, which was later resected and confirmed as an adenocarcinoma. No metabolically active metastases were detected (Figs. 14, 15, 16, 17, 18, and 19) [27, 28].

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